Introduction of NiSO4 to Ni/SiO2 catalyst in hydrogenation of furfuryl alcohol: Tailoring metallic nickel sites to switch major product from tetrahydrofurfuryl alcohol to cyclopentanone

Nickel-based catalysts are widely used in hydrogenation of varied types of organics. However, the nickel catalyst, like Ni/SiO 2 , lacks selectivity for hydrogenation of C=C and C=O. This is undesirable in some scenarios, such as conversion of biomass-derived furfuryl alcohol (FA) to cyclopentanone (CPO), a fine chemical, in which the C=C in furan ring of FA needs to be retained. In this study, introduction of sulfur species to Ni/SiO 2 catalyst via loading NiSO 4 was adopted to inhibit hydrogenation of furan ring in FA, aiming to achieve conversion of FA to CPO via ring-opening route. The results indicated that NiSO 4 was reduced to Ni x S y , which further reacted with metallic Ni, forming Ni 3 S 2 species and introducing the acidic sites with high-strength. The co-existence of Ni x S y and metallic Ni species effectively hindered hydrogenation of furan ring in FA, reducing tetrahydrofurfuryl alcohol (THFA) yield from 97% over Ni/SiO 2 to 0 over the NiS x /SiO 2 catalysts and shifting the major product to CPO. Nonetheless, the enhanced acidic sites along with the introduction of NiSO 4 catalyzed polymerization of reaction intermediates, competing with the production of CPO. The acidic sites, however, facilitated hydrogenolysis of vanillyl alcohol to selectively produce (yield: 94.3%) in hydrogenation of vanillin. Characterization of hydrogenation of FA with in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) technique suggested the oxygen-containing functionalities in FA, instead of furan ring, could strongly adsorb on the NiS 10 /SiO 2 catalyst, enhancing rearrangement reaction to form CPO while suppressing hydrogenation of the furan ring.