Location：Conference Room of Basic Energy Sciences Building
Time：2015.07.24（Friday）03:30 p.m.
Lecturer：Daniel E. Resasco
University of Oklahoma
Abstract：
Reactive-separation processes using solid nanoparticles with amphiphilic character and catalytic activity are investigated. These systems combine the advantages of phase transfer and heterogeneous catalysis with increased interfacial area, enhanced rate of mass transfer between the two phases, effective separation of products from the reaction mixture by differences in the water/oil solubility, and catalyst stability. We are investigating the fundamental phenomena involved in the catalysis at liquid-solid-liquid interfaces and its application in biomass upgrading (upgrading of pyrolysis oil and sugars), Fischer-Tropsch synthesis, and enhanced oil recovery. By anchoring metal catalysts selectively on either the hydrophobic or the hydrophilic side of the amphiphilic particles it has been possible to selectively convert compounds, which are primarily present in one of the phases, i.e. “phase-selectivity”. Interestingly, when the hydrophobization of the catalyst is extended to the entire surface the resulting catalyst exhibits enhanced stability in aqueous environments, while preserving the same emulsification properties. The susceptibility of zeolites to hot liquid water may hamper their full utilization in aqueous phase processes, such as those involved in biomass conversion and upgrading reactions. Interactions of zeolites with water strongly depend on the presence of hydrophilic moieties including Br?nsted acid sites (BAS), extraframework cations, and silanol defects, which facilitate wetting of the surface. However, it is not clear which of these moieties are responsible for the susceptibility of zeolites to liquid water. Previous studies have offered contradictory explanations because the role of each of these characteristics has not been investigated independently. In this work, a systematic comparison has been attempted by relating crystallinity losses to the variation of each of the five 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. In this study, we have systematically monitored the crystallinity changes 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 upon exposure to liquid water at 200 ℃. The results of this comparison unambiguously indicate that the density of silanol defects play the most crucial role in determining susceptibility of zeolites to hot liquid water. By functionalizing the silanol defects with organosilanes, the hydrophobicity of defective zeolite is increased and the tolerance to hot liquid water is significantly enhanced. Consequently, hydrophobization of microporous zeolites and metal-oxides catalysts has been successfully employed in the upgrading of bio-fuels in biphasic liquid systems, in which the use of conventional zeolites or metal-oxide catalysts is hindered by fast rates of deactivation due to dissolution into the bulk aqueous phase.
Contacts：Group 505 Jia Mao（9307）