5 research outputs found
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
Steam-Induced Coarsening of Single-Unit-Cell MFI Zeolite Nanosheets and Its Effect on External Surface Brønsted Acid Catalysis.
A quantitative study of the structure-activity relationship in hierarchical zeolites using liquid-phase reactions
Micro/meso/macroporous (hierarchical) zeolites show remarkable catalytic performance for reactions involving bulky reactants. However, quantitative assessment of the microstructural characteristics contributing to the observed performance remains elusive. Here, structureâactivity relationships are established for a set of micro/mesoporous selfâpillared pentasil (SPP) zeolites using two parallel liquidâphase reactions (benzyl alcohol alkylation and selfâetherification) based on analysis of mass transport and reaction kinetics. A reactionâdiffusion mathematical model is developed that quantitatively assigns the catalytic contributions of the external surface and micropores of SPP zeolites for these reactions. In addition, the effect of the zeolite external surface structure on the corresponding catalytic activity is quantitatively assessed by comparing SPP zeolites (with MFI structure) with MCMâ22 (with MWW structure). This work demonstrates that reactionâdiffusion modeling allows quantitative description of the catalytic performance of hierarchical zeolites and provides a model reaction to assess nmâsized characteristic diffusion lengths in MFI
A quantitative study of the structure-activity relationship in hierarchical zeolites using liquid-phase reactions
Micro/meso/macroporous (hierarchical) zeolites show remarkable catalytic performance for reactions involving bulky reactants. However, quantitative assessment of the microstructural characteristics contributing to the observed performance remains elusive. Here, structureâactivity relationships are established for a set of micro/mesoporous selfâpillared pentasil (SPP) zeolites using two parallel liquidâphase reactions (benzyl alcohol alkylation and selfâetherification) based on analysis of mass transport and reaction kinetics. A reactionâdiffusion mathematical model is developed that quantitatively assigns the catalytic contributions of the external surface and micropores of SPP zeolites for these reactions. In addition, the effect of the zeolite external surface structure on the corresponding catalytic activity is quantitatively assessed by comparing SPP zeolites (with MFI structure) with MCMâ22 (with MWW structure). This work demonstrates that reactionâdiffusion modeling allows quantitative description of the catalytic performance of hierarchical zeolites and provides a model reaction to assess nmâsized characteristic diffusion lengths in MFI