Hierarchical Catalysts Prepared by Interzeolite Transformation

Abstract

Interzeolite transformation has been used to produce a novel family of hierarchical catalysts featuring excellent textural properties, strong acidity, and superior catalytic performance for the Friedel–Crafts alkylation of indole with benzhydrol, the Claisen–Schmidt condensation of benzaldehyde and hydroxyacetophenone, and the cracking of polystyrene. Intermediate solids of the FAU interzeolite transformation into BEA display both increased accessibility—due to the development of mesoporosity—and strong acidity—caused by the presence of ultrasmall crystals or zeolitic fragments in their structure. The use of surfactants allows for the development of the hierarchical catalysts with very narrow pore size distribution. The properties of interzeolite transformation intermediates (ITIs) can be fine-tuned simply by stopping the interconversion at different times.

Synthesis strategies to control the Al distribution in zeolites: thermodynamic and kinetic aspects

“…Recently, Linares and García-Martínez reported the synthesis of hierarchical catalysts whose mesoporosity and acidity evolved during partial interzeolite conversion of FAU into *BEA. 131 Three different synthesis media were prepared from (i) the parent FAU zeolite (Si/Al = 15.5) in the presence of TEAOH, (ii) an uncalcined surfactant (CTAB)-templated FAU zeolite (Si/Al = 16.0) with TEAOH, and (iii) the parent FAU zeolite with a mixture of TEAOH and CTAB. In the intermediate stage of all three media, amorphous mesoporous intermediates containing zeolite building units were formed, and their textural properties and consequent catalytic performance involving large molecules were tuned over time.…”

Superior Thermostability of Poly-Silicic Acid Analogues of Zeolite Composite/Secondary Building Units: A Theoretical Investigation

“…45−47 In this sense, the formation and evolution of S/CBUs are vital to understand the nucleation and growth of zeolites, but the detailed mechanisms remain challenging. Recently, considerable research attention has been put to interzeolite conversion, 29,48,49 as it makes synthesis of desired zeolites at high yield with Si/Al ratio tunable over a wider range and controllable crystallite size 13 at moderate conditions in shorter reaction time from zeolites, aluminum silicates, clays, etc. that are less stable in the reaction conditions possible.…”

Understanding the Anion‐Templated, OSDA‐Free, Interzeolite Conversion Synthesis of High Silica Zeolite ZK‐5**

“…Also, many high silica zeolites usually prepared by the use of OSDAs have been prepared by OSDA‐free IZC routes in the presence of seeds [17] . An interesting modification of the synthesis, which interrupts the conversion of USY to Beta in the presence of tetraethylammonium hydroxide, can be tuned to give a series of ‘Interzeolite transformation intermediates’, with little long range order but well‐defined mesoporosity [18] …”

“…[17] An interesting modification of the synthesis, which interrupts the conversion of USY to Beta in the presence of tetraethylammonium hydroxide, can be tuned to give a series of 'Interzeolite transformation intermediates', with little long range order but well-defined mesoporosity. [18] The mechanism of IZC remains incompletely understood, and is likely to differ between examples. [19] In the majority of cases, the parent and daughter structures have common building units (CBUs), such as small rings and cages, suggesting a pathway where the CBUs prepared in the dissolution step facilitates rapid, directed crystallisation.…”

“… [17] An interesting modification of the synthesis, which interrupts the conversion of USY to Beta in the presence of tetraethylammonium hydroxide, can be tuned to give a series of ‘Interzeolite transformation intermediates’, with little long range order but well‐defined mesoporosity. [18] …”