Design of Nickel Supported on Water-Tolerant NbO Catalysts for the Hydrotreating of Lignin Streams Obtained from Lignin-First Biorefining.

In biomass conversion, NbO has attracted increasing attention as a catalyst support presenting water-tolerant Lewis acid sites. Herein, we address the design of Ni/NbO catalysts for hydrotreating of lignin to hydrocarbons. To optimize the balance between acidic and hydrogenating properties, the catalysts were first evaluated in the hydrotreating of diphenyl ether. The best catalyst candidate was further explored in the conversion of lignin oil obtained by catalytic upstream biorefining of poplar. As primary products, cycloalkanes were obtained, demonstrating the potential of Ni/NbO catalysts for the lignin-to-fuels route. However, the Lewis acidity of NbO also catalyzes coke formation via lignin species condensation. Thereby, an acidity threshold should be found so that dehydration reactions essential to the hydrotreatment are not affected, but the condensation of lignin species prevented. This article provides a critical "beginning-to-end" analysis of aspects crucial to the catalyst design to produce lignin biofuels.