Inhibition of methane formation in steam reforming reactions through modification of Nicatalyst and the reactants

Abstract

Methane, a greenhouse gas and a main by-product in steam reforming reaction, can greatly diminish hydrogen yield. Modifications of both the catalyst and reactants were performed in this study to suppress methane formation. Ni/Al₂O₃ catalysts modified with a series of promoters (Li, Na, K, Mg, Fe, Co, Zn, Zr, La, Ce) were evaluated in acetic acid reforming reaction. The addition of Co, Zr, La, or Ce to Ni/Al₂O₃ promoted the methanation reaction, and consequently promoted methane formation. Conversely, alkali metal modified samples effectively inhibited methane formation, especially the Ni–K/Al₂O₃ catalyst. Moreover, the addition of alkali metal remarkably increased the number of metallic Ni sites on the catalyst surface by promoting the reduction of Ni oxides, which enhanced the catalytic activity. In addition, the presence of K on alumina also promoted stability of the Ni catalyst through suppression of coke formation. Type of fuels reformed also affected methane formation. Methane selectivity was much higher in steam reforming of the neutral fuels (ethanol, 1-propanol) than in steam reforming of the acidic fuels (acetic acid, propanoic acid). Acidification of neutral alcohols with nitric acid remarkably suppressed methane formation, which was accomplished through the suppression of the methanation reaction. Besides, the addition of nitric acid to ethanol can help eliminate coke deposition in ethanol reforming reactions, since production of the main carbon precursor, ethylene, is suppressed to a significant extent in the presence of nitric acid.