Defects Tune the Strong Metal-Support Interactions in Copper Supported on Defected Titanium Dioxide Catalysts for CO2 Reduction

Photo-assisted thermal catalytic CO2 reduction over Ru-TiO2 catalysts

Photothermal catalysis is a promising technology to convert CO2 into high value-added products. Here, we show that loading Ru NPs on TiO2 achieved a remarkable photothermal synergistic effect and the Ru-TiO2 demonstrated a high efficiency for the photothermal conversion of low CO2 concentration to CH4 at the gas-solid interface. The photothermal activity of the Ru-TiO2 (217.9 µmol/(g·h)) was nearly 6 times higher than pure thermal activity (38.08 µmol/(g·h)), and nearly 20 times than the photocatalytic activity (10.9 µmol/(g·h)). We revealed that the light excitation could drive the generated electrons from TiO2 to Ru particles, beneficial to CO2 reduction, while external heating showed no influence on the charge separation of the Ru-TiO2. Hence, the photothermal synergy is not a heat-assisted photocatalytic process, but a photo-assisted thermal catalytic process. We finally demonstrated that the CO2 was firstly converted to CO, and the CO was further hydrogenated to CH4. The introduction of light could promote the activation of intermediate CO species at the Ru-Ti interface sites, thus greatly accelerating CO hydrogenation to CH4. This work contributes to further understanding of the mechanism of photothermal catalytic CO2 reduction.

Dendritic fibrous nanosilica supported Zn-based sorbents towards enhanced hot-coal-gas desulfurization: Structural design and metal modification

Designing suitable carriers of sorbents for hot-coal-gas desulfurization is still a challenging task so far. In this study, dendritic fibrous nanosilica (DFNS) carriers with central radial pore structures were synthesized via microemulsion method, and the formation mechanism was proposed. The mean particle diameter (MPD) and mean surface wrinkle spacing (MSWS) of DFNS could be directionally controlled by regulating the emulsion phase behavior during DFNS synthesis. A series of mesoporous Zn-based desulfurizers were then constructed based on these DFNS carriers. The results indicate that the proposed parameter, pore slope, could be well positively correlated with the breakthrough sulfur capacity of desulfurizers. The activation energy (20.5 kJ/mol) of sorbent with the optimized carrier is significantly lower than that of previously reported desulfurizers. Additionally, the desulfurization performance of DFNS-supported sorbents could be further improved by 1.27 %-34.6 % by metal (Sm/Mo/Ni) modification. Sorbents with Ni/Zn molar ratio of 1/5 exhibit the highest breakthrough sulfur capacity of 15.85 g S/100 g sorbents. Moreover, the optimized sorbent demonstrated good stability over multiple sulfidation/regeneration cycles, highlighting its potential for hot-coal-gas desulfurization applications.

Synthesis of synergistic catalysts: integrating defects, SMSI, and plasmonic effects for enhanced photocatalytic CO2 reduction

This study explores how the strategic material design introduced synergetic coupling of strong metal-support interaction (SMSI) between copper (Cu) nanoparticles and titanium dioxide (TiO2) loaded on dendritic fibrous nanosilica (DFNS), defects within TiO2, and localized surface plasmon resonance (LSPR) of Cu. Mechanistic insights were gained using in situ high-energy radiation fluorescence detection X-ray absorption near edge structure (HERFD-XANES) spectroscopy, electron microscopy, and finite-difference time-domain (FDTD) simulations. The introduction of copper nanoparticles onto the TiO2 surface induces a change in the electronic structure and surface chemistry of TiO2, due to the electronic interactions between Cu sites and TiO2 at the interface, inducing SMSI. This resulted in enhancing light absorption, efficient charge transfer, reducing electron-hole recombination and enhancing the overall catalytic efficiency. The activation energy for CO2 reduction was significantly reduced in light as compared to dark. Control experiments revealed a dominant role of photoexcited hot carriers, alongside photothermal effects, in driving CO2 reduction, supported by super-linear light intensity dependence and reduced activation energies. The unique interplay of O-vacancy defects, electron-hole separation in TiO2 and LSPR effects in Cu led to the excellent performance of the DFNS/TiO2-Cu10 catalyst. The catalyst outperformed the reported photocatalytic systems with a CO production rate of ∼3600 mmol gCu -1 h-1 (360 mmol gcat -1 h-1) with nearly 100% selectivity. A reaction mechanism was proposed based on the intermediates observed using the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and co-related to the electron transfer pathways to different reactants using HERFD-XANES. The study concluded that the synergistic coupling of Cu LSPR, charge carrier separation via SMSI at the Cu-TiO2 interface, and O-vacancy defects stabilized by SMSI enhance the photocatalytic CO2 reduction performance of this hybrid system.

Visualizing the dynamic evolution of light-sensitive Cu1+/Cu2+ sites during photocatalytic CO2 reduction with an advanced in situ EPR spectroscopy

Elucidation of the dynamic evolution of active sites is still a challenge in investigating the catalytic mechanism mainly due to the difficulty in accurately detecting the transient structural changes of active sites under operating conditions. Here, we develop an advanced in situ electron paramagnetic resonance (EPR) spectroscopy, which could sensitively monitor and visualize the dynamic evolution of paramagnetic active sites during photoreduction CO2. In situ results reveal that the photoactivated Cu1+ sites from CuO nanoclusters/TiO2 serve as the authentic active sites in the reaction and exhibit self-regenerative capability. The CO2 molecules can acquire electrons and get activated by the photoactivated Cu1+, leading to the transition of Cu1+ sites into Cu2+ sites. Subsequently, the Cu2+ sites expedite the generation of hydrogen protons through antiferromagnetic coupling with hydroxyl radicals, thereby promoting the production of the final product CH4 via a multi proton-coupled electron transfer (PCET) process. This work reveals and visualizes the dynamic evolution of Cu-based active sites during photocatalytic reactions by combined in situ characterizations, providing new perspectives on the mechanistic understanding of paramagnetic active sites under operation.

Synergizing Mg Single Atoms and Ru Nanoclusters for Boosting the Ammonia Borane Hydrolysis to Produce Hydrogen

Development of efficient catalysts with high H2O molecule activation ability holds great importance for H2 production. Herein, enzyme-mimic Mg single atoms catalysts (SACs) coordinated by B/N-doped carbon nanotube (BNC), was constructed as a high-performance support for ruthenium (Ru) nano-clusters. Dual functions of Mg SACs were discovered, where the Mg atoms beneath Ru catalysts built an interfacial electron polarization, inducing electron transfer from Ru to the Mg-BNC support. In addition, the oxyphilic Mg SACs adjacent to the Ru catalysts could actively participate in H2O adsorption. The combination of experimental characterization, reaction kinetics study and density functional theory (DFT) calculations validated a stronger intrinsic H2O activation capability at the positive Ru sites. Meanwhile, the synergistic Mg SACs jointly contribute to the acceleration of the sluggish H2O dissociation process in ammonia borane (AB) hydrolysis reaction, resulting in exceptional hydrogen production activity and catalytic stability, outperforming most state-of-the-art Ru-based catalysts. This work provides a new strategy for utilizing alkaline earth metals as both the electronic promoter and the reactant activator, offering inspiration for the development of advanced heterogeneous catalysts.

Nonequilibrium-corrosive engineering synthesis of Pt anchored on Fe3O4 with oxygen vacancy for efficient electrocatalytic hydrogen evolution reaction

The development of suitable support to maximize the atomic utilization efficiency of platinum is of great significance for the hydrogen evolution reaction (HER). Herein, we report a simple and fast nonequilibrium-corrosive approach to prepare oxygen defect-enriched Fe3O4 decorated with trace Pt onto nickel-iron foam (Pt/Fe3O4-Ov/NIF). The Pt/Fe3O4-Ov/NIF electrode is superhydrophilic with intimate contact with the electrolyte. In addition, the strong electronic interactions between Fe3O4 and Pt and the oxygen-rich vacancies contribute to the catalytic process and improve the electrochemical interfacial properties. Thus, the Pt/Fe3O4-Ov/NIF electrocatalyst only requires an overpotential of 29 and 39 mV at 10 mA cm-2 in alkaline freshwater/alkaline seawater, respectively, exhibiting superior HER activity. Furthermore, the anion exchange membrane water electrolyzer (AEMWE) owns low cell voltage of 1.86 V at 1000 mA cm-2 and long-term electrocatalysis durability. This work provides an effective approach for designing efficient AEMWE electrocatalysts for hydrogen production.

Recent Progress in the Design and Application of Strong Metal-Support Interactions in Electrocatalysis

The strong metal-support interaction (SMSI) in supported metal catalysts represents a crucial factor in the design of highly efficient heterogeneous catalysts. This interaction can modify the surface adsorption state, electronic structure, and coordination environment of the supported metal, altering the interface structure of the catalyst. These changes serve to enhance the catalyst's activity, stability, and reaction selectivity. In recent years, a multitude of researchers have uncovered a range of novel SMSI types and induction methods including oxidized SMSI (O-SMSI), adsorbent-mediated SMSI (A-SMSI), and wet chemically induced SMSI (Wc-SMSI). Consequently, a systematic and critical review is highly desirable to illuminate the latest advancements in SMSI and to deliberate its application within heterogeneous catalysts. This article provides a review of the characteristics of various SMSI types and the most recent induction methods. It is concluded that SMSI significantly contributes to enhancing catalyst stability, altering reaction selectivity, and increasing catalytic activity. Furthermore, this paper offers a comprehensive review of the extensive application of SMSI in the electrocatalysis of hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and carbon dioxide reduction reaction (CO2RR). Finally, the opportunities and challenges that SMSI faces in the future are discussed.

Electronic metal-support interaction modulates Cu electronic structures for CO2 electroreduction to desired products

In this work, the Cu single-atom catalysts (SACs) supported by metal-oxides (Al2O3-CuSAC, CeO2-CuSAC, and TiO2-CuSAC) are used as theoretical models to explore the correlations between electronic structures and CO2RR performances. For these catalysts, the electronic metal-support interaction (EMSI) induced by charge transfer between Cu sites and supports subtly modulates the Cu electronic structure to form different highest occupied-orbital. The highest occupied 3dyz orbital of Al2O3-CuSAC enhances the adsorption strength of CO and weakens C-O bonds through 3dyz-π* electron back-donation. This reduces the energy barrier for C-C coupling, thereby promoting multicarbon formation on Al2O3-CuSAC. The highest occupied 3dz2 orbital of TiO2-CuSAC accelerates the H2O activation, and lowers the reaction energy for forming CH4. This over activated H2O, in turn, intensifies competing hydrogen evolution reaction (HER), which hinders the high-selectivity production of CH4 on TiO2-CuSAC. CeO2-CuSAC with highest occupied 3dx2-y2 orbital promotes CO2 activation and its localized electronic state inhibits C-C coupling. The moderate water activity of CeO2-CuSAC facilitates *CO deep hydrogenation without excessively activating HER. Hence, CeO2-CuSAC exhibits the highest CH4 Faradaic efficiency of 70.3% at 400 mA cm-2.

Tuning the electronic structure and SMSI by integrating trimetallic sites with defective ceria for the CO2 reduction reaction

Heterogeneous catalysts have emerged as a potential key for closing the carbon cycle by converting carbon dioxide (CO2) into value-added chemicals. In this work, we report a highly active and stable ceria (CeO2)-based electronically tuned trimetallic catalyst for CO2 to CO conversion. A unique distribution of electron density between the defective ceria support and the trimetallic nanoparticles (of Ni, Cu, Zn) was established by creating the strong metal support interaction (SMSI) between them. The catalyst showed CO productivity of 49,279 mmol g-1 h-1 at 650 °C. CO selectivity up to 99% and excellent stability (rate remained unchanged even after 100 h) stemmed from the synergistic interactions among Ni-Cu-Zn sites and their SMSI with the defective ceria support. High-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) confirmed this SMSI, further corroborated by in situ electron energy loss spectroscopy (EELS) and density functional theory (DFT) simulations. The in situ studies (HERFD-XAS & EELS) indicated the key role of oxygen vacancies of defective CeO2 during catalysis. The in situ transmission electron microscopy (TEM) imaging under catalytic conditions visualized the movement and growth of active trimetallic sites, which completely stopped once SMSI was established. In situ FTIR (supported by DFT) provided a molecular-level understanding of the formation of various reaction intermediates and their conversion into products, which followed a complex coupling of direct dissociation and redox pathway assisted by hydrogen, simultaneously on different active sites. Thus, sophisticated manipulation of electronic properties of trimetallic sites and defect dynamics significantly enhanced catalytic performance during CO2 to CO conversion.

Electronic and geometric effects in an Au@NiO core-shell nanocatalyst on the oxidative esterification of aldehydes

Strong metal-support interactions (SMSIs) are important in heterogeneous catalysis to control stability, activity, and selectivity. Core-shell nanostructures as a unique SMSI system not only stabilize the metal nanoparticles in the core, but also offer tunable structural and electronic properties via their interaction with the support shell. The Au@NiOx core-shell system, for example, is the first commercial nanogold catalyst to produce bulk chemicals via the oxidative esterification of aldehydes. However, how the SMSI effect in Au@NiOx manifests on its oxidative esterification activity is unclear. Here we use a model of an Au13@(NiO)48 core-shell nanocatalyst to examine the Au-NiO interaction and the associated electronic and geometric factors in enabling the oxidation of a hemiacetal (an intermediate from a ready reaction between an aldehyde and an alcohol) to an ester. We found 1.27 (e-) electrons flowing from the NiO shell to the Au core, leading to a higher oxide state of Ni atoms and the stabilization of key intermediates on the NiO shell. More importantly, lower activation energy was found on the Au13@(NiO)48 catalyst than on the Au(111) and NiO(100) surfaces for the rate-limiting step. Microkinetic modeling confirmed the high activity of the Au13@(NiO)48 catalyst in ester production in the experimental temperature range. Our work demonstrates the unique geometric and electronic effects of the Au@NiOx core-shell nanostructure on the catalytic oxidative esterification of aldehydes.

In-Situ Dynamic Carburization of Mo Oxide with Unprecedented High CO Formation Rate in Reverse Water-Gas Shift Reaction

In situ construction of active structure under reaction conditions is highly desired but still remains challenging in many important catalytic processes. Herein, we observe structural evolution of molybdenum oxide (MoOx) into highly active molybdenum carbide (MoCx) during reverse water-gas shift (RWGS) reaction. Surface oxygen atoms in various Mo-based catalysts are removed in H2-containing atmospheres and then carbon atoms can accumulate on surface to form MoCx phase with the RWGS reaction going on, both of which are enhanced by the presence of intercalated H species or Pt-dopants in MoOx. The structural evolution from MoOx to MoCx is accompanied by enhanced CO2 conversion, which is positively correlated with the surface C/Mo ratio but negatively with the surface O/Mo ratio. As a result, an unprecedented CO formation rate of 7544.6 mmol ⋅ gcatal -1 ⋅ h-1 at 600 °C has been achieved over in situ carbonized H-intercalated MoO3 catalyst, which is even higher than those from noble metal catalysts. During 100 h stability test only a minimal deactivation rate of 2.3 % is observed.

Pr doping promotes the formation of Pt single atoms by regulating metal-support interaction for remarkable photocatalytic hydrogen production

Since the metal-support interaction (MSI) has a great influence on the structure and properties of single atom catalysts (SACs), the activity and stability of SACs can be effectively regulated by adjusting the structure of the matrix. Herein, the morphology of surface supported Pt species can be controlled by doping to adjust the properties of TiO2 support. Specifically, under the same conditions, the Pt species on the Pr doped TiO2 surface are Pt SAs (PtSA/TiO2(Pr)), while on the pure TiO2 surface are particles (PtNP/TiO2). Experimental and theoretical studies demonstrate that Pr doping weakens the interaction of Ti-O bond, stabilizes the O-Pt unit site and Pt SAs. Impressively, PtSA/TiO2(Pr) shows superior photocatalytic hydrogen production performance (196.43 mmol g-1 h-1), far exceeding PtNP/TiO2 (91.96 mmol g-1 h-1). Additionally, Pr dopant modulates the electronic interaction between TiO2 support and Pt SAs, thus the adsorption/desorption behavior of H intermediates (H*) is balanced. Besides, the electron delocalization of O adjacent to Pt SAs can be adjusted by Pr doping, prompting the establishment of efficient Pt-O electron transfer channels and further enhances the utilization of photogenerated carriers. This study presents a promising strategy to prepare SACs with high activity for photocatalyst hydrogen production.

Metal-support interactions in metal oxide-supported atomic, cluster, and nanoparticle catalysis

Supported metal catalysts are essential to a plethora of processes in the chemical industry. The overall performance of these catalysts depends strongly on the interaction of adsorbates at the atomic level, which can be manipulated and controlled by the different constituents of the active material (i.e., support and active metal). The description of catalyst activity and the relationship between active constituent and the support, or metal-support interactions (MSI), in heterogeneous (thermo)catalysts is a complex phenomenon with multivariate (dependent and independent) contributions that are difficult to disentangle, both experimentally and theoretically. So-called "strong metal-support interactions" have been reported for several decades and summarized in excellent review articles. However, in recent years, there has been a proliferation of new findings related to atomically dispersed metal sites, metal oxide defects, and, for example, the generation and evolution of MSI under reaction conditions, which has led to the designation of (sub)classifications of MSI deserving to be critically and systematically evaluated. These include dynamic restructuring under alternating redox and reaction conditions, adsorbate-induced MSI, and evidence of strong interactions in oxide-supported metal oxide catalysts. Here, we review recent literature on MSI in oxide-supported metal particles to provide an up-to-date understanding of the underlying physicochemical principles that dominate the observed effects in supported metal atomic, cluster, and nanoparticle catalysts. Critical evaluation of different subclassifications of MSI is provided, along with discussions on the formation mechanisms, theoretical and characterization advances, and tuning strategies to manipulate catalytic reaction performance. We also provide a perspective on the future of the field, and we discuss the analysis of different MSI effects on catalysis quantitatively.

The potential utility of dendritic fibrous nanosilica as an adsorbent and a catalyst in carbon capture, utilization, and storage

Anthropogenic emissions of greenhouse gases (GHG; e.g., CO2) are regarded as the most critical cause of the current global climate crisis. To combat this issue, a plethora of CO2 capture, utilization, and storage (CCUS) technologies have been proposed and developed based on a number of technical principles (e.g., post-combustion capture, chemical looping, and catalytic conversion). In this light, the potential utility of dendritic fibrous nanosilica (DFNS) materials is recognized for specific CCUS applications (such as adsorptive capture of CO2 and its catalytic conversion into a list of value-added products (e.g., methane, carbon monoxide, and cyclic carbonates)) with the highly tunable properties (e.g., high surface area, pore volume, multifunctional surface, and open pore structure). This review has been organized to offer a comprehensive evaluation of the approaches required for tuning the textural/morphological/surface properties of DFNS (based on multiple synthesis and modification scenarios) toward CCUS applications. It further discusses the effects of such approaches on the properties of DFNS materials in relation to their CCUS performance. This review is thus expected to help develop and implement advanced strategies for DFNS-based CCUS technologies.

In situ observation of catalyst nanoparticle sintering resistance on oxide supports via gas phase transmission electron microscopy

Oxide-supported metal catalysts are essential components in industrial processes for catalytic conversion. However, the performance of these catalysts is often compromised in high temperature reaction environments due to sintering effects. Currently, a number of studies are underway with the objective of improving the metal support interaction (MSI) effect in order to enhance sintering resistance by surface modification of the oxide support, including the formation of inhomogeneous defects on the oxide support, the addition of a rare earth element, the use of different facets, encapsulation, and other techniques. The recent developments in in situ gas phase transmission electron microscopy (TEM) have enabled direct observation of the sintering process of NPs in real time. This capability further allows to verify the efficacy of the methods used to tailor the support surface and contributes effectively to improving sintering resistance. Here, we review a few selected studies on how in situ gas phase TEM has been used to prevent the sintering of catalyst NPs on oxide supports.

Accelerating Toluene Oxidation over Boron-Titanium-Oxygen Interface: Steric Hindrance of the Methyl Group Induced by the Plane-Adsorption Configuration

Elimination of dilute gaseous toluene is one of the critical concerns within the field of indoor air remediation. The typical degradation route on titanium-based catalysts, "toluene-benzaldehyde-carbon dioxide", necessitates the oxidation of the methyl group as a prerequisite for photocatalytic toluene oxidation. However, the inherent planar adsorption configuration of toluene molecules, dominated by the benzene rings, leads to significant steric hindrance for the methyl group. This steric hindrance prevents the methyl group from contacting the active species on the catalyst surface, thereby limiting the removal of toluene under indoor conditions. To date, no effective strategy to control the steric hindrance of the methyl group has been identified. Herein, we showed a B-Ti-O interface that exhibits significantly enhanced toluene removal efficiency under indoor conditions. In-depth investigations revealed that, compared to typical Ti-based photocatalysts, the steric hindrance between the methyl group and the catalyst surface decreased from 3.42 to 3.03 Å on the designed interface. This reduction originates from the matching of orbital energy levels between Ti 3dz2 and C 2pz of the benzene ring. The decreased steric hindrance improved the efficiency of toluene being attacked by surface active species, allowing for rapid conversion into benzaldehyde and benzoic acid species for subsequent reactions. Our work provides novel insights into the steric hindrance effect in the elimination of aromatic volatile organic compounds.

Reaction-induced unsaturated Mo oxycarbides afford highly active CO2 conversion catalysts

Sustainable CO2 conversion is crucial in curbing excess emissions. Molybdenum carbide catalysts have demonstrated excellent performances for catalytic CO2 conversion, but harsh carburization syntheses and poor stabilities make studies challenging. Here an unsaturated Mo oxide (Mo17O47) shows a high activity for the reverse water-gas shift reaction, without carburization pretreatments, and remains stable for 2,000 h at 600 °C. Flame spray pyrolysis synthesis and Ir promoter facilitate the formation of Mo17O47 and its in situ carburization during reaction. The reaction-induced cubic α-MoC with unsaturated Mo oxycarbide (MoOxCy) on the surface serves as the active sites that are crucial for catalysis. Mechanistic studies indicate that the C atom in CO2 inserts itself in the vacancy between two Mo atoms, and releases CO by taking another C atom from the oxycarbide to regenerate the vacancy, following a carbon cycle pathway. The design of Mo catalysts with unsaturated oxycarbide active sites affords new territory for high-temperature applications and provides alternative pathways for CO2 conversion.

Unveiling the Mechanism of Plasma-Catalytic Low-Temperature Water-Gas Shift Reaction over Cu/γ-Al2O3 Catalysts

The water-gas shift (WGS) reaction is a crucial process for hydrogen production. Unfortunately, achieving high reaction rates and yields for the WGS reaction at low temperatures remains a challenge due to kinetic limitations. Here, nonthermal plasma coupled to Cu/γ-Al2O3 catalysts was employed to enable the WGS reaction at considerably lower temperatures (up to 140 °C). For comparison, thermal-catalytic WGS reactions using the same catalysts were conducted at 140-300 °C. The best performance (72.1% CO conversion and 67.4% H2 yield) was achieved using an 8 wt % Cu/γ-Al2O3 catalyst in plasma catalysis at ∼140 °C, with 8.74 MJ mol-1 energy consumption and 8.5% H2 fuel production efficiency. Notably, conventional thermal catalysis proved to be ineffective at such low temperatures. Density functional theory calculations, coupled with in situ diffuse reflectance infrared Fourier transform spectroscopy, revealed that the plasma-generated OH radicals significantly enhanced the WGS reaction by influencing both the redox and carboxyl reaction pathways.

Defects tune the acidic strength of amorphous aluminosilicates

Crystalline zeolites have high acidity but limited utility due to microporosity, whereas mesoporous amorphous aluminosilicates offer better porosity but lack sufficient acidity. In this work, we investigated defect engineering to fine-tune the acidity of amorphous acidic aluminosilicates (AAS). Here we introduced oxygen vacancies in AAS to synthesize defective acidic aluminosilicates (D-AAS). 1H, 27Al, and 17O solid-state nuclear magnetic resonance (NMR) studies indicated that defects induced localized structural changes around the acidic sites, thereby modifying their acidity. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy studies substantiated that oxygen vacancies alter the chemical environment of Brønsted acidic sites of AAS. The effect of defect creation in AAS on its acidity and catalytic behavior was demonstrated using four different acid-catalyzed reactions namely, styrene oxide ring opening, vesidryl synthesis, Friedel-Crafts alkylation, and jasminaldehyde synthesis. The defects played a role in activating reactants during AAS-catalyzed reactions, enhancing the overall catalytic process. This was supported by in-situ FTIR, which provided insights into the molecular-level reaction mechanism and the role of defects in reactant activation. This study demonstrates defect engineering as a promising approach to fine-tune acidity in amorphous aluminosilicates, bridging the porosity and acidity gaps between mesoporous amorphous aluminosilicates and crystalline zeolites.

Polyoxometalate-HKUST-1 composite derived nanostructured Na-Cu-Mo2C catalyst for efficient reverse water gas shift reaction

Transforming CO2 to CO via reverse water-gas shift (RWGS) reaction is widely regarded as a promising technique for improving the efficiency and economics of CO2 utilization processes. Moreover, it is also considered as a pathway towards e-fuels. Cu-oxide catalysts are widely explored for low-temperature RWGS reactions; nevertheless, they tend to deactivate significantly under applied reaction conditions due to the agglomeration of copper particles at elevated temperatures. Herein, we have synthesized homogeneously distributed Cu metallic nanoparticles supported on Mo2C for the RWGS reaction by a unique approach of in situ carburization of metal-organic frameworks (MOFs) using a Cu-based MOF i.e. HKUST-1 encapsulating molybdenum-based polyoxometalates. The newly derived Na-Cu-Mo2C nanocomposite catalyst system exhibits excellent catalytic performance with a CO production rate of 3230.0 mmol gcat-1 h-1 with 100% CO selectivity. Even after 250 h of a stability test, the catalyst remained active with more than 80% of its initial activity.

Oxygen vacancy enhanced photocatalytic activity of Cu2O/TiO2 heterojunction

In this study, a method was developed to create oxygen vacancies in Cu2O/TiO2 heterojunctions. By varying the amounts of ethylenediaminetetraacetic acid (EDTA), sodium citrate, and copper acetate, Cu2O/TiO2 with different Cu ratios were synthesized. Tests on CO2 photocatalytic reduction revealed that Cu2O/TiO2's performance is influenced by Cu content. The ideal Cu mass fraction in Cu2O/TiO2, determined by inductively coupled plasma (ICP), is between 0.075% and 0.55%, with the highest CO yield being 10.22 μmol g-1 h-1, significantly surpassing pure TiO2. High-resolution transmission electron microscopy and electron paramagnetic resonance studies showed optimal oxygen vacancy in the most effective heterojunction. Density functional theory (DFT) calculations indicated a 0.088 eV lower energy barrier for ∗CO2 to ∗COOH conversion in Cu2O/TiO2 with oxygen vacancy compared to TiO2, suggesting that oxygen vacancies enhance photocatalytic activity.

An active, stable cubic molybdenum carbide catalyst for the high-temperature reverse water-gas shift reaction

Although technologically promising, the reduction of carbon dioxide (CO2) to produce carbon monoxide (CO) remains economically challenging owing to the lack of an inexpensive, active, highly selective, and stable catalyst. We show that nanocrystalline cubic molybdenum carbide (α-Mo2C), prepared through a facile and scalable route, offers 100% selectivity for CO2 reduction to CO while maintaining its initial equilibrium conversion at high space velocity after more than 500 hours of exposure to harsh reaction conditions at 600°C. The combination of operando and postreaction characterization of the catalyst revealed that its high activity, selectivity, and stability are attributable to crystallographic phase purity, weak CO-Mo2C interactions, and interstitial oxygen atoms, respectively. Mechanistic studies and density functional theory (DFT) calculations provided evidence that the reaction proceeds through an H2-aided redox mechanism.

Regulating oxygen vacancies by Zn atom doping to anchor and disperse promoter Ba on MgO support to improve Ru-based catalysts activity for ammonia synthesis

In heterogeneous catalysis, surface defects are widely regarded as an effective means to enhance the catalytic performance of catalysts. In this study, the oxygen vacancy-rich Mg(1-X)ZnXO solid solution support was successfully prepared by doping a small amount of Zn into MgO nanocrystals. Based on this support, Ru/Ba-Mg(1-X)ZnXO catalyst for ammonia synthesis was prepared. Characterization using TEM, EPR, XPS, and DFT calculations confirmed the successful substitution of Zn atoms for Mg atoms leading to the formation of more oxygen vacancies (OVs). N2-TPD, SEM and TEM analyses revealed that a small amount of Zn had minimal influence on the surface morphology and the size of Ru nanoparticles. The abundance of OVs in the support was identified as the primary factor enhancing the catalytic activity. XPS, H2-TPD and kinetics experiment studies further elucidated the mechanism by which OVs promote the reaction, with OVs serving as an anchor point for the promoter Ba on the MgO support and promoted the dispersion of Ba. This anchoring effect not only enhanced the electron density on Ru, favoring the dissociation of the N[triple bond, length as m-dash]N bond, but also mitigated hydrogen poisoning. As a result,the ammonia synthesis rate reached 1.73 mmol g-1 h-1. Furthermore, the CO2-TPD and H2-TPR analyses indicated that Zn doping effectively promotes the metal-support interaction (MSI) and surface alkalinity. The findings of this study offers valuable insights for the design of defective modified catalyst supports.

Bottom-Up Construction of Mesoporous Cerium-Doped Titania with Stably Dispersed Pt Nanocluster for Efficient Hydrogen Evolution

Hydrogen generation is one of the crucial technologies to realize sustainable energy development, and the design of advanced catalysts with efficient interfacial sites and fast mass transfer is significant for hydrogen evolution. Herein, an in situ coassembly strategy was proposed to engineer a cerium-doped ordered mesoporous titanium oxide (mpCe/TiO2), of which the abundant oxygen vacancies (Ov) and highly exposed active pore walls contribute to good stability of ultrasmall Pt nanoclusters (NCs, ∼ 1.0 nm in diameter) anchored in the uniform mesopores (ca. 20 nm). Consequently, the tailored mpCe/TiO2 with 0.5 mol % Ce-doping-supported Pt NCs (Pt-mpCe/TiO2-0.5) exhibits superior H2 evolution performance toward the water-gas shift reaction with a 0.73 molH2·s-1·molPt-1 H2 evolution rate at 200 °C, which is almost 6-fold higher than the Pt-mpTiO2 (0.13 molH2·s-1·molPt-1 H2). Density functional theory calculations confirm that the structure of Ce-doped TiO2 with Ce coordinated to six O atoms by substituting Ti atoms is thermodynamically favorable without the deformation of Ti-O bonds. The Ov generated by the six O atom-coordinated Ce doping is highly active for H2O dissociation with an energy barrier of 2.18 eV, which is obviously lower than the 2.37 eV for the control TiO2. In comparison with TiO2, the resultant Ce/TiO2 support acts as a superior electron acceptor for Pt NCs and causes electron deficiency at the Pt/support interface with a 0.17 eV downshift of the Pt d-band center, showing extremely obvious electronic metal-support interaction (EMSI). As a result, abundant and hyperactive Ti3+-Ov(-Ce3+)-Ptδ+ interfacial sites are formed to significantly promote the generation of CO2 and H2 evolution. In addition, the stronger EMSI between Pt NCs and mpCe/TiO2-0.5 than that between Pt and mpTiO2 contributes to the superior self-enhanced catalytic performance during the cyclic test, where the CO conversion at 200 °C increases from 72% for the fresh catalyst to 99% for the used one. These findings reveal the subtle relationship between the mesoporous metal oxide-metal composite catalysts with unique chemical microenvironments and their catalytic performance, which is expected to inspire the design of efficient heterogeneous catalysts.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Confinement-Induced Indium Oxide Nanolayers Formed on Oxide Support for Enhanced CO2 Hydrogenation Reaction

An enclosed nanospace often shows a significant confinement effect on chemistry within its inner cavity, while whether an open space can have this effect remains elusive. Here, we show that the open surface of TiO2 creates a confined environment for In2O3 which drives spontaneous transformation of free In2O3 nanoparticles in physical contact with TiO2 nanoparticles into In oxide (InOx) nanolayers covering onto the TiO2 surface during CO2 hydrogenation to CO. The formed InOx nanolayers are easy to create surface oxygen vacancies but are against over-reduction to metallic In in the H2-rich atmospheres, which thus show significantly enhanced activity and stability in comparison with the pure In2O3 catalyst. The formation of interfacial In-O-Ti bonding is identified to drive the In2O3 dispersion and stabilize the metastable InOx layers. The InOx overlayers with distinct chemistry from their free counterpart can be confined on various oxide surfaces, demonstrating the important confinement effect at oxide/oxide interfaces.

Oxygen Vacancy Engineering of FeOx toward Oxygen-Tolerant Hydrogen Peroxide Reduction for Reliable Bioassays

The accurate determination of hydrogen peroxide (H2O2), an important clinical disease relevant biomarker, is of great importance for the diagnosis and management of illnesses. By using the cathodic monitoring approach, H2O2 can be accurately detected because interfering signals from easily oxidizable endogenous and exogenous species in biofluids can be avoided. However, the simultaneous occurrence of the oxygen reduction reaction (ORR) restricts the practical use of this cathodic method. In this study, via oxygen vacancy modulation, we synthesized FeOx catalysts that can selectively reduce H2O2 over O2. The H2O2 detection system based on this catalyst exhibits an outstanding ORR inhibition ability. Furthermore, by integrating this catalyst with glucose oxidase, a model enzyme, a reliable bioassay system was developed that can selectively detect glucose over a wide variety of interferents in artificially simulated tissue fluids. The bioassay system employing this catalyst in conjunction with oxidases is generally applicable to accurate detect a wide range of biomarkers.