Mild hydrogenation of bio-oil and its derived phenolic monomers over Pt–Ni bimetal-based catalysts

Mild prehydrogenation of phenolics in bio-oil is known to effectively alleviate the severe coking that occurs on the surface of the cracking catalysts. This study investigated the hydrogenation of phenolic monomers (i.e., phenol, catechol, and guaiacol) over Pt–Ni/SiO2 at different Ni/Pt ratios. The results show that the hydrogenation of aromatic rings preferentially occurred over the Pt–Ni/SiO2 catalyst, with a slight hydrogenolysis of the Caryl–OR bond. The prepared Pt–Ni/SiO2 catalysts not only offered a good dispersion of the Pt and Ni species on SiO2, but also promoted spontaneous dissociation of H2 and facile diffusion of the resulting H atoms on Pt–Ni/SiO2, thereby contributing to its remarkable catalytic performance. The optimized 3Pt6Ni/SiO2 catalyst not only achieved a high phenolic conversion of 66%−99% and a high liquid product yield of 80%, but also significantly inhibited the side reaction of the products leading to gas formation. Furthermore, a stable phenolic conversion of ~80% within 24 h indicates the superior stability of 3Pt6Ni/SiO2. Subsequently, catalytic cracking of the hydrotreated bio-oil was investigated. The results indicate that mild hydrogenation benefits the formation and aromatization of light olefin intermediates, leading to increased formation of monocyclic aromatic hydrocarbons. The oil phase yield of the bio-oil fraction was 38.6%, comprising entirely hydrocarbons, of which 82.2% were monocyclic aromatic hydrocarbons. Hence, this study provides a promising approach for converting the phenolics in bio-oil into highly hydrogenated products, which are ready for the subsequent catalytic cracking.