Multifunctional Pd@UiO-66 Catalysts for Continuous Catalytic Upgrading of Ethanol to n-Butanol

Heterogeneous activation of self-generated H2O2 by Pd@UiO-66(Zr) for trimethoprim degradation: Efficiency and mechanism

The Fenton reaction is recognized as an effective technique for degrading persistent organic pollutants, such as the emerging pollutant trimethoprim (TMP). Recently, due to the excellent reducibility of active hydrogen ([H]), Pd-H2 has been preferred for Fenton-like reactions and the specific H2 activation of Pd-based catalysts. Herein, a heterogeneous Fenton catalyst named the hydrogen-accelerated oxygen reduction Fenton (MHORF@UiO-66(Zr)) system was prepared through the strategy of building ships in the bottle. The [H] has been used for the acceleration of the reduction of Fe(III) and self-generate H2O2. The systematic characterization demonstrated that the nano Pd0 particle was highly dispersed into the UiO-66(Zr). The results found that 20 mg L-1 of TMP was thoroughly degraded within 90 min in the MHORF@UiO-66(Zr) system under conditions of initial pH 3, 30 mL min-1 H2, 2 g L-1 Pd@UiO-66(Zr) and 25 μM Fe2+. The hydroxyl radical as well as the singlet oxygen were evidenced to be the main reactive oxygen species by scavenging experiments and electron spin resonance. In addition, both reducing Fe(III) and self-generating H2O2 could be achieved due to the strong metal-support interaction (SMSI) between the nano Pd0 particles and UiO-66(Zr) confirmed by the correlation results of XPS and calculation of density functional theory. Finally, the working mechanism of the MHORF@UiO-66(Zr) system and the possible degradation pathway of the TMP have been proposed. The novel system exhibited excellent reusability and stability after six cyclic reaction processes.

Nanoscale solvent organization in metal-organic framework ZIF-8 probed by EPR of flexible β-phosphorylated nitroxides

Metal-organic frameworks (MOFs) draw increasing attention as nanoenvironments for chemical reactions, especially in the field of catalysis. Knowing the specifics of MOF cavities is decisive in many of these cases; yet, obtaining them in situ remains very challenging. We report the first direct assessment of the apparent polarity and solvent organization inside MOF cavities using a dedicated structurally flexible spin probe. A stable β-phosphorylated nitroxide radical was incorporated into the cavities of a prospective MOF ZIF-8 in trace amounts. The spectroscopic properties of this probe depend on local polarity, structuredness, stiffness and cohesive pressure and can be precisely monitored by Electron Paramagnetic Resonance (EPR) spectroscopy. Using this approach, we have demonstrated experimentally that the cavities of bare ZIF-8 are sensed by guest molecules as highly non-polar inside. When various alcohols fill the cavities, remarkable self-organization of solvent molecules is observed leading to a higher apparent polarity in MOFs compared to the corresponding bulk alcohols. Accounting for such nanoorganization phenomena can be crucial for optimization of chemical reactions in MOFs, and the proposed methodology provides unique routes to study MOF cavities inside in situ, thus aiding in their various applications.

Designed Synthesis of Fe/Zr Bimetallic Organic Framework to Enhance the Selective Conversion of H2S to Sulfur

The development of stable and effective catalysts to convert toxic H2S into high value-added sulfur is essential for production safety and environmental protection. However, the inherent defects of traditional iron- and zirconium-based catalysts, such as poor activity, high oxygen consumption, and low sulfur selectivity, limit their further developments and applications. Herein, the Fe-Zr bimetallic organic framework FeUIO-66(x) with different cubic morphologies was synthesized via a facile solvothermal method. The results indicate that the introduction of Fe not only increases the specific surface area and weak L-sites of the catalyst without changing its crystal structure, which provides enough reaction space and more active sites for the adsorption and activation of H2S, but also reduces the activation energy of the reaction, significantly promoting the selective oxidation of H2S. As a result, the as-obtained FeUIO-66(1) catalyst exhibits the highest desulfurization activity and superior durability and water resistance stability, and its H2S conversion and sulfur selectivity within 50 h are 100 and 88%, respectively. More importantly, the structure of the catalyst after the desulfurization reaction is consistent with that of the fresh counterpart. The study offers new insights into the development of effective and stable bimetallic catalysts to eliminate H2S and recycle sulfur.

One-Step Hydrothermal/Solvothermal Preparation of Pt/TiO2: An Efficient Catalyst for Biobutanol Oxidation at Room Temperature

The selective oxidation of biobutanol to prepare butyric acid is an important conversion process, but the preparation of low-temperature and efficient catalysts for butanol oxidation is currently a bottleneck problem. In this work, we prepared Pt-TiO2 catalysts with different Pt particle sizes using a simple one-step hydrothermal/solvothermal method. Transmission electron microscopy and X-ray diffraction results showed that the average size of the Pt particles ranged from 1.1 nm to 8.7 nm. Among them, Pt-TiO2 with an average particle size of 3.6 nm exhibited the best catalytic performance for biobutanol. It was capable of almost completely converting butanol, even at room temperature (30 °C), with a 98.9% biobutanol conversion, 98.4% butyric acid selectivity, and a turnover frequency (TOF) of 36 h-1. Increasing the reaction temperature to 80 and 90 °C, the corresponding TOFs increased rapidly to 355 and 619 h-1. The relationship between the electronic structure of Pt and its oxidative performance suggests that the synergistic effect of the dual sites, Pt0 and Pt2+, could be the primary factor contributing to its elevated reactivity.

Synthesis of Long Chain Oxygenates via Aldol Condensation of Furfural and Acetone over Metal-Organic Frameworks

Enormous efforts have been made to convert biomass to liquid fuels and products catalytically. Long molecules with a suitable structure are ideal precursors for fuels and value-added products. Here, a C21 oxygenate was synthesized for the first time in one step through aldol condensation of furfural and acetone over the amine-functionalized zirconium-based metal-organic framework (MOF), UiO-66-NH2. Structural changes of UiO-66-NH2 were investigated to improve the yield and evaluate the role of the ligand, cluster node, defectiveness, modulator, surface area, and textural properties on the product distribution. We demonstrate the possibility of making long-chain oxygenates without using vegetable oil-derived fatty acids toward 100% waste biomass-derived renewable fuels, lubricants, and surfactants.

Enabling direct-growth route for highly efficient ethanol upgrading to long-chain alcohols in aqueous phase

Upgrading ethanol to long-chain alcohols (LAS, C6+OH) offers an attractive and sustainable approach to carbon neutrality. Yet it remains a grand challenge to achieve efficient carbon chain propagation, particularly with noble metal-free catalysts in aqueous phase, toward LAS production. Here we report an unconventional but effective strategy for designing highly efficient catalysts for ethanol upgrading to LAS, in which Ni catalytic sites are controllably exposed on surface through sulfur modification. The optimal catalyst exhibits the performance well exceeding previous reports, achieving ultrahigh LAS selectivity (15.2% C6OH and 59.0% C8+OH) at nearly complete ethanol conversion (99.1%). Our in situ characterizations, together with theoretical simulation, reveal that the selectively exposed Ni sites which offer strong adsorption for aldehydes but are inert for side reactions can effectively stabilize and enrich aldehyde intermediates, dramatically improving direct-growth probability toward LAS production. This work opens a new paradigm for designing high-performance non-noble metal catalysts for upgrading aqueous EtOH to LAS.

Ni-Based Hydrotalcite (HT)-Derived Cu Catalysts for Catalytic Conversion of Bioethanol to Butanol

Catalytic conversion of biomass-derived ethanol into n-butanol through Guerbet coupling reaction has become one of the key reactions in biomass valorization, thus attracting significant attention recently. Herein, a series of supported Cu catalysts derived from Ni-based hydrotalcite (HT) were prepared and performed in the continuous catalytic conversion of ethanol into butanol. Among the prepared catalysts, Cu/NiAlOx shows the best performance in terms of butanol selectivity and catalyst stability, with a sustained ethanol conversion of ~35% and butanol selectivity of 25% in a time-on-stream (TOS) of 110 h at 280 °C. While for the Cu/NiFeOx and Cu/NiCoOx, obvious catalyst deactivation and/or low butanol selectivity were obtained. Extensive characterization studies of the fresh and spent catalysts, i.e., X-ray diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Hydrogen temperature-programmed reduction (H2-TPR), reveal that the catalysts' deactivation is mainly caused by the support deconstruction during catalysis, which is highly dependent on the reducibility. Additionally, an appropriate acid-base property is pivotal for enhancing the product selectivity, which is beneficial for the key process of aldol-condensation to produce butanol.

Homologous RuO2-Ru heterostructures for tandem catalytic upgrading of ethanol

The homologous RuO₂-Ru heterostructure was demonstrated as an efficient tandem catalyst for upgrading ethanol. The adjacent RuO₂ and Ru separately serve as aldol condensation/dehydration and dehydrogenation/hydrogenation sites for ethanol conversion.

Boosting Activity and Selectivity of UiO-66 through Acidity/Alkalinity Functionalization in Dimethyl Carbonate Catalysis

The acid-base properties of supports have an enormous impact on catalytic reactions to regulate the selectivity and activity of supported catalysts. Herein, a train of Pd-X-UiO-66 (X = NO₂ , NH₂ , and CH₃ ) catalysts with different acidity/alkalinity functional groups and encapsulated Pd(II) species is first developed, whose activities in dimethyl carbonate (DMC) catalysis are then investigated in details. Thereinto, the Pd-NO₂ -UiO-66 catalyst with acidity functionalization exhibits the best catalytic behavior: the DMC selectivity stemmed from methyl nitrite (MN) is up to 68%, the conversion of CO is 73.4%. The obtained experimental results demonstrate that the NO₂ group not only affected the interaction between X-UiO-66 and Pd(II) active sites but also play an indispensable role in the adsorption and activation of MN and CO, which remarkably promote the formation of the COOCH₃ ^* intermediate and DMC product.

Confined-based catalyst investigation through the comparative functionalization and defunctionalization of Zr-MOF

In metal-organic frameworks, confined space as a chemical nanoreactor is as important as organocatalysis or coordinatively unsaturated metal site catalysis. In the present study, a set of mixed-ligand structures with UiO-66 architecture have been prepared. To the best of our knowledge, for the first time, structures derived by the solvothermal mixing ligand method and ultrasonic-assisted linker exchange approaches have been compared. Additionally, the relationship between the preparation method, structural properties, and catalytic efficiency of the prepared materials in the Knoevenagel condensation of aldehydes has been investigated. The prepared catalyst is very stable and can be recovered and reused for at least ten periods.

Enabling alcohol as a hydrogen carrier using metal-organic framework-stabilized Ir-Sc bifunctional catalytic sites

Alcohols are attractive portable chemical carriers of hydrogen thanks to their reversible dehydrogenation, but the hydrogen release reaction is thermodynamically unfavorable. Coupling the alcohol dehydrogenation to acetal formation can shift the reaction thermodynamics for hydrogen production. Here, we stabilized Ir³⁺ and Sc³⁺ in a metal-organic framework (MOF) for tandem catalysis. The Ir³⁺ center bearing an α-hydroxybipyridine ligand catalyzes alcohol dehydrogenation, and the Sc³⁺ Lewis acid site catalyzes acetal formation that allows further dehydrogenation to form esters. The bifunctional UiO-bpyOH-IrCp-Sc catalyst effectively converts ethylene glycol to ester and H₂ without producing CO.

Preparation and characterization of an edible metal-organic framework/rice wine residue composite

In this communication, using rice wine residue (RWR) as the support, an edible γ-cyclodextrin-metal-organic framework/RWR (γ-CD-MOF/RWR) composite with a macroscopic morphology was synthesized. The obtained edible composite is promising for applications in drug delivery, adsorption, food processing, and others.

Preparation of CeO2/UiO-66-NH2 Heterojunction and Study on a Photocatalytic Degradation Mechanism

CeO2/UiO-66-NH2 (marked as Ce/UN) composites were in-situ synthesized by a hydrothermal method. The properties, photocatalytic aspects, and degradation mechanism of Ce/UN were studied carefully. SEM results show that Ce/UN have a 3D flower-like structure, where octahedral UiO-66-NH2 nanoparticles are embedded in the two-dimensional sheet of CeO2. TEM results demonstrate that CeO2 and UiO-66-NH2 are bonded interfacially to constitute a hetero-junction construction. Data obtained by electrochemical impedance spectroscopy and fluorescence spectroscopy established that Ce/UN has less charge shift resistance and luminescence intensity than these of two pure substances. When the ratio of Ce/UN is 1:1, and the calcination temperature 400 °C is used, the degradation efficiency of RhB in photocatalysis by obtained Ce/UN is about 96%, which is much higher than in the case of CeO2 (4.5%) and UiO-66-NH2 (54%). The improved photocatalytic properties of Ce/UN may be due to the formation of hetero-junction, which is conducive for most photo-carriers and thus the interfacial charge shift efficiency is enhanced. By the free radical capture test, it can be inferred that the major active substances involved in the degradation related to photocatalysis is H+ and · O2−.

Construction of a sandwich-like UiO-66-NH2@Pt@mSiO2 catalyst for one-pot cascade reductive amination of nitrobenzene with benzaldehyde

Heterogeneous noble metal-based catalysts with stable, precise structures and high catalytic performance are of great research interest for sustainable catalysis. Herein, we designed the novel sandwich-like metal-organic-framework composite nanocatalyst UiO-66-NH₂@Pt@mSiO₂ using UiO-66-NH₂@Pt as the core, and mesoporous SiO₂ as the shell. The obtained UiO-66-NH₂@Pt@mSiO₂ catalyst shows a well-defined structure and interface, and the protection of the mSiO₂ shell can efficiently prevent Pt NPs from aggregating and leaching in the reaction process. In the one-pot cascade reaction of nitroarenes and aromatic aldehydes to secondary amines, UiO-66-NH₂@Pt@mSiO₂ shows excellent catalytic performance due to acid catalytic sites provided by UiO-66-NH₂ and Pt hydrogenation catalytic sites. Furthermore, the porous structure of the UiO-66-NH₂@Pt@mSiO₂ catalyst also enhances reactant diffusion and improves the reaction efficiency. This work provides a new avenue to meticulously design well-defined nanocatalysts with superior catalytic performance and stability for challenging reactions.

Renewable Butanol Production via Catalytic Routes

Fluctuating crude oil price and global environmental problems such as global warming and climate change lead to growing demand for the production of renewable chemicals as petrochemical substitutes. Butanol is a nonpolar alcohol that is used in a large variety of consumer products and as an important industrial intermediate. Thus, the production of butanol from renewable resources (e.g., biomass and organic waste) has gained a great deal of attention from researchers. Although typical renewable butanol is produced via a fermentative route (i.e., acetone-butanol-ethanol (ABE) fermentation of biomass-derived sugars), the fermentative butanol production has disadvantages such as a low yield of butanol and the formation of byproducts, such as acetone and ethanol. To avoid the drawbacks, the production of renewable butanol via non-fermentative catalytic routes has been recently proposed. This review is aimed at providing an overview on three different emerging and promising catalytic routes from biomass/organic waste-derived chemicals to butanol. The first route involves the conversion of ethanol into butanol over metal and oxide catalysts. Volatile fatty acid can be a raw chemical for the production of butanol using porous materials and metal catalysts. In addition, biomass-derived syngas can be transformed to butanol on non-noble metal catalysts promoted by alkali metals. The prospect of catalytic renewable butanol production is also discussed.

Interfacial Sites in Ag Supported Layered Double Oxide for Dehydrogenation Coupling of Ethanol to n-Butanol

Upgrading of ethanol to n-butanol through dehydrogenation coupling has received increasing attention due to the wide application of n-butanol. But the enhancement of ethanol dehydrogenation and followed coupling to produce high selectivity to n-butanol is still highly desired. Our previous work has reported an acid-base-Ag synergistic catalysis, with Ag particles supported on Mg and Al-containing layered double oxides (Ag/MgAl-LDO). Here, Ag-LDO interfaces have been manipulated for dehydrogenation coupling of ethanol to n-butanol by tailoring the size of Ag particles and the interactions between Ag and LDO. It has been revealed that increasing the population of surface Ag sites at Ag-LDO interfaces promotes not only the dehydrogenation of ethanol to acetaldehyde but also the subsequent aldol condensation of generated acetaldehyde. A selectivity of up to 76 % to n-butanol with an ethanol conversion of 44 % has been achieved on Ag/LDO with abundant interfacial Ag sites, much superior to the state-of-the-art catalysts.

Boosting free radical type photocatalysis over Pd/Fe-MOFs by coordination structure engineering

The development of novel heterogeneous photocatalytic systems, along with a deep understanding of the relationship between the catalytic center chemical environment and the catalytic performance, is of great significance.

Role of Lewis Acids of MIL-101(Cr) in the Upgrading of Ethanol to n-Butanol

The upgrading of bioethanol to n-butanol has recently been a focus of considerable attention due to the advantages of n-butanol over bioethanol as a sustainable fuel. The efficiency of this reaction is highly dependent on the development of catalysts, where understanding how catalysts perform is essential. However, traditional catalysts are normally composed of several kinds of active sites that work together synergistically in reactions, making it challenging to identify the role that individual active sites play. Herein, we synthesized three chromium-based MOFs ((MIL-101(Cr), where MIL stands for Matériaux Institut Lavoisier) with different Lewis acidities but without any basic sites. The linear relationship between Lewis acidities and their dehydration and condensation abilities suggests that there is a competition between the ethanol dehydration to diethyl ether and acetaldehyde condensation on Lewis acids. Upon the introduction of Pd, the Lewis acidity also dominates the particle size of Pd and then the dehydrogenation and hydrogenating abilities of catalysts.

An active and stable multifunctional catalyst with defective UiO-66 as a support for Pd over the continuous catalytic conversion of acetone and hydrogen

The one-pot synthesis of methyl isobutyl ketone (MIBK) and methyl isobutyl methanol (MIBC) from acetone and hydrogen is a typical cascade reaction comprised of aldol condensation-dehydration-hydrogenation. Pd loss and aggregation during long term operation are typical problems in industrial application. In this paper, an active and stable catalyst was achieved with defective UiO-66 as a support for Pd, which was synthesized with the ratio 15 : 1 of ZrOCl2·8H2O to ZrCl4 as Zr-precursors. The resultant Pd catalyst remained active for at least 1000 h with a MIBK + MIBC selectivity of 84.87-93.09% and acetone conversion of 45.26-53.22% in a continuous trickle-bed reactor. Besides the increased Brønsted acid amount generated by the defect sites was favorable for the activity, the cavity confinement in the UiO-66 (R = 15 : 1) structure also efficiently prevented Pd loss and aggregation during the long term run. The contrast of the characterization of the fresh and used Pd/UiO-66 (R = 15 : 1) indicated that the deactivation of the catalyst was attributed to carbonaceous accumulation on the catalyst surface, which could be easily regenerated by calcination. This work supplied a new alternative for the design and utilization of industrial catalysts for MIBK and MIBC synthesis.

An enzyme-free electrochemical biosensor based on target-catalytic hairpin assembly and Pd@UiO-66 for the ultrasensitive detection of microRNA-21

MicroRNA-21 (miR-21) has been widely investigated as important biomarkers for cancer diagnosis and treatment. Herein, a highly sensitive nonenzymatic electrochemical biosensor based on Pd@metal-organic frameworks (Pd@UiO-66) and target-catalytic hairpin assembly (CHA) with target recycling approach has been proposed for the detection of miR-21. The proposed biosensor integrates the efficient CHA strategy and excellent electrocatalytic performance of Pd@UiO-66 nanocomposites. The concentration of miRNA-21 is related to the amount of the adsorbed electrocatalyst, leading to the different electrochemical signals for readout towards paracetamol (AP). This biosensor shows a low limit of detection of 0.713 fM with the dynamic range of 20 fM -600 pM under the optimal experimental conditions, providing a powerful platform for detecting miR-21. Furthermore, the designed biochemical self-assembly strategy of this electrochemical biosensor is promising candidate for potential applications in the analysis of other important genetic biomarkers for early diagnosis of cancers.

Electronic Structure Modeling of Metal-Organic Frameworks

Owing to their molecular building blocks, yet highly crystalline nature, metal-organic frameworks (MOFs) sit at the interface between molecule and material. Their diverse structures and compositions enable them to be useful materials as catalysts in heterogeneous reactions, electrical conductors in energy storage and transfer applications, chromophores in photoenabled chemical transformations, and beyond. In all cases, density functional theory (DFT) and higher-level methods for electronic structure determination provide valuable quantitative information about the electronic properties that underpin the functions of these frameworks. However, there are only two general modeling approaches in conventional electronic structure software packages: those that treat materials as extended, periodic solids, and those that treat materials as discrete molecules. Each approach has features and benefits; both have been widely employed to understand the emergent chemistry that arises from the formation of the metal-organic interface. This Review canvases these approaches to date, with emphasis placed on the application of electronic structure theory to explore reactivity and electron transfer using periodic, molecular, and embedded models. This includes (i) computational chemistry considerations such as how functional, k-grid, and other model variables are selected to enable insights into MOF properties, (ii) extended solid models that treat MOFs as materials rather than molecules, (iii) the mechanics of cluster extraction and subsequent chemistry enabled by these molecular models, (iv) catalytic studies using both solids and clusters thereof, and (v) embedded, mixed-method approaches, which simulate a fraction of the material using one level of theory and the remainder of the material using another dissimilar theoretical implementation.

Boosting Catalysis of Pd Nanoparticles in MOFs by Pore Wall Engineering: The Roles of Electron Transfer and Adsorption Energy

The chemical environment of metal nanoparticles (NPs) possesses significant influence on their catalytic performance yet is far from being well understood. Herein, tiny Pd NPs are encapsulated into the pore space of metal-organic frameworks (MOFs), UiO-66-X (X = H, OMe, NH₂ , 2OH, 2OH(Hf)), affording Pd@UiO-66-X composites. The surface microenvironment of the Pd NPs is readily modulated by pore wall engineering, via the functional group and metal substitution in the MOFs. Consequently, the catalytic activity of Pd@UiO-66-X follows the order of Pd@UiO-66-OH > Pd@UiO-66-2OH(Hf) > Pd@UiO-66-NH₂ > Pd@UiO-66-OMe > Pd@UiO-66-H toward the hydrogenation of benzoic acid. It is found that the activity difference is not only ascribed to the distinct charge transfer between Pd and the MOF, but is also explained by the discriminated substrate adsorption energy of Pd@UiO-66-X (-OH < -2OH(Hf) < -NH₂ < -OMe < -H), based on CO-diffuse reflectance infrared Fourier transform spectra and density-functional theory (DFT) calculations. The Pd@UiO-66-OH, featuring a high Pd electronic state and moderate adsorption energy, displays the highest activity. This work highlights the influence of the surface microenvironment of guest metal NPs, the catalytic activity of which is dominated by electron transfer and the adsorption energy, via the systematic substitution of metal and functional groups in host MOFs.

A Pyridyltriazol Functionalized Zirconium Metal-Organic Framework for Selective and Highly Efficient Adsorption of Palladium

This work reports the synthesis of pyridyltriazol-functionalized UiO-66 (UiO stands for University of Oslo), namely, UiO-66-Pyta, from UiO-66-NH₂ through three postsynthetic modification (PSM) steps. The good performance of the material derives from the observation that partial formylation (∼21% of -NHCHO groups) of H₂BDC-NH₂ by DMF, as persistent impurity, takes place during the synthesis of the UiO-66-NH₂. Thus, to enhance material performance, first, the as-synthesized UiO-66-NH₂ was deformylated to give pure UiO-66-NH₂. Subsequently, the pure UiO-66-NH₂ was converted to UiO-66-N₃ with a nearly complete conversion (∼95%). Finally, the azide-alkyne[3+2]-cycloaddition reaction of 2-ethynylpyridine with the UiO-66-N₃ gave the UiO-66-Pyta. The porous MOF was then applied for the solid-phase extraction of palladium ions from an aqueous medium. Affecting parameters on extraction efficiency of Pd(II) ions were also investigated and optimized. Interestingly, UiO-66-Pyta exhibited selective and superior adsorption capacity for Pd(II) with a maximum sorption capacity of 294.1 mg g^-1 at acidic pH (4.5). The limit of detection (LOD) was found to be 1.9 μg L^-1. The estimated intra- and interday precisions are 3.6 and 1.7%, respectively. Moreover, the adsorbent was regenerated and reused for five cycles without any significant change in the capacity and repeatability. The adsorption mechanism was described based on various techniques such as FT-IR, PXRD, SEM/EDS, ICP-AES, and XPS analyses as well as density functional theory (DFT) calculations. Notably, as a case study, the obtained UiO-66-Pyta after palladium adsorption, UiO-66-Pyta-Pd, was used as an efficient catalyst for the Suzuki-Miyaura cross-coupling reaction.

Highly Dispersed Ni Catalyst on Metal-Organic Framework-Derived Porous Hydrous Zirconia for CO2 Methanation

We report the preparation of porous hydrous zirconia by treatment of zirconium-based metal-organic framework (MOF) UiO-66 with a strong base. Microporosity of the original MOF was partially retained in the resultant porous hydrous zirconia. Ni^II centers were then adsorbed onto the OH-rich hydrous zirconia and in situ converted to highly dispersed Ni⁰ for CO₂ hydrogenation to CH₄. The activated catalyst after an induction period showed a turnover frequency of 345 h^-1 or a space-time yield of 5851 mmol·g_Ni^-1·h^-1 with a CH₄ selectivity of over 99%. The catalyst was tested for 100 h on stream, showing only a 4% decrease in activity, and was found to convert atmospheric CO₂ to CH₄ via CO₂ collection through Na₂CO₃/NaHCO₃ cycling. Thermal decomposition of NaHCO₃ released CO₂ for hydrogenation to CH₄, and the resultant Na₂CO₃ absorbed CO₂ from air to form NaHCO₃. This work highlights the opportunity in using MOFs as precursors to prepare highly porous metal oxide/hydroxide supports for solid-gas phase catalysis.

Preparation of Quasi-MIL-101(Cr) Loaded Ceria Catalysts for the Selective Catalytic Reduction of NOx at Low Temperature

At present, the development of novel catalysts with high activity Selective Catalytic Reduction (SCR) reaction at the low temperature is still a challenge. In this work, the authors prepare CeO2/quasi-MIL-101 catalysts with various amounts of deposited ceria by a double-solvent method, which are characterized by X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and so on. The results show that the increase of Ce content has a great influence on the catalytic property of the catalyst. The introduction of Ce can promote the conversion between Cr3+ and Cr5+ and increase the proportion of lattice oxygen, which improves the activity of the catalyst. However, the catalyst will be peroxidized when the content of Ce is too high, resulting in the decline of the catalytic activity. This experiment indicates that CeO2/quasi-MIL-101 plays a significant role in the NH3-SCR process at the low temperature when the loading of Ce is 0.5%. This work has proved the potential of this kind of material in NH3-SCR process at the low temperature, providing help for subsequent studies.

Lewis acid sites in MOFs supports promoting the catalytic activity and selectivity for CO esterification to dimethyl carbonate

We studied the effect of Lewis acidity in metal–organic frameworks (MOFs) on their activity as catalyst supports for the esterification of CO to dimethyl carbonate.

Preparation of a Series of Pd@UIO-66 by a Double-Solvent Method and Its Catalytic Performance for Toluene Oxidation

This paper reports on the preparation, characterization, and catalytic properties of the Pd@UIO-66 for toluene oxidation. The samples are prepared by the double-solvent method to form catalysts with large specific surface area, highly dispersed Pd⁰ (Elemental palladium) and abundant adsorbed oxygen, which are characterized by X-ray Photoelectron Spectroscopy (XPS), Brunauer-Emmett-Teller (BET) and Transmission Electron Microscopy (TEM). The results show that as the Pd content increases, the adsorbed oxygen content further increases, but at the same time Pd⁰ will agglomerate and lose some active sites, which will affect its catalytic performance. While 0.2%Pd@UIO-66 has the highest concentration of Pd⁰, the result shows it has the best catalytic activity and the T₉₀ temperature is 210 °C.