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The reduction of cold start emission is widely recognized method to meet the stringent automotive emission norms using catalytic converters. One of the effective ways is to use HC traps before the main converters. This system mainly consist of ceramic honeycomb coated with the zeolite molecular sieves which can adsorb HC during the transient cold start period and release to the main converters when it has reached light-off. High catalytic surface area, good HC trapping efficiency, high thermal durability and good mechanical strength are the important properties of zeolite coated honeycombs. They are prepared either by washcoating the zeolite on the substrate or by in-situ crystallization by wet hydrothermal method. The adhesion of the coating is better in the wet hydrothermal process but the honeycombs become mechanically weaker. To overcome this, a new method of forming the zeolite film on the ceramic honeycombs by solid state in situ crystallization has been developed.