Modification of nickel-based catalyst with transition metals to tailor reaction intermediates and property of coke in steam reforming of acetic acid

Abstract

Modification of Ni/Al2O3 with transition additives is known to affect physiochemical properties of the catalyst, while this will also inevitably impact evolution of reaction intermediates and property of coke formed in steam reforming. In this study, Ni/Al2O3 catalyst was modified with Fe, Zn, Cu or Co and the influences on formation of intermediate product and nature of coke was paid particular attention in steam reforming of acetic acid. The results indicated that iron or cobalt oxide reacted with NiO, forming NiFe2O4 and NiCo2O4, while copper or zinc oxide reacted with alumina, forming Al2CuO4 and ZnAl2O4, respectively. This weakened interaction between nickel oxide and alumina but also led to increase of nickel size, except Zn additive. Presence of Zn or Co in the catalyst enhanced adsorption of –OH or CO2, facilitating gasification of precursors of amorphous coke. The Cu additive intensifies adsorption/activation of oxygen-containing intermediates, while Fe was the opposite. The additive of Zn, Cu or Co, with exception of Fe, enhanced catalytic stability by suppressing formation of polymeric coke, although overall amount of coke was much higher. The coke formed in Zn, Cu or Co modified catalyst was mainly catalytic coke with a higher C/H ratio, higher crystallinity, higher thermal stability, higher portion of graphite structures, and nanotube-like structure of irregular inner cavity but with less impacts on catalytic stability.