Preparation of beta-coated cordierite honeycomb monoliths by in situ synthesis -: Utilisation as Pt support for NOx abatement in diesel exhaust

In this paper, a method for the preparation of beta-coated cordierite honeycomb monoliths suitable as Pt supports for deNO(x) application is described. The main advantage of this in situ process is the elimination of the need for a binder. The presence of beta zeolite on the supports was confirmed by XRD and SEM. SEM characterisation clearly showed that zeolite grows both into the cordierite macroporous structure and on the surface of the monolith channels. The formation of a compact zeolite network may be the reason of the strong anchorage of zeolite to the cordierite support. Maximum thickness of the zeolite-coating layer is 10 mu m and coating is stable up to 600 degrees C in air. Single- and two-step syntheses have been performed in order to increase zeolite loading. Single-step syntheses yielded monolith samples with average size of beta crystallites ca. 0.5 mu m and BET surface areas that present a linear relationship with zeolite loading. Samples prepared in a two-step synthetic procedure had an average crystal size of I mu m and present diffusion limitations in N-2 adsorption measurements. NOx conversion of 70% with 0.5 wt.% Pt-beta-coated monolith has been reached at 210 degrees C under a simulated diesel exhaust (5600 h(-1)) containing 1000 ppm NOx, 1500 ppm C3H6 and 5% O-2 in He. This value is similar to the previously observed for Pt-beta powder catalysts. (c) 2004 Elsevier B.V. All rights reserved.