Methane partial oxidation on Pt/CeO_2–ZrO_2 in the absence of gaseous oxygen

Abstract

Partial oxidation of methane to synthesis gas over platinum or ruthenium supported on Ce_(1−x)Zr_xO_2 (x = 0, 0.2 and 0.5) was studied at 550–700°C in the absence of gaseous oxygen. The reaction was carried out in a packed-bed reactor under continuous or pulsed flows of methane. Oxidation utilized oxide oxygen and was initially very fast but slowed down as the oxide support became progressively reduced. Addition of ZrO_2 into CeO_2 considerably increased the rate of methane oxidation and enhanced the reducibility of CeO_2 but decreased the selectivity to carbon monoxide and hydrogen. Specifically it was found that significant production of carbon dioxide and water occurred on the freshly oxidized solid until a certain degree of reduction was reached beyond which the selectivity to carbon monoxide and hydrogen rose to 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 carried out using carbon monoxide pulses showed that carbon monoxide oxidation declines sharply and becomes negligible beyond this degree of reduction while oxidation of methane continues much further. Comparison of the two metals showed that platinum is more active but the reaction rate did not change much in the range of platinum loadings of 0.25–1 wt.%.

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