Zeolites washcoating onto cordierite honeycombs for environmental applications

J. M. ZAMARO; M. A. ULLA; E. E. MIRÓ

CHEMICAL ENGINEERING JOURNAL

Elsevier

Lugar: Amsterdam; Año: 2005 vol. 106 p. 25 - 33

1385-8947

The preparation conditions to obtain zeolite washcoating with optimum loading and homogeneous distribution are studied for mordenite, ferrierite and ZSM-5. The slurry concentration and the number of immersions were combined to obtain different coating thickness and geometry. The solid concentration increases the viscosity of the slurry resulting in a exponential growth of the zeolite loading. In order to obtain more homogeneous washcoating it is preferable to use diluted suspensions and perform more than one immersion. It was found that the washcoating adherence increases with the decrease in the size of aggregates deposited on the monolith. This improves the packaging and the interaction between particles and facilitates a convenient filling of the surface cordierite macropores, producing a more effective anchorage. In this vein, the order of washcoat stability tested with an ultrasound method is ZSM-5 > mordenite > ferrierite. The addition of SiO2 as binder improves the adherence of the three zeolites under study probably due to an improvement in the interparticle cohesion. The performance of an In-ZSM5 washcoated monolith was tested for the selective reduction of NOx with methane under oxygen excess. It was observed that the activity of the monolith catalyst was as good as for the In-ZSM5 powder, which indicates that there qre no diffusive restrictions due to coating thickness.