(112e) Reverse Water Gas Shift (RWGS) Reaction over Ceria-Supported Single Metal Oxide (MOx/CeO2) Catalysts Developed Via Novel One-Pot Chemical Vapor Deposition (OP-CVD) Method.

Environmental concerns have risen with the generation and direct emission of huge amounts of greenhouse gas, majorly carbon dioxide (CO₂). For a sustainable environment, carbon capture and recycling (CCR) technologies are an effective source of renewable energy, wherein reverse water gas shift (RWGS) reaction is a very crucial step with high desired selectivity for syngas (H₂+CO) production. Although transition metals (TMs) and platinum group metals (PGMs)-based supported catalysts were reported [1-3], understanding on the catalyst design, actual active site(s), and the effect of reaction conditions remains challenging [4].

In this study, a novel one-pot chemical vapor deposition (OP-CVD) method was developed for the synthesis of ceria-supported metal oxide (3% MO_x/CeO₂) catalysts: 1) Cu, Zn and Ni as TMs; and 2) Pd as PGM. OP-CVD involves gas-solid interaction of organometallic precursors with support material in a thermally controlled mechanism, avoiding agglomerations and achieving the desired morphology (Fig. 1a). The catalysts were tested for physicochemical characterizations (Fig. 1b,c): XRD spectra predict extreme small-sized surface species (only ceria peaks), and EDX mapping show uniform distribution of surface species throughout the catalyst surface. The XAS analysis states the surface species cluster size as ~0.6-1 nm. Above-mentioned data confirms the feasibility of OP-CVD method to produce effective catalysts. The RWGS reaction data shows that CO₂ conversion increases with temperature (Fig. 1d). The CO selectivity in CuO_x/CeO₂ and ZnO_x/CeO₂ was observed to be ~100% throughout, while NiO_x/CeO₂ catalyst produces both CH₄ and CO and show different trend revealing change in the reaction pathway (Fig. 1e). The RWGS reaction over PdO_x/CeO₂ proceeds at lower temperature than that for any TM-based catalysts, with ~27.7% CO₂ conversion and ~100% CO selectivity. The in-situ DRIFTS and in-situ XRD data confirm surface-species dependent mechanism and stable catalyst structure throughout the reaction. These results confirm that surface species could control CO selectivity.