Abstract
The catalytic performance for partial oxidation of methane(POM) to syngas over the Ru/Al2O3 catalyst calcined in air(Ru/Al2O3-Air) and Ar(Ru/Al2O3-Ar) was studied.Steady-state reactivity was observed on the Ru/Al2O3-Ar sample,whereas oscillations in CH4,CO,H2,CO2,and H2O were observed on the Ru/Al2O3-Air sample.Comparative studies using CO and O2 chemisorption,X-ray diffraction,Raman,and temperature-programmed reduction(TPR) techniques were carried out in order to elucidate the property-structure relationship of the samples.The Ru dispersion on Ru/Al2O3-Air was only 1%,whereas that on Ru/Al2O3-Ar was about 9%.The significant difference in the Ru dispersion on the two samples is the major factor affecting the POM reaction.Two types of Ru species,RuO2 species weakly interacting with Al2O3 and the Ru-O-Al species strongly interacting with the support,were identified by H2-TPR experiments on the fresh catalyst.The former species could be easily reduced by H2(below 200 °C),while the latter can only be reduced by H2 at above 700 °C.During the POM reaction at above 600 °C,the RuO2 species were in the metal state,whereas the Ru-O-Al species could undergo cyclic redox transformation.Such transformation is responsible for the oscillation on Ru/Al2O3-Air sample.
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