Reaction Mechanism for the Photocatalytic Isomerisation and Hydrogenation of cis-2-Butene over TiO2

Article abstract of DOI:10.1021/j100348a033

Photocatalytic isomerization and hydrogenation of cis-2-butene over TiO2 were investigated.The reaction products were 1-butene and trans-2-butene on TiO2, and CH4, C2H6, C3H8, n-C4H10, 1-butene and trans-2-butene on water-adsorbed TiO2.The formation amounts of these products were observed as functions of the reaction time and the light intensity.The initial rates (R⁰) in 1E-9 mol s^-1 units, measures as a function of the relative light intensity (I_r), were R⁰(1-C4H8)=6.09I_r+1.2I_r^1/2 and R⁰(trans-2-C4H8)=3.39I_r^1/2 on TiO2 and R⁰(CH4)=0.0087I_r, R⁰(C2H6)=0.236I_r, R⁰(n-C4H10)=0.045I_r,R⁰(1-C4H8)=2.23I_r^1/2 , and R⁰(trans-2-C4H8)=2.45I_r^1/2 on water adsorbed TiO2.No C3H8 as a promary product was found.From these results, it was found that the reaction modes of four kinds exist on the photocatalytic isomerization of cis-2-butene over TiO2 and the overall isomerization rate on TiO2 is about 50 times faster as compared with the total hydrogenation rate to CH4, C2H6, and n-C4H10 on water-adsorbed TiO2 at I_r=1.Reaction mechanism in which Ti(3+) and O(1-) for the isomerization to trans-2-butene depending I_r, Ti(3+), O(1-), and OH(1-) for the isomerization to 1-butene and trans-2-butene depending on I_r^1/2, OH and H for the hydrogenolyses to CH4 and C2H6; and 2H for the hydrogenation to n-C4H10 are concerned in their formations were postulated.