| The large-scale usage of automobile has brought many conveniences to human daily life. In detail, the automobile could improve people’s quality of life, promote social progress, and boost economic development. Due to the advantage of high thermal efficiency, low fuel consumption, strong power, good durability and low emission of greenhouse gas, the diesel vehicles are getting popular in the automotive field. Although its lean-burn technology can help to significantly reduce the emission of carbon monoxide (CO), hydrocarbons (HC) and other pollutants, the diesel vehicles is the main nitrogen oxides (NOX) contributor in environment. NOx, one of the major environmental pollutants, combining with SOX and particulate matter has caused the continual emergence of fog and haze. Therefore, the removal of NOx has become current problem. Now, more and more restrictive legislations for diesel exhaust emissions promote the development and application of the exhaust after-treatment techniques, meanwhile, selective catalytic reduction (SCR) with reductants (such as NH3) is considered as a leading NOx emission control method. Catalyst is the key factor of SCR technology. High oxygen content and the presence of water vapor-in the diesel exhausts contribute to the low catalytic activity of the conventional three-way catalyst that can remove carbon monoxide, hydrocarbons and nitrogen oxides effectively at the same time. In addition, the catalyst used for the diesel vehicle should meet the characteristics of good thermal stability, low ignition temperature, good performance of poisoning resistance, high mechanical strength, suitable shape and so on.Based on targets above, we selected the monolithic catalyst, which was prepared by in-situ synthesis method. The cordierite was used as the carrier, and combined firmly with the active metal based molecular sieve. The metal-containing molecular sieve has suitable pore structure and large specific surface area, appropriate acidic, excellent thermal stability and hydrothermal stability. By taking these advantages, the research on the removal of NOx from diesel exhaust was carried out. In this paper, Cu-SAPO-34/cordierite was successfully prepared by one step hydrothermal synthesis method. At the same time, in order to obtain small Cu-SAPO-34grains, the ultrasonic method and composite template synthesis method were used. Recent research results showed that Cu-SSZ-13molecular sieves exhibit more excellent de-NOx activity and anti-aging property than the other molecular sieves. The Cu-SSZ-13/cordierite monolith catalyst was also prepared by in-situ hydrothermal synthesis method, and the copper amine complex as the new template. The surface morphology, crystal structure, and loading amount of different samples were analyzed, and the NOx-SCR activity of the fresh and aged samples was investigated. Moreover, with the purpose of exploring how the aging process affects the physical and chemical properties of the catalyst, and further impairing their catalytic activity, Cu-SSZ-13/cordierite of different aging time were characterized by XRD, SEM, ICP and N2adsorption-desorption. The NOx-SCR activity over Cu-SSZ-13/cordierite monolithic catalyst under the term of high space velocity was investigated, and the effect of height to diameter ratio on catalytic activity was analyzed. After collecting and analyzing the experimental data, the following conclusions are drew:(1) During the process of Cu-SAPO-34/cordierite monolith catalyst in situ synthesis, the use of composite template (TEAOH-Morpholine) and ultrasonic irradiation could significantly reduce the size of SAPO-34crystal grain, and improve the purity and relative crystallinity of Cu-SAPO-34molecular sieve on the surface of cordierite. At the same time, the ultrasonic irradiation could effectively enhance the NH3-SCR activity as well as the anti-aging performance. However, the addition of tetraethylammonium hydroxide during the preparation of Cu-SAPO-34/cordierite can reduce the Cu-SAPO-34loading amount, which can cause that the NH3-SCR activity can not be significantly improved.(2) Compared with Cu-SAPO-34/cordierite, Cu-SSZ-13/cordierite monolithic catalyst has higher specific surface area and the copper content as well as the higher de-NOx at the higher space velocity. When the space velocity was36,000h-1, the highest NOx conversion rate reached98.6%, and the NOX conversion rate could reach over90%in the active temperature window range of300-600℃on the Cu-SSZ-13/cordierite. However, within a narrow temperature range on Cu-SAPO-34/cordierite under the same condition, the NOx conversion rate remains only80%.(3) Cu-SSZ-13/cordierite has a good anti-aging property. After the aging treatment for50h, Cu-SSZ-13/cordierite monolith catalyst still retained a certain degree of catalytic activity. The NOx conversion rate could reach over70%between360and520℃, and the maximum NOx conversion rate was81.1%.(4) The high ratio of height to diameter of Cu-SSZ-13/cordierite monolith catalyst can effectively improve the catalytic activity. When the reaction space velocity was72,000h-1, and the ratio of height to diameter is8:6, the highest NOX conversion can increase from95%to99%, and NOx conversion rate could reach over90%between300to640℃. |
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