Steam reforming of acetic acid over nickel-based catalysts: The intrinsic effects of nickel precursors on behaviors of nickel catalysts

Abstract

The paper investigated the effects of various nickel precursors (Ni(NO3)2, NiCl2, NiSO4, Ni(CH3COO)2, Ni(NH2SO3)2) on the catalytic behaviors of Ni/Al2O3 catalysts in steam reforming of acetic acid, aiming to understand the fundamental influences of nickel metal precursors. The catalysts were characterized with TPR, TPO, TPR-MS, TPO-MS, XRD, TG-MS, FT-IR, FT-Raman, BET method, element analysis, TEM and SEM. The results revealed the substantial influence of the nickel precursors on properties of Ni/Al2O3 catalysts. The use of NiSO4 and Ni(NH2SO3)2 as nickel precursors led to the low activities of the catalysts, due to the formation of Ni3S2 during reduction of the catalysts with hydrogen. The sulfur species were removed in the form of SO2 during the calcination of the catalysts precursors in air and in the form of H2S during the reduction of the calcined catalyst in hydrogen. NiCl2/Al2O3 catalyst showed a negligible activity as the chlorine poisoned the catalyst and was difficult to be removed via calcination. Furthermore, chlorine could accelerate sintering of alumina. In comparison, Ni(CH3COO)2 as nickel precursor could effectively suppress the formation of NiAl2O4. Ni(CH3COO)2/Al2O3 catalyst showed comparable activity to that of Ni(NO3)2/Al2O3, but the resistivity towards coking was higher. In addition, the coke species produced over the catalysts have both large and small aromatic ring systems with the morphology of both amorphous and fibrous structures.