Partial oxidation of methane on Rh/ZrO2 and Rh/Ce-ZrO2 on monoliths: Catalyst restructuring at reaction conditions

0.5%Rh catalysts on ZrO2 or CeO2-ZrO2, coated on monoliths were tested for partial oxidation of methane, (GHSV = 100 000 h(-1)). We ran temperature cycles up to 850 degrees C, varying the O-2/CH4 ratio from 0.5 to 0.7. The catalysts were characterized by XRD, TPR/TPO, BET and chemisorption. ZrO2 required a long conditioning step, to reach stable performance, while the CeO2-ZrO2 catalyst quickly gained steady activity. The conditioning step is explained with a restructuring of the surface, with the metallic particles becoming smaller. Ceria lowers the ignition temperature by 60 degrees C. At low temperature, ceria allows an increase in CH4 conversion and selectivity to syngas. At high temperature, the CeO2-ZrO2 catalyst significantly increases the CH4 conversion, compared to ZrO2, approaching 100%. However, the selectivity to syngas decreases below 80%. The syngas selectivity is higher at lower O-2/CH4 ratio, at any temperature, but the absolute amount of syngas can be larger with more O-2. (C) 2015 Elsevier B.V. All rights reserved.