Mechanistic insights on Ru nanoparticle in situ formation during hydrodeoxygenation of lignin-derived substances to hydrocarbons

Abstract

We present the conversion of guaiacol and diphenyl ether (DPhE) with ∼100% selectivity towards hydrocarbons over a ruthenium oxide-containing catalyst on a micro–mesoporous support (ZM). To elucidate the structure–catalytic activity correlation of the ruthenium oxide catalysts and achieve a high hydrocarbon yield via deoxygenation–hydrogenation, three supports were used: non-acidic mesoporous SBA-15, bulk ZSM-5 (CBV 3024E) and micro–mesoporous ZM. It was demonstrated that the acidity of the support was a key factor in the deoxygenation of guaiacol and DPhE, while a developed catalyst surface played an important role in the case of bulk molecule hydrogenation. The best catalytic performance was obtained over the micro–mesoporous RuO₂/ZM catalyst. Complete conversion of guaiacol and DPhE with a high cyclohexane yield of ∼100% was achieved after 1 h at 473–498 K under an initial H₂ pressure of 50 bar in n-alkane solution. Operando XAS and in situ DRIFT spectroscopy analyses of the RuO₂-based catalysts during guaiacol hydrogenation revealed that the reaction initiates simultaneously with the formation of the metallic Ru phase. It was shown that RuO₂ catalysts demonstrated better catalytic activity compared to reduced catalysts.