Catalytic conversion of guaiacol to phenol and alkylphenols over Mo-promoted Ni/CeO₂ catalyst in supercritical ethanol

The study explored the catalytic hydrodeoxygenation (HDO) of guaiacol using nickel-loaded cerium oxide (Ni/Ce) and molybdenum-promoted Ni/Ce (Mo-Ni/Ce) catalysts in supercritical ethanol. The use of Mo-Ni/Ce at 300 °C maximized H₂ production, guaiacol conversion (84.1%), and deoxygenation compared to Ni/Ce. Mo-Ni/Ce also achieved the highest efficiency for producing desired products, resulting in 7.8% phenol and 29.0% alkylphenols selectivities. Mo-Ni/Ce's better efficiency stemmed from enhanced ethanol dehydrogenation, H₂ dissociation and spillover, and accelerated HDO reactions owing to improved Ni dispersion and catalyst oxygen vacancies. Testing different Ni and Mo loading amounts revealed the optimum catalyst efficiency when using 20% Ni and 5% Mo (5Mo-20Ni/Ce). Temperature optimization with 5Mo-20Ni/Ce increased guaiacol conversion (up to 95.6% at 340 °C) and yielded more phenol (27.4%) and alkylphenols (66.1%). DFT calculations revealed that adding molybdena clusters notably reduced the energy required for creating oxygen vacancies, indicating enhanced catalytic properties for oxygen vacancy generation in 5Mo-20Ni/Ce.