PHOTOCATALYTIC REACTIONS OF 1,3-BUTADIENE OVER WATER-ADSORBED TIO2

Photocatalytic reactions of 1,3-butadiene over water-adsorbed TiO2 were investigated at 293 K. The initial formation rates of C2H4, C2H6, C3H6, C3H8, 1-C4H8, and trans-2-C4H8, which hardly depend on the pressure of 1,3-butadiene (2.0-13.3 kPa), were 8.1, 7.1, 267, 177, 209, and 34 pmol s-1, respectively. The formations of CH4, n-C4H10, CO, n-C3H7CHO, s-C4H9OH, and n-C4H9OH were also observed. The drastic decrease of the hydrocarbon yields by the addition of O2 was not found except for C2H6 and C3H8. The increase of formation yield by the loading of Pt was observed for all products, especially n-C4H10. From these results, the reaction mechanisms that the photoformed OH radical and H atom at close range are concerned cooperatively were proposed for the formations of C2H4, C2H6, C3H6, and C3H8 by the photocatalytic hydrogenolysis reaction. From the reaction mechanisms and the initial formation rates for the hydrogenolysis, it was found that the addition of OH to the C(1) position of 1,3-butadiene is 29.2 times faster than that to the C(2) position. No cis-2-butene was observed, though trans-2-butene and 1-butene resulting from the addition of two H atoms to 1,3-butadiene were found. It suggests that the geometrical structure of 1,3-butadiene (trans form) is conserved during the hydrogenation reaction. The photocatalytic hydrogenolysis and hydrogenation reaction rates are 1.9 and 5.4 times faster than those of cis-2-butene, respectively. These results are explainable by the facts that both addition rates of OH and H to 1,3-butadiene in the vapor phase are faster than those to cis-2-butene. © 1990 American Chemical Society.