W e have shown that by anchoring specific catalytic functions over supports of controlled hydrophobization greatly enhanced stability in aqueous environments can be achieved.  For example, MgO is a typical basic oxide commonly used in aldol-condensation reactions for biomass upgrading.  However, this catalyst is susceptible to rapid deactivation.  Finding catalytic materials that are effective for aldol condensation and at the same time more resistant to deactivation than conventional basic catalyst is an appealing objective.  In this presentation, the development of novel materials with improved stability during aldol condensation is discussed. MgO catalysts have been modified with overlayers of silica grafted with an hydrophobic organosilane (octodecyl trichlorosilane). These basic catalytic materials have excelled in the conversion of cyclopentanone and acetone, two compounds directly derived from furanics and acetic acid obtained from biomass pyrolysis vapors.  Likewise, the notorious susceptibility of acid zeolite catalysts to hot liquid water hampers their full utilization in aqueous phase processes, such as those involved in biomass conversion and upgrading reactions. We will describe a systematic comparison of the possible zeolite characteristics that may influence their stability in liquid water, including number of BAS, Si-O-Si bonds, framework type, silanol defects, and extraframework Al.  Changes in crystallinity of a series of HY and H-ZSM-5 zeolite samples with varying Si/Al ratio, density of BAS, zeolite structure, and density of silanol defects were evaluated upon exposure to hot liquid water.   The results unambiguously indicate that the density of silanol defects play the most crucial role in determining susceptibility of zeolites to hot liquid water. Remarkably, by functionalizing the silanol defects with organosilanes, the hydrophobicity of defective zeolite is increased and the tolerance to hot liquid water is significantly increased.   That is, a controlled degree of functionalization opens up opportunities for designing heterogeneous catalysts with enhanced performance under the severely deactivating conditions typically found in biomass conversion processes.  Finally, the effects of hydrophobizing mesoporous silica and incorporating controlled density of SO3H+ moieties will be discussed in regards to applications in C-C bond forming reactions, specifically alkylation.

Improving stability of zeolites and mesoporous materials in hot liquid water by hydrophobization with organosilanes

255th National Meeting (2018)

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