Catalytic transfer hydrogenolysis mechanism of benzyl phenyl ether over NiCu/Al2O3 using isopropanol as hydrogen source

Abstract

Efficient transfer hydrogenolysis of benzyl phenyl ether (BPE) was accomplished over Ni1.5Cu1.5/Al2O3 using isopropanol as hydrogen source. The characterization results demonstrated that the formation of NiCu alloy and electron transfer between Ni and Cu were responsible for the excellent catalytic performance. Isopropanol displayed better hydrogen-donating ability than other low-carbon alcohols because of its unique dehydrogenation pathway and small steric hindrance. The results of isotopic experiments elucidated that active hydrogen species for the CO bond cleavage originated from isopropanol rather than H2, while both isopropanol and H2 were responsible for hydrogenation of phenol to cyclohexanol when reaction was conducted with mixed hydrogen sources. A mechanism study illustrated that transfer hydrogenolysis of BPE proceeded through direct cleavage of CO bond followed by phenol hydrogenation, in which the active hydrogen species were in the form of H+ and H−.