With growing concern about air quality and increase of city population is renewed interest in transportation sector. The challenge for governments is to find and develop cost-effective ways to improve urban air quality without scarifying economy. Natural gas as vehicle fuel can reduce compared to conventional Diesel technology, particulate matter by as much as 99%, nitrous oxides (NOx) by as much as 85%, and carbon monoxide (CO) by more than 90%. Relative to gasoline, the global warming impact (GWI) for dedicated natural gas vehicles (NGVs) is generally more than 20 % lower. When non-regulated emissions are included on a well-to-wheel basis, NGVs still show advantages over gasoline and Diesel vehicles.
Nowadays, there are more than 4.7 million NGVs in operation all around the world. It seems that the catalysts used in NGVs are close to Three-Way Catalysts (TWC) typically used for gasoline engines. However, there are very few studies about the impact of catalysis for NGVs. This work deals with a comparative study of natural gas vehicles commercial catalysts in order to evaluate their efficiency to reduce emissions of CO, NOx and CH4. All tested catalysts are efficient in the CO and NOx treatment. The CO light off temperature varies from 75 to 145°C. The NOx reduction depends on the reductants available in the exhaust gases (H2 at low temperature, CO at medium temperature and CH4 at high temperature). However, at low temperature, the selectivity on N2 is lower than 20%. Finally, the major problem is the methane treatment. Only one catalyst leads to a Tlight off, CH4 around 315°C. For the other catalysts, Tlight off, CH4 were found around 375-400°C.