Removal of methane from compressed natural gas fueled vehicle exhaust

Abstract

The objective of this study is to investigate the modes of methane (CH$ removal from simulated compressed natural gas (CNG) fueled vehicle exhaust under net oxidizing, net reducing, and stoichiometric conditions. Model reaction studies were conducted. The results suggest that the oxidation of methane with oxygen contributes to the removal of methane under net oxidizing conditions. In contrast, the oxidation of methane with oxygen as well as nitric oxide contributes to ita removal under net reducing conditions. The steam reforming reaction does not eignificantly contribute to the removal of methane. The methane conversions under net reducing conditiona are higher than those observed under net oxidizing conditions. The study shows that the presence of carbon monoxide in the feed gas lea& to a gradual decrease in the methane conversion with increasing redox ratio, under net oxidizing conditions. A minimum in methane conversion is observed at a redox ratio of 0.8. The higher activity for the methane-oxygen reaction resulting from a lowering in the overall oxidation state of palladium and the contribution of the methane-nitric oxide reaction toward the removal of CH4 appear to account for the higher CHI conversions observed under net reducing conditions. IntroductionNatural gas is an attractive source of fuel for vehicles. The advantagea provided by natural gas include lower fuel cost, longer engine life, lower maintenance, and reduced oil consumption. Methane (CHJ is the major constituent of natural gas. The development of catalysts for oxidizing the unburnt methane in the exhaust stream of natural gas fueled vehiclea is of importance. Several inveatigators have reported studies on noble metal and base metal catalysts

Pt-Rh/CeO2-Al2O3 for Controlling Emissions from Natural Gas Engines: Three-Way Catalytic Activity at Low Temperatures and Effects of SO2 Aging

“…Subramanian and coworkers extensively investigated model reactions (CH 4 -NO-CO-H 2 -O 2 , CH 4 -NO-CO-O 2 , CH 4 -O 2 , CH 4 -NO, etc.) over 1 % Pd/Al 2 O 3 with different feedstream compositions, from reducing to stoichiometric to oxidizing atmospheres [16]. However, the temperature examined in their study was limited to 550°C, and activity at lower temperatures was not examined.…”

The effect of sodium on the Pd-catalyzed reduction of NO by methane

“…Subramanian et al [17] reported high conversion efficiencies for Pd-based catalysts, and recent systematic studies of silica or alumina supported Pd, Pt and Rh catalysts have been reported by Burch et al [18,19]. Measurements were made both in the absence and in the presence of oxygen.…”

PdO x /Pd at Work in a Model Three-Way Catalyst for Methane Abatement Monitored by Operando XANES

“…The effect of the addition of ceria is to stabilize PdO [11] thus avoiding large activity losses after exposure to high temperatures, especially under oscillating red-ox conditions. Additionally, there is also indication that the complex chemistry involved in the operation of TWC maybe different between natural gas and gasoline engines and other reactions (than CH 4 oxidation) alone can contribute to CH 4 removal from the exhaust [12,13]. Therefore, it is of interest to investigate CH 4 oxidation over Pd-based catalysts under simulated exhaust of stoichiometric natural gas engines [12][13][14][15][16][17][18].…”