Guaiacol to Aromatics: Efficient Transformation over In Situ-Generated Molybdenum and Tungsten Oxides

The development of catalysts for the hydrodeoxygenation of bio-based feedstocks is an important step towards the production of fuels and chemicals from biomass. This paper describes in situ-generated bulk molybdenum and tungsten oxides in the hydrodeoxygenation of the lignin-derived compound guaiacol. The catalysts obtained were studied using powder X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transition electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, and Raman spectroscopy. The use of metal carbonyls as precursors was shown to promote the formation of amorphous molybdenum oxide and crystalline tungsten phosphide under hydrodeoxygenation conditions. The catalysts’ activity was investigated under various reaction conditions (temperature, H2 pressure, solvent). MoOx was more active in the partial and full hydrodeoxygenation of guaiacol at temperatures of 200–380 °C (5 MPa H2, 6 h). However, cyclohexane, which is an undesirable product, was formed in significant amounts using MoOx (5 MPa H2, 6 h), while WOx was more selective to aromatics. When using dodecane as a solvent (380 °C, 5 MPa H2, 6 h), the benzene-toluene-xylenes fraction was obtained with a 96% yield over the WOx catalyst.