HYDROGENATION OF 1-ALKENES BY GAS-PHASE HYDROGEN TRANSFER

This work reports the hydrogenation of 1-alkenes by gas-phase hydrogen transfer using cyclohexene as donor. Pd/AIPO4 and related systems synthesized by impregnation were used as catalysts, and the precursor metal salt was reduced in the pulse reactor itself by injecting cyclohexene pulses. Under the working conditions, the cyclohexene was exclusively dehydrogenated to benzene and the hydrogen released reduced the metal salt to palladium. The conditions under which the reduction of the metal salt took place led us to believe that the excess hydrogen produced in the transformation of cyclohexene into benzene accumulates both on the metal and on the support. Thus, the hydrogenation process took place via two competing pathways, namely a classical hydrogenation involving hydrogen adsorbed on the catalyst, and a concerted hydrogen transfer from the donor to the acceptor. However, the hydrogenation is also feasible if the catalyst is previously treated with cyclohexene pulses followed by olefin pulses. Only this last process seems to require the occurrence of a direct and a reverse hydrogen spillover mechanism.