Operando studies of CuO-CeO2 catalysts for WGS and CO-PROX reactions

Abstract

Operando DRIFTS and high pressure XPS experiments are used to study CuO-CeO2 catalysts active in CO conversion reactions relevant for hydrogen production technology. Operando HP-XPS results show that in a CeO2/CuO catalyst with inverse configuration the addition of H2O to a CO stream on the sample at 473 K promotes the reduction of both Cu and Ce in the catalyst, facilitating the progress towards the Cu(0) state active in the WGS reaction. On the basis of DRIFTS data and exiting gas analysis this is ascribed to the displacement by water of surface carbonate groups which hinder catalyst activation. We will report also data on impregnated 1% CuO/CeO2 catalysts active in CO-PROX prepared using as support different types of CeO2 particles: nanocubes (NC) exposing only (001) surfaces, nanorods (NR) exposing as well (110) surfaces (these two being made hydrothermally) and sphere-like nanoparticles (NS) prepared via microemulsion and exposing mainly (111) and (001) surfaces. CuO/NC samples, besides showing in DRIFTS experiments surface species different from the others, display distinctly higher selectivity in the CO-PROX reaction. Operando DRIFTS data allow to ascribe this to a higher stability of Cu+ species in highly dispersed CuO clusters which interact more strongly with the ceria (001) surface (as confirmed by DFT modeling), so that the formation of hydrogen-activating Cu(0) is retarded. Operando HP-XPS experiments on this system are on their way.