Water-gas shift reaction catalyzed by layered double hydroxides supported Au-Ni/Cu/Pt bimetallic alloys

摘要

Water-gas shift reaction (WGSR) is an industrialized chemical process with numerous applications in CO removal, H-2 generation and coupled in energy storage and reforming reactions involving hydrocarbons, alcohols and Fisher-Tropsch synthesis (FTS). The challenge of WGSR has been the lack of highly active and stable catalyst at low operational temperatures because conventional Cu-Zn and Co-Mo based catalysts suffer quick activity loss under working conditions. Au and AuM (M=Ni, Cu, Pt) alloy nanoparticles supported on layered double hydroxides (LDHs) were prepared and characterized in terms of their structural, morphological and chemical properties. It was found that the incorporation of Au significantly enhances the catalytic activity of LDHs for WGSR at temperatures of practical catalytic relevance (450-550 K) and the performance can be further engineered via tuning the geometrical environment of Au by alloying with a 2nd metal (Ni, Cu and Pt). Temperature programmed reduction (TPR) and Au dispersion experiments suggest that the addition of AuM modulates the redox circle at the metal/LDHs interface with Au2Cu1 yielding the highest turnover frequency (TOF). In-situ DRIFTS captures the evolution of surface reactive species and suggests a reaction pathway via the formation of formate (HCOO*). While the formate route dominates the AuM/LDHs catalyzed WGSR, the redox mechanism can also be activated by bypassing a direct *O-H bond breakage step that requires prohibitively high activation energy. Consistent results were obtained in our DFT calculations, where the AuM/LDHs catalysts were found facilitating the WGSR reaction by preferentially mediating a formate pathway. Our combinative theoretical and experimental study suggests that LDHs is a family of promising low-cost, stable and highly active supporting materials for practical heterogeneous catalysis and demonstrates a strategic way to understand and engineer the fundamentals of a reaction that benefits the whole chemical transformation.