Mechanism of Ni-catalyzed selective C-O 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 alpha-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 degrees 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 center dot 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 (C6H5-C center dot) and phenoxy radicals (C6H5O center dot); H center dot atoms spill from active species Ni-H recombined together with C6H5-C center dot and C6H5O center dot forming the products of toluene and phenol, respectively. (C) 2017 Energy Institute. Published by Elsevier Ltd. All rights reserved.