Comparative Assessment of First-Row 3d Transition Metals (Ti-Zn) Supported on CeO2 Nanorods for CO2 Hydrogenation

Abstract

Herein, motivated by the excellent redox properties of rod-shaped ceria (CeO2-NR), a series of TM/CeO2 catalysts, employing the first-row 3d transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) as active metal phases, were comparatively assessed under identical synthesis and reaction conditions to decipher the role of active metal in the CO2 hydrogenation process. Notably, a volcano-type dependence of CO2 hydrogenation activity/selectivity was disclosed as a function of metal entity revealing a maximum for the Ni-based sample. Ni/CeO2 is extremely active and fully selective to methane (YCH4 = 90.8% at 350 °C), followed by Co/CeO2 (YCH4 = 45.2%), whereas the rest of the metals present an inferior performance. No straightforward relationship was disclosed between the CO2 hydrogenation performance and the textural, structural, and redox properties, whereas, on the other hand, a volcano-shaped trend was established with the relative concentration of oxygen vacancies and partially reduced Ce3+ species. The observed trend is also perfectly aligned with the previously reported volcano-type dependence of atomic hydrogen adsorption energy and CO2 activation as a function of 3d-orbital electron number, revealing the key role of intrinsic electronic features of each metal in conjunction to metal–support interactions.