Preparation of zeolite-coated cordierite honeycombs prepared by an in situ crystallization method

Zeolite thin films were prepared on cordierite (Mg2Al4Si5O18) honeycomb substrates by in situ crystallization using soft hydrothermal conditions. The synthesized zeolite films (zeolite A and ZSM-5) were characterized by XRD, FTIR, SEM, NH3-TPD, and Ns(2) and propane gas adsorption. Zeolite-A films were prepared by dip-coating on a cordierite substrate in a precursor of molar composition of Na2O:Al2O3:SiO2:H2O = 4:1:2:100 and heating in an autoclave at 80 degreesC for 6-10 h. The resultant zeolite-A films consisted of cubic crystals about 2-3 mum in size, achieving a thickness of 20 mum after re-coating. ZSM-5 films were similarly formed using a microporous silica precursor obtained by selective leaching of metakaolinite with tetrapropylammonium hydroxide (TPAOH) as the templating agent. The molar composition of the precursor was NaOH:microporous silica:TPAOH:H2O = 1:10:1:200. The dipped substrate covered with the wet precursor gel was heated in an autoclave at 150 degreesC for 24 h. The resultant films were composed of short prismatic <1 mum crystals achieving thickness of several to 10 mum after re-coating. The microstructure and porous properties of the ZSM-5 films were found to change according to the chemical composition and surface treatment of the cordierite substrates. The presence of a SiO2-rich interfacial layer between the substrate and zeolite film increased the amount of zeolite formed and the physical adsorption but decreased the solid acidity and amount of chemisorption. (C) 2004 Elsevier Ltd. All rights reserved.