Achieving cleaner air throughout the world requires reducing diesel emissions. Therefore, after-treatment system without using a urea solution (DEF) called DPR-II has been developed in-house. It uses diesel fuel as a reducing agent (HC-SCR) to reduce NOx emission in diesel exhaust. The development of the fundamental technology could result in high NOx reduction performance at low to high temperature ranges, to meet the Japan 2016 emissions regulation. DPR-II is composed of two mufflers. The first muffler consists of a front diesel oxidation catalyst (F-DOC) and a catalyzed filter (Filter). The F-DOC uses a Pt/Pd type HC-SCR catalyst to achieve NOx reduction performance at low temperatures. In contrast, the second muffler is comprised of HC-SCR catalysts and a rear diesel oxidation catalyst (R-DOC). Ag type HC-SCR catalyst exhibit NOx reduction performance at high temperatures. Cu type NH3-SCR catalyst was added in front of the R-DOC to improve NOx reduction performance. The Pt and Pt/Pd type HC-SCR catalysts developed exhibit high NOx reduction activity around temperatures of 150 to 250 deg. C. However, it exhibits lower activity at temperatures higher than 250 deg. C because the HC species are all oxidized. Therefore new catalysts that have slow HC oxidation as the temperature rises are required. It is also necessary that HC species still remain on the catalyst at high temperatures. Based on these requirements, Ag type catalyst was found to have a high NOx reduction performance. It was found that with the Ag type catalyst, NH3 formed at the same time as the NOx reduction reaction. To use NH3 as a reducing agent, a Cu type catalyst was adopted downstream of the Ag type catalyst. Based on these results, it was confirmed that the DPR-II could reduce by 50 to 60 % in NOx emission over regulation modes on engine bench testing.