A review on exhaust gas after-treatment of lean-burn natural gas engines – From fundamentals to application

Modern lean-operated internal combustion engines running on natural gas, biogas or methane produced from wind or solar energy are highly fuel-efficient and can greatly contribute to securing energy supply, e.g. by mitigating fluctuations in the power grid. Although only comparably low emission levels form during combustion, a highly optimized emission control system is required that converts pollutants over a wide range of operation conditions. In this context, this review article pinpoints the main challenges during methane and formaldehyde oxidation as well as selective catalytic reduction of nitric oxides. The impact of catalyst formulation and operation conditions on catalytic activity and selectivity as well as the combination of several technologies for emission abatement is critically discussed. Additionally, recent experimental and theory-based progress and developments are assessed, allowing coverage of all time and length scales relevant in emission control, i.e. ranging from mechanistic and fundamental insights including atomic-level phenomena to full-scale applications.