In Situ Time-Resolved Observation of the Development of Intracrystalline Mesoporosity in USY Zeolite

Abstract

The development of intracrystalline mesoporosity within zeolites has been a long-standing goal in catalysis as it greatly contributes to alleviating the diffusion limitations of these widely used microporous materials. The combination of in situ synchrotron X-ray diffraction and liquid-cell transmission electron microscopy enabled the first in situ observation of the development of intracrystalline mesoporosity in zeolites and provided structural and kinetic information on the changes produced in zeolites to accommodate the mesoporosity. The interpretation of the time-resolved diffractograms together with computational simulations evidenced the formation of short-range hexagonally ordered mesoporosity within the zeolite framework, and the in situ electron microscopy studies allowed the direct observation of structural changes in the zeolite during the process. The evidence for the templating and protective role of the surfactant and the rearrangement of the zeolite crystal to accommodate intracrystalline mesoporosity opens new and exciting opportunities for the production of tailored hierarchical zeolites.

Thermochemistry of Surfactant‐Templating of USY Zeolite

“…Different structure‐directing agents (SDAs) have been used to drive the interconversion of one zeolite into the other . Building on this idea, we have transformed a USY (FAU) zeolite into its hierarchical mesoporous version, while keeping its crystalline structure, by the use of a cationic surfactant, namely cetyltrimethylammonium bromide (CTAB) . Some of the advantages of using surfactants to introduce mesoporosity in zeolites are: 1) the ability to tailor the mesoporosity generated and 2) to preserve the crystallinity, strong acidity, and excellent hydrothermal stability of the original zeolite as evidenced, not only in lab‐scale experiments, [7] but also at commercial scale in a number of refineries where they are currently used as fluid catalytic cracking (FCC) catalysts.…”

“…[1, 2] Buildingo nt his idea, we have transformed aU SY (FAU) zeolite into its hierarchicalm esoporousv ersion, while keeping its crystalline structure, by the use of ac ationic surfactant, namely cetyltrimethylammonium bromide (CTAB). [3][4][5][6] Someo ft he advantages of using surfactants to introduce mesoporosity in zeolites are:1 )t he ability to tailort he mesoporosity generated and 2) to preservet he crystallinity,s trong acidity,a nd excellent hydrothermals tabilityo ft he originalz eolite as evidenced, not only in lab-scale experiments, [7] but also at commercial scale in an umber of refineries where they are currently used as fluid catalytic cracking (FCC) catalysts.. [8] Recently,w eh aves tudied the kinetics of the different steps involved in the generation of surfactant-templated mesopores in USY (CBV 720, Si/Al = 15) zeolite.B yc ombiningi ns itu and ex situ techniques, we determined the apparenta ctivation energies of those processes, resulting in values in the same range as those involved in the crystallization of zeolites (30-65 kJ mol À1 ). [9] Chem.…”

Development of Bifunctional Hydrodeoxygenation Catalyst Rh‐HY for the Generation of Biomass‐Derived High‐Energy‐Density Fuels

“…The limited N 2 uptake after the initial value in the micropores indicated a low external/mesopore surface area . Otherwise, after the incorporation of Rh followed by the calcination–reduction process, the adsorbed volume increased, and the hysteresis widened, which is attributed to an increase in the mesoporous volume . The N 2 physisorption profile of 0.8Rh‐HY‐R corresponded to a type II isotherm but conserved the H4 hysteresis loop.…”

Reflections on the value of electron microscopy in the study of heterogeneous catalysts

“…This constitutes a breakthrough in the potential that EM has for the future study of heterogeneous catalysts that function in a liquid (or gas-liquid) environment (figure 22). And this approach, coupled with in situ synchrotron X-ray diffraction [95] has already been profitably exploited in charting the development of intracrystalline mesoporosity in commercially important zeolitic catalysts. Figure 23.…”

“…Figure 23. Illustration of the wealth of 'sub-techniques' emanating from Zewail's introduction in 1991 of ultra-fast electron diffraction, ultra-fast EC and 4D ultra-fast EM [95].…”