Enhancing direct deoxygenation of m-cresol to toluene through inhibiting C-C hydrogenolysis via alloying Ni with Cu

Abstract

Selective hydrodeoxygenation (HDO) of biomass lignin derived phenolics to aromatics is an attractive approach for utilization of biomass lignin, since minimal H2 is consumed. Herein, bimetallic Ni-Cu/SiO2 catalysts with varying Cu/Ni molar ratios were synthesized by a modified homogeneous precipitation-deposition method and tested for HDO of m-cresol at 350 °C and atmospheric pressure. Characterizations indicate the formation of Ni-Cu alloys with an enrichment of Cu on the surface, which breaks the contiguous surface Ni atoms and reduces the Ni ensemble size. Despite bare Ni/SiO2 favors both C-C hydrogenolysis to CH4 and direct deoxygenation (DDO) to toluene, Ni-Cu/SiO2 makes DDO the dominant pathway (yield of 7.6% at conversion of 9.6% and yield of 90.4% at conversion of 95.2%) while suppresses the C-C hydrogenolysis to a very minor one. Ni-Cu/SiO2 with an optimal Cu/Ni molar ratio of 0.5 produced a turnover frequency (TOF) of 3.09 min−1 for m-cresol conversion. The TOF for toluene formation on Ni-Cu/SiO2 increases by ∼3 times to 2.24 min−1 from that on bare Ni/SiO2 whereas the TOF of CH4 formation is reduced by ∼10 times to 0.16 min−1. This study demonstrates that dilution of Ni by an inert metal such as Cu can effectively enhance DDO through inhibiting C-C hydrogenolysis during HDO of phenolics at atmospheric pressure.