Pd/TiO₂ catalysts prepared using different methods (impregnation, chemical reduction, and deposition–precipitation) were evaluated in rWGS at low-temperature and high-pressure. Very high CO yield was archived with the Pd/TiO₂ catalyst prepared via deposition–precipitation method.

Abstract

In this study, Pd/TiO₂ catalysts were prepared using different methods (impregnation (IMP), chemical reduction (CR), and deposition–precipitation (DP)) to evaluate the effects of metal dispersion and metal-support interfacial sites on the activity for the reverse water–gas shift (rWGS) reaction (CO₂ + H₂ ↔ CO + H₂O) under low-temperature and high-pressure conditions. Under challenging low-temperature reaction conditions, the highest CO yield (711.2 mmol_CO·min⁻¹·mol_Pd ⁻¹) was achieved with the Pd/TiO₂ catalyst prepared via deposition–precipitation method. Characterization results revealed that this method exhibited the best surface exposure of metallic Pd particles and altered the support morphology by decorating the TiO₂ and Pd surfaces with amorphous TiO₂ particles. The structure–activity correlation indicated that the key factors influencing catalyst activity and selectivity were: surface exposure and particle size of metallic Pd (from XPS, XRD, and HRTEM), the development of Pd–TiO₂ interfacial region (from XPS and DRIFTS-CO), and surface hydroxylation (from DRIFTS-OH). The Pd-PD catalysts with moderate SMSI seem to develop an optimal interaction that leads to better selectivity toward CO with respect to methanation.