CO Cleavage of Diphenyl Ether Followed by CC Coupling Reactions over Hydrophobized Pd/HY Catalysts

The catalytic conversion of diphenyl ether (DPE), a dimeric model compound representing 4-O-5 lignin linkages, has been investigated using a hydrophobized bifunctional Pd/HY catalyst since the hydrophobicity of the catalyst significantly improved conversion and carbon balance. Partial hydrogenation of DPE was found to be an essential step before C-O bond cleavage and C-C bond formation, which are the target reactions in this study. The main products resulting from the C-O cleavage are phenol and cyclohexanone, which subsequently can undergo C-C coupling via alkylation and aldol condensation. The balance between hydrogenation activity of the metal and the acidic function of zeolite was found to play an important role for maximizing the yield of C-C coupling products, which are desirable in the upgrading of lignin-derived compounds to fuel components.