Insights into the Hydrogenolysis Mechanism of Diphenyl Ether over Cl-Modified Pt/γ-Al<sub>2</sub>O<sub>3</sub> Catalysts by Experimental and Theoretical Studies
Chen Zhu, Hajime Hojo, Hisahiro Einaga
Abstract
Catalytic hydrogenolysis is an efficient method for converting lignin-derived aryl ethers into monoaromatic products by cleaving the C–O bond and maintaining the phenyl rings. However, it is difficult to obtain aromatics with high selectivity because ring hydrogenation proceeds in parallel. Herein, we showed that a Cl-modified Pt/γ-Al2O3 catalyst exhibited higher selectivity for aromatics (91.6%) compared to unmodified Pt/γ-Al2O3 (3.9%) in C–O bond cleavage of diphenyl ether (DPE, 4-O-5 linkage in lignin). Characterization of the catalysts and density functional theory (DFT) calculations indicated that the Cl species preferred to localize at the terrace sites of Pt nanoparticles (NPs). Due to the decrease in the number of active sites, the Cl-modified Pt/γ-Al2O3 catalyst exhibited low activity for 2-propanol dehydrogenation, and thus the catalytic activity for the hydrogenation of aromatic products was suppressed. On the other hand, DPE adsorbed at the low coordination site, which caused the phenyl rings to move away from the metal surface; this configuration was unfavorable for the hydrogenation reaction. According to DFT calculations, the high selectivity for benzene was mainly attributed to the lower energy barrier for C–O bond cleavage of phenol at the low-coordination sites.