CO Chemisorption Research Articles

Carbon Dioxide Capture by Niobium Polyoxometalate Fragmentation.

High oxidation state metal cations in the form of oxides, oxoanions, or oxoperoxoanions have diverse roles in carbon dioxide removal (direct air capture and point source). Features include providing basic oxygens for chemisorption reactions, direct binding of carbonate, and catalyzing low-temperature CO2 release to regenerate capture media. Moreover, metal oxides and aqueous metal-oxo species are stable in harsh, point-source conditions. Here, we demonstrate aqueous niobium polyoxometalate (POM) carbon capture ability, specifically [Nb6O19]8-, Nb6. Upon exposure of aqueous Nb6 to CO2, Nb6 fragments and binds chemisorbed carbonate, evidenced by crystallization of Nb-carbonate POMs including [Nb22O53(CO3)16]28-and [Nb10O25(CO3)6]12-. While Rb/Cs+ counter cations yield crystal structures to understand the chemisorption processes, K+ counter cations enable higher capture efficiency (based on CO3/Nb ratio), determined by CHN analysis and thermogravimetry-mass spectrometry of the isolated solids. Sum frequency generation spectroscopy also showed higher carbon capture efficiency of the K-Nb6 solutions at the air-water interface, while small-angle X-ray scattering (SAXS) provided insights into the role of the alkalis in influencing these processes. Tetramethylammonium counter cations, like K+, demonstrate high efficiency of carbonate chemisorption at the interface, but SAXS and Raman of the bulk showed a predominance of a Nb24-POM (HxNb24O72, x ∼ 9) that does not bind carbonate. Control experiments show that carbonate detected at the interface is Nb-bound, and the Nb-carbonate species are stabilized by alkalis, demonstrating their supporting role in aqueous Nb-POM CO2 chemisorption. Of fundamental importance, this study presents rare examples of directing POM speciation with a gas, instead of liquid phase acid or base.

CoCorrole-Functionalized PCN-222 for Carbon Monoxide Selective Adsorption.

The high risk of CO poisoning justifies the need for indoor air quality control and warning systems based on the detection of low concentrations (ppm-ppb) of CO. Cobalt corrole complexes selectively bind CO vs. O2, CO2, N2, opening new fields of applications. By combining the CO chemisorption properties of cobalt corroles with the known sorption capacity of MOFs, we hope to obtain high performance sensing materials for CO detection. In addition, the exposed metal sites of MOFs lead to CO2 physisorption, allowing the co-detection of CO and CO2. In this work, PCN-222 a stable Zr-based MOF made from Ni(TCPP) with natural vacancies has been used as a porous matrix for the grafting of electron-poor metallocorroles. The materials were characterized by powder XRD, SEM and optical microscopy, BET analyses and gas adsorption measurements at 298 K. No degradation of the crystalline structure of PCN-222 was observed. At 1 atm, the adsorbed CO(g) volumes measured for the best materials were 12.15 cm3 g-1 and 14.01 cm3 g-1 for CoCorr2@PCN-222 and CoCorr3@PCN-222 respectively, and both materials exhibited high CO chemisorption and selectivity against O2, N2, and CO2 at low pressure due to the highest energy of the chemisorption process vs physisorption. (198 Words).

Highly Efficient and Reversible Carbon Dioxide Capture by Carbanion-Functionalized Ionic Liquids.

Due to the active unstable nature of carbon anions, it is challenging to develop carbanion-functionalized ionic liquids (ILs) for efficient and reversible carbon dioxide (CO2) capture. Here, a series of carbanion-based ILs with large conjugated structures were designed and a promising system was achieved through tuning the nucleophilicity of carbanions and screening the cation. The ideal carbanion-functionalized IL trihexyl(tetradecyl)phosphonium N,N-diethycyanoacetoamide ([P66614][DECA]) showed equimolar chemisorption of CO2 (up to 0.98 mol CO2 /mol IL) under ambient pressure and excellent absorption rate. What's more, the combined CO2 can be released easily, leading to excellent reversibility due to high stability of anion conjugated structures. More importantly, the presence of water had negligible effect on the absorption capacity, which makes it potential to be applied to the CO2 capture in industrial flue gas. The chemisorption mechanism of the carbanion and CO2 was confirmed by spectroscopic investigations and DFT calculations, where carboxylic acid product was formed through proton transfer after the carbanions reacted with CO2. Considering that high capacity, quick rate as well as excellent reversibility, these carbanion-functionalized IL should certainly represent competitive candidates for further scale up and practical application in CO2 capture.

Ultrafast electron transfer at the In2O3/Nb2O5 S-scheme interface for CO2 photoreduction

Constructing S-scheme heterojunctions proves proficient in achieving the spatial separation of potent photogenerated charge carriers for their participation in photoreactions. Nonetheless, the restricted contact areas between two phases within S-scheme heterostructures lead to inefficient interfacial charge transport, resulting in low photocatalytic efficiency from a kinetic perspective. Here, In2O3/Nb2O5 S-scheme heterojunctions are fabricated through a straightforward one-step electrospinning technique, enabling intimate contact between the two phases and thereby fostering ultrafast interfacial electron transfer (<10 ps), as analyzed via femtosecond transient absorption spectroscopy. As a result, powerful photo-electrons and holes accumulate in the Nb2O5 conduction band and In2O3 valence band, respectively, exhibiting extended long lifetimes and facilitating their involvement in subsequent photoreactions. Combined with the efficient chemisorption and activation of stable CO2 on the Nb2O5, the resulting In2O3/Nb2O5 hybrid nanofibers demonstrate improved photocatalytic performance for CO2 conversion.

Effect of method of preparation of Ni and/or Cu supported on ZSM-5 catalysts for the aqueous phase hydrogenation of levulinic acid to γ-valerolactone

A series of Cu and Ni supported on ZSM-5 catalysts were synthesized by ion exchange (IE) and impregnation (IMP) techniques and examined for the aqueous phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) at atmospheric pressure. Hydrogenation of LA to GVL proceeds through LA dehydration to AL (angelica lactone) and subsequent hydrogenation of it to GVL, emphasizing the combined role of an acid and a metal site present on the catalyst surface. The interaction of Cu and/or Ni with ZSM-5 was elucidated using various characterization techniques such as powder XRD, XPS, H2-TPR, NH3-TPD, CO and/or H2 pulse chemisorption and SS NMR techniques. The CO chemisorption results indicated a lower uptake on Cu-ZSM-5(IMP) than on Cu-ZSM-5(IE). The H2 uptake was lower on Ni-ZSM-5(IE) than on Ni-ZSM-5(IMP). In the comparative analysis, the Ni-ZSM-5(IMP) catalyst exhibited a high rate of GVL formation, while the Cu-ZSM-5(IE) catalyst displayed a larger proportion of AL formation than the other catalysts prepared under similar protocols. The influence of the surface active sites on the product distribution was rationalized based on the physico-chemical characteristics of the fresh and reduced catalysts.

Highly active and selective ZIF‐derived cobalt catalyst for methanol conversion to dimethyl carbonate

The oxidative carbonylation of methanol to synthesize dimethyl carbonate (DMC) has been extensively studied over Cu‐based catalysts, but the activity and selectivity are not high. The Co catalysts exhibit high DMC selectivity, but the difficulty in recycling homogeneous Co catalyst and the low conversion of heterogeneous Co catalyst limit the application of Co catalysts. Here, the core–shell ZIFs materials were synthesized and carbonized to obtain solid core–shell cobalt catalysts, and then the catalytic performance for methanol conversion to DMC was investigated. The CoNC@NC catalyst, carbonized from Z67@Z8 with Z67 as the core and Z8 as the shell, shows that the carbonized NC shell effectively suppressed the aggregation of Co NPs and the Co NPs were only 15.4 nm, which was much smaller than those of NC@CoNC (34.5 nm) and CoNC (48.1 nm) catalysts. Compared with the CoNC catalyst, CoNC@NC significantly improved the pulse chemisorption of CH3OH and CO, leading to a significant increase in methanol conversion from 6.9% to 17.1%. Furthermore, the deactivation rate of the CoNC@NC catalyst (22.8%) was much lower than that of CoNC (59.4%) after five reaction cycles. The results of this work provide a new strategy for the design and preparation of solid cobalt catalysts for the oxidative carbonylation of methanol to DMC.

The adsorption of carbon and nitrogen oxides on the PuO2 {110} surface: A DFT + U study

The adsorptions of CO, CO2, N2O, NO and NO2 on the PuO2 {110} surface have been studied using density functional theory with a Hubbard U correction. Different approaching pathways are analysed to locate physisorbed states. Starting from the most stable physisorbed structures, reaction paths leading to stable chemisorbed structures are determined. The chemisorptions of CO, CO2, N2O, NO and NO2 are extensively studied and the following aspects are compared: molecule/surface structures, atomic magnetic moments, surface work functions, density of states, adsorption energies and reaction barriers. With the exception of N2O, chemisorption is energetically favourable on PuO2 {110}. Dioxide adsorption is more favourable than monoxide, and the chemisorption of nitrogen monoxide/dioxide is easier than carbon monoxide/dioxide. Chemisorption of monoxides reduces a neighbouring surface Pu, thereby providing an active site for interaction with further incoming residual molecules.

Unified mechanistic understanding on CO2 sorption by Na-doped Li4SiO4: Experimental and DFT study

The addition of molten Na2CO3 can drastically accelerated the extremely slow sorption kinetics of Li4SiO4-based CO2 sorbents in the sorption enhanced reforming process. However, the lack of a unified consensus about the effect of doped Na2CO3 on the CO2 capture process, now delays the development of more-effective Li4SiO4 sorbents. Here, sorption tests, sturactural characterzations and periodic density functional theory calculations were combined to develop a better mechanistic understanding CO2 sorption on Na-doped Li4SiO4. The Na-doped Li4SiO4 exhibited a better CO2 capture performance than pure Li4SiO4 even below the melting point of any eutectic mixtures. Structural characterizations revealed that rather than generating physical favorable characteristics, the Na doping substituted at the Li site and created lithium–sodium orthosilicates (Li4-xNaxSiO4). Theoretical calculations agreeing with experimental results further demonstrated that Li4-xNaxSiO4 presented a weaker Na-O bond and generated more active phases (quasi Li2O groups) for larger sorption energies, more charge transfers and stronger CO32– bond formation, in turn providing more reactive sites for enhanced CO2 chemisorption as comparing with pure Li4SiO4. Finally, we propose a new and unified sorption mechanism independent of the traditional “melting layer” explanation.

Photocatalytic CO2 reduction of CuO-Zn1-xCuxO (ZCO)/Ti3C2Tx MXene heterojunctions with enhanced interfacial charge transfer

Photocatalytic CO2 reduction reaction (CO2RR) synthesis of recycled fuel is a promising pathway to assist the mitigating fossil fuel depletion. Finding efficient and inexpensive high performance CO2RR semiconductor photocatalysts is a giant challenge in the field of photocatalytic reduction. This work constructs the novel-designed interfacial Schottky junction of CuO-Zn1-xCuxO (ZCO)/Ti3C2Tx via electrostatic spinning and electrostatic self-assembly techniques. The catalysts exhibit tight contact heterogeneous interface companies with enhanced CO2 chemisorption capability and proved by various characterizations for efficient carrier separation and migration capacity. The optimized ZCO/Ti3C2Tx nanosheet composites significantly improved their photocatalytic performance. The best samples yielded 5.855 and 2.518 μmol g−1 h−1 of CO and CH4, which are 6 and 1.73 times higher than the conversion of ZCO, respectively, and maintain stability after four cycles without the use of sacrificial agents. In addition, the mechanism and reaction pathways of the photocatalytic process are proposed through In-situ diffuse reflectance Infrared Fourier Transform Spectroscopy (In-situ DRIFTS) and X-ray absorption near edge structure (XANES) analysis. This work provides a new semiconductor/co-catalyst system for the photocatalytic reduction of CO2 and demonstrates that Ti3C2Tx MXene is a hopeful and inexpensive co-catalyst.

Simulating CO2 diffusivity in rigid and flexible Mg-MOF-74 with machine-learning force fields

The flexibility of metal–organic frameworks (MOFs) affects their gas adsorption and diffusion properties. However, reliable force fields for simulating flexible MOFs are lacking. As a result, most atomistic simulations so far have been carried out assuming rigid MOFs, which inevitably overestimates the gas adsorption energy. Here, we show that this issue can be addressed by applying a machine-learning potential, trained on quantum chemistry data, to atomistic simulations. We find that inclusion of flexibility is particularly important for simulating CO2 chemisorption in MOFs with coordinatively unsaturated metal sites. Specifically, we demonstrate that the diffusion of CO2 in a flexible Mg-MOF-74 structure is about one order of magnitude faster than in a rigid one, challenging the rigid-MOF assumption in previous simulations.

Collective Synergistic Catalysis of Electrochemical CO2 Reduction on Nonstoichiometric Double Perovskites

AbstractPerovskite oxides show great promise as an alternative catalyst to the conventional nickel cermets for CO2 reduction reactions (CO2RR) in solid oxide electrolysis cells (SOECs) owing to their advantages of redox stability and coking resistance. Nevertheless, practical applications of these oxides are prevented largely by their poor CO2RR activities. Herein, a novel donor and acceptor co‐doped nonstoichiometric double perovskite, La0.3Sr1.55Fe1.5Ni0.1Mo0.4O6−δ (LSFNM), is developed with in situ exsolved FeNi3 nanoparticles to efficiently catalyze CO2RR in SOECs. Pure CO2 electrolysis over the impregnated FeNi3@LSFNM catalysts is evaluated on two types of SOECs—one with thin (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 (SSZ) electrolytes supported on 430L alloys and the other with thin La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolytes supported on impregnated SmBa0.5Sr0.5Co2O5+δ (SBSCO)@LSGM anodes, producing unprecedently high current densities of 2.84 A cm−2 for the former and 3.07 A cm−2 for the latter at 1.5 V and 800 °C. Experimental analysis and density‐functional theory (DFT) calculations reveal collective synergistic catalysis of oxygen vacancies (), the doping Ni2+ ions and FeNi3 nanoparticles via the cooperative ‐O(CO2), and Ni(II)–C(sp) and Ni(0)–O(CO2) interactions in LSFNM, not only facilitating CO2 chemisorption on oxygen vacancies but also destabilizing and dissociating surface carbonates in the vicinity of FeNi3 spontaneously into CO.

The role of reverse Boudouard reaction during integrated CO2 capture and utilisation via dry reforming of methane

Integrated carbon capture and utilisation (ICCU) is an emerging technology for simultaneous CO2 adsorption and conversion into value-added products. This provides a more sustainable approach compared to carbon capture and storage. Dual-functional materials (DFMs) that couple CO2 sorbents (e.g. CaO) and catalysts (e.g. Ni) enable direct utilisation of sorbed CO2 for reactions like dry reforming of methane (DRM). However, the potential interactions between sorbent and catalyst components within DFMs may induce distinct mechanisms compared to individual materials. Elucidating these synergies and interfacial phenomena is vital for guiding the rational design of DFMs. This article investigates the respective roles of Ni/SiO2 catalyst and sol–gel synthesised CaO sorbent in integrated CO2 capture and utilisation via dry reforming of methane (ICCU-DRM) using a decoupling approach. Through decoupled reactor experiments, it is found that Ni/SiO2 activates CO2 to react with carbon deposits from CH4 decomposition, achieving maximal CO and H2 yields of 43.41 mmol g−1 and 46.78 mmol g−1 as well as 87.2 % CO2 conversion at 650 °C. Characterisation shows that coke would encapsulate Ni nanoparticles and be active for CO2 conversion via Boudouard reaction, indicating sufficient catalyst-sorbent contact is necessary for CO2 spillover. In-situ DRIFTS reveals that no obvious CH4-CaCO3 reaction occurs, CO2 chemisorption on Ni/SiO2 enables the reverse Boudouard reaction, which is further verified by DFT calculations. The findings elucidate the dependent and synergistic roles of Ni/SiO2 and CaO/CaCO3 in ICCU-DRM, and highlight the importance of catalyst-adsorbent interactions in optimising dual-functional materials.

Post‐combustion carbon dioxide adsorption of concurrent activated and surface modified palm kernel shell‐derived activated carbon

AbstractThis research applied a concurrent activation and surface modification (CAM) process to synthesize palm kernel shell‐derived activated carbon (PKSdAC) to obtain CO2 affinity surface functionalization. The CAM process is a simplified activated carbon activation process that is cost‐effective. The CAM process used in this study integrates sulphuric acid activation and barium chloride functionalization. The formation of barium sulphate is targeted to incorporate barium through a reduction process with carbon‐containing material at elevated temperatures into PKSdAC to obtain basic metal surfaces functional group for chemical adsorption. The optimal temperature for CAM‐PKSdAC CO2 adsorption performance was at 40–60 °C, established through temperature‐programmed desorption of CO2 (TPD‐CO2) analysis. The CAM‐PKSdAC adsorption performance was tested using a lab‐scale adsorption system. The bed CO2 content was determined using gas chromatography coupled with a thermal conductivity detector (GC‐TCD) by manual syringe injection. CAM‐PKSdAC exhibited a high CO2 adsorption capacity of 0.89 mmol g−1 from TPD‐CO2, and 1.91 mmol g−1 from GC‐TCD at 40 °C and 1 bar. It showed comparable CO2 adsorption capacity to conventional surface modified‐activated PKSdAC (1.96 mmol g−1) while higher than commercial and modified ACs (1.14–1.60 mmol g−1), but lower than potassium hydroxide modified ACs (1.81–2.10 mmol g−1) at 40 °C and 1 bar. Barium promoted chemisorption of CO2 as supplementary reaction, which increases adsorption capacity. The non‐linear Dubinin Radushkevich model strongly correlates with the experimental adsorption data for CAM‐PKSdAC adsorption, indicating the physisorption process via micropore filling on CAM‐PKSdAC. CAM‐PKSdAC showed moderate reusability with negligible variation in adsorption capacity after 10 adsorption–desorption cycles. © 2024 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Effective Prevention of Palladium Metal Particles Sintering by Histidine Stabilization on Silica Catalyst Support

AbstractA robust method for enhancing the dispersion and stabilization of small metal nanoparticles in heterogeneous catalysts is developed. It involves in situ complexation of palladium(II) by histidine, in water, prior to impregnation in fumed silica. TEM images show that the histidine facilitates dispersion of the Pd(II) into finer nanoscale particles (≈2 nm) uniformly distributed on the support, rather than the large clusters (≈5 nm) seen in the absence of histidine. After hydrogen reduction, assessments using CO chemisorption and propylene hydrogenation indicate that the coordinated histidine might obscure the active sites on the Pd particles. However, as histidine decomposes between 220 and 300 °C in air, these materials are treated at 225 °C in air for 48 h. Afterwards the Pd(II) particles remain the same size, but after hydrogen reduction, there is a 2.4‐fold increase in CO gas adsorption, indicative of an expanded Pd surface area. Furthermore, superior catalyst stability (activity &gt;200 h) is observed during propylene hydrogenation at 250 °C. This is consistent with histidine use having generated widely spaced, uniformly small, Pd nanoparticles on the silica support which is expected to help prevent agglomeration (sintering) during catalysis. This is a convenient low‐cost strategy for reducing metal content, preventing sintering and optimizing catalyst performance.

Valorization of Crab Shells as Potential Sorbent Materials for CO2 Capture.

This study delves into the potential advantage of utilizing crab shells as sustainable solid adsorbents for CO2 capture, offering an environmentally friendly alternative to conventional porous adsorbents, such as zeolites, silicas, metal-organic frameworks (MOFs), and porous carbons. The investigation focuses on crab shell waste, which exhibits inherent natural porosity and N-bearing groups, making them promising candidates for CO2 physisorption and chemisorption applications. Selective deproteinization and demineralization treatments were used to enhance textural properties while preserving the natural porous structure of the crab shells. The impact of deproteinization and demineralization treatments on CO2 adsorption and speciation at the atomic scale, via solid-state NMR, and correlated findings with textural properties and biomass composition were investigated. The best-performing sample exhibits a surface area of 36 m2/g and a CO2 adsorption capacity of 0.31 mmol/g at 1 bar and 298 K, representing gains of ∼3.5 and 2, respectively, compared to the pristine crab shell. These results underline the potential of fishing industry wastes as a cost-effective, renewable, and eco-friendly source to produce functional porous adsorbents.

Thermally Induced Structure and Functionality Evolution of a Pt‐based Lean NOx Trap Catalyst

Applying a NOx trap catalyst to effectively remove NOx contaminants from the oxygen‐rich exhaust is still very challenging, due to the lack of use guidance based on deactivation mechanisms. The temperature‐dependent Pt sintering rate constant was described using Pt dispersion determined by pulse CO chemisorption. It was found that 700‐850 ºC was the determining temperature regions for the significant Pt sintering, according to the sintering kinetics and the evolution of active Ptδ+ sites. The weak basicity plays a critical role in trapping NOx at low‐temperature (≤ 300 ºC), and the NOx trap efficiency decreases because of the loss of catalytic activity and medium basicity caused by forming BaAl2O4 phase. The reduction of NOx towards N2 on the Pt crystallites smaller than 18 nm is structure sensitive and decreases with losing the reducibility of catalysts. The security for long‐time use of a NOx trap catalyst should be exposed to the exhaust gas within 750 ºC, and effectively removing NOx contaminants requires it to be worked in the 350‐500 ºC regions. These findings can guide engineers and applied chemists how to efficiently use a NOx trap catalyst in the automotive exhaust purification system.

Photocatalytic conversion of CH4 and CO2 to acetic acid over Cu/ZnO catalysts under mild conditions

The conversion of methane (CH4) and carbon dioxide (CO2) into high-value products under mild conditions is crucial for addressing the greenhouse effect and advancing C1 chemistry. In this study, Cu/ZnO catalysts were prepared through a one-step wet reduction process, and the catalytic conversion of CH4 and CO2 into acetic acid molecules (CH3COOH) was achieved via photon activation at ambient temperature. The yield of acetic acid was 411.6 μmol/Lgcat−1h−1 with a selectivity of 89.5 % under optimal conditions (100 mWcm−2 light intensity, 25 ± 2 °C, 2 MPa pressure, and a 1:1 CH4:CO2 volume ratio). Enhanced solubility of CH4 in aqueous under increased pressure and temperature was observed to improve acetic acid production. Additionally, the catalytic mechanism involved surface chemisorption of CH4 and CO2, facilitated by ZnO and Cu in the catalyst, leading to C-C coupling and subsequent acetic acid formation, driven by photogenerated electron-hole migration. This study provides a foundational understanding for the synthesis of value-added chemicals through CH4 and CO2 conversion via C-C coupling in mild environments.

Co-ZIF-derived dual Co and Co3S4 nanoparticles encapsulated in N-doped carbon matrix for efficient photocatalytic CO2 reduction

In this study, a novel N-doped carbon-coated dual Co and Co3S4 nanoparticles composite (Co-Co3S4@NC) has been developed by pyrolysis of an ideal flower-like Co-ZIF precursor followed via subsequent hydrothermal sulfidation. Under visible-light irradiation, the Co-Co3S4@NC exhibits outstanding performances for CO2 reduction with H2O vapor into CO (23.14 μmol g−1 h−1) and CH4 (0.62 μmol g−1 h−1) in a continuous flow system, significantly outperforming the single Co@NC photocatalyst. The experimental results demonstrate that the energy band structure in Co-Co3S4@NC can provide a more favorable reduction potential for the effective reduction of CO2. Moreover, the presence of Co3S4 is beneficial for the rapid separation and transfer of charges, thereby enhancing the utilization of photogenerated charge carriers. Thanks to its unique composition, Co-Co3S4@NC possesses abundant active sites for chemisorption and activation of CO2, which facilitates CO2 photoreduction. The reaction mechanism is revealed in detail by analyzing the key intermediate species obtained through in situ DRIFTS. The current work offers a facile route for the construction of MOF-derived composites for promising photocatalytic reactions.

Understanding the catalytic performance and deactivation behaviour of second-promoter doped Pt/WOx/γ-Al2O3 catalysts in the glycerol hydrogenolysis for selective and cleaner production of 1,3-propanediol

The selective aqueous-phase glycerol hydrogenolysis is a promising reaction to produce commercially useful 1,3-propanediol (1,3-PDO). The Pt-WOx bifunctional catalyst can catalyse the glycerol hydrogenolysis but the catalyst deactivation via sintering, metal leaching, and coking can predominantly occur in the aqueous phase reaction. In this work, the effect of reaction temperature, pressure and second promoter (Cu, Fe, Rh, Mn, Re, Ru, Ir, Sn, B, and P) on catalytic performance and deactivation behaviour of Pt/WOx/γ-Al2O3 was investigated. When doped with Rh, Mn, Re, Ru, Ir, B, and P, the second promoter boosts catalytic activity by promoting great dispersion of Pt on support and increasing Pt surface area. The increased Brønsted acid sites lead to selective synthesis of 1,3-PDO than 1,2-propanediol (1,2-PDO). The characterization studies of fresh and spent catalysts reveal that the main cause of catalyst deactivation is the Pt sintering, as interpreted based on XRD, CO chemisorption, and TEM analyses. The Pt sintering is affected depending on the second promoter that can either or reduce the interaction between Pt, WOx, and Al2O3. As an electron acceptor of Pt in Pt/WOx/γ-Al2O3, Re and Mn as second promoters resulted in increased Pt2+ on the catalytic surface, which strengthens the contact between Pt and γ-Al2O3 and WOx, resulting in a decrease in Pt sintering. The metal leaching and coking are not affected by the presence of second promoter. The catalyst modified with a second promoter possesses improved catalytic activity and 1,3-PDO production, however the stability continues to remain a challenge. The present work unravelled the determining parameters of catalytic activity and deactivation, thus providing a promising protocol toward effective catalysts for glycerol hydrogenolysis.

Vacancy pair induced surface chemistry reconstruction of Cs2AgBiBr6/Bi2WO6 heterojunction to enhance photocatalytic CO2 reduction

Cs2AgBiBr6/Bi-O vacancy pair Bi2WO6 (Cs2AgBiBr6/VBi-OBi2WO6) heterojunction was synthesised for photocatalytic CO2 reduction under visible light irradiation. The characterisation results show that the Bi-O vacancy pairs can reconstruct the surface electronic states of the heterojunction. The optimal 10%Cs2AgBiBr6/VBi-OBi2WO6 heterojunction exhibited a substantial CO yield of 48.5 μmol/g, approximately 22 times higher than that of Bi2WO6, exceeding the performance of most of the Bi-based photocatalysts reported to date. The enhanced activity of 10%Cs2AgBiBr6/VBi-OBi2WO6 was due to exposed Bi sites that facilitate the chemisorption and activation of CO2 and the lower reaction energy barrier for the protonation of CO2 to CO via the formation of COOH* intermediates with the cooperation of surface four-coordinated H2O molecules. Furthermore, charge migration from Cs2AgBiBr6 to VBi-OBi2WO6 and space-charge distribution in the heterojunction under visible light irradiation were demonstrated. This work reveals defective heterojunction catalysts that facilitate the transformation of reactive molecules in surface/interfacial reactions.