Reduction of Non-CO2Greenhouse Gas Emissions by Catalytic Processes

Abstract

Catalysis and related technologies and processes play an important role in reducing greenhouse gases (GHGs) emissions and in mitigation of the related climate change effects. After shortly introducing catalysis and the general aspects of catalytic technologies for GHG abatement, the state of the art in the reduction of anthropogenic emissions of non-CO2 GHGs (N2O, CH4, fluorocarbons) is discussed. Although developments in this area are still possible in terms of catalysts, catalytic technologies, and field of application, this area fits within the general one of established and mature technologies. Catalytic technologies operate mainly as downstream cleaning technologies in stationary or mobile source emissions, by converting the non-CO2 GHGs to not-or less-harmfully chemicals: (i) N2 in the case of N2O; (ii) CO2 for methane, thus significantly reducing, but not eliminating GHG impact, and (iii) chemicals without the strong C–F bonds present in fluorocarbons. For N2O, when large concentrations are present, its reuse is also possible. The catalytic combustion for controlling methane emissions yields economic benefits, due to the usually low concentration of methane in its emissions and avoids the formation of by-products in traces like formaldehyde, which may be more harmful than methane itself. Different relevant cases are discussed, particularly control of confined fugitive methane emissions (mines, waste treatment processes, natural gas processing) and elimination of unconverted methane in natural gas-fueled cars. The case of controlling unconfined methane emissions in also shortly discussed with the case of cattle emissions and the possibilities of methane capture from the air. The catalysts, their mechanism of action, and reactor options (regenerative catalytic combustion, reverse flow catalytic combustion, and catalytic combustion using a rotating concentrator) are discussed. The catalytic control of N2O emissions shows different specificities because different types of emission sources are present. The catalytic abatement or reuse of N2O from industrial emissions (particularly adipic and nitric acid production), the treatment of emissions from power plants or waste combustion, the alternatives of catalytic decomposition or reduction, and the role of the other gas components (O2, NOx, SOx) are discussed. In the case of the catalytic conversion of fluorocarbons (F-gases), catalysis plays a role in developing new paths to produce less-harmfully chemicals, where the strong C–F bond is substituted by weaker bonds. There are also some studies on the catalytic conversion of fluorocarbons to inert chemicals.