Grantee Research Project Results
1998 Progress Report: Novel Catalysts for Lean-NOx Reduction by Methane
EPA Grant Number: R825430Title: Novel Catalysts for Lean-NOx Reduction by Methane
Investigators: Flytzani-Stephanopoulos, Maria
Institution: Tufts University
EPA Project Officer: Hahn, Intaek
Project Period: December 5, 1996 through December 4, 1999
Project Period Covered by this Report: December 5, 1997 through December 4, 1998
Project Amount: $479,533
RFA: Exploratory Research - Air Engineering (1996) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Land and Waste Management , Air , Safer Chemicals
Objective:
The objectives of this project are to prepare, evaluate, and characterize novel zeolite-based and alumina-based catalysts for the selective catalytic reduction (SCR) of NOx with methane in excess oxygen-containing exhaust gas streams. The zeolite catalysts comprise bifunctional metal ion-exchanged zeolites with one metal at high loading (primary catalyst) and a secondary metal ion at lower loading (promoter). The metal-loaded alumina catalysts are prepared by a cogelation method that results in highly dispersed metal active sites. The specific objectives of this project are to investigate the promotion mechanism and the SCR reaction kinetics over the zeolite catalysts and to transfer knowledge gained to nonzeolite systems that typically have a better hydrothermal stability than their zeolite counterparts.Progress Summary:
Measurements of the kinetics of the SCR reaction and characterization of bi-cation exchanged Ce-Ag-ZSM-5 catalysts were conducted during this period. The kinetics of the SCR reaction and the direct methane oxidation were measured in the presence and absence of water. New silver catalysts carried on high surface area alumina were prepared and found active for the SCR of NO by methane at high CH4/NO feed ratio. These catalysts have potential for application to simultaneous removal of NO and CH4 from exhaust gases.
The kinetics of the SCR reaction were measured over various catalyst compositions. The rate of NO reduction to N2 over Ce(21)-ZSM-5 was much lower than that over Ag(77)-ZSM-5 and over Ce(24)-Ag(78)-ZSM-5. The highest NO reduction rate was measured over the bi-metal Ce(24)-Ag(78)-ZSM-5. Incorporation of a small amount of cerium into Ag-ZSM-5 promoted the activity of the latter for the SCR reaction. The presence of cerium also significantly enhanced the CH4 selectivity of Ag-ZSM-5. In separate tests of the combustion of methane over Ce-ZSM-5, Ag-ZSM-5, and Ce-Ag-ZSM-5 catalysts with various Ce and Ag loadings, the Ce exchange level found was unimportant; however, the rates of CH4 oxidation over Ag-ZSM-5 increased linearly with Ag loading, indicating that in the Ag-ZSM-5 material all Ag sites are equally effective for CH4 combustion. For Ce-Ag-ZSM-5, the CH4 combustion rate increased sublinearly with Ag/Al. For a fixed cerium loading, the lower the silver loading, the stronger the suppression of the combustion reaction. Scanning transmission electron microscopy/energy dispersive x-ray spectroscopy (STEM/EDS) and high resolution transmission electron microscopy (HRTEM) studies showed that silver in both fresh and dry-gas-aged Ag(54)-ZSM-5 samples is highly dispersed and water vapor enhanced silver migration, even in low silver-content Ag-ZSM-5 samples. The presence of metallic silver particles on the catalyst surface was observed. Exposure to water vapor had little effect on the cerium distribution. X-ray photoelectron spectroscopy (XPS) comparison of Ce-promoted and nonpromoted Ag-ZSM-5 found a lower amount of silver on the catalyst surface in the presence of cerium. The silver-alumina catalysts prepared by cogelation were very stable and active over the temperature range 450?650?C, both in dry and wet conditions. Silver was well distributed in alumina up to 7 wt percent loading. Silver aluminate and metallic silver were found only at very high Ag loadings. STEM/EDS showed well-distributed silver in the alumina matrix for the low (1.5?7 wt percent) Ag-content samples. In situ UV-Visible diffuse reflectance spectroscopy (DRS) studies of cyclic reduction-oxidation of the catalysts showed complete redox reversibility of the silver state up to 600? C.
Future Activities:
Future research will focus on detailed in situ UV-Visible and Fourier transform infrared spectroscopy (FTIR) adsorption-desorption studies of the metal-loaded zeolites with various gas components; on the interaction of cerium and silver in temperature-programmed desorption (TPD) of NO in O2 and other gas components; and on further studies of the silver catalysts supported on other materials such as alumina.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 19 publications | 4 publications in selected types | All 4 journal articles |
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Type | Citation | ||
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Li ZJ, Flytzani-Stephanopoulos M. On the promotion of Ag-ZSM-5 by cerium for the SCR of NO by methane. Journal of Catalysis 1999;182(2):313-327. |
R825430 (1998) R825430 (Final) |
Exit Exit |
Supplemental Keywords:
selective catalytic reduction, nitrogen oxides, lean-NOx catalysts, methane, silver, cerium, ZSM-5, alumina, zeolites., RFA, Scientific Discipline, Air, Toxics, Waste, INDUSTRY, Ecology, Environmental Chemistry, HAPS, mobile sources, Industrial Processes, tropospheric ozone, Incineration/Combustion, Engineering, Chemistry, & Physics, Nitrogen Oxides, Nox, nitrous oxide, urban air, hydrocarbon, industrial waste, mass spectrometry, emission control technologies, emissions measurement, air pollution control, combustion emissions, Ammonia, electric utilities, emission controls, catalyst formulations, smog, methane, combustion technology, industrial boilers, methane , combustion, catalytic combustion, incineration, urban air , atmospheric deposition, acid rainProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.