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

Abstract

Nickel-based catalysts are widely used in hydrogenation of varied types of organics. However, the nickel catalyst, like Ni/SiO2, 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/SiO2 catalyst via loading NiSO4 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 NiSO4 was reduced to NixSy, which further reacted with metallic Ni, forming Ni3S2 species and introducing the acidic sites with high-strength. The co-existence of NixSy and metallic Ni species effectively hindered hydrogenation of furan ring in FA, reducing tetrahydrofurfuryl alcohol (THFA) yield from 97% over Ni/SiO2 to 0 over the NiSx/SiO2 catalysts and shifting the major product to CPO. Nonetheless, the enhanced acidic sites along with the introduction of NiSO4 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 NiS10/SiO2 catalyst, enhancing rearrangement reaction to form CPO while suppressing hydrogenation of the furan ring.