A review of solid SCR systems as an alternative for NOx reduction from diesel engines

Several NOx reduction technologies have been developed to alleviate the impact of NOx emissions on the environment and meet the more stringent upcoming emission legislation. Although UWS is the most commonly used NOx reduction technology, it has various issues listed in this article. Several alternative technologies based on solid materials as a gaseous ammonia source are developed to eradicate these issues. This article reviewed the solid SCR systems currently being developed as an alternative to UWS for deNOx applications. Furthermore, the chemistry of the various ammonia storage materials used in these systems and their potential to produce gaseous ammonia for use in SCR have been evaluated. Furthermore, the deNOx performance of ammonium salts-based and metal ammine chlorides-based solid SCR systems have been evaluated. Besides, we have discussed various numerical modeling and simulation approaches applied to develop these solid SCR systems. Due to gaseous ammonia injection solid SCR systems offer better NOx conversion efficiency compared with UWS systems, especially at low exhaust gas temperatures. The authors believe this article will be helpful for future studies in this field to further develop and establish these solid SCR systems as a viable alternative deNOx technology.