Ceramic bodies, such as aluminum titanate and cordierite ceramics, may be used in a variety of applications. For example, such bodies are viable for use in the severe conditions of exhaust gas environments, including, for example, as catalytic converters and as diesel particulate filters. Among the many pollutants in the exhaust gases filtered in these applications are, for example, hydrocarbons and oxygen-containing compounds, the latter including, for example, nitrogen oxides (NOx) and carbon monoxide (CO), and carbon-based soot and particulate matter.
Ceramic bodies exhibit high thermal shock resistance, enabling them to endure the wide temperature variations encountered in their application, and they also exhibit other advantageous properties for diesel particulate filter applications, such as, for example, high porosity, low coefficient of thermal expansion (CTE), resistance to ash reaction, and a modulus of rupture (MOR) adequate for the intended application.
With engine management schemes becoming more and more sophisticated, there exists a need for the application of a variety of catalytic coatings on ceramic bodies or ceramic catalyst supports to control hydrocarbon and/or nitrogen oxide emissions. The adverse effect of catalyst coating processes on the thermal properties of ceramic bodies or catalyst supports, such as cellular ceramics, however, are well-known. For example, one problem that may be encountered is that oxide constituents of the catalyst or catalyst support coatings, such as alumina, will penetrate into the microstructure of the ceramic supports during the coating and curing processes, filling the microstructure in a manner that may increase the thermal expansion coefficient of the catalyzed ceramic and thereby reduce the thermal shock resistance.
Thus, there exists a need to improve the design and performance of ceramic catalyst supports and methods of making such ceramic catalyst supports, for example to provide catalyst loading sufficient for effective catalytic treatment of exhaust streams while maintaining high gas permeability and low coefficient of thermal expansion of the catalyzed filter.
The inventors have now discovered novel methods for coating ceramic catalyst supports with a base coating comprising at least one polyvinyl alcohol homopolymer and at least one blocked isocyanate crosslinker, and catalyst supports having a base coating comprising at least one polyvinyl alcohol homopolymer and at least one blocked isocyanate crosslinker. In various embodiments, the coated ceramic catalyst supports of the disclosure may provide catalyst loading sufficient for effective catalytic treatment, while not adversely affecting the properties of the ceramic support.