Basic Research On Simultaneous Catalytic Removal Of Diesel PM And NO_x Over Mixed Metal Oxides

Gasoline engine and diesel engine are two primary kinds of engines used in vehicles. The high efficiency, economy and durability of diesel engines have resulted in widely first choice for automobiles in recent years. However, the pollutants emitted by diesel engines have caused severe environmental and human health problems. The high PM and NO_x emissions slow down the development of diesel engines. So the emissions control on diesel engines has been an important research topic in energy and environmental area.Nitrogen oxides (NO_x) and particulate matters (PM) are the main harmful substances. PM and NO_x are generated by the different mechanisms. The simple use of the control techniques in engine technology is not enough to reduce PM and NO_x at the same time. The after-treatment technologies for reducing the emissions of both harmful substances should be developed.Basic research on simultaneous catalytic removal of diesel PM and NO_x over mixed metal oxides was investigated in this paper. Diesel emissions condition was simulated by TPR (Temperature Programmed Reaction) technology with carbon black as substitute of PM. Using mixed metal oxides as catalyst, the simultaneous catalytic removal of NO_x and carbon black (C) were realized via their redox reaction over the same catalytic bed. Several modern analyses were introduced to disclose the relationship between structure and activity of the catalysts and speculate the mechanism of the catalytic reaction. The detailed works are as follows:1. Mixture oxides which were based on rare metal oxides and loaded with potassium and transition metal have been investigated. The influences of the loading amounts have also been discussed. It was found that Nd2O3 was more active than the other rare metal oxides, and Chromium oxide was superior to the other transition metal oxides with respect to enhancing the activity of carbon black oxidation. The optimum level of Chromium was about 10 wt%, while the ignition temperature Ti was 250?C lower than pure Carbon-NO_x (C-NO_x) reaction. Mn-loading resulted in the biggest conversion efficiency of NO to N₂. The formation of complex crystalline phase in the catalyst promoted the catalytic reaction of C-NO_x.2. M(П)Al-HT (where M = Co, Mn and Cu) nanometer materials were prepared by conventional co-precipitation (the CP method) as precursors. And then two types of mixed oxides CoCuAlO (CAO) and CoMnAlO (CMAO) with the same meso-porous structure were prepared for investigating the influence of replace amounts of M on characteristic and activity. CAO and CMAO both showed effective catalytic activity on simultaneously removing C-NO_x. Their activities raised first then dropped down along with the increasing of Cu or Mn replacement. The CAO2 showed the best carbon catalytic combustion activity with Ti was 222?C. Meanwhile, CMAO1 showed the strongest catalysis on NO_x with the maximum conversion rate XN2max up to 41%. Considered of simultaneity removing carbon and NO_x, the remarkably catalytic activity of the CAO and CMAO were related to the micro-porous structure and the crystallite size of HT precursors.3. NiFe₂O₄ nano-particles with stably chemical properties and crystalline phase were synthesized by liquid catalytic phase transformation method at low temperature. The prepared nano-particles were characterized by XRD,BET and TEM. Simultaneous catalytic removal of C-NO_x over NiFe₂O₄ nano-particles was investigated and compared with NiFe₂O₄ prepared by traditional method. It turned out that NiFe₂O₄ produced by both methods could promote carbon and NO_x transferring to CO2 and N2 in tight-contact with carbon black. Liquid catalytic phase transformation method resulted in good activity for simultaneously catalytic removing carbon and NO_x in the loose-contact with carbon black. The ignition temperature of carbon black was as low as 282?C, and the XN2max was 14.1%.Compared with the traditional method, NiFe₂O₄ nano-particles produced by liquid catalytic phase transformation method showed higher catalytic activity, which was kept well after calcined in high temperature. And it decreased the ignition temperature of carbon black remarkably.4. Effects of reaction conditions including carbon content, concentrations of inlet gas such as NO and O2, total flow rate, heating rate, contact conditions and reuse of catalyst were investigated over NiFe₂O₄ samples. Carbon content and total flow rate hardly affected the ignition temperature of carbon black, while NO and O2 concentration positively affected the catalytic activity. The contact between catalyst and carbon black was a very important factor for the catalytic performance. Although the catalytic activity decreased slightly, NiFe₂O₄ catalyst still kept high activity under loose contact. And it almost kept the same after reusing. Furthermore, the reaction mechanism of simultaneous C-NO_x removal over NiFe₂O₄ was discussed based on the former researchers as well as the present experimental results.