The preparation of highly ordered single layer ZSM-5 coating on prefabricated stainless steel microchannels

An elegant way to prepare catalytically active microreactors is by applying a coating of zeolite crystals onto a metal microchannel structure. In this study the hydrothermal formation of ZSM-5 zeolitic coatings on AISI 316 st ainless steel plates with a microchannel structure has been investigated at different synthesis mixture compositions. The procedures of coating and th ermal treatment have also been optimized. Obtaining a uniform thickness of the coating within 0.5 mm wide microchannels requires a careful control of various synthesis variables. The role of these factors and the problems in the synthesis of these zeolitic coatings are discussed. In general, the syn thesis is most sensitive to the H2O/Si ratio as well as to the orientation of the plates with respect to the gravity vector. Ratios of H2O/Si=130 and Si/template=13 were found to be optimal for the formation of a zeolitic fil m with a thickness of one crystal at a temperature of 130 degreesC and a sy nthesis time of about 35 h. At such conditions, ZSM-5 crystals were formed with a typical size of 1.5 mu mx1.5 mu mx1.0 mum and a very narrow (within 0.2 mum) crystal size distribution. The prepared samples proved to be activ e in the selective catalytic reduction (SCR) of NO with ammonia. The activi ty tests have been carried out in a plate-type microreactor. The microreact or shows no mass transfer limitations and a larger SCR reaction rate is obs erved in comparison with pelletized Ce-ZSM-5 catalysts; (C) 2001 Elsevier S cience B.V. All rights reserved.