Effect of the preparation methods and alumina nanoparticles on the catalytic performance of Rh/ZrxCe1-xO2-Al2O3 in methane partial oxidation

Rh supported on ZrxCe1-xO2-Al2O3 (x = 1, 0.5, 0.25, 0) catalysts are studied for catalytic partial oxidation of methane to synthesis gas. Alumina based nanocomposites are prepared through a citrate mediated route by modifying the alumina support with cerium and zirconyl nitrates via a simple evaporation-drying or a spray drying method. The effect of the commercial alumina types and the preparation method on the structure and thermostability of the nanocomposites has been studied based on the characterization by XRD, Raman spectroscopy, DTA, TEM and nitrogen adsorption-desorption measurements. Evonik Aeroxide AluC based nanocomposites prepared by spray drying give the highest thermostability concerning the sintering and phase transformation of the composites. Rh with a 0.1 or 0.5 wt.% loading is deposited on these nanocomposites by incipient wetness impregnation method. After calcination at 1173 K for 5 h, these nanocomposites supported Rh catalysts are tested in the fixed-bed reactor for methane partial oxidation. It is found that the smaller c-CeO2 crystal size in the nanocomposites, i.e. the higher oxygen vacancy concentration, would be responsible of the lower ignition temperature due to the enhanced reducibility, whereas the higher Rh dispersion would be responsible of the higher methane conversion and selectivity to synthesis gas. Additionally the Rh dispersion is found to be linked to the BET surface area. The stability of the nanocomposites is also studied under reaction conditions. (C) 2011 Elsevier B. V. All rights reserved.