CO<sub>2</sub> Hydrogenation to CH<sub>3</sub>OH over PdZn Catalysts, with Reduced CH<sub>4</sub> Production
Jonathan Ruiz Esquius, Hasliza Bahruji, Stuart H. Taylor, Michael Bowker, Graham J. Hutchings
Abstract
Abstract Metallic Pd, under CO 2 hydrogenation conditions (>175 °C, 20 bar in this work), promotes CO formation via the reverse water gas shift (RWGS) reaction. Pd‐based catalysts can show high selectivity to methanol when alloyed with Zn, and PdZn alloy catalysts are commonly reported as a stable alternative to Cu‐based catalysts for the CO 2 hydrogenation to methanol. The production of CH 4 is sometimes reported as a minor by‐product, but nevertheless this can be a major detriment for an industrial process, because methane builds up in the recycle loop, and hence would have to be purged periodically. Thus, it is extremely important to reduce methane production for future green methanol synthesis processes. In this work we have investigated TiO 2 as a support for such catalysts, with Pd, or PdZn deposited by chemical vapour impregnation (CVI). Although titania‐supported PdZn materials show excellent performance, with high selectivity to CH 3 OH+CO, they suffer from methane formation (>0.01 %). However, when ZnTiO 3 is used instead as a support medium for the PdZn alloy, methane production is greatly suppressed. The site for methane production appears to be the TiO 2 , which reduces methanol to methane at anion vacancy sites.