Catalytic dehydration of crotyl alcohol into 1,3-butadiene over silica-supported metal oxides: Mechanistic features

Catalytic dehydration of crotyl alcohol (2B1OL) to 1,3-butadiene (BD) over silica-supported metal oxides such as V2O5/SiO2, Al2O3/SiO2, and WO3/SiO2 was investigated by kinetic analysis, acid-base titration including poisoning experiments, and theoretical calculations. The BD production over V2O5/SiO2 catalyst proceeded via stepwise reaction, in which isomerization of 2B1OL into 3-butene-2-ol (3B2OL) occurred before consecutive dehydration of 3B2OL proceeded to give BD. Both direct dehydration of 2B1OL into BD and stepwise reaction via 3B2OL proceeded over Al2O3/SiO2 catalyst. Meanwhile, the mechanism for the BD production over WO3/SiO2 catalyst was affected by the W loading. The poisoning experiment by use of 2,6- and 3,5-dimethylpyridine clarified the role of Bronsted and Lewis acid sites in the transformation of 2B1OL into BD over these catalysts. The density functional theory calculations show that the activation energies of elemental reactions and desorption energy of 3B2OL dominate the reaction selectivity, which clarifies the behaviors of different metal oxide catalysts.