Catalytic Abatement of Methane Emission from CNG Vehicles: An Overview

Compressed natural gas (CNG) is a substitution of alternative fuel for automotive application with significant environmental advantages as it is the only fuel cheaper than gasoline or diesel, comparatively lower air pollution emissions, lesser CO2 emissions. However, emission of methane is 40% more in CNG fuelled engines compared to gasoline and diesel. With the exponential growth in CNG fuelled vehicles, CH4 concentrations have reached an alarming level in the environment. It affects human health and climate change as the Global Warming Potential (GWP) of methane is 21 times more than CO2 which means that CH4 will cause 21 times as much warming as an equivalent mass of CO2. Stringent regulations have been adopted to curb the menace of vehicular pollution. In order to meet the stringent regulations Catalytic convertor using noble metals proved to a boon in vehicular industry. Noble metals are highly active for removal of methane as a pollutant. However, their expensiveness, deterioration with time can generate even more toxic volatile pollutants. So, researchers have tried to substitute the noble metals with transition base metals. Further, low cost, easy availability and advance synthesis methods of catalyst preparation advocates for the use of base metals in an auto exhaust purification catalysts. Ample literature has been accumulated which constitutes of review articles, research papers, PhD thesis, proceedings etc. on methane oxidation, but still there is a gap in literature for a review article which directs the methane oxidation with CNG exhaust emissions. Therefore in order to fill this gap present review updates and evaluates the progress of various catalysts for purification of CNG exhaust emissions. This paper reveals a brief discussion on CNG as an alternative fuel, various catalysts, operating parameters reported in the literature.