Catalytic reduction of nitric oxide by solid carbonaceous material under lean condition
Department of Chemical Engineering, Chemistry and Environmental Science
Doctor of Philosophy
Stevens, John G.
Kebbekus, Barbara B.
Nitric Oxide (NO) reduction
The reactions of O2, NOx and soot from Diesel exhaust over Cu containing catalysts can significantly reduce soot and NOx emissions while producing N2 and CO2. The author has evaluated the performance of Cu ion exchanged ZSM-5 and Cu adsorbed on Granulated Activated Carbon (Cu-GAC) using GAC as a surrogate for soot in a packed bed reactor. CO, formed primarily by the oxidation of GAC with O2, appears to be a stable intermediate in the reduction of NO. With experimental parameters chosen to simulate Diesel exhaust conditions, Cu-GAC is much more effective than GAC mixed with Cu-ZSM-5, converting six times more NOx to N2 at 500°C at the representative gas hourly space velocity of 50,000. Both catalysts are poisoned by H2O and SO2. A mechanism is presented that is consistent with the experimental results.
Catalytic reduction of nitric oxide (NO) with solid carbonaceous materials to N2 was also investigated over palladium based catalysts. Catalysts consisting of 4 wt.% Palladium on CeO2, A1203 and TiO2, prepared by the impregnation method, were evaluated as lean NOx control catalysts with granular activated carbon (GAC) as the reductant. The performance of these catalysts was measured with a gas containing 590 ppm NO, 10% 02, and the balance He at gaseous hourly volumetric space velocities of 50,000 and 80,000 and at temperatures in the range of 200-600°C. All catalysts exhibited high activity for NO reduction with GAC. The PdO/Al2O3 showed the highest activity among the tested catalysts with maximum conversion over 80% at GHSV of 50,000. The PdO/CeO2 had the lowest light-off temperature of 450°C with a maximum conversion of 80% at GHSV of 50,000.
The effects of SO2 and water on the catalysts were also investigated by including 20 ppm SO2 and 10% water into the gas feed mixture. The results indicated that the palladium catalysts outperform fresh copper exchanged ZSM-5, and are much more slowly poisoned by sulfur compounds and water while promoting NO reduction with GAC to N2.
The purpose of this study was to develop a novel catalyst that can be used in a rotating fluidized bed reactor (RFBR) containing an attrition resistant high surface area catalytic powder to filter soot and promote the reaction between soot and NO at elevated temperatures and at high space velocities. Consequently, this system is self-cleaning i.e., the soot layer is oxidized by NOx + O2 and removed as CO2, while the NOx is removed as N2. The RFBR provides good contact between the catalyst and reactants, and a lower relative pressure drop compared to particulate traps and other existing particulate control devices.
njit-etd2002-083 (173 pages ~ 10,280 KB pdf)
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Created August 13, 2003