Preparation and Properties of Washcoats for Three Way Catalyst

The washcoats deposited on a ceramic honeycomb were prepared with pseudoboehmite as γ-Al_2O_3 precursor, CeO_2-ZrO_2-La_2O_3, pore enlarger and other additives. The relations of apparent viscosity and solid content in the coating gel to the loading of coating, and the effect of the particle size distribution in the coating gel on the properties of washcoats were studied. The microstructures and surface performances of the washcoats deposited on a ceramic honeycomb were characterized by scanning electron microcopy (SEM), BET surface area, vibration by ultrasonic and hot impact simulation. The results show that the solid content of 30%～40% in the coating gel should be used propositionally, the loading of coating in the first impregnationthat in the second impregnationthat in the third impregnation, the feasible loading of coating is 8%～15%. The viscosity in the coating gel affects the performance of washcoats on a ceramic honeycomb. When an apparent viscosity of the gel is lower, an arrow particle size distribution and smaller particles in the coating gel can be obtained, and the prepared coating has excellent properties of the vibration- resistant by ultrasonic, heat-resistant and so on; when an apparent viscosity is higher, there are a wide particle size distribution and mainly micron-meter particles in the coating gel, which is available to form the higher loading of the coating on a ceramic support, but its performance is poorer. After supporting the washcoats, the BET surface area of the ceramic honeycomb can reach 50m~2/g.