Efficient hydrodeoxygenation of phenolic compounds and raw lignin-oil under a temperature-controlled phase-transfer catalysis

An effective binary catalyst by using tungstic acid (H2WO4) and Ru/C was employed for the hydrodeoxygenation (HDO) of phenolic compounds and raw lignin-oil. H2WO4 was presented as solid at ambient temperature, but it dissolved at high temperature above 100 °C and therefore functioned as an active homogeneous catalyst. This phenomenon resulted in a temperature-controlled phase-transfer behavior in the HDO of phenolic compounds. An efficient HDO performance and an exceptional reusability for guaiacol HDO were presented by this bifunctional catalyst, which can be reused more than 10 times with guaiacol conversion and cyclohexane selectivity over 90%. The comparison of traditional liquid organic and mineral acids, as well as solid acids, with H2WO4 confirmed the outstanding catalytic performance of H2WO4 and highlighted the advantages of H2WO4 as a homogeneous catalyst. Besides guaiacol, other phenolic compounds including various monomers and dimers all exhibited good HDO results, with 100% conversion and cycloalkanes selectivity. Moreover, the raw lignin-oil can be efficiently deoxygenated under the catalysis of this bifunctional catalyst. 99.3% content of hydrocarbons was obtained in the upgraded lignin-oil, which was promising to be used as fuel directly. This catalytic system has great potential for the industrial application of lignin-oil upgrade.