Steam reforming of acetic acid over Ni/ZrO2 catalysts: Effects of nickel loading and particle size on product distribution and coke formation

Steam reforming of acetic acid has been carried out over a series of Ni/ZrO2 catalysts to measure the effects of nickel loading on distribution of the reforming products and coke formation. Ni (<= 13 wt.%)/ZrO2 catalysts do not contain enough active metal sites for steam reforming of both acetic acid and organic by-products. Ni (>= 20 wt.%)/ZrO2 catalysts can effectively catalyze steam reforming but lack selectivity, since methanation and reverse water gas shift reactions are promoted, leading to low hydrogen yields. Ni (16 wt.%)/ZrO2 catalyst is the most selective one, due to its low activity to the secondary reactions that contribute to by-product production. Coke formation is suppressed with the increase of nickel loading up to 16 wt.%, and then restarts to increases with the further increase of nickel loading. Polymerization of acetone is the main route for coke deposition over the Ni (<= 13 wt.%)/ZrO2 catalysts. Methane decomposition and CO disproportion are the two main routes for coke formation over the Ni (>= 20 wt.%)/ZrO2 catalysts, and methane contributes more to coke formation than CO. In addition, activity of Ni/ZrO2 catalyst towards the secondary reactions such as methanation, reverse water gas shift reaction, methane decomposition, and CO disproportion are closely related to nickel loading and nickel particle sizes. (C) 2012 Elsevier B.V. All rights reserved.