Novel Catalysts for Lean-NOx Reduction by MethaneEPA Grant Number: R825430
Title: Novel Catalysts for Lean-NOx Reduction by Methane
Investigators: Flytzani-Stephanopoulos, Maria
Institution: Tufts University
EPA Project Officer: Shapiro, Paul
Project Period: December 5, 1996 through December 4, 1999
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 , Engineering and Environmental Chemistry
The efficient removal of nitrogen oxides, NOx, which are known precursors of acid rain and urban smog, from the exhaust gas of both stationary and mobile combustion sources continues to be a challenge. While fuel switch and more so combustion modifications are used to suppress NOx emissions, it is recognized that removal of NOx to very low levels should also involve the application of catalytic post-combustion emissions control technology. For electric and gas utilities and industrial boilers, with oxygen-rich exhaust gas, the only commercial lean NOx reduction technology is presently the selective catalytic reduction (SCRO of NOx by ammonia, an expensive and complex process. More attractive processes involving injection of hydrocarbon reductants are under intensive research and development at the present time. Among these, the SCR of NO by methane is particularly attractive because natural gas is best integrated with the power plant operation. A powerful NOx reduction catalyst can also relax the steam addition requirement and CO emission problem from gas turbines. Since some unconverted methane is present in the exhaust gas stream, the control system may be simplified to one requiring no injection of reductants and associated controls. A simple catalytic converter is, thus, envisioned for application to gas turbines, compressed natural gas vehicles, etc.
Due to the refractory nature of methane, the SCR of NOx by methane is hard to accomplish. Only a few catalyst systems have been identified to date. These catalysts typically comprise a well dispersed metal in a zeolite host matrix. Generally, the catalyst activity drops in the presence of water vapor and is at least an order of magnitude lower than that of commercial ammonia-SCR catalysts. This proposal involves the development and testing of promoter-modified, metal ion-exchanged zeolites, which in preliminary work in this lab have shown promising activity for the SCR of NO by methane at exhaust gas temperatures in the range of 400-650?C. Detailed evaluation of the effects of catalyst composition and preparation conditions on catalyst activity is planned though kinetic and structural measurements and parametric activity studies. Microreactor testing of catalysts, gas uptake experiments in a TGA, temperature programmed desorption of NO, O2, and CH4 coupled with mass spectrometry, TGA/IR experiments, and detailed surface and bulk analyses of solid catalysts will be used in this work. The knowledge gained from the study of metal ion interactions in the zeolite structure will be transferred to open oxide supports. This will both provide mechanistic insight into the methane-SCR process as well as lead to the development of less expensive, practical lean-NOx reduction catalyst.