Photo-induced CO2 reduction by hydrogen for selective CO evolution in a dynamic monolith photoreactor loaded with Ag-modified TiO2 nanocatalyst

Abstract

Ag-promoted TiO2 nanoparticles immobilized over the cordierite monolithic support for dynamic and selective photo-reduction of CO2 to CO by the use of hydrogen has been investigated. Ag-loaded TiO2 NPs synthesized by a facile sol–gel method were coated over the monolith channels by dip-coating method. The samples were characterized by XRD, Raman, FTIR, SEM, TEM, XPS, N2 adsorption–desorption, UV–Vis and PL spectroscopy. The photo-activity test of Ag-modified TiO2 NPs was conducted for dynamic photocatalytic CO2 reduction with H2 as a reductant via a reverse water gas shift (RWGS) reaction in a cell type and monolith photo-reactors. Using 5 wt. % Ag/TO2 NPs, CO2 was energetically converted to CO with a yield rate 1335 μmole g-catal.−1 h−1, a 111 fold-higher than the amount of CO produced over the pure TiO2 catalyst. More importantly, photo-activity of Ag/TiO2 catalyst for CO evolution can be improved by 209 fold using monolith photo-reactor than the cell type reactor under the same operating conditions. This enactment was evidently due to the efficient light harvesting with larger illuminated surface area inside monolith micro-channels and efficient charges separation in the presence of Ag-metal. The reusability of Ag/TiO2 NPs loaded over the monolithic support showed favorable recycling capability than the catalyst dispersed in a cell reactor. A possible reaction mechanism for this observation has been discussed in detail.