The Formation and Decay of the Paramagnetic Species Formed on the Surface of Al2O3–MoO3 with Anthracene/Benzene Solution

Abstract

MoO3 supported on alumina in a flow-through type sample tube was fixed in an e.s.r. cavity and anthracene solutions in benzene were passed through it at 20 °C. Three paramagnetic species were observed. One was Mo5+, one was the anthracene cation R+, and the remaining one was R+O*2− previously reported. Formation of R+ and R+O*2− was complete within a few minutes after the contact of the solution after which the decay of R+ became apparent. R+ disappeared in a pseudo-first order reaction which actually was a second order reaction with the water dissolved in the solution. The rate constant for the reaction, R+ + H2O → diamagnetic products, was 0.341 mol−1 s−1. R+O*2− was completely stable during the measurement and even after draining the solvent or after drying the oxide particles with N2 gas. It was concluded that Mo5+ was formed from two R+ and H2O molecules. The time dependence of the concentration of R+ was found to be [R+] = [R+]0 exp(−kt) and that of Mo5+, [Mo5+] = [Mo5+]∞ (1 − exp (–kt)) where the subscripts zero and infinity indicate the time t = 0 and t = ∞ respectively. The present results seem to indicate that the more important paramagnetic species which influences the catalytic processes is not the cation R+ but the complex ion R+O2−.