Steam-Induced Coarsening of Single-Unit-Cell MFI Zeolite Nanosheets and Its Effect on External Surface Brønsted Acid Catalysis.

Commonly used methods to assess crystallinity, micro-/mesoporosity, Brønsted acid site density and distribution (in micro- vs. mesopores), and catalytic activity suggest nearly invariant structure and function for aluminosilicate zeolite MFI two-dimensional nanosheets before and after superheated steam treatment. Yet, pronounced reaction rate decrease for benzyl alcohol alkylation with mesitylene, a reaction that cannot take place in the zeolite micropores, is observed. Transmission electron microscopy images reveal pronounced changes in nanosheet thickness, aspect ratio and roughness indicating that nanosheet coarsening and the associated changes in the external (mesoporous) surface structure are responsible for the changes in the external surface catalytic activity. Superheated steam treatment of hierarchical zeolites can be used to alter nanosheet morphology and regulate external surface catalytic activity while preserving micro- and mesoporosity, and micropore reaction rates.

Correlations for adsorption of oxygenates onto zeolites from aqueous solutions.

Henry's constants (K(ads)) for adsorption of C(3) polyfunctional molecules onto zeolites from aqueous solutions at 278 K were obtained and compared with the octanol-water partition coefficients, K(ow), which were calculated using the prevalent ClogP group contribution method. K(ads) increases linearly with K(ow) for these adsorbates on H-ZSM-5 (MFI), FAU, BEA, and ITQ-1 (MWW). K(ads) values for C(2)-C(6) diol adsorption at 278 K are also linearly correlated with K(ow) regardless of interactions in the bulk phase as measured by the solution activity coefficient. Exceptions to the correlation established between K(ads) and K(ow) are the adsorption of 1,2,ω-triols with carbon number greater than three on H-ZSM-5 and adsorption of all oxygenates studied on FER, which we postulate to be due to the effect of changing adsorption configuration with adsorbate/zeolite structure which cannot be captured by K(ow) alone. These results enable the prediction of separation selectivities of biomass-derived compounds on zeolite adsorbents.