The X-ray photoelectron spectroscopy (XPS) was used to investigate the surface characteristic of potassium-promoted or un-promoted both β-Mo2C and α-MoC1-x pretreated by syngas at different temperatures,and the promotional effect of potassium on the catalytic performance was also studied.XPS results revealed that the content of surface Mo and its valence distribution between β-Mo2C and α-MoC1-x were quite different.Promoted by potassium,the remarkable changes were observed for surface composition and valence of Mo distribution over β-Mo2C.Potassium had strong electronic effect on β-Mo2C,which led to a higher Mo4+ content.On the contrary,potassium had little electronic effect on α-MoC1-x,and K-Mo interaction was weak.Therefore,Mo0 and Mo2+ became the dominant species on the catalyst surface,and the Mo4+ content showed almost no increase as the pretreatment temperature enhanced.In terms of catalytic performance of molybdenum carbides,the increase in Mo0 most likely explained the increase in hydrocarbon selectivity,yet Mo4+ might be responsible for the alcohols synthesis.
Minglin XiangDebao LiJuan ZouWenhuai LiYuhan SunXichun She
The promotion effect of CO in methane dehydroaromatization was investigated using 13CO probe molecules. By alternative injection of 13CO to the methane feed,the distribution of 13CxC6-xH6(x=0-3)products changed significantly,confirming the participation of13CO in the reaction network.The addition of 13CO did not change the conversion of CH4 but improved slightly the durability of the methane dehydroaromatization(MDA)reaction,which might be caused by the interaction of the dissociated oxygen species and the deposited carbon species.The ratio of 13CxC6-xH6(x=0-3)varied with the time on stream,which was determined by the competitive reactions of methane decomposition and 13CO dissociation.
Songdong Yao, Changyong Sun, Juan Li, Xiumin Huang, Wenjie Shen State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China
