Monolithic reactors are used in a number of environmental applications including for automobile exhaust control and for the reduction of organic compounds and nitrogen oxides from stationary sources. Typically, such catalysts are designed for high initial activity and poisoning resistance. In some cases, the catalysts may have to operate in particulate-laden environments. The present paper calls attention to the design of monolith catalysts for improved fouling resistance. A simple model is used to illustrate the design of monolith catalysts for the selective catalytic reduction of nitrogen oxides.