Zeolite–supported nickel phyllosilicate catalyst for C[sbnd]O hydrogenolysis of cyclic ethers and polyols

Abstract

In this study, a series of zeolites, including small pore (SAPO–34), medium pore (Ferrierite, ZSM–5, and ZSM–11), and large pore (MOR and BETA) zeolites were explored as supports for nickel catalysts. The catalysts were prepared by the deposition–precipitation (D–P) method to obtain ca. 10 wt% Ni loading. The structures of prepared catalysts were elucidated using a wide range of characterization techniques such as BET, XRD, TEM, H2–TPR, NH3–TPD, FTIR, and XPS. It was found that 1:1 nickel phyllosilicate structures is formed over D–P nickel catalysts, while 2:1 nickel phyllosilicate was identified only over Ni/BETA catalyst. Furthermore, Ni/ZSM–5 catalyst was also prepared by impregnation method as a reference to investigate the effect of preparation method. The impact of the topological structures of zeolite on the catalytic activity of reactants (i.e., cyclic ethers derived from furanic compounds), reaction intermediates (i.e., polyols) was subsequently investigated. The ring–opening of THFA can proceed over Ni/Ni phyllosilicate species on the external surface of the catalyst, producing pentane polyols. Then, the pentane polyol intermediates can further undergo ring–closure pathway, predominantly over the internal acid sites within zeolite structures (except for Ni/SAPO–34). It was found that medium–pore zeolites (ZSM–5 and ZSM–11) with mild acidity exhibit the highest reaction rate with a THP yield up to ca. 64%. Similarly, the highest catalytic activity during THPM conversion was achieved over ZSM–5– and ZSM–11– supported nickel catalysts, with up to 51% selectivity towards 16HDO. Comparing the zeolite maximum pore sizes and the kinetic diameters of the reactants and products with the catalytic performance, it is clear that topological structures of ZSM–5 and ZSM–11 have pore confinement effect on the reaction mechanism and catalytic activity in the hydrogenolysis of cyclic ethers and polyols.