Zeolite Coatings on Microcellular Ceramic Foams: A Novel Route to Microreactor and Microseparator Devices

Abstract

Zeolites are microporous crystalline aluminosilicates with molecular sieving capabilities (pore size < 1.3 nm).[1±3] The use of zeolite coatings on different supports (metal substrates, porous glass, ceramic honeycombs, mesoporous materials) has recently been proposed for catalysis, adsorption, and separation.[4±8] Open-cell ceramic foams [9±15] (connected pores in the 0.1±4 mm range) are gaining interest as zeolite carriers [11±15] due to their unique properties, for the development of new reactor concepts (monolithic, catalytic wall configurations) for technical catalytic and adsorption±separation processes. [15,16] Here we present, for the first time, a novel zeolite±ceramic composite material, with a bimodal (nano-, macroscale) pore system, obtained by coating the cell walls of microcellular polymer-derived ceramic foams (cell size~8 lm) with a thin, binder-free layer of MFI-type zeolite (Silicalite-1 and ZSM-5), produced by an in-situ conventional supported hydrothermal synthesis. To our knowledge, these materials represent the smallest microreactors/separators fabricated to date.Ceramic foams, with low thermal expansion coefficients and high thermal, mechanical, and chemical stability, are suitable as zeolite supports because they provide enhanced mass and heat transfer and a low pressure drop when compared to zeolite pellets used in fixed-bed reactors. [9,10] The fabrication of ceramic foams from preceramic polymers allows tailoring of the composition and morphology, and therefore of the final properties, of the porous material. [17,18] Very recently, [19,20] we fabricated mechanically stable ceramic microcellular [21,22] foams with a homogeneous interconnected porosity and an average cell size in the range of~1±100 lm, bulk density from 0.2±0.6 g cm ±3, and cell density from~10 7 ±10 12 cells cm ±3 . The starting materials were poly(methyl methacrylate) (PMMA) microbeads, acting as sacrificial template, and a COMMUNICATIONS

Zeolitic Materials with Hierarchical Porous Structures

“…Depending on their applications the support structure can be either dense or porous, resulting in different devices, such as wall reactors (esp. microreactors [ 110 ] ) or membrane reactors, [ 140 ] respectively. In addition, metal/ zeolite composites have been adopted for heat transformation processes [ 113 ] as well.…”

A hierarchically porous diatomite/silicalite-1 composite for benzene adsorption/desorption fabricated via a facile pre-modification in situ synthesis route

“…In addition, the macroporous structure of the support shortens the diffusion path and reduces the resistance to gas penetration, increasing the mass transfer efficiencies of guest molecules. Various porous materials, including a-alumina [19,20], stainless steel [21], porous carbon discs [22] and ceramics [23], have been developed as supports for the preparation of hierarchically porous composites. Nonetheless, the pre-synthesis or pretreatment process of such supports may increase the synthesis costs of the composites.…”

In situ CCVD synthesis of carbon nanotubes within zeolite crystal coated porous ceramic foam

“…A porous support exhibits a non-continuous surface and high surface area, not only contributing significantly to the particle stabilization and producing a fine dispersion of well-defined NPs, but also drastically increasing the number of catalytic particles (nucleation sites) present in it, which are all properties that are advantageous to the synthesis of CNTs. 24) As molecular sieve materials, zeolites have proved to have a significant impact due to their structural homogeneity and high reactive surface area, 25) and a pore size ranging from 310 ¡ 26) which makes them excellent supports for catalyst particles in the synthesis of CNTs.…”