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Selective Catalytic Reduction (SCR) of Nitrogen Oxide (NOx) emissions using ammonia or a 32.5%-urea solution has been used for many years in a variety of stationary applications. These applications include but are not limited to coal fired power plants, gas turbines, diesel locomotives, marine engines, as well as other stationary diesel and non-diesel engine applications. Global emission limits for mobile heavy-duty diesel engines are becoming increasingly rigid. In response to this trend the diesel industry has begun testing and applying various emission control technologies to mobile applications. SCR is one such technology. Europe is the first major market to introduce SCR into the heavy-duty (class 8) as well as medium-duty (class 4-7) truck applications. The EURO4 standards (effective Oct. 2005/2006) and the EURO5 standard (effective 2008) favor SCR as the NOx reduction technology of choice in the European Union (EU).