NOx Reduction with the HC-SCR System over Cu/Zeolite Based Catalysts 2015-01-2012

Diesel engine is one the effective solutions for reducing CO₂ and recognized as a leading candidate for mitigating global warming. To comply with increasingly stringent emission standards, all diesel engines require some sort of NOx control systems such as selective catalytic reduction (SCR) systems. The SCR catalyst for reducing NOx from diesel engines is classified into two groups, urea-SCR and HC-SCR catalyst, respectively. Although the urea-SCR catalyst is widely recognized as promising de-NOx technology in respect to the NOx conversion efficiency, it have some outstanding issues such as ammonia slip, urea injection, storage space, freezing and some infrastructures for supplying urea water solutions. In an attempt to overcome the inherent shortcoming of existing urea-SCR catalyst, hydrocarbons have been considered as alternative reducing agents for SCR process, instead of NH₃. SCR of NOx with hydrocarbons (HC-SCR) is an attractive way for NOx abatement under lean burn conditions, i.e. in an oxygen rich atmosphere, especially when the diesel exhaust is used as reducing agents. In this system, high NOx conversion efficiency is required over wide temperature range and exhaust flow rate. This study focuses on the HC-SCR system to evaluate the de-NOx performance with a newly developed catalytic reactor in steady and transient conditions, respectively. The performance of HC-SCR catalysts, Cu/ZSM-5 and Cu/β-zeolite prepared by Cu ion-exchange of the parent zeolites, was contrasted and compared under a variety of operating conditions using a laboratory scale test bench. The catalytic reactor has an advantage of evaluating the NOx conversion for all after-treatment devices at both steady and transient conditions. In this study 4 kinds of Cu/zeolite catalysts with a volume of 8 cc were evaluated with the synthetic gas supply module and 25,000 and 50,000 h⁻¹ of GHSV (Gas Hourly Space Velocity). The reducing agent, n-C₄H₁₀, was injected from a gas injector equipped upstream of a catalytic reactor.