A nickel silicate MFI-type zeolite catalyst prepared by interzeolite transformation: tailoring the catalytic active sites for glucose conversion

We first report an MFI-type nickel silicate (Ni-MFI) via the hydrothermal interzeolite transformation of an MWW-type nickel silicate. The synthesis was systematically investigated at various crystallization temperatures (135, 150, and 190 °C) and times (0-168 h). Several analytical techniques were employed to comprehensively characterize solid products to confirm the structural transformation, the chemical states of Ni species, and the acid properties of framework Ni species and silanol groups. The structural transformation and the stabilization of framework Ni species were found to occur via independent kinetics, which could be controlled by adjusting the crystallization temperature and time. Certain silanol groups including silanol nests and defective silanols, along with the isolated framework Ni species in Ni-MFI, which were controlled by the two separate kinetics of structural transformation and chemical states of framework Ni species, facilitated the Brønsted and Lewis acidities of Ni-MFI solids. As a result, the bi-acidities of Ni-MFI solids, established during the synthetic stages, efficiently catalyzed the cascade conversion of glucose to fructose and subsequently to 5-(hydroxymethyl)furfural, utilizing their Lewis and Brønsted acid sites, respectively.