The impact of dopants on the activity and selectivity of a Ni-based methanation catalyst

Abstract

The influence of different dopants in varying contents on the activity and selectivity of Ni-based methanation catalysts under proton exchange membrane fuel cell (PEMFC) relevant conditions (hydrogen-rich gas reformate with low concentrations of CO and excess CO 2) was investigated. The modification of Ni 100O x with 2.2 mol% of Re resulted in a catalyst highly inactive for both the methanation of CO and CO 2 while the addition of Zr led to an enhanced CO and CO 2 methanation activity. Further modification of Zr 10Ni 90O x with small amounts of Re caused a drastically decreased reactivity towards the undesired hydrogenation of CO 2 while that for CO was practically unchanged. Solo methanation experiments unambiguously reveal that this increase in selectivity is based on a loss of the intrinsic CO 2 reactivity and not necessarily associated with any competition for active sites between the different kinds of carbon oxides. A detailed study of the impact of the compositional variations on structural and chemical properties was performed using nitrogen physisorption, hydrogen chemisorption, temperature-programmed reduction (TPR), temperature-programmed desorption experiments of CO 2 (CO 2 TPD), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) as well as TEM. As a part of the catalytically active Ni particles, Re changes the surface of the catalyst resulting in drastically altered catalytic properties while Zr or the Ni–ZrO 2 interfacial region seems to play a decisive role in the activation of the CO molecule.