Catalytic reduction of nitric oxide by solid carbonaceous material under lean condition

Author

Shan Xiao, New Jersey Institute of Technology

Document Type

Dissertation

Date of Award

Summer 8-31-2002

Degree Name

Doctor of Philosophy in Chemistry - (Ph.D.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Robert Pfeffer

Second Advisor

Henry Shaw

Third Advisor

John G. Stevens

Fourth Advisor

Barbara B. Kebbekus

Fifth Advisor

Daniel Watts

Sixth Advisor

Laurent Simon

Abstract

The reactions of O₂, NO_x and soot from Diesel exhaust over Cu containing catalysts can significantly reduce soot and NO_x 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 NO_x 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 NO_x 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 NO_x + O₂ and removed as CO₂, while the NO_x 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.

Recommended Citation

Xiao, Shan, "Catalytic reduction of nitric oxide by solid carbonaceous material under lean condition" (2002). Dissertations. 550.
https://digitalcommons.njit.edu/dissertations/550