The driver for lean NOx treatment is the need to meet regulatory standards for diesel engines & gasoline direct injection spark-ignited engines that offer better fuel economy. Efforts over the last decade have focused toward finding an active lean NOx catalyst that can reduce NOx under oxidising conditions or strategies such as selective catalytic reduction (SCR), plasma-catalysis, plasma catalyst SCR & lean NOx traps with varying degrees of success. At present, it appears that SCR with urea & lean NOx traps are the leading contender technologies for commercial development. Key issues that remain to be resolved for these two technologies include by-product formation, dosing control, & durability. This review summarises material-related issues that are unique to each of these technologies, & point out improvements necessary to facilitate their deployment.
