Development of Clean Diesel NOx After-Treatment System with Sulfur Trap Catalyst
Hiromasa Nishioka, Toyota Motor Corporation
Diesel engine with good fuel economy is an effective means of CO2 reduction. So, it is expected the spread of clean diesel cars against global warming. Diesel particulate and NOx reduction system (DPNR) which has been developed in 2003 for first introduction in European and Japanese market. It shows high purification performance which has a potential for a more stringent regulations in the future. However, it decline due to the poisoning by sulfur components in exhaust gas that derive from fuel and lubricant. So, we developed a new DPNR with sulfur-trap catalyst that could trap sulfur components in exhaust gases, and the high purification performance could be achieved with small amount of platinum group metal thanks to low sulfur poisoning and thermal deterioration. However, we needed the exchange of the sulfur trap catalyst every 40,000 km because of a limited sulfur trap capacity. In this paper, we tried to investigate sulfur trap mechanism, and it was found that the potassium sulfate on the surface of the sulfur-trap catalyst work to prevent diffusion of gases into the catalyst surface pore. So, we try to adsorb sulfur without vitriolization by using a component which has oxygen. Furthermore, we try to transport the sulfur which is adsorbed on the surface of a catalyst to the sulfur trap material by increasing temperature. As a result, it can be achieved to increase a sulfur trap capacity. A high NOx conversion efficiency of 80% was obtained after 80,000 km mileage accumulation with new concept sulfur trap catalysts, which shows the over 50 % lower emission level of Japanese Post Long Term emission regulation.