Diffusion Study by IR Micro-Imaging of Molecular Uptake and Release on Mesoporous Zeolites of Structure Type CHA and LTA

Abstract

The presence of mesopores in the interior of microporous particles may significantly improve their transport properties. Complementing previous macroscopic transient sorption experiments and pulsed field gradient NMR self-diffusion studies with such materials, the present study is dedicated to an in-depth study of molecular uptake and release on the individual particles of mesoporous zeolitic specimens, notably with samples of the narrow-pore structure types, CHA and LTA. The investigations are focused on determining the time constants and functional dependences of uptake and release. They include a systematic variation of the architecture of the mesopores and of the guest molecules under study as well as a comparison of transient uptake with blocked and un-blocked mesopores. In addition to accelerating intracrystalline mass transfer, transport enhancement by mesopores is found to be, possibly, also caused by a reduction of transport resistances on the particle surfaces.

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

“…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. 34,200,201 Since these methods require a very specific methodology and often costly technical setups, a variety of catalytic reactions are commonly used to study the positive effect of the hierarchical porosity in zeolite systems on their catalytic performance, i.e. increase in conversion and/or selectivity as well as better resistance to coke formation.…”

“…This improvement enables higher activities and/or improved kinetics of catalytic and sorptive processes which is kind of the ''driving force'' for the growing interest in hierarchically porous materials in general. [34][35][36][37] In the following, zeolite-based hierarchical materials shall be discussed according to their compositional, textural and structural properties as well as according to the underlying preparation principles.…”

Interactions of pectins with cellulose during its synthesis in the absence of calcium

“…(1) and Eq. (2)) are as follows (Bonilla et al, 2013;Rincon Bonilla, Valiullin, K€ arger, & Bhatia, 2014):…”

“…Diffusion models have been widely used to investigate the detailed diffusional behaviour in porous materials for the development, design and optimization of adsorption and desorption processes (K€ arger et al, 2012), which can lead to a better understanding of the interactions between molecules and solid surfaces (Ruthven et al, 2008). Therefore, models of two limiting cases of diffusion-limited and surface-limited release (Bonilla et al, 2013) were used to determine whether diffusion within the cellulose composite or surface permeability was rate-limiting. The internal diffusion and surface permeability were quantified by diffusion coefficient D and permeability coefficient a in this model and the Biot number was used to determine which factor played the more important role in the process of de-binding.…”

“…To investigate the de-binding behaviour, the experimental data were compared with the predicted behaviour using two models of limiting cases of diffusion rate control by diffusion inside pellicles and by surface resistance with a few modifications (Bonilla et al, 2013;K€ arger, Ruthven, & Theodorou, 2012;Ruthven, Brandani, & Eic, 2008). Here different washing temperatures were used.…”