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. [Display omitted] •Low-temperature methane oxidation as main challenge in NGE emission control.•Strong mass transfer limitation of catalytic formaldehyde oxidation.•Undesired side reaction of formaldehyde and NH3 reduces efficiency of SCR of NOx.•Formation of secondary emissions like N2O or HCN and their abatement is discussed.•Chances and challenges of different catalyst technology combinations are presented.