Catalytic abatement of methane emissions from natural gas vehicles

Gianni  Caravaggio, Natura Resources Canada

Authors: Gianni Caravaggio*, Lioudmila Nossova, Ray Burich and Nicola Maffei

Natural Resources Canada, CanmetENERGY, Ottawa, ON, K1A 1M1, Canada

*Corresponding author: Gianni.Caravaggio@NRCan-RNCan.gc.ca, 613-992-8934

Natural gas (NG), has received increased interest as a fuel for the transportation sector since it is abundant and inexpensive. Lean burn natural gas engines are similar in performance to diesel engines and can be used in a wide variety of transportation applications such as light and medium duty vehicles, vocational and long haul trucks and ships. Natural gas engines offer a cleaner alternative and produce approximately 20 – 25% less greenhouse gases (GHG) on a life-cycle basis than diesel and gasoline engines due to the lower carbon content of methane. However, NG engines suffer from high levels of unburned methane in the exhaust which need to be eliminated because methane is a potent GHG (21 times GHG impact compared to CO2) and can negate the NG engine’s GHG benefit. It is therefore essential to develop efficient catalysts to completely oxidize methane at the low temperatures of NGV exhaust (in the range of 350-480°C). Pd-alumina based catalysts are known to be the most effective for oxidizing methane. In this work, methane oxidation catalysts were prepared by loading Pd and other active metals on various supports with the objective of improving the methane oxidation activity. The catalysts were tested for methane oxidation activity by temperature programmed oxidation. A Pd catalyst loaded on a commercially available doped alumina was found to be the most active catalyst among the series of catalysts prepared. The improved low-temperature performance of the novel Pd catalyst made it possible to reduce the amount of expensive noble metal without sacrificing catalytic activity. In order to study the effect of various supports on catalytic activity, catalyst characterization techniques were used including Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) under isothermal conditions. The DRIFT analysis showed smaller amounts of oxygenates species on the Pd catalyst loaded on a commercially available doped alumina compared to a Pd/alumina catalyst. This may be the result of structural defects caused by the dopant, supplying a larger amount of lattice oxygen that accelerates the oxidation of surface oxygenates and enhancing the methane oxidation catalytic activity by eliminating the surface oxygenates competing for the Pd active sites.

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