A study of steam reforming of hydrocarbon fuels on Pd/ceria Original Research Article

Differential steam-reforming rates were measured for methane, ethane, n-butane, n-hexane, 2,4-dimethylhexane, n-octane, cyclohexane, benzene, and toluene over 1 wt.% Pd/ceria between 620 and 770 K and were compared to rates observed on 1 wt.% Pd/alumina and 1 wt.% Pt/ceria. The H2O:C ratios at which stable rates were observed on Pd/ceria depended on the hydrocarbon, varying from less than 1:1 for methane to 3:1 for 2,4-dimethylhexane. In the series of alkanes from methane to n-hexane, for a H2O:C ratio of 2:1, the only products were CO, CO2, and H2O and the rate of formation of CO2 and CO increased with carbon number. Benzene was also selectively converted to COx and H2, but at lower rates than the alkanes with the exception of methane. For 2,4-dimethylhexane and n-octane, a significant amount of cyclohexane was observed in the initial products and cyclohexane was selectively converted to benzene at low conversions. Steam reforming of toluene also gave benzene as the initial product. FTIR measurements of Pd/ceria under methane-steam-reforming conditions indicate the formation of carbonates on the ceria. Pd/alumina showed significantly lower rates than Pd/ceria and much lower CO2:CO ratios in the initial products, implying ceria plays an important role in the reaction. Pt/ceria gave rates and selectivities that were essentially identical to that of Pd/ceria. The implications of these results for hydrocarbon fuel processing are discussed.