The selective hydrogenolysis of the C-O bonds of lignin-derived aryl ethers into aromatics is challenging because it is always accompanied by hydrogenation (HYD). Most metal-supported catalysts tested so far exhibit high efficiency for the C-O bond cleavage of diphenyl ether (DPE, 4-O-5 linkage in lignin) but low selectivity toward valuable aromatic compounds. Here, we report our discovery showing the feasibility of controlling the selectivity of products by tuning the catalyst support and reaction conditions. Pt/γ-Al2O3 exhibited a higher selectivity (95.7%) for aromatic products (benzene and phenol) with a nearly 100% conversion at 160 °C when 2-propanol was used as a hydrogen source. In contrast, up to 99% selectivity for saturated aromatic products (cyclohexane and cyclohexanol) and the full conversion of DPE were yielded over Pt/TiO2 at 140 °C. The H2 evolution from 2-propanol dehydrogenation confirmed that the dehydrogenation activity of 2-propanol over Pt/γ-Al2O3 was lower than that over Pt/TiO2, which effectively suppressed the deep HYD of the formed aromatics. The role of supports and reaction active sites for 2-propanol dehydrogenation was studied by first-principles calculations. Based on the experimental results and ab initio molecular dynamics simulations, the detailed mechanisms of DPE hydrogenolysis over two Pt/oxide catalysts were proposed.
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