Developing descriptors for CO2 methanation and CO2 reforming of CH4 over Al2O3 supported Ni and low-cost Ni based alloy catalysts

Abstract

The catalytic performance of Ni can be modified by alloying with a suitable amount (25% of total metal loading) of another low-cost metal such as Fe, Co or Cu. These alumina supported Ni and Ni based alloy catalysts are gaining attention for certain important reactions due to their promising activity, stability, selectivity and low-cost. The reduced form of the supported Ni–M (M = Fe, Co or Cu) catalysts formed different Ni–M alloys. To understand the reactivity trends for CO₂ methanation and CO₂ reforming of CH₄ (DRM), we analyzed the correlations between turnover frequencies and the d-density of states (d-DOS) based electronic properties of surface Ni in Ni and Ni–M model catalysts. The composition and components of the most active catalysts for each reaction were different. The dissimilar trend in activity of the Ni and Ni–M alloy catalysts resulted in different descriptors for the two reactions. The Ni–Fe alloy catalyst (with a Ni to Fe ratio of 3 : 1) was the most active in CO₂ methanation due to the minimum number of Ni d-density of states at the E_F. In contrast, the Ni–Co alloy catalyst (with a Ni to Co ratio of 3 : 1) was the most active in the CO₂ reforming of CH₄ due to the lowest d-band center (with respect to Ni d-density of states), and the Ni–Cu alloy catalyst (with a Ni to Cu ratio of 3 : 1) was the least active for both reactions. Moreover, step sites were better correlated for CO₂ methanation, whereas terrace sites were better correlated for the CO₂ reforming of CH₄.