Mechanism of Ni-catalyzed selective CO cleavage of lignin model compound benzyl phenyl ether under mild conditions

Selective cleavage of C O bonds in benzyl phenyl ether (BPE) as a typical lignin α-O-4 ether to produce aromatics is a challenging and attractive topic. Herein, the earth-abundant first-row transition metals, such as Co, Ni and Cu were supported on activated carbon (Co/AC, Ni/AC and Cu/AC) to identify their ability for cleaving C O bond of BPE. Among these catalysts, Ni/AC exhibit highest activity for cleavage of C O bond. The reaction with BPE was carried out at pretty mild condition of 140 °C and 2 MPa H 2 , which is highly selective afforded toluene and phenol as the major products with the optimum yields of 88.5 and 86.5%, respectively. Based on the test, the reaction pathways were proposed. A abundant of dissociated H· atoms on Ni(0) sites forms surface active Ni H species; Ni(0) activates and facilitates cleavage of the C O bond in BPE to form benzyl (C 6 H 5 C·) and phenoxy radicals (C 6 H 5 O·); H· atoms spill from active species Ni H recombined together with C 6 H 5 C· and C 6 H 5 O· forming the products of toluene and phenol, respectively.