Sn-assisted nickel synergistically catalyzes the direct cleavage of CAr[sbnd]O bond in lignin-derived m-cresol: Theoretical and experimental analysis

Abstract

Refining lignin for aromatic hydrocarbons was crucial in the development of clean energy. The most effective way to enhance the carbon efficiency of the raw materials was to reduce the hydrogen consumption and maximize the retention of aromatic ring by directly breaking the CArO bond. In this regard, Sn was introduced to regulate the selectivity of Ni/SiO2 for m-cresol hydrodeoxygenation (HDO) products at low hydrogen consumption. Thanks to the formation of the Ni-Sn alloy in the system, the bimetallic sites synergistically catalyze the CArO bond scission through lowering the reaction energy barrier. Further from charge analysis, it was concluded that the charge transfer from Sn to Ni promotes the hydrogenolysis, and the charge transfer between the slab and the adsorbate provides the possibility for the occurrence of direct deoxygenation reaction. The COHP analysis resulted that the introduction of Sn accelerated the CArO bond cleavage. Interestingly, another deoxygenation pathway was proposed from the isomerization conversion of m-cresol to dienone intermediate (3-methyl-3,5-cyclohexadienone) in the calculation of transition state. Further HDO can form toluene effortlessly due to the presence of the oxyphilic metal Sn. This also explains the high selectivity of Ni-Sn to toluene. Moreover, the introduction of the Sn promoter effectively prolongs the lifetime of the catalyst by enhancing the tolerance to carbon deactivation.