Ultrathin NiV Layered Double Hydroxide for Methanol Electrooxidation: Understanding the Proton Detachment Kinetics and Methanol Dehydrogenation Oxidation

Electrochemical methanol oxidation reaction (MOR) is regarded as a promising pathway to obtain value-added chemicals and drive cathodic H2 production, while the rational design of catalyst and in-depth understanding of the structure-activity relationship remains challenging. Herein, the ultrathin NiV-LDH (u-NiV-LDH) with abundant defects is successfully synthesized, and the defect-enriched structure is finely determined by X-ray adsorption fine structure etc. When applied for MOR, the as-prepared u-NiV-LDH presents a low potential of 1.41 V versus RHE at 100 mA cm-2, which is much lower than that of bulk NiV-LDH (1.75 V vs RHE) at the same current density. The yield of H2 and formate is 98.2% and 88.1% as its initial over five cycles and the ultrathin structure of u-NiV-LDH can be well maintained. Various operando experiments and theoretical calculations prove that the few-layer stacking structure makes u-NiV-LDH free from the interlayer hydrogen diffusion process and the hydrogen can be directly detached from LDH laminate. Moreover, the abundant surface defects upshift the d-band center of u-NiV-LDH and endow a higher local methanol concentration, resulting in an accelerated dehydrogenation kinetics on u-NiV-LDH. The synergy of the proton detachment from the laminate and the methanol dehydrogenation oxidation contributes to the excellent MOR performance of u-NiV-LDH.

Accessing Z-Enynes via Cobalt-Catalyzed Propargylic Dehydrogenation

Alkenes constitute an enabling motif in organic synthesis, as they can be functionalized to form highly substituted molecules. Z-alkenes are generally challenging to access due to the thermodynamic preference for the formation of E-alkenes compared to Z-alkenes. Dehydrogenation methodologies to selectively form Z-alkenes have not yet been reported. Herein, we report a Z-selective, propargylic dehydrogenation that provides 1,3-enynes through the invention of a Co-catalyzed oxidation system. Observation of a kinetic isotope effect (KIE) revealed that deprotonation of the propargylic position is the rate limiting step. Additionally, isomerization experiments were conducted and confirmed that the observed Z-selectivity is a kinetic effect. A proposed stereomechanistic model for the Z-selectivity is included.

B(C6F5)3-Catalyzed Dehydrogenation of Pyrrolidines to Form Pyrroles

Pyrroles are important N-heterocycles found in medicines and materials. The formation of pyrroles from widely accessible pyrrolidines is a potentially attractive strategy but is an underdeveloped approach due to the sensitivity of pyrroles to the oxidative conditions required to achieve such a transformation. Herein, we report a catalytic approach that employs commercially available B(C6F5)3 in an operationally simple procedure that allows pyrrolidines to serve as direct synthons for pyrroles. Mechanistic studies have revealed insights into borane-catalyzed dehydrogenative processes.

Ni and Co Active Site Transition and Competition in Fluorine-Doped NiCo(OH)2 LDH Electrocatalysts for Oxygen Evolution Reaction

The oxygen evolution reaction (OER) performance of NiCo LDH electrocatalysts can be improved through fluorine doping. The roles of Ni and Co active sites in such catalysts remain ambiguous and controversial. In addressing the issue, this study draws upon the molecular orbital theory and proposes the active center competitive mechanism between Ni and Co. The doped F-atoms can directly impact the valence state of metal atoms or exert an indirect influence through the dehydrogenation, thereby modulating the active center. As the F-atoms are progressively aggregate, the eg orbitals of Ni and Co transition from e2 g to e1 g , and subsequently to e0 g . The corresponding valence state elevates from +2 to +3, and then to +4, signifying an initial increase followed by a subsequent decrease in the electrocatalytic performance. Furthermore, a series of F-NiCo LDH catalysts are synthesized to verify the eg orbital occupancy analysis, and the catalytic OER overpotentials are 303, 243, 240, and 246 mV at the current density of 10 mA cm-2 , respectively, which coincides well with the theoretical prediction. This investigation not only provides novel mechanistic insights into the transition and competition of Ni and Co in F-NiCo LDH catalysts but also establishes a foundation for the design of high-performance catalysts.

Dehydrogenation and Transfer Hydrogenation of Alkenones to Phenols and Ketones on Carbon-Supported Noble Metals

The catalytic dehydrogenation of substituted alkenones on noble metal catalysts supported on carbon (Pt/C, Pd/C, Rh/C, and Ru/C) was investigated in an organic phase under inert conditions. The dehydrogenation and semihydrogenation of the enone starting materials resulted in aromatic compounds (primary products), saturated cyclic ketones (secondary products), and cyclic alcohols (minor products). Pd/C exhibits the highest catalytic activity, followed by Pt/C and Rh/C. Aromatic compounds remain the primary products, even in the presence of hydrogen donors. Joint experimental and theoretical analyses showed that the four catalytic materials stabilize a common dienol intermediate on the metal surfaces, formed by keto-enol tautomerization. This intermediate subsequently forms aromatic products upon dehydrogenation. The binding orientation of the enone reactants on the catalytic surface is strongly metal-dependent, as the M-O bond distance changes substantially according to the metal. The longer M-O bonds (Pt: 2.84 Å > Pd: 2.23 Å > Rh: 2.17 Å > Ru: 2.07 Å) correlate with faster reaction rates and more favorable keto-enol tautomerization, as shorter distances correspond to a more stabilized starting material. Tautomerization is shown to occur via a stepwise surface-assisted pathway. Overall, each of the studied metals exhibits a distinct balance of enthalpy and entropy of activation (ΔH°‡, ΔS°‡), offering unique possibilities in the realm of enone dehydrogenation reactions that can be achieved by suitable selection of catalytic materials.

A Fine Analysis of Zn Species Structure and Distribution in Zn/ZSM-5 Catalysts by Linear Combination Fitting Analysis of XANES Spectra

Investigating the distribution of different Zn species on Zn-containing zeolite catalysts is crucial for identifying the active sites and establishing the relationship between the catalyst's structure and its activity in the process of ethylene aromatization. By utilizing X-ray absorption near edge spectra (XANES) of various reference samples, this study employed linear combination fitting (LCF) analysis on XANES spectra of real samples to accurately measure the changes in the distribution of Zn species in Zn-containing HZSM-5 zeolites under different Zn sources and loadings. The results showed that ZnOH+, ZnO clusters, and ZnO crystalline structures coexist in Zn/HZSM-5 catalysts prepared through physical mixing and incipient wet impregnation methods. A similar trend was observed for catalysts prepared using different methods, with an increase in Zn content resulting in a decrease in the proportion of ZnOH+ and a significant increase in the amount of larger ZnO crystals. Furthermore, ZnO clusters were confined within the zeolite pores. The findings of this study established a direct correlation between the amount of ZnOH+ determined through LCF analysis and both the rate of hydrogen production and the rate of aromatics formation, providing strong evidence for the catalytic role of ZnOH+ as an active center for dehydrogenation, which plays a key role in promoting the formation of aromatics. The method of LCF analysis on XANES spectra allows for the determination of the local structure of Zn species, facilitating a more precise analysis based on the distribution of these species. This method not only provides detailed information about the Zn species but also enhances the accuracy of the overall analysis.

Development of Liquid Organic Hydrogen Carriers for Hydrogen Storage and Transport

The storage and transfer of energy require a safe technology to mitigate the global environmental issues resulting from the massive application of fossil fuels. Fuel cells have used hydrogen as a clean and efficient energy source. Nevertheless, the storage and transport of hydrogen have presented longstanding problems. Recently, liquid organic hydrogen carriers (LOHCs) have emerged as a solution to these issues. The hydrogen storage technique in LOHCs is more attractive than those of conventional energy storage systems like liquefaction, compression at high pressure, and methods of adsorption and absorption. The release and acceptance of hydrogen should be reversible by LOHC molecules following favourable reaction kinetics. LOHCs comprise liquid and semi-liquid organic compounds that are hydrogenated to store hydrogen. These hydrogenated molecules are stored and transported and finally dehydrogenated to release the required hydrogen for supplying energy. Hydrogenation and dehydrogenation are conducted catalytically for multiple cycles. This review elaborates on the characteristics of different LOHC molecules, based on their efficacy as energy generators. Additionally, different catalysts used for both hydrogenation and dehydrogenation are discussed.

Transmetalation

Monocarbonyl rhodium complex LRh(CO), 1, which is stabilized by a pyrrole-based bis(phosphinimine) pincer ligand (L=κ3 -NNN'=2,5-[i Pr2 P=N(4-i PrC6 H4 )]2 -N'(C4 H2 )- ), serves as a versatile platform for the dehydrogenation of group 14 substrates. Reaction with primary and secondary silanes and germanes (MesSiH3 , Et2 SiH2 , Ph2 GeH2 , t BuGeH3 ; Mes=mesityl) liberates H2 and yields base-stabilized tetrylene compounds of the form κ2 -L(CO)Rh(ER2 ) (E=Si: R=Mes, H, 2; R=Et, 5; E=Ge: R=Ph, 6; R=t Bu, H, 8). The ":ER2 " fragment in these species bridges between the rhodium center and a phosphinimine donor. Preliminary reactions between pinacol (Pin) and κ2 -L(CO)Rh(ER2 ), E=Si, Ge, indicate that such complexes can serve as silylene and germylene synthons, releasing :ER2 and catalytically generating PinER2 . In contrast, combination of complex 1 and MesGeH3 does not yield the anticipated dehydrogenation product, but rather, transmetalation similar to that observed upon reaction between 1 and 3,5-dimethylphenylborane prevails.

Iridium Catalyst Immobilized on Crosslinked Polyethyleneimine for Continuous Hydrogen Production Using Formic Acid

Hydrogen is an alternative fuel that can play a critical role in achieving net zero emissions, leading to global environment sustainability. An iridium-immobilized catalyst based on polyethyleneimine (PEI) was synthesized and utilized for hydrogen production via formic acid dehydrogenation (FADH). Iridium complex is cross-linked with its ligand and PEI to form the immobilized catalyst, where the iridium content could be easily varied in the range of 1-10 %. The structure of the iridium-immobilized catalyst was confirmed using solid-state NMR, DNP NMR, and FTIR spectroscopies. The iridium-immobilized catalyst with PEI showed excellent catalytic activity for FADH, exhibiting the catalyst's highest turnover frequency (TOF) value of 73 200 h-1 and a large turnover number (TON) value of over 1 130 000. The catalyst could be used for continuous hydrogen production via FADH, exhibiting high durability for over 2 000 h with TON value of 332 889 without any degradation in catalytic activity. The obtained hydrogen gas was evaluated for power generation using a standard fuel cell, as well as achieved 5 h of stable power generation.

A Theoretical Study on the Mechanisms Involved in Catalytic Dehydrogenation and Dehydration of Isopropanol on SrTiO3

The dehydrogenation and dehydration of isopropanol on the SrO and TiO2 terminated surfaces, of the SrTiO3 perovskite, is addressed by periodic DFT calculations in order to shed light on the involved mechanisms. The results show that the dehydrogenation occurs through a mechanism involving the dissociative adsorption of the alcohol on the SrO terminated surface, followed the nucleophilic attack of a hydride species on the previously adsorbed hydrogen atom to form molecular hydrogen and the corresponding carbonyl compound. The dehydration instead occurs by the molecular adsorption of the alcohol on the TiO2 terminated surface, followed by various possible E1 elimination pathways leading to the formation of the corresponding alkene and a water molecule. The article reports a thorough study on the involved mechanisms, including identification of the transition states and intermediates along the reaction paths, and evaluation of the respective activation barriers, as well. Thus, this article provides significant insights about the mechanisms of dehydrogenation and dehydration of isopropanol on the SrTiO3 , not reported earlier in literature. The calculated barrier energies are in good agreement with experimental values.

Catalyst-Free Transfer Hydrogenation from Amine-Borane Small Oligomers

Amine-borane dimers and oligomers with varied steric and electronic profiles were prepared via capping agent-controlled AA/BB polycondensations. They were used for transfer hydrogenations to aldehydes, ketones, imines as well as electron-poor alkene/alkyne moieties. The amine-borane Lewis-paired oligomers and the congested bis(amine-borane)s provided the highest yields. This was likely helped by facilitated dissociation (oligomers) or H-bond assistance. In the case of the oligomers, the second equivalent of H2 present was also engaged in the reaction. Solid-state NMR characterization provides evidence that the boron-containing materials obtained after transfer dehydrogenation are highly similar to those obtained from thermal dehydrogenation. The oligomers bridge the gap between simple amine-borane molecular reductants and the poly-amine-boranes and provide a full picture of the reactivity changes at the different scales.

Acceptorless or Transfer Dehydrogenation of Glycerol Catalyzed by Base Metal Salt Cobaltous Chloride - Facile Access to Lactic Acid and Hydrogen or Isopropanol

The dehydrogenation of glycerol to lactic acid (LA) under both acceptorless and transfer dehydrogenation conditions using readily available, inexpensive, environmentally benign and earth-abundant base metal salt CoCl2 is reported here. The CoCl2 (0.5 mol %) catalyzed acceptorless dehydrogenation of glycerol at 160 °C in the presence of 0.75 equiv. of KOH, gave up to 33 % yield of LA in 44 % selectivity apart from hydrogen. Alternatively, with acetone as a sacrificial hydrogen acceptor, the CoCl2 (0.5 mol %) catalyzed dehydrogenation of glycerol at 160 °C in the presence of 1.1 equiv. of NaOt Bu resulted in up to 93 % LA with 96 % selectivity along with another value-added product isopropanol. Labelling studies revealed a modest secondary KIE of 1.68 which points to the involvement of C-H bond activation as a part of the catalytic cycle but not as a part of the rate-determining step. Catalyst poisoning experiments with PPh3 and CS2 are indicative of the homogeneous nature of the reaction mixture involving molecular species that are likely to be in-situ formed octahedral Co(II) as inferred from EPR, HRMS and Evans magnetic moment studies. The net transfer dehydrogenation activity is attributed to exclusive contribution from the alcoholysis step.

Advances in Group VI Metal-Catalyzed Homogeneous Hydrogenation and Dehydrogenation Reactions

Transition metal-catalyzed homogeneous hydrogenation and dehydrogenation reactions for attaining plethora of organic scaffolds have evolved as a key domain of research in academia and industry. These protocols are atom-economic, greener, in line with the goal of sustainability, eventually pave the way for numerous novel environmentally benign methodologies. Appealing progress has been achieved in the realm of homogeneous catalysis utilizing noble metals. Owing to their high cost, less abundance along with toxicity issues led the scientific community to search for sustainable alternatives. In this context, earth- abundant base metals have gained substantial attention culminating enormous progress in recent years, predominantly with pincer-type complexes of nickel, cobalt, iron, and manganese. In this regard, group VI chromium, molybdenum and tungsten complexes have been overlooked and remain underdeveloped despite their earth-abundance and bio-compatibility. This review delineates a comprehensive overview in the arena of homogeneously catalysed (de)hydrogenation reactions using group VI base metals chromium, molybdenum, and tungsten till date. Various reactions have been described; hydrogenation, transfer hydrogenation, dehydrogenation, acceptorless dehydrogenative coupling, hydrogen auto transfer, along with their scope and brief mechanistic insights.

Few-Atomic Zero-Valent Palladium Ensembles for Efficient Reductive Dehydrogenation and Dehalogenation Catalysis

Single-atom catalysts (SACs) offer immense potential in heterogeneous catalysis due to their maximized atomic utilization and high selectivity but suffer the problem of low reactivity in catalytic reductive reactions due to their high-valent state. Here, we demonstrate that supported palladium (Pd) ensembles consisting of a few zero-valent Pd atoms (Pd1+c-red/CN) exhibit exceptional reactivity in formic acid (FA) dehydrogenation and 4-chlorophenol (4-CP) dechlorination. The initial FA dehydrogenation and 4-CP dechlorination rates of Pd1+c-red/CN are 42-104 and 16-210 times higher than that of supported Pd SACs (Pd1-ox/CN), respectively. Experimental results and density functional theory (DFT) calculations reveal that optimal adsorption sites of Pd1+c-red/CN stimulate the formation of H*, which is indispensable for 4-CP dechlorination. Moreover, direct electron transfer from Pd atoms to FA with a high electron density on Pd1+c-red/CN also contributes to the rapid 4-CP dechlorination. The superior dehalogenation capability of Pd1+c-red/CN for organohalides of great environmental and health concerns suggested its immense application potential in environmental remediation. This work highlights the pivotal roles of the structure and valence state of Pd ensembles in catalytic reductive reactions and provides a strategy to broaden the application of Pd-based catalysts for dehydrogenation and dehalogenation.

Synthesis of Thiophene-Substituted Ketones via Manganese-Catalyzed Dehydrogenative Coupling Reaction

This study reports an efficient and green one-step method for synthesizing thiophene-substituted ketones from 2-thiophenemethanol and ketones via dehydrogenative coupling using manganese complexes as catalysts. The manganese complex demonstrated a broad applicability under mild conditions and extended the range of usable substrates. Utilizing this strategy, we carried out an efficient and diverse reaction of ketones with 2-thiophenemethanol, and successfully synthesized a series of thiophene-substituted saturated ketones and α, β-unsaturated ketones in good isolated yields.

Oxidative Dehydrogenation of Alkanes through Homogeneous Base Metal Catalysis

Preparing valuable olefins from cheap and abundant alkane resources has long been a challenging task in organic synthesis, which mainly suffers from harsh reaction conditions and narrow scopes. Homogeneous transition metals catalyzed dehydrogenation of alkanes has attracted much attention for its excellent catalytic activities under relatively milder conditions. Among them, base metal catalyzed oxidative alkane dehydrogenation has emerged as a viable strategy for olefin synthesis for its usage of cheap catalysts, compatibility with various functional groups, and low reaction temperature. In this review, we discuss recent development of base metal catalyzed alkane dehydrogenation under oxidative conditions and their application in constructing complex molecules.

Crystal Facet Structure Dependence and Promising Pd-Pt Catalytic Materials for Perhydroacenaphthene Dehydrogenation

Designing an effective Pd-Pt catalytic material with excellent catalytic performance for perhydroacenaphthene (PHAN) dehydrogenation is a great challenge. In this work, in order to explore the crystal facet structure over the bimetallic Pd-Pt catalyst on the dehydrogenation performance of PHAN, the surface compositions of two kinds of Pd (Pt) atoms with different coverage on Pd modulated Pt (PdPt) and Pt modulated Pd (PtPd) catalysts were designed and studied by means of density functional theory (DFT). Through the investigation of the reaction path of PHAN dehydrogenation on PdMLPt(111) and PtMLPd(111) surfaces, it was found that PdMLPt(111) was advantageous to PHAN dehydrogenation (Ea = 2.317 eV). This was attributed to a lower energy barrier, more stable dehydrogenation products, and the fact that Pd doping brought Pt(111) close to the Fermi level. Apparently, Pd modulated Pt catalyst has a broad application prospect in the dehydrogenation of PHAN. In the process of optimizing the PdPt morphology, a method for selecting the minimum active unit of PdPt catalysts with different ratios was proposed, that is, the most stable active unit: rhombus structure was determined according to the surface formation energy. Moreover, we correlated the relationship among the number of H atoms removed, adsorption energy, surface charge, activation energy, reaction energy, and surface coverage, and obtained the important parameters to predict the performance of PdPt catalyst in PHAN dehydrogenation system: surface charge and d-band center. Finally, the essential correlativity among Pd-Pt surface characteristics, catalytic PHAN activity, and adsorption energy was constructed; that is, the relationship model among d-band center, H atom, and product C12H8 adsorption energy was established. This work opens a new simultaneous path to improve the catalytic performance of Pd-Pt-based catalytic materials for PHAN dehydrogenation, which can be achieved by regulating the rhombic active units of Pt modulated by Pd.

Effects of P:Ni Ratio on Methanol Steam Reforming on Nickel Phosphide Catalysts

This study investigates the influence of the phosphorus-to-nickel (P:Ni) ratio on methanol steam reforming (MSR) over nickel phosphide catalysts using density functional theory (DFT) calculations. The catalytic behavior of Ni(111) and Ni12P5(001) surfaces was explored and contrasted to our previous results from research on Ni2P(001). The DFT-predicted barriers reveal that Ni(111) predominantly favors the methanol decomposition route, where methanol is converted into carbon monoxide through a stepwise pathway involving CH3OH* → CH3O* → CH2O* → CHO* → CO*. On the other hand, Ni12P5 with a P:Ni atomic ratio of 0.42 (5:12) exhibits a substantial increase in selectivity towards methanol steam reforming (MSR) relative to methanol decomposition. In this pathway, formaldehyde is transformed into CO2 through a sequence of reactions involving CH2O*→ H2COOH* → HCOOH* → HCOO* → CO2. The introduction of phosphorus into the catalyst alters the surface morphology and electronic structure, favoring the MSR pathway. However, with a further increase in the P:Ni atomic ratio to 0.5 (1:2) on Ni2P catalysts, the selectivity towards MSR decreases, resulting in a more balanced competition between methanol decomposition and MSR. These results highlight the significance of tuning the P:Ni atomic ratio in designing efficient catalysts for the selective production of CO2 through the MSR route, offering valuable insights into optimizing nickel phosphide catalysts for desired chemical transformations.

Visible-Light-Driven Photocatalytic Dehydrogenation of Alcohols on TiO2 via Ligand-to-Metal Charge Transfer for Coproduction of H2 and Aldehydes

Developing visible-light-driven photocatalysts for the catalytic dehydrogenation of organics is of great significance for sustainable solar energy utilization. Here, we first report that aromatic alcohols could be efficiently split into H₂ and aldehydes over TiO₂ under visible-light irradiation through a ligand-to-metal charge transfer (LMCT) mechanism. A series of TiO₂ catalysts with different surface contents of the hydroxyl group (-OH) have been synthesized by controlling the hydrothermal and calcination synthesis methods. An optimal H₂ production rate of 18.6 μmol h^-1 is obtained on TiO₂ synthesized from the hydrothermal method with a high content of surface -OH. Experimental characterizations and comparison studies reveal that the surface -OH markedly influences the formation of LMCT complexes and thus changes the visible-light-driven photocatalytic performance. This work is anticipated to inspire further research endeavors in the design and fabrication of visible-light-driven photocatalyst systems based on the LMCT mechanism to realize the simultaneous synthesis of clean fuel and fine chemicals.

Computational Studies on Microreactors for the Decomposition of Formic Acid for Hydrogen Production Using Heterogeneous Catalysts

Sustainable alternatives to conventional fuels have emerged recently, focusing on a hydrogen-based economy. The idea of using hydrogen (H₂) as an energy carrier is very promising due to its zero-emission properties. The present study investigates the formic acid (FA) decomposition for H₂ generation using a commercial 5 wt.% Pd/C catalyst. Three different 2D microreactor configurations (packed bed, single membrane, and double membrane) were studied using computational fluid dynamics (CFD). Parameters such as temperature, porosity, concentration, and flow rate of reactant were investigated. The packed bed configuration resulted in high conversions, but due to catalyst poisoning by carbon monoxide (CO), the catalytic activity decreased with time. For the single and double membrane microreactors, the same trends were observed, but the double membrane microreactor showed superior performance compared with the other configurations. Conversions higher than 80% were achieved, and even though deactivation decreased the conversion after 1 h of reaction, the selective removal of CO from the system with the use of membranes lead to an increase in the conversion afterwards. These results prove that the incorporation of membranes in the system for the separation of CO is improving the efficiency of the microreactor.

Innovative Long-Lasting Catalytic Hydrothermal Reaction for High Efficient Energy Harvest and Carbon Capture from Recalcitrant Wastewater

Simultaneous recovery of energy and carbon from recalcitrant wastewater has attracted ever-growing interest for water management. However, the existing technologies to break down recalcitrant pollutants are mainly energy and chemical intensive. Here, a novel hydrothermal reaction amended with activated carbon (AC) was demonstrated to enable an unprecedented 99.5% removal of an exemplar difficult-to-degrade contaminant, polyvinyl alcohol (PVA), from wastewater. Meanwhile, an easy-separated hydrochar (C₆H_7.08O_0.99) with an abundance of unsaturated aromatic rings was produced, exhibiting 118.46% of energy yield with a high heating value of 32.9 MJ/kg, outperforming the hydrochar(s) reported to date. The retrieved energy from the hydrochar was able to entirely offset the energy needs for this hydrothermal process. Interestingly, the AC catalyst can sustain in situ reuse over 125 cycles with no evidence of irreversible deactivation. The adjacent carbonyl groups on AC were revealed to provide active sites for dehydrogenation from either the C-H (1.24 Å) or O-H (1.40 Å) bond in PVA, forming hydroxyl groups on AC and highly reactive intermediates (ΔG⁰ = -11.5 kcal/mol). It was further proved that the free oxygen in the headspace extracted H atoms from the newly formed hydroxyl groups on AC (ΔG⁰ = -4.7 kcal/mol), thus regenerating the carbonyl sites on AC for the next catalytic hydrothermal dehydrogenation cycles. The long-lasting catalyst reusability and energy self-sufficient approach offer a sustainable route to carbon neutrality in recalcitrant wastewater treatment.

Steering the Selectivity of Electrocatalytic Glucose Oxidation by the Pt Oxidation State

Electrocatalytic glucose oxidation can produce high value chemicals, but selectivity needs to be improved. Here we elucidate the role of the Pt oxidation state on the activity and selectivity of electrocatalytic oxidation of glucose with a new analytical approach, using high-pressure liquid chromatography and high-pressure anion exchange chromatography. It was found that the type of oxidation, i.e. dehydrogenation of primary and secondary alcohol groups or oxygen transfer to aldehyde groups, strongly depends on the Pt oxidation state. Pt0 has a 7-fold higher activity for dehydrogenation reactions than for oxidation reactions, while PtOx is equally active for both reactions. Thus, Pt0 promotes glucose dialdehyde formation, while PtOx favors gluconate formation. The successive dehydrogenation of gluconate is achieved selectively at the primary alcohol group by Pt0, while PtOx also promotes the dehydrogenation of secondary alcohol groups, resulting in more complex reaction mixtures.

Nanoscale Ni-NiO-ZnO Heterojunctions for Switchable Dehydrogenation and Hydrogenation through Modulation of Active Sites

Catalysts consisting of metal-metal hydroxide/oxide interfaces are highly in demand for advanced catalytic applications as their multicomponent active sites will enable different reactions to occur in close proximity through synergistic cooperation when a single component fails to promote it. To address this, herein we disclosed a simple, scalable, and affordable method for synthesizing catalysts consisting of nanoscale nickel-nickel oxide-zinc oxide (Ni-NiO-ZnO) heterojunctions by a combination of complexation and pyrolytic reduction. The modulation of active sites of catalysts was achieved by varying the reaction conditions of pyrolysis, controlling the growth, and inhibiting the interlayer interaction and Ostwald ripening through the efficient use of coordinated acetate and amide moieties of Zn-Ni materials (ZN-O), produced by the reaction between hydrazine hydrate and Zn-Ni-acetate complexes. We found that the coordinated organic moieties are crucial for forming heterojunctions and their superior catalytic activity. We analyzed two antagonistic reactions to evaluate the performance of the catalysts and found that while the heterostructure of Ni-NiO-ZnO and their cooperative synergy were crucial for managing the effectiveness and selectivity of the catalyst for dehydrogenation of aryl alkanes/alkenes, they failed to enhance the hydrogenation of nitro arenes. The hydrogenation reaction was influenced by the shape, surface properties, and interaction of the hydroxide and oxide of both zinc and nickel, particularly accessible Ni(0). The catalysts showed functional group tolerance, multiple reusabilities, broad substrate applicability, and good activity for both reactions.

Selective Catalytic Behavior Induced by Crystal-Phase Transformation in Well-Defined Bimetallic Pt-Sn Nanocrystals

The Pt-Sn bimetallic system is a much studied and commercially used catalyst for propane dehydrogenation. The traditionally prepared catalyst, however, suffers from inhomogeneity and phase separation of the active Pt-Sn phase. Colloidal chemistry offers a route for the synthesis of Pt-Sn bimetallic nanoparticles (NPs) in a systematic, well-defined, tailored fashion over conventional methods. Here, the successful synthesis of well-defined ≈2 nm Pt, PtSn, and Pt₃ Sn nanocrystals with distinct crystallographic phases is reported; hexagonal close packing (hcp) PtSn and fcc Pt₃ Sn show different activity and stability depending on the hydrogen-rich or poor environment in the feed. Moreover, face centred cubic (fcc) Pt₃ Sn/Al₂ O₃ , which exhibited the highest stability compared to hcp PtSn, shows a unique phase transformation from an fcc phase to an L1₂ -ordered superlattice. Contrary to PtSn, H₂ cofeeding has no effect on the Pt₃ Sn deactivation rate. The results reveal structural dependency of the probe reaction, propane dehydrogenation, and provide a fundamental understanding of the structure-performance relationship on emerging bimetallic systems.

Synthesis of Tetrahydro-β-carbolines via Manganese-Catalysed Oxidative Pictet-Spengler Reaction

Herein, an efficient and green procedure for the synthesis of tetrahydro-β-carbolines via dehydrogenative coupling of alcohols with tryptamines is reported. The reaction was carried out under mild conditions in the presence of a catalytic amount of the i PrPNP-Mn catalyst and a weak base (Na2CO3). This method tolerated a variety of benzylic and aliphatic alcohol substrates with different functional groups and afforded diverse products in good to excellent isolated yields using tryptamines. Using this strategy, we successfully synthesised pharmaceutical molecules harman, harmaline, and harmine in a concise manner.

DFT mechanistic investigation on manganese pincer complex catalyzed cross-coupling of methanol with benzyl alcohol to afford methyl benzoate

In this paper the density functional theory (DFT) method was employed to investigate the cross-coupling of methanol with benzyl alcohol to afford methyl benzoate catalyzed by Mn-PNN pincer complex. The whole reaction process mainly includes three stages: the dehydrogenation of benzyl alcohol to benzaldehyde, the coupling of benzaldehyde with methanol to hemiacetal and the dehydrogenation of hemiacetal to methyl benzoate. The calculated results indicated that two dehydrogenation processes are influenced by two competitive mechanisms of inner and outer spheres. Dehydrogenation of benzyl alcohol to benzaldehyde is the rate-determining step of the whole reaction, with the energy barrier of 22.1 kcal/mol. In addition, the regeneration of catalyst is also extremely important. Compared with direct dehydrogenation, the dehydrogenation mode assisted by formic acid is more advantageous. This work might provide theoretical insights and shed light on the design of cheap transition-metal catalysts for the dehydrogenation reaction.

Brønsted Acid Promoted Facile Synthesis of Benzoacridines from Aromatic Aldehydes and N-Phenyl Naphthylamines

A facile method for the rapid synthesis of benzoacridines has been described. This protocol promoted by p-toluenesulfonic acid starts from aromatic aldehydes and N-phenyl naphthylamines, affording a variety of benzoacridines in 30-90 % yields under metal-free conditions. The present approach involves a cascade of condensation, Friedel-Crafts alkylation, annulation and dehydroaromatization in one pot.

Carboxylic-Phosphoric Anhydrides as Direct Electrophiles for Decarbonylative Hirao Cross-Coupling of Carboxylic Acids: DFT Investigation of Mechanistic Pathway

In this anniversary issue, we present a DFT study of the mechanism of decarbonylative Hirao cross-coupling of carboxylic-phosphoric anhydrides to afford aryl phosphonates. Traditionally, the direct activation of carboxylic acids to participate in decarbonylative couplings is performed in the presence of carboxylic acid anhydride activators. We discovered that direct dehydrogenative decarbonylative phosphorylation of benzoic acid can be performed in high yield via dehydrogenative and decarbonylative coupling in the presence of phosphite as dual activating and nucleophilic reagent, enabling direct decarbonylative phosphorylation. Control studies demonstrated that carboxylic-phosphoric anhydride (acyl phosphate) is an intermediate in this process. DFT studies were conducted to gain insight into this decarbonylative process and compare the selectivity of C-O and P-O bond activations. Considering the utility of ubiquitous carboxylic acids, this alternative activation pathway may find applications in decarbonylative coupling of carboxylic acids for the synthesis of valuable molecules in organic synthesis.

Preparation, Structure-Performance Relationship, and Reaction Network of ZnZSM-5 for Oxidative Dehydrogenation of Ethane with CO2

Ethylene (C₂ H₄ ) is a major chemical for the modern society, and new technologies for its production are of strategic importance globally. Recently, oxidative dehydrogenation of ethane (C₂ H₆ ) using CO₂ as a milder oxidant (CO₂ -ODH) is proposed as a potential way for C₂ H₄ production, and development of effective catalysts for the process is drawing wide attention. Here, we report on a facilely prepared ZSM-5 supported Zn system, i. e., ZnZSM-5, which showed great promise in CO₂ -ODH. Samples with different Zn loadings were prepared and evaluated, and the highest performance was obtained over 0.05ZnZSM-5 at 700 °C and a CO₂ :C₂ H₆ feeding ratio of 5 : 1. During 340 min TOS, the C₂ H₆ conversion decreased moderately from 36.2 % to 23.1 %, and the C₂ H₄ yield stabilized at 21.9 % to 27.9 %. Based on systematic characterization and investigation of reaction conditions, the structure-performance relationship and reaction network were discussed in detail.

Liquid-Phase Reactions

Formic acid has recently been revealed to be an excellent hydrogen carrier, and interest in the development of efficient and selective catalysts towards its dehydrogenation has grown. This reaction has been widely explored using homogeneous catalysts; however, from a practical and scalable point of view, heterogeneous catalysts are usually preferred in industry. In this work, formic acid dehydrogenation reactions in both liquid- and vapor-phase conditions have been investigated using heterogeneous catalysts based on mono- or bimetallic Pd/Ru. In all of the explored conditions, the catalysts showed good catalytic activity and selectivity towards the dehydrogenation reaction, avoiding the formation of undesired CO.

Influence of Citrates and EDTA on Oxidation and Decarboxylation of Betacyanins in Red Beet (Beta vulgaris L.) Betalain-Rich Extract

The influence of stabilizing activity of citric buffers on betacyanins, as well as their thermal dehydrogenation and decarboxylation in a beetroot betalain-rich extract (BRE), was studied at pH 3-8 and temperature 30, 50 and 85 °C with an additional effect of EDTA. In acetate/phosphate buffers, the highest stability is observed at pH 5 and it decreases toward pH 3 as well as pH 8, which is more remarkable at 85 °C. For the citrates, a contradictory effect was observed. Citric buffers tend to stabilize the substrate pigments and their intermediary products in acidic solutions, although increase their reactivity at pH 6-8. The highest impact of EDTA addition on pigment retention in acetate buffers is observed at 85 °C and pH 3-5 as well as 8, reflecting the preserving activity of EDTA at the most unfavorable conditions. At lower temperatures, pigment stability in more acidic conditions is still at higher levels even without addition of citrates or EDTA. The most striking effect on generation of betanin derivatives during heating is 2-decarboxylation which preferentially proceeds in the most acidic environment and this generation rate at 85 °C is much higher in the citrate buffers compared to acetates.

Activity of Mono-, Bi-, and Trimetallic Catalysts Pt-Ni-Cr/C in the Bicyclohexyl Dehydrogenation Reaction

The influence of metals with different redox properties and a carbon carrier on the activity of mono-, bi- and trimetallic Pt-Ni-Cr/C catalysts has been studied in the bicyclohexyl dehydrogenation reaction as the hydrogen release stage in hydrogen storage. An increase in the conversion (X > 62%) of bicyclohexyl and selectivity for biphenyl (S > 84%) was observed on trimetallic catalysts Pt-Ni-Cr/C compared with the monometallic catalyst Rt/C (X > 55%; S > 68%). It has been established that the increase in the conversion of bicyclohexyl and selectivity for biphenyl in the dehydrogenation reaction on trimetallic catalysts is due to an increase in the activity of Pt nanoparticles in the vicinity of local Cr-Ni clusters of solid substitution solutions.

Understanding the Behaviour of Real Metaborates in Solution

Alkali metal borohydrides are promising candidates for large-scale hydrogen storage. They react spontaneously with water, generating dihydrogen and metaborate salts. While sodium borohydride is the most studied, potassium has the best chance of commercial application. Here we examine the physical and chemical properties of such self-hydrolysis solutions. We do this by following the hydrogen evolution, the pH changes, and monitoring the reaction intermediates using NMR. Most studies on such systems are done using dilute solutions, but real-life applications require high concentrations. We show that increasing the borohydride concentration radically changes the system's microstructure and rheology. The changes are seen already at concentrations as low as 5 w/w%, and are critical above 10 w/w%. While dilute solutions are Newtonian, concentrated reaction solutions display non-Newtonian behaviour, that we attribute to the formation and (dis)entanglement of metaborate oligomers. The implications of these findings towards using borohydride salts for hydrogen storage are discussed.

Precursor prioritization for p-cymene production through synergistic integration of biology and chemistry

The strategy of synergistic application of biological and chemical catalysis is an important approach for efficiently converting renewable biomass into chemicals and fuels. In particular, the method of determining the appropriate intermediate between the two catalytic methods is critical. In this work, we demonstrate p-cymene production through the integration of biosynthesis and heterogenous catalysis and show how a preferred biologically derived precursor could be determined. On the biological side, we performed the limonene and 1,8-cineole production through the mevalonate pathway. Titers of 0.605 g/L and a 1.052 g/L were achieved, respectively. This difference is in agreement with the toxicity of these compounds toward the producing microorganisms, which has implications for subsequent development of the microbial platform. On the heterogeneous catalysis side, we performed the reaction with both biological precursors to allow for direct comparison. Using hydrogenation/dehydrogenation metals on supports with acid sites, both limonene and 1,8-cineole were converted to p-cymene with similar yields under equivalent reaction conditions. Thus, we could determine that the most promising strategy would be to target 1,8-cineole, the higher titer and lower toxicity bio-derived precursor with subsequent catalytic conversion to p-cymene. We further optimized the biological production of 1,8-cineole via fed-batch fermentation and reached the titer of 4.37 g/L which is the highest known 1,8-cineole titer from microbial production. This work provides a valuable paradigm for early stage considerations to determine the best route for the high-efficiency production of a target biobased molecule using an integration of biology and chemistry.

Selective Oxidation of Glycerol via Acceptorless Dehydrogenation Driven by Ir(I)-NHC Catalysts

Iridium(I) compounds featuring bridge-functionalized bis-NHC ligands (NHC = N-heterocyclic carbene), [Ir(cod)(bis-NHC)] and [Ir(CO)₂(bis-NHC)], have been prepared from the appropriate carboxylate- or hydroxy-functionalized bis-imidazolium salts. The related complexes [Ir(cod)(NHC)₂]⁺ and [IrCl(cod)(NHC)(cod)] have been synthesized from a 3-hydroxypropyl functionalized imidazolium salt. These complexes have been shown to be robust catalysts in the oxidative dehydrogenation of glycerol to lactate (LA) with dihydrogen release. High activity and selectivity to LA were achieved in an open system under low catalyst loadings using KOH as a base. The hydroxy-functionalized bis-NHC catalysts are much more active than both the carboxylate-functionalized ones and the unbridged bis-NHC iridium(I) catalyst with hydroxyalkyl-functionalized NHC ligands. In general, carbonyl complexes are more active than the related 1,5-cyclooctadiene ones. The catalyst [Ir(CO)₂{(MeImCH₂)₂CHOH}]Br exhibits the highest productivity affording TONs to LA up to 15,000 at very low catalyst loadings.

Endothermic Dehydrogenation-Driven Preventive Magnesiation of SiO for High-Performance Lithium Storage Materials

Silicon monoxide (SiO)-based materials have gained much attention as high-capacity lithium storage materials based on their high capacity and stable capacity retention. However, low initial Coulombic efficiency associated with the irreversible electrochemical reaction of the amorphous SiO₂ phase in SiO inhibits the wide usage of SiO-based anode materials for lithium-ion batteries. Magnesiation of SiO is one of the most promising solutions to improve the initial efficiency of SiO-based anode materials. Herein, we demonstrate that endothermic dehydrogenation-driven magnesiation of SiO employing MgH₂ enhanced the initial Coulombic efficiency of 89.5% with much improved long-term cycle performance over 300 cycles compared to the homologue prepared by magnesiation of SiO with Mg and pristine SiO. High-resolution transmission electron microscopy with thermogravimetry-differential scanning calorimetry revealed that the endothermic dehydrogenation of MgH₂ suppressed the sudden temperature rise during magnesiation of SiO, thereby inhibiting the coarsening of the active Si phase in the resulting Si/Mg₂SiO₄ nanocomposite.

Dehydrogenation versus deprotonation of disaccharide molecules in vacuum: a thorough theoretical investigation

Dehydrogenation and deprotonation of sucrose and trehalose molecules in vacuum is theoretically studied by using ab initio calculations in the framework of the density functional theory. The differences in the structural, electronic, energetic and vibrational properties of dehydrogenated and deprotonated molecules are discussed, depending on the site from which the hydrogen atom or the proton has been removed. The dehydrogenated molecules are found to be stable, regardless of which hydrogen atom is removed. This contrasts with the instability of the deprotonated molecules, where break-ups or structural reorganizations of the molecule are observed in 20-30% of the cases, but only when the hydrogen atom whose proton is removed was bonded to a carbon atom. Considering the stability and possible rearrangements of the hydrogen network of the deprotonated/dehydrogenated molecule, the formation of additional hydrogen-bridge bonds compared with the nominal molecule appears to be more pronounced for the deprotonated molecules than for the dehydrogenated ones. Moreover, our calculations show that the hydrogen-transfer energy barriers are usually larger for the deprotonated molecules than for the dehydrogenated ones. Finally, compared with the nominal molecule, the vibrational frequency spectrum is shifted to lower frequencies for both the dehydrogenated and the deprotonated molecules.

Dissecting the Mechanism of the Nonheme Iron Endoperoxidase FtmOx1 Using Substrate Analogues

FtmOx1 is a nonheme iron (NHFe) endoperoxidase, catalyzing three disparate reactions, endoperoxidation, alcohol dehydrogenation, and dealkylation, under in vitro conditions; the diversity complicates its mechanistic studies. In this study, we use two substrate analogues to simplify the FtmOx1-catalyzed reaction to either a dealkylation or an alcohol dehydrogenation reaction for structure-function relationship analysis to address two key FtmOx1 mechanistic questions: (1) Y224 flipping in the proposed COX-like model vs α-ketoglutarate (αKG) rotation proposed in the CarC-like mechanistic model and (2) the involvement of a Y224 radical (COX-like model) or a Y68 radical (CarC-like model) in FtmOx1-catalysis. When 13-oxo-fumitremorgin B (7) is used as the substrate, FtmOx1-catalysis changes from the endoperoxidation to a hydroxylation reaction and leads to dealkylation. In addition, consistent with the dealkylation side-reaction in the COX-like model prediction, the X-ray structure of the FtmOx1•Co^II•αKG•7 ternary complex reveals a flip of Y224 to an alternative conformation relative to the FtmOx1•Fe^II•αKG binary complex. Verruculogen (2) was used as a second substrate analogue to study the alcohol dehydrogenation reaction to examine the involvement of the Y224 radical or Y68 radical in FtmOx1-catalysis, and again, the results from the verruculogen reaction are more consistent with the COX-like model.

Continuous Room-Temperature Hydrogen Release from Liquid Organic Carriers in a Photocatalytic Packed-Bed Flow Reactor

Despite the potential of hydrogen (H₂ ) storage in liquid organic carriers to achieve carbon neutrality, the energy required for H₂ release and the cost of catalyst recycling have hindered its large-scale adoption. In response, a photo flow reactor packed with rhodium (Rh)/titania (TiO₂ ) photocatalyst was reported for the continuous and selective acceptorless dehydrogenation of 1,2,3,4-tetrahydroquinoline to H₂ gas and quinoline under visible light irradiation at room temperature. The tradeoff between the reactor pressure drop and its photocatalytic surface area was resolved by selective in-situ photodeposition of Rh in the photo flow reactor post-packing on the outer surface of the TiO₂ microparticles available to photon flux, thereby reducing the optimal Rh loading by 10 times compared to a batch reactor, while facilitating catalyst reuse and regeneration. An example of using quinoline as a hydrogen acceptor to lower the energy of the hydrogen production step was demonstrated via the water-gas shift reaction.

Enhanced Catalytic Performance of N-Doped Carbon Sphere-Supported Pd Nanoparticles by Secondary Nitrogen Source Regulation for Formic Acid Dehydrogenation

The development of catalysts with high selectivity, good catalytic activity, and excellent cycle performance is of significance for the application of formic acid (HCOOH, FA) as a hydrogen support. Herein, Pd is deposited on a series of N-doped carbons, which are prepared by cocarbonization of N-containing zeolite imidazole frameworks (ZIF-8) and other N/C sources (melamine, xylitol, urea, and glucose), for hydrogen generation from FA. The results demonstrate that the introduction of a secondary N/C source further affects the catalytic performance of Pd by adjusting the morphology, specific surface area, N content, and type of carbon. The effects of N atoms and the favorable reaction pathways of FA dehydrogenation were revealed by theoretical calculation. This work will improve the understanding of N doping on the decomposition mechanism of FA and provide a new approach for the rational design of metal-N-C materials.

Iridium-Catalyzed Dehydrogenation in a Continuous Flow Reactor for Practical On-Board Hydrogen Generation From Liquid Organic Hydrogen Carriers

To enable the large-scale use of hydrogen fuel cells for mobility applications, convenient methods for on-board hydrogen storage and release are required. A promising approach is liquid organic hydrogen carriers (LOHCs), since these are safe, available on a large scale, and compatible with existing refueling infrastructure. Usually, LOHC dehydrogenation is carried out in batch-type reactors by transition metals and their complexes and suffers from slow H₂ release kinetics and/or inability to reach high energy density by weight, owing to low conversion or the need to dilute the reaction mixture. In this study, a continuous flow reactor is used in combination with a heterogenized iridium pincer complex, which enables a tremendous increase in LOHC dehydrogenation rates. Thus, dehydrogenation of isopropanol is performed in a regime that, in terms of gravimetric energy density, hydrogen generation rate, and precious metal content, is potentially compatible with applications in a fuel-cell powered car.

Superior Dehydrogenation Performance of α-AlH3 Catalyzed by Li3 N: Realizing 8.0 wt.% Capacity at 100 °C

The high dehydrogenation temperature of aluminum hydride (AlH₃ ) has always been an obstacle to its application as a portable hydrogen source. To solve this problem, lithium nitride is introduced into the aluminum hydride system as a catalyst to optimize the dehydrogenation drastically, which reduces the initial dehydrogenation temperature from 140.0 to 66.8 °C, and provides a stable hydrogen capacity of 8.24, 6.18, and 5.75 wt.% at 100, 90, and 80 °C within 120 min by adjusting the mass fraction of lithium nitride. Approximately 8.0 wt.% hydrogen can be released within 15 min at 100 °C for the sample of 10 wt.% doping. Moderate dehydrogenation temperature slows down the inevitable self-dehydrogenation process during the ball-milling process, and the enhanced kinetics at lower temperature shows the possibility of application in the fuel cell.

Kinetic Modeling of Hydrogen Production by Dehydrogenation of Polycyclic Naphthenes with Varying Degrees of Condensation

The kinetics of reactions of dehydrogenation of polycyclic naphthenes (cyclohexane, decalin, bicyclohexyl, ortho-, meta-, and para-isomers of perhydroterphenyl) is modeled on the basis of a formal comparison of kinetic equations of the 1st and 2nd orders based on real experimental data. It is shown that the reaction of the 1st order is predominating in the series of cyclohexane–bicyclohexyl–perhydroparatherphenyl. For all other substrates, the probability of describing the reaction in accordance with the equation of the 2nd order increases markedly, and for trans-decalin it becomes the predominant form of describing the kinetics of the reaction.

Tailoring Single-Atom Platinum for Selective and Stable Catalysts in Propane Dehydrogenation

Propane dehydrogenation has been a promising method for producing propylene that has the potentials to meet the increasing global demand for propylene. However, owing to the restricted equilibrium conversion caused by the high endothermicity, even the Pt-based catalysts, which exhibit high activity and selectivity, severely suffer significantly from coke formation and/or nanoparticle sintering at realistic reaction temperatures, resulting in a short catalyst lifetime. As a result, few innovative catalysts in terms of catalytic activity, selectivity, and stability, have been produced. In this Review, we focus on the characteristics of single-atom-like Pt sites for PDH and attempt to provide suggestions for developing highly efficient catalysts. First, we briefly describe the fundamental strategies. Following that, the remarkable catalysis is addressed by three different distinct sorts of state-of-the-art single-atom-like Pt catalysts are discussed. Additionally, we present other promising catalyst design approaches that are not based on single-atom-like Pt catalysts, as well as future research challenges in this field.

Dehydrogenation of Betacyanins in Heated Betalain-Rich Extracts of Red Beet (Beta vulgaris L.)

Betacyanins are a group of water-soluble red-violet compounds containing nitrogen in their structure. These are biosynthesized in red beetroot (Beta vulgaris L.), a widely consumed vegetable that contains significant amounts of nutritious and bioactive compounds which are also found in dietary supplements. This contribution presents results of betacyanin thermal oxidation (resulting in dehydrogenation) interrelated with decarboxylation in selected acetate/phosphate buffers at pH 3–8 and at 85 °C, which may be of particular significance for formulation and performance of foods. Most of the reaction products were detected at the highest concentrations in the acidic solutions (pH 3–4). The main dehydrogenation reaction pathways were monitored by LC-DAD-MS/MS and were associated with decarboxylation of the principal extract pigments, betanin/isobetanin and neobetanin, at carbon positions C-2 and C-17. Additional reactions are accompanied by the 2,15-decarboxylation processes at different dehydrogenation levels with 15-decarboxy-betanin and 2,15-bidecarboxy-betanin, structurally elucidated by NMR analysis, as the distinct indicators of this route type. For other novel pigments detected, 2,15-bidecarboxy-xanbetanin, 2,15-bidecarboxy-xanneobetanin and 2,15,17-tridecarboxy-neobetanin, additional high resolution mass spectrometric analyses were performed and confirmed their molecular formulas.

Acceptorless Dehydrogenation of Methanol to Carbon Monoxide and Hydrogen using Molecular Catalysts

The acceptorless dehydrogenation of methanol to carbon monoxide and hydrogen was investigated using homogeneous molecular complexes. Complexes of ruthenium and manganese comprising the MACHO ligand framework showed promising activities for this reaction. The molecular ruthenium complex [RuH(CO)(BH4 )(HN(C2 H4 PPh2 )2 )] (Ru-MACHO-BH) achieved up to 3150 turnovers for carbon monoxide and 9230 turnovers for hydrogen formation at 150 °C reaching pressures up to 12 bar when the decomposition was carried out in a closed vessel. Control experiments affirmed that the metal complex mediates the initial fast dehydrogenation of methanol to formaldehyde and methyl formate followed by subsequent slow decarbonylation. Depending on the catalyst and reaction conditions, the CO/H2 ratio in the gas mixture thus varies over a broad range from almost pure hydrogen to the stoichiometric limit of 1:2.

Experimental Assessment of Perhydro-Dibenzyltoluene Dehydrogenation Reaction Kinetics in a Continuous Flow System for Stable Hydrogen Supply

The development of alternate clean energy resources is among the most pressing issues in the energy sector in order to preserve the global natural environment. One of the ideal candidates is the utilization of hydrogen as a primary fuel in lieu of fossil fuels. It can be safely stored in liquid organic hydrogen carrier (LOHC) materials and recovered on demand. A uniform supply of hydrogen is essential for power production systems for their smooth operation. This study was conducted to determine the operating conditions of the dehydrogenation of perhydro-dibenzyltoluene (H18-DBT) to ensure that hydrogen supply in a continuous flow reactor remains stable over a wide range of temperatures. The hydrogen flow rate from the dehydrogenation reaction was measured and correlated with the degree of dehydrogenation (DoD) evaluated from the refractive index of reactant liquid samples at various temperatures, WHSV and the initial reactant concentrations. Moreover, a kinetic model is presented holding validity up to a WHSV of 67 h⁻¹. The results acquired present a range for an order of reaction from 2.3 to 2.4 with the required activation energy of 171 kJ/mol.

Direct transformation of n-alkane into all-trans conjugated polyene via cascade dehydrogenation

Selective C(sp³) −H activation is of fundamental importance in processing alkane feedstocks to produce high-value-added chemical products. By virtue of an on-surface synthesis strategy, we report selective cascade dehydrogenation of n-alkane molecules under surface constraints, which yields monodispersed all-trans conjugated polyenes with unprecedented length controllability. We are also able to demonstrate the generality of this concept for alkyl-substituted molecules with programmable lengths and diverse functionalities, and more importantly its promising potential in molecular wiring.

Reduced Graphene Oxides as Carbocatalysts in Acceptorless Dehydrogenation of N-Heterocycles

The catalytic properties of graphene-derived materials are evaluated in acceptorless dehydrogenation of N-heterocycles. Among them, reduced graphene oxides (rGOs) are active (quantitative yields in 23 h) under mild conditions (130 °C) and act as efficient heterogeneous carbocatalysts. rGO exhibits reusability and stability at least during eight consecutive runs. Mechanistic investigations supported by experimental evidence (i.e., organic molecules as model compounds, purposely addition of metal impurities and selective functional group masking experiments) suggest a preferential contribution of ketone carbonyl groups as active sites for this transformation.

Recent Advances in Catalysts and Membranes for MCH Dehydrogenation: A Mini Review

Methylcyclohexane (MCH), one of the liquid organic hydrogen carriers (LOHCs), offers a convenient way to store, transport, and supply hydrogen. Some features of MCH such as its liquid state at ambient temperature and pressure, large hydrogen storage capacity, its well-known catalytic endothermic dehydrogenation reaction and ease at which its dehydrogenated counterpart (toluene) can be hydrogenated back to MCH and make it one of the serious contenders for the development of hydrogen storage and transportation system of the future. In addition to advances on catalysts for MCH dehydrogenation and inorganic membrane for selective and efficient separation of hydrogen, there are increasing research interests on catalytic membrane reactors (CMR) that combine a catalyst and hydrogen separation membrane together in a compact system for improved efficiency because of the shift of the equilibrium dehydrogenation reaction forwarded by the continuous removal of hydrogen from the reaction mixture. Development of efficient CMRs can serve as an important step toward commercially viable hydrogen production systems. The recently demonstrated commercial MCH-TOL based hydrogen storage plant, international transportation network and compact hydrogen producing plants by Chiyoda and some other companies serves as initial successful steps toward the development of full-fledged operation of manufacturing, transportation and storage of zero carbon emission hydrogen in the future. There have been initiatives by industries in the development of compact on-board dehydrogenation plants to fuel hydrogen-powered locomotives. This review mainly focuses on recent advances in different technical aspects of catalytic dehydrogenation of MCH and some significant achievements in the commercial development of MCH-TOL based hydrogen storage, transportation and supply systems, along with the challenges and future prospects.