CATALYTIC NOx REDUCTION BY HYDROCARBON IN AN OXIDIZING ATMOSPHERE ON OXIDE-SUPPORTED CATALYSTS
Dr. Harold Kung
Department of Chemical Engineering
Northwestern University, Evanston, IL
Tuesday, February 22, 2000 2:00 pm
Ben Bandy Conference Center
Center for Applied Energy Research
NOx is an atmospheric pollutant and its emission is strictly regulated. One option to remove NOx is to reduce it to N2 using hydrocarbons. This could have applications to treat exhaust from a fossil-fuel power plant, diesel engine, or lean-burn gasoline engine. A typical exhaust from these sources contains fifty to one hundred times higher concentration of oxygen than NOx. Therefore, an effective catalyst for this reaction must be able to promote the reaction between hydrocarbon and NO with respect to the combustion reaction of hydrocarbon.
Transition metal ion-exchanged ZSM-5 catalysts have been extensively studied for this lean NOx removal reaction. However, the hydrothermal instability of these catalysts poses problems for their commercial applications. Alumina-supported catalysts can be potentially much more stable. Early results of screening tests, however, showed that oxide-supported catalysts were inferior to ZSM-5 supported ones. Recently, it has been shown that oxide-supported catalysts can be made quite effective for NOx reduction. For alumina-supported cobalt oxide, Ag, and Au, the effectiveness of the catalysts depends on the dispersion of the active phase, which affects the redox properties of these phases. The dispersion is not important for supported SnO2 catalysts. In the latter case, there is strong evidence that the alumina support participates directly in the formation of N2.