Study Of Low-temperature Catalysts For Removing Diesel Soot Particles

Although diesel engine has a lot of advantages and powerful impetus,in this light,it has been applicated in the production practice (it was particularly used in the cars), it affected the lives of the human and brought about the serious air pollution problems. As the diesel engine exhaust is much too complex, its composition is mainly produced by CO₂ (complete combustion of fuel), water vapor (H₂O), excess O₂ and N₂, emissions usually contain CO, HC and soot particulate matter PM (Particulate Matter) and other products of incomplete combustion, and NO_x, SO₂ and other acid gases. Diesel exhaust in less than 1% of total emissions, including CO and HC content was low, only a few one-tenth of gasoline, but compared with gasoline , diesel NOx emissions is in the same order of magnitude or more, exhaust emissions of PM is 30-100 times as gasoline. the most direct and effective post-processing method of reducing the diesel soot particle pollution emissions is that soot particles are oxidized to CO₂, thermal oxidation temperature of soot particles is as high as 550 600℃, while the exhaust temperature of diesel is approximately 175 400℃,therefore making a high catalytic activity of catalysts to reduce the oxidation temperature of soot particles, so that soot particles in the filter are oxidized or removed and recycled ,which is to prevent soot particles accumulate excessively in the filter or block filters, and affect the diesel vehicle performance. Therefore, this article focuses on the removal of diesel particulate matter (PM) and making an effective post-processing technique, namely preparating an efficient catalyst to catalyze combustion of PM (or Soot) at the low-temperature.A new type of catalytic materials for purifying the automobile exhaust has been studied,nanostructured Cu_xCe_1-xO_2-σ catalysts with high surface area were prepared by coprecipitation process.A serials of CuO,MnO_x,CeO₂,Cu-Mn-O(x) and Cu-Mn-Ce-O(x) catalysts and the factors affecting their catalytic activities(such as precipitant dosage,pH value,calcinations temperature,the period of calcinations and crystal size et al) have been investigated by the author.what's more,we found the optimum experimental conditions.Its catalytic activity was tested in a fixed-bed reactor by exposing the sample to the atmosphere of simulating automobile exhaust.The main work carried out the research is as followings.First and foremost, I set up the testing system for automobile exhaust purification. Secondly,a series of different samples were prepared by Coprecipitation Process. I initially investigated the effect of different preparing process on the activities of the catalysts by comparing the activity of different samples.Then we studied that hot nitric acid solution and the impregnation decoration methods could affect the catalytic activity of samples.the research showed that the thermal decomposition temperature affected morphology,partical size and distribution of the catalyst samples. The loading of non-cryatal CuO on the CeO₂ supports was different and it was the highest on the CeO₂ prepared by thermal decomposition at 500℃,and the corresponding CuO/CeO₂ catalysts exhibited higher activity for PM &CO oxidation than those with CeO₂ prepared by thermal decomposition at 400 and 700℃.A part of non-crystal CuO in CuO/CeO₂ catalysts entered CeO₂ lattice and the others dispersed over the CeO₂ surface. When the calcination temperature was lower than 600℃,it had little effect on the catalytic activity.However,high calcination temperature (e.g.800℃) resulted in a significant impact on the catalytic activity because of CeO₂ crystal growth and CuO aggregation. Preparation of catalyst samples by a large number of studies, the optimal experimental conditions: precipitant selected NaOH, pH value of 10±0.5 or so, the roasting time of 4h, calcination temperature was 500℃.Finally, the samples were characterized by X-ray diffraction, BET nitrogen adsorption, FT-IR spectroscopy,Raman spectroscopy and TPO technologies. such as joint research with the characterization results show that:use of NaOH as precipitating agent and pH = 10±0.5 in the vicinity,which can effectively prevent the catalyst grain growth, access to high surface area (more than 50m2?g-1), small grain size (average diameter of about 10nm) of the nano-CuO-CeO₂ catalysts, Cu_xCe_1-xO_2-σsolid solution was formed under the high calcination temperature. Based on the decrease of grain size, surface area increases and the Cu_xCe_1-xO_2-σ solid solution formation; when the Cu / Ce ratio is 1:1, leading the ignition temperature (Tig) of the diesel soot particals lower, and generating a small amount of CO after the oxidation , most of the generated CO₂, in this light,which confirmed that it had the best catalytic activity. According to the convertion of the PM and CO oxidation,the lowest ignition temperature (Tig)of the Cu/Ce=1:1 sample is 281℃,which perfectly affirmed that Cu_xCe_1-xO_2-σ solid were much too super catalysts. The maximum formation amount of CO is 392ppm,nearly completely produce CO₂.The result shows that the catalyst exhibits high catalytic activity at low temperature and has good redox property.In summary, from the XRD, Raman and FT-IR characterization results known, there are three forms of CuO species in the CuO-CeO₂ catalysts, which were highly dispersed catalyst CuO, crystal CuO, CeO₂ lattice within Cu²⁺ and Cu⁺. Low-temperature catalytic combustion of PM, its essence is the analysis of CO and the active center of Cu0, Cu +, Cu²⁺ in the catalyst, and other redox species of CuO, Cu₂O. By the temperature programmed oxidation (TPO) test results show that the largest contribution of the activity for PM and CO oxidation is ascribed to CuO, Cu+ species highly dispersed on the catalyst surface ,followed to CuO crystal phase, and the weakest contribution is attributed to Cu2+ activity entered into the CeO₂ lattice.