Low temperature selective catalytic reduction of NO over Pt-Zeolite using hydrogen

It has been found that platinum based zeolite catalysts are very active for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with hydrogen at low reaction temperatures, i.e. 200 C. The catalysts are active for NOx reduction in the presence of oxygen, water vapor (steam), and sulfur dioxide. It is notable that the use of hydrogen instead of ammonia as the reducing agent greatly reduces the formation of N{sub 2}O from NO over these low temperature catalysts. A testing protocol was established for testing NO reduction catalysts, and the reaction conditions utilized in this study, carried out at approximately ambient pressure, were the following (on a dry basis): NO = 400 ppm, H{sub 2} = 40000-20,000 ppm (0.4--2 vol%), O{sub 2} = 5 vol%, CO{sub 2} = 13 vol%, and N{sub 2} = balance. When water was added to the reactant mixture, it was added so that H{sub 2}O = 8 vol%. The total gas flow, expressed as gas hourly space velocity (GHSV), was 10,000 hr{sup {minus}1}, unless specified otherwise. Comparison tests were carried out using NH{sub 3} = 400 ppm in place of the H{sub 2}. Each of the gases was fed into the reactor gas manifold andmore » controlled by a separate flow meter. The NO, H{sub 2} and NH{sub 3} components were utilized as mixtures in N{sub 2}, while CO{sub 2}, and O{sub 2} were added as pure gases. When experiments were carried out in the presence of sulfur dioxide, the SO{sub 2} was added via a SO{sub 2}/N{sub 2} gas mixture to achieve the desired SO{sub 2} concentration in the reactant gas mixture. In the exit stream, NO and N{sub 2}O were determined by an infrared analyzer.« less