Performance of NOx reduction catalysts with simulated dimethyl ether diesel engine exhaust gas

Characteristics of dimethyl ether oxidation and formaldehyde formation with NOX reduction catalysts were investigated in comparison with noble metal catalysts. The catalysts used in this research were Co and Sri as NOX catalysts and Pt, Pd, Rh as noble metal catalysts. Moreover, all the catalysts were loaded with gamma alumina (gamma-Al2O3). In addition, a pure gamma-Al2O3 catalyst was also used. Laboratory experiments were conducted by using the above catalysts in the presence of oxygen-rich simulated dimethyl ether engine exhaust gas. The catalyst temperature and the concentration of NO in the simulated exhaust gas were selected as experimental parameters. The experimental results showed that low-temperature dimethyl ether oxidation was possible with Pt, Pd and Rh catalysts, whereas higher-temperature dimethyl ether oxidation was observed with Co, Sri and pure gamma-Al2O3 catalysts. A large amount of formaldehyde was formed during the use of NOX reduction catalysts over a certain temperature range. However, the noble metal catalysts did not show any formation of formaldehyde. The effect of NO on dimethyl ether oxidation and formaldehyde formation with NOX reduction catalysts was significant. The dimethyl ether oxidation ratio became lower and the amount of formaldehyde formation increased with increase in NO in the simulated exhaust gas.