The effect of different slurry compositions and solvents upon the properties of ZSM5-washcoated cordierite honeycombs for the SCR of NOx with methane

ZSM5-washcoated monoliths were prepared using different slurry compositions and the following solvents: water, methyl alcohol, ethyl alcohol, isopropyl alcohol, butyl alcohol, ethyl acetate, and acetone. The effect of the different solvents on the coating characteristics was studied and two of their properties, viscosity and volatility, were used to analyze the results obtained. The solvents giving rise to high-viscosity slurries – butyl alcohol, ethyl acetate, and acetone – were not effective for the washcoating process. In the case of the other solvents, when viscosity and vapor pressure increased the load obtained was higher, probably due to a combined effect of viscosity and partial evaporation during the blowing step. Water yielded zeolite coatings with the best mechanical stability, measured by ultrasonic test. When water was used as solvent, the zeolite load increased linearly with the square root of viscosity. Finally, an In/HZSM5-coated honeycomb was tested for NOx reduction with methane under excess oxygen. It showed a behavior very similar to that of the powder catalyst, which is one of the main objectives pursued when coating monoliths.