Hydrogen Activation and its Role in Co2 Hydrogenation on Isolated Pd Species of Cupd0.1/Γ-Al2o3: The Effect of Pd Location

Abstract

CO 2 hydrogenation is one of the most effective solutions for mitigating excessive CO 2 emissions. In this work, a series of CuPd x /γ-Al 2 O 3 catalysts were prepared by co-impregnation and used to investigate the effect of Pd location on the CO 2 hydrogenation process. The activity evaluation results show that CuPd 0.1 /γ-Al 2 O 3 achieves the highest CO 2 conversion of 24.6% and CO selectivity of 94% at 250 o C. It is demonstrated that Pd species in CuPd 0.1 /γ-Al 2 O 3 is highly dispersed on the γ-Al 2 O 3 support at atomic level and separated from Cu nanoparticles as revealed by AC-HAADF-STEM, rather than forming CuPd alloy. Part of the hydrogen species activated on the isolated Pd species overflows onto the support and influences the reduction of Cu species, thus effectively increases the Cu + /(Cu + +Cu 0 ) ratio which is correlated with good CO 2 hydrogenation activity. Hydrogen species can also activate the bicarbonate (*HCO 3 ) intermediates in different way from those H atoms dissociated on Cu 0 species. And this makes the bicarbonate intermediates take the carboxylates path instead of the formate path to transform to CO, which was confirmed by in-situ DRIFTs of CO 2 +H 2 . Hence, the Pd location and structure of CuPd x /γ-Al 2 O 3 catalysts affect the activation of hydrogen, reduction of Cu species, and transformation of bicarbonate intermediates, ultimately influence the activity of CO 2 hydrogenation.

Keywords: CO2 hydrogenation, hydrogen activation, isolated Pd, CuPd alloy, location