High-loaded nickel-alumina catalyst for direct CO2 hydrogenation into synthetic natural gas (SNG)

The methanation of carbon dioxide was carried out over a high-loaded Ni-Al mixed oxide catalyst (ca. molar ratio Ni/Al = 5), prepared by conventional coprecipitation of the metal precursors. This route makes possible to obtain multimetallic mixed oxides upon calcination with high metal loading and high surface area. X-ray powder diffraction (XRD), temperature-programmed reduction (TPR), transmission electron microscope (TEM) and thermogravimetric analysis were used for studies of the precursors and catalysts. Calcined samples were activated under H-2 at 500 degrees C, leading to the formation of small metallic nickel particles (ca. 6 nm) dispersed on a high surface area Ni(Al)O-x matrix. Activity tests were conducted using different H-2/CO2 molar ratios (3-5), WHSV (0.2-1.0 molCO(2)/(g(cat) h), temperatures (250-500 degrees C), and pressures (5-20 bar). Despite the high nickel loading (ca. 70 wt.%), which is theoretically thought to be counter-productive for the nickel-based catalyst performance, our Ni-Al activated catalyst exhibited high CO2 conversion, and rendered a CH4 selectivity very close to 1. This is originated by the formation of small metallic nickel crystallites (ca. 6 nm) dispersed over NiO-alumina upon partial reduction of the mixed oxide. The catalyst experiences complete reduction during reaction, which slightly increases the Ni crystallite size, but preserves the high activity in ca. 500 h lifetime tests even at high space velocity. (C) 2013 Elsevier Ltd. All rights reserved.