The effects of zeolite micropore topology, mesoporosity, and acidity on the hydrolysis of polysaccharides were probed in reactions of sucrose and inulin over a variety of zeolite catalysts (FER, MFI, MOR, MWW, BEA, FAU, pillared MFI (PMFI), and pillared MWW (PMWW)) in aqueous medium in a batch reactor at the temperature of 343-364 K. The measured rate of polysaccharides hydrolysis over microporous zeolites varied by a factor of ~100 following a trend of FER &lt; MOR ~ MFI &lt; BEA ~ MWW &lt; FAU, indicating that hydrolysis of polysaccharides increases with increasing zeolite micropore sizes. The PMFI and PMWW are meso-/microporous zeolites, consisting of a zeolitic layer structure, with micropore and mesopore within the layers and between the layers, respectively. The presence of mesoporosity in PMFI and PMWW zeolites enhanced the rates of sucrose reactions by a factor of ~2 in comparison with the microporous MWW and MFI zeolites, which may result from the enhanced acid site accessibility and mitigated diffusion constraints. The examination on the effects of zeolite acidity on the hydrolysis of sucrose by employing MFI, PMFI, BEA, MWW, and FAU zeolites with a range of Si/Al ratios showed that Si/Al ratio of ~70-150 provides a maximal rate constant per acid site in the catalysts. The improved hydrophobic interactions between the zeolite and sucrose in catalysts with relatively high Si/Al ratios facilitate the adsorption of sucrose on the catalyst, and thus, the hydrolysis rate per acid site of the catalysts. The measured activation energies of the catalytic reactions in all zeolites were similar. The measured entropies, however, increased abruptly with increasing micropore sizes of zeolites and slightly with increasing mesoporosity in the zeolites. The present study suggests that the hydrolysis of sucrose and inulin is driven primarily by the reaction entropies that are dominated consecutively by the micropore topology, acidity, and mesoporosity of the zeolite catalysts.

Catalytic consequences of micropore topology, mesoporosity, and acidity on the hydrolysis of biomass over zeolite catalysts

252nd National Meeting (2016)

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