Feed Effects on Water-Gas Shift Activity of M/Co3O4-ZrO2 (M = Pt, Pd, and Ru) and Potassium Role in Methane Suppression

Water-gas shift (WGS) is an industrial process to tackle CO abatement and H-2 upgradation. The syngas (CO and H-2 mixture) obtained from steam or dry reformers often has unreacted (from dry reforming) or undesired (from steam reforming) CO2, which is subsequently sent to downstream WGS reactor for H-2 upgradation. Thus, industrial processes must deal with CO2 and H-2 in the reformate feed. Achieving high CO2 or H-2 selectivities become challenging due to possible CO and CO2 methanation reactions, which further increases the separation costs to produce pure H-2. In this study, M/Co3O4-ZrO2 (M = Ru, Pd and Pt) catalysts were prepared using sonochemical synthesis. The synthesized catalysts were tested for WGS activity under three feed conditions, namely, Feed A (CO and steam), Feed B (CO, H-2 and steam) and Feed C (CO, H-2, CO2 and steam). All the catalysts gave zero methane selectivity under Feed A conditions, whereas the methane selectivity was significant under Feed B and C conditions. Among all catalysts, PtCZ was found to be the best performing catalyst in terms of CO conversion and CO2 selectivity. However, it still suffered with low but significant methane selectivity. This best performing catalyst was further modified with an alkali component, potassium to suppress undesirable methane selectivity. All the catalysts were well characterized with BET, SEM, TEM to confirm the structural properties and effective doping of the noble metals. Additionally, the apparent activation energies were obtained to showcase the best catalyst.