Bulk MoP and WP were investigated and compared in guaiacol hydrodeoxygenation to phenol. The catalysts obtained were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and temperature-programmed desorption of NH 3 (NH 3 -TPD) analyses. MoP was shown to be more active than WP. However, WP was more selective in phenol production. Guaiacol conversion using MoP was 90−98%. The highest selectivity for phenol was 66% (340 °C). By increasing the temperature to 380 °C, phenol selectivity decreased to 31%, while selectivity for cyclohexane increased to 29%. Thus, MoP was active not only in hydrodeoxygenation but also in hydrogenation. Guaiacol conversion over WP was 53− 90%. The highest selectivity for phenol was 84% (380 °C). Hydrogenation products were also detected but with low selectivity. Thus, WP was active in the partial hydrodeoxygenation of guaiacol and was more suitable for the selective production of phenol than MoP. It was shown that after a 30 h recycling test, the activity of MoP did not decrease (1st and 5th cycle conversion value was 91%), while the activity of WP reduced (1st and 5th cycle conversion values were 81 and 64%, respectively). However, the activity of both catalysts at average conversion values decreased. Selectivity for phenol remained unaltered over both catalysts. It was supposed that catalyst activity decreased due to partial destruction of the crystalline phosphide phase and the surface phosphide oxidation to phosphate.

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.

Amorphous catalysts based on molybdenum and tungsten phosphides were prepared in situ from oil-soluble precursors such as triphenylphosphine and carbonyls of the corresponding metals during hydrodeoxygenation of guaiacol. These catalysts were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, extended X-ray absorption fine structure spectroscopy, and transmission electron microscopy. After 6 h of reaction at 320–380°C and an initial hydrogen pressure of 5 MPa, the guaiacol conversion amounted to 89–91% in the presence of the molybdenum phosphide catalyst and 80–86% with tungsten phosphide. The selectivity towards phenol as the main reaction product reached as high as 80% in the presence of molybdenum phosphide (360°C, 6 h) and 78% in the tungsten phosphide case (340°C, 1 h). In the presence of both catalytic systems, the reaction products also contained anisole, cresols, and toluene.

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