Micro/Macroporous System: MFI‐Type Zeolite Crystals with Embedded Macropores

Abstract

Zeolite crystals with an embedded and interconnected macropore system are prepared by using mesoporous silica particles as a silica source and as a sacrificial macroporogen. These novel hierarchical zeolite crystals are expected to reduce diffusion limitations in all zeolite-catalyzed reactions, especially in the transformation of larger molecules like in the catalytic cracking of polymers and the conversion of biomass.

Synthesis and Characterisation of Hierarchically Structured Titanium Silicalite‐1 Zeolites with Large Intracrystalline Macropores

“…Volumetric data on the pore geometries was analysed and percentage macroporosity in the particlee stimated at around 27 %o ver the complete particle volume, again significantly lower than the 45 %m acroporosityo bservedf or silicalite-1, [26] but in general agreement with the ET results( 33.6 %). The rather low measured macroporosity is probably due to partial zeolite growth into the macropores as noted previously, whereas the difference in values observed from ET can likely be attributed to natural variation among different particles.…”

“…The value is smaller than the 45 %m acroporosity reported for macroporouss ilicalite-1. [26] The Video of the electron tomography reconstruction provided in the Supporting Information shows that most of the pores are interconnected to each other with only someisolated macropores visible inside the crystal.…”

“…In comparison to the macroporous silicalite-1 reported by Machoke et al,t he synthesised macroporous TS-1 shows ahigher wall thickness between the macropores. [26] Another crystal of the same sample wasa lso investigated by using hard X-ray PXCT.P XCT is ap hase contrast imaging technique which is sensitivetol ocal electron density in the sample, and despite the use of hard X-rays can therefore be used to image low-atomic-number materials, such as zeolites (e.g.,S i, Al, Ti), providing location and identification of structural components.F igure 5s hows the reconstructed TS-1 particle observedb yP XCT.T he 3D spatialr esolution of the volumes is approximately 47 nm. The residual glue commonly resulting from focused ion beam (FIB) preparationc an be easily detected and segmented out of the 3D volumes.…”

Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity

“…Very often it is still difficult to characterise the interconnectivity of the existing -at least two different -pore systems with the different length scales precisely. Few recent papers have shown the progress in this respect in specified methods such as 3D reconstruction from data by STEM-tomography 55,196 or by face-scanning techniques, 197 spectroscopic techniques such as positron annihilation lifetime spectroscopy 198 or continuously improved conventional methods like physical sorption. 199 Alternatively, molecular uptake and release studies have been performed to demonstrate the role of pore interconnectivity and the enhancement of mass transport properties of zeolites with hierarchical porosity.…”

“…This approach utilises the steam-assisted crystallisation of mesoporous silica particles (MSPs) after their impregnation with tetrapropylammonium hydroxide (TPAOH) acting as the zeolite structure directing agent and source of alkalinity. 55 Nevertheless, the hard templating strategy is often limited by multistep procedures, relatively high costs and health hazards related to some of the hard templates used. Some of these limitations can be alleviated by using biological templates like starch and bacteria.…”