Influence of the structure of trigonal Mo-V-M3rd oxides (M3rd=-, Fe, Cu, W) on catalytic performances in selective oxidations of ethane, acrolein, and allyl alcohol

摘要

Crystalline "MoVO", "MoVCuO", "MoVFeO" and "MoVWO" catalysts with a trigonal symmetry were successfully synthesized and characterized. The influence of the as-obtained structures on catalytic performances in selective oxidation reactions was investigated. MoVFeO and MoVCuO accomodated Fe and Cu species inside heptagonal channels, while W in MoVWO was incorporated in pentagonal {Mo6O21}(6-) units. Whereas MoVO and MoVWO showed catalytic activity in the selective oxidation of ethane and acrolein, MoVFeO and MoVCuO performed very poorly in the same reaction, suggesting that the presence of empty heptagonal channels is related to ethane and acrolein activations. In the selective oxidation of allyl alcohol, substantial amounts of acrolein (formed by oxidative dehydrogenation) and propanal (formed by isomerization) were formed as primary products over MoVO and MoVWO, whereas MoVFeO and MoVCuO preferentially promoted the formation of acrolein. It was found that the local crystal structure around the heptagonal channel was related with a modification of the reaction pathway for the selective oxidation of allyl alcohol. Due to the prevention of isomerization over MoVFeO, a high acrylic acid yield of 83.1% from allyl alcohol was achieved at 350 degrees C over this sample.