Methane partial oxidation on Pt/CeO2-ZrO2 in the absence of gaseous oxygen

Partial oxidation of methane to synthesis gas over platinum or ruthenium su pported on Ce1-xZrxO2 (x=0, 0.2 and 0.5) was studied at 550-700 degrees C i n the absence of gaseous oxygen. The reaction was carried out in a packed-b ed reactor under continuous or pulsed flows of methane. Oxidation utilized oxide oxygen and was initially very fast but slowed down as the oxide suppo rt became progressively reduced. Addition of ZrO2 into CeO2 considerably in creased the rate of methane oxidation and enhanced the reducibility of CeO2 but decreased the selectivity to carbon monoxide and hydrogen, Specificall y it was found that significant production of carbon dioxide and water occu rred on the freshly oxidized solid until a certain degree of reduction was reached beyond which the selectivity to carbon monoxide and hydrogen rose t o over 90%. This critical degree of reduction was 10%, 40% and 65% for the solid compositions x=0, 0.2 and 0.5, respectively. Additional experiments c arried out using carbon monoxide pulses showed that carbon monoxide oxidati on declines sharply and becomes negligible beyond this degree of reduction while oxidation of methane continues much further. Comparison of the two me tals showed that platinum is more active but the reaction rate did not chan ge much in the range of platinum loadings of 0.25-1 wt.%. (C) 2000 Elsevier Science B.V. All rights reserved.