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The catalytic conversion of CO2 to CO by the reverse water gas shift (RWGS) reaction followed by well-established synthesis gas conversion technologies could be a practical technique to convert CO2 to valuable chemicals and fuels in industrial settings. For catalyst developers, prevention of side reactions like methanation, low-temperature activity, and selectivity enhancements for the RWGS reaction are crucial concerns. Cerium oxide (ceria, CeO2) has received considerable attention in recent years due to its exceptional physical and chemical properties. This study reviews the use of ceria-supported active metal catalysts in RWGS reaction along with discussing some basic and fundamental features of ceria. The RWGS reaction mechanism, reaction kinetics on supported catalysts, as well as the importance of oxygen vacancies are also explored. Besides, recent advances in CeO2 supported metal catalyst design strategies for increasing CO2 conversion activity and selectivity towards CO are systematically identified, summarized, and assessed to understand the impacts of physicochemical parameters on catalytic performance such as morphologies, nanosize effects, compositions, promotional abilities, metal-support interactions (MSI) and the role of selected synthesis procedures for forming distinct structural morphologies. This brief review may help with future RWGS catalyst design and optimization.

Hydrogen (H2) is an environmentally-safe power source and its demands is continuously growing worldwide. The most important approach for its generation is water–gas shift (WGS) reaction through various catalysts. This work investigates feasibility of neural network method named Multilayer Perceptron Neural Network (MLP-NN) to estimate CO conversion in WGS reactions based on different active phase compositions and various supports. The approach considers the intrinsic parameters of the catalyst to estimate reaction performance. This research investigates the most influential variables by conducting a sensitivity analysis study on the predictions of the implemented method. The results of the modeling study revealed that the MLP-NN method can accurately approximate the experimental CO conversion values. The sensitivity analysis study revealed temperature and H2 feed concentration are the most crucial parameters on the reaction performance. The reliability of neural network methods is proved such as the MLP-NN to accurately estimate the CO conversion values in WGS reaction.

Green methanol is a viable alternative for the storage of hydrogen and may be produced from captured anthropogenic sources of carbon dioxide. The latter was hydrogenated over Cu-ZnO catalysts supported on an aluminum fumarate metal-organic framework (AlFum MOF). The catalysts, prepared via slurry phase impregnation, were assessed for thermocatalytic hydrogenation of CO2 to methanol. PXRD, FTIR, and SBET exhibited a decrease in crystallinity of the AlFum MOF support after impregnation with Cu-Zn active sites. SEM, SEM-EDS, and TEM revealed that the morphology of the support is preserved after metal loading, where H2-TPR confirmed the presence of active sites for hydrogen uptake. The catalysts exhibited good activity, with a doubling in Cu and Zn loading over the AlFum MOF, resulting in a 4-fold increase in CO2 conversions from 10.8% to 45.6% and an increase in methanol productivity from 34.4 to 56.5 gMeOH/Kgcat/h. The catalysts exhibited comparatively high CO selectivity and high yields of H2O, thereby favoring the reverse water-gas shift reaction. The selectivity of the catalysts towards methanol was found to be 12.9% and 6.9%. The performance of the catalyst supported on AlFum MOF further highlights the potential use of MOFs as supports in the heterogeneous thermocatalytic conversion of CO2 to value-added products.

Herewith, an overview is provided on the recent developments in the utilization of multimetallic catalysts to produce large amounts of molecular hydrogen, especially via the steam reforming of hydrocarbons and the water–gas shift reaction. Emphasis is given on the explanation of the problems affecting the currently used catalysts and how the addition/incorporation of other metals in available or new catalysts may lead to improved catalyst activity, selectivity and stability. We compare results from selected key examples taken from the literature where multimetallic catalysts are used for the aforementioned reactions. The methanol and ammonia decompositions are also critically analyzed, with focus on Earth-abundant metal elements.

The construction of synergistic catalysis of single atom catalysts (SACs) and oxygen vacancies (O V ) on supports is crucial for the enhancement of heterogeneous catalytic efficiency, yet presents considerable challenges. Herein, we have developed an amine-molecule-assisted in-situ anchoring strategy that effectively stabilizes Pt SACs on O V sites of reduced TiO 2 (TiO 2− x ) by controlling the interaction of amine with Pt species and TiO 2− x . Direct evidence indicates that Pt SACs are anchored on the O V with forming Pt δ+ –O V –Ti 3+ sites and strong metal-support interaction, which not only prevents the sintering of Pt SACs under high-temperature reduction treatments, but also enhances the hydrogen spillover process to facilitate the formation of more O V sites. During the reverse water-gas shift (RWGS) reaction, the enhanced amount of O V sites can increase CO 2 adsorption, while the Pt SACs can efficiently promote the activation and spillover of hydrogen. Their combined synergistic effects greatly improve its catalytic performance with a high turnover frequency (TOF) of 9289 h −1 at 330°C and notable stability for over 200 h, surpassing those of Pt clusters and nanoparticles on TiO 2− x . This work provides a new avenue for the controllable synthesis of synergistic catalysts with SACs and O V , significantly advancing catalytic efficiency.

Due to tunable redox properties and cost‐effectiveness, copper‐ceria (Cu‐CeO2) materials have been investigated for a wide scope of catalytic reactions. However, accurately identifying and rationally tuning the local structures in Cu‐CeO2 have remained challenging, especially for nanomaterials with inherent structural complexities involving surfaces, interfaces, and defects. Here, a nanocrystal‐based atom‐trapping strategy to access atomically precise Cu‐CeO2 nanostructures for enhanced catalysis is reported. Driven by the interfacial interactions between the presynthesized Cu and CeO2 nanocrystals, Cu atoms migrate and redisperse onto the CeO2 surface via a solid–solid route. This interfacial restructuring behavior facilitates tuning of the copper dispersion and the associated creation of surface oxygen defects on CeO2, which gives rise to enhanced activities and stabilities catalyzing water–gas shift reaction. Combining soft and solid‐state chemistry of colloidal nanocrystals provide a well‐defined platform to understand, elucidate, and harness metal–support interactions. The dynamic behavior of the supported metal species can be further exploited to realize exquisite control and rational design of multicomponent nanocatalysts. Understanding and harnessing the restructuring of nanocrystals is important for catalytic applications, while elucidating the surface and bulk characteristics remains challenging. A nanocrystal‐based atom‐trapping strategy is reported to access well‐defined copper‐ceria nanostructures with tunable copper dispersions. The optimized copper‐ceria nanocatalysts exhibit enhanced activities and stabilities catalyzing water−gas shift reaction.

The structure of copper species, dispersed on nanostructured ceria (particles, rods and cubes), was analyzed by scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS). It was interestingly found that the density of surface oxygen vacancies (or defect sites), induced by the shape of ceria, determined the geometrical structure and the chemical state of copper species. Atomically dispersed species and monolayers containing few to tens of atoms were formed on ceria particles and rods owing to the enriched anchoring sites, but copper clusters/particles co-existed, together with the highly dispersed atoms and monolayers, on cubic ceria. The atomically dispersed copper sites and monolayers interacted strongly with ceria, involving a remarkable charge transfer from copper to ceria at their interfaces. The activity for the low-temperature water-gas shift reaction of the Cu/CeO 2 catalysts was associated with the fraction of the positively-charged copper atoms, demonstrating that the active sites could be tuned by dispersing Cu species on shape-controlled ceria particles.

Hydrogen is mainly produced by steam reforming of fossil fuels. Thus, research has been continuously conducted to produce hydrogen by replacing fossil fuels. Among various alternative resources, waste is attracting attention as it can produce hydrogen while reducing the amount of landfill and incineration. In order to produce hydrogen from waste, the water–gas shift reaction is one of the essential processes. However, syngas obtained by gasifying waste has a higher CO concentration than syngas produced by steam reforming of fossil fuels, and therefore, it is essential to develop a suitable catalyst. Research on developing a catalyst for producing hydrogen from waste has been conducted for the past decade. This study introduces various catalysts developed and provides basic knowledge necessary for the rational design of catalysts for producing hydrogen from waste-derived syngas.

Previous work showed that the copper oxide nanoparticles confined in titania nanotubes (Cu-in-TiO 2 NT) can effectively enhance the water–gas shift (WGS) activity. The WGS activity is directly related to the concentration of active copper species and oxygen vacancies (O v ). The addition of potassium is found to enhance WGS activity of copper catalysts to some extent. Herein, the K-promoted copper oxide (2 wt% Cu) nanoparticles confined in TiO 2 nanotubes catalysts (Cu-in-K/TiO 2 NT) with different potassium contents were synthesized and investigated for the WGS reaction. The K-promoted catalysts exhibit the enhanced WGS activity. Especially, the Cu-in-K 20 /TiO 2 NT with the molar ratio of K/Cu = 20 displays twofold higher WGS activity compared with the Cu-in-TiO 2 NT. XRD, Raman, XPS, H 2 -TPR and in situ DRIFTS have verified that the addition of appropriate potassium can make active copper species bound with oxygen of the TiO 2 , leading to a partial reduction of TiO 2 to TiO 2-x , which is beneficial to form Cu–O v –Ti site for the WGS reaction. Graphic abstract

The structure and catalytic activity of Pd monolayers versus single Pd atoms were studied for the reverse water–gas shift reaction (rWGSR) at the anatase (101) and (001) facets for which Pd flat fragments have been observed experimentally. Thermodynamic and partial kinetic analyses of five steps of the rWGSR scheme were considered on the two facets. The projected density of states for the d-orbitals of single Pd atoms of the (101) facet of a-TiO2 are compared to the ones for Pd atoms in both monolayers at (101) and (001) facets to interpret the different activity of Pd. The low activity of single Pd atoms is probably related to the (001) facet, while a Pd monolayer participates at the (101) facet due to its heterogeneity induced by the support.