Zeolites, microporous solid acids, are promising catalysts for biomass conversion, e.g. aqueous lignin derived phenol hydrodeoxygenation. The rate-limiting dehydration step must be performed in aqueous medium due to ubiquitous presence of water and it's high content in the feedstock material. The catalytic dehydration reactions are often performed on solid acid catalysts, in particular zeolites. Understanding the behavior of zeolite active sites, tetrahedral Al sites (Al T-sites), framework structural integrity and the lattice degradation mechanism in hot liquid water is critically needed to advance catalyst life-time and activity. Analysis of zeolite structural modifications under hot liquid water treatment conditions was performed on a series of HBEA zeolites by combination of EXAFS and NMR spectroscopies supported by theory. The catalytic performance of both parent and treated zeolites was also studied. The turnover frequencies (TOF) for all parent samples were similar at approximately 10-2 mol�molBAS-1s-1 at 160 �C. The zeolite samples treated at this temperature for 48 h exhibited an approximately 30% decrease in both meso- and micropore surface area indicating zeolite framework degradation. The EXAFS showed elongation of the Al � O and Al � Si atom distances providing evidence for local pore structure degradation. While the tortuosity of the zeolite framework was likely decreased upon treatment benefiting the transport of molecules through the pores, the loss of pore structure appears to have reduced the performance of the active sites, as the TOFs for the treated zeolites were ~ 3 � 5 times lower than those of the parent samples. The effect of hot liquid water treatment on the zeolite framework also indicates that lattice defects facilitate desilication. A spectroscopic study of Si removal from the zeolite framework during hot liquid water treatment is thus suggested and currently in progress.

Biomass conversion: Impact of zeolite stability on aquoeus phase catalysis

248th National Meeting (2014)

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