On the activity of low-loaded CeOx-Pd/alpha-Al2O3 and Pd-CeOx/alpha-Al2O3 catalysts for CO2 hydrogenation

Abstract

In this study the catalytic properties of low-loaded CeOx-Pd/alpha-Al2O3 and Pd-CeOx/alpha-Al2O3 catalysts for CO2 hydrogenation with and without CH4 at 873 K is investigated. It was found that the presence of ceria significantly enhanced CO2 conversion and selectivity to CO, even with Pd content of about 0.1 wt%. The Ce and Pd impregnation order did not affect the catalytic performance. While CeOx-Pd/alpha-Al2O3 catalysts exclusively produced CO, Pd-CeOx/alpha-Al2O3 exhibited selectivity to CO over 99%. Both catalyst preparations were found suitable for syngas production, as needed for the CAMERE process. In a CH4-CO2-H2 gas mixture, only the RWGS reaction occurred, and the reaction rate increased by about 5 times compared to Pd/alpha-Al2O3, depending on Ce content. Pd-CeOx/alpha-Al2O3 showed rate independence with the Ce loading, while CeOx-Pd/alpha-Al2O3 exhibited a maximum rate for 3 wt% of Ce. FTIR spectroscopy and chemisorption measurements confirmed the surface characteristics of fresh and used catalysts. CeOx-Pd/alpha-Al2O3 catalysts exhibited a surface consistent with the absence of CH4 formation and promoted the formation of adsorbed bicarbonate species, potentially as intermediate reactions involving CO2 and surface hydroxyls.