Hydrodeoxygenation of Guaiacol to Cyclohexanol Using Noble Metal-Supported Ni-Based Perovskite-Derived Catalysts

Abstract

This study focuses on the role of noble metal-doped Ni-based perovskites, specifically LaNiO₃ and NiTiO₃ catalysts in the hydrodeoxygenation (HDO) of guaiacol. The findings demonstrate that reduced Ru-LaNiO₃ catalyst achieved superior performance with 100% guaiacol conversion and a 75% selectivity toward cyclohexanol, compared to reduced Ru-NiTiO₃, which achieved only 43% conversion and 25% cyclohexanol selectivity under identical conditions (240 °C, 30 bar H₂, and 4 h). High-resolution transmission electron microscopic (HR-TEM) analysis reveals that LaNiO₃-supported catalysts exhibit better metal dispersion and smaller nickel nanoparticle sizes compared to NiTiO₃-supported counterparts. X-ray photoelectron spectroscopy (XPS) analysis shows that the reduction of nickel and noble metals is more facile on LaNiO₃. Additionally, the O 1s XPS profile for reduced Ru-LaNiO₃ indicates a higher proportion of lattice oxygen (O_Lat ∼ 79%) and a lower proportion of oxygen vacancies (O_Vac ∼ 21%) compared to other catalyst systems. The optimized O_Lat/O_Vac ratio is shown to be critical for the effective HDO of guaiacol. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrates a high HDO reaction rate using reduced Ru-LaNiO₃ than reduced Ru-NiTiO₃, with cyclohexanol formation attributed to the keto-enol tautomerization pathway. Overall, this study underscores the critical roles of oxygen vacancies, metal dispersion, and metal–metal oxide interactions in the HDO of guaiacol.