MANGANESE OXIDES AS CATALYSTS FOR THE SELECTIVE REDUCTION OF NITROBENZENE TO NITROSOBENZENE

The activity and selectivity of various MnOx catalysts for the selecti ve reduction of nitrobenzene to nitrosobenzene have been studied, meas uring the rate in a continuous flow reactor. Characterisation of the c atalysts has been performed with XRD, IR, UV/VIS, EM, and TPR. It appe ared that the steady-state catalyst is in all cases the spinel Mn3O4 i n a slightly reduced form. Without the addition of an external reducta nt to the feed, nitrobenzene was not only reduced but also oxidised, w hich created oxygen vacancies in the catalyst surface. Addition of an external reductant did not cause a change in the amount of nitrosobenz ene formed, but the concentration of side products, like aniline and d imerisation products, increased. It is suggested that the selective re duction of nitrobenzene with the catalyst Mn3O4 runs by the Mars and V an Krevelen mechanism. (C) 1994 Academic Press, Inc.