The Optimization On Insitu Synthesis Conditions Of Cu-SSZ-13Denitration Catalyst

As the global petroleum resources shorten increasingly, the greenhouseeffect aggravates, diesel engine has been widely used in road and transportfacility because of its high efficiency and durability. The worldwide trend touse diesel engine into vehicles is becoming more and more obvious. In face ofincreasingly stringent emission regulations, NOxremoval of diesel exhaustemissions becomes one of the most prominent difficulties in the field ofexhaust catalytic purification at home and abroad. Due to its characteristics ofhigh efficiency and low cost, ammonia selective catalytic reductiontechnology (NH3-SCR) has currently become the main source of mobiledenitration technology. The core problem is to develop highly efficient, stableand environmental friendly SCR catalysts. Too much emphasis has beenplaced on zeolite or molecular sieve as denitration catalyst researched by thescholars in the domestic and overseas, especially SSZ-13microporousmolecular sieve shows a broad application prospect in many areas and isbecoming a hot spot in recent years on account of its unique physical and chemical properties. Therefore in our topic, research and discussion wereconducted about the effect of the parameters during the process of Cu-SSZ-13catalysts preparation by in-situ hydrothermal synthesis method, such as metalsalt types, ion modification (ion exchange with cerium nitrate or ammoniumnitrate) and the templates (Cu-TEPA and N, N, N-trimethyl-adamantylammonium hydroxide), on the catalytic activity, N2selectivityand physicochemical properties of fresh and hydrothermal aging samples inexpectation that Cu-SSZ-13catalyst would obtain neat morphology structure,excellent catalytic deNOxactivity and anti-aging performance. The mainconclusions of the research are as follows:A series of Cu-SSZ-13catalyst can be successfully prepared withdifferent copper salts (Cu(NO3)2, CuCl2, CuSO4, etc.) and Cu-TEPA astemplate (crystallization for72h and ion exchange with ammonium nitrate for12h). In the process of crystallization, adsorption ability of different anions onthe template agent micelle (NO3-> Cl-> SO42-) because of hofmeister anioneffects, resulting in that Cu species distribution, Si and Al atoms in molecularsieve skeleton and different micro-structure properties of molecular sievecarrier varied for three kinds of samples before and after aging. Under theother same preparation conditions, the Cu-SSZ-13synthesized using coppernitrate (Cu(NO3)2) as active metal sources displayed the most outstanding NOxreduction rate before and after hydrothermal aging. The NOxconversion offresh samples and hydrothermal aging (for20h at800oC) samples could be up to90%in temperature range from180°C to700°C and240°C to600°C,respectively. The Cu-SSZ-13synthesized using Cu(NO3)2as active metalsources presents a neat cubic type, good dispersion and shape-selectivefunction.On the basis of the preparation with different copper salts as copperspecies, ammonium exchange and Ce exchange were added to investigate theeffect of the two operations on the catalytic activity and anti-aging ability.When Cu-SSZ-13samples were prepared with CuSO4as copper source anddifferent ion-exchange methods, samples exchanged for12h with NH4NO3and next with Ce(NO3)2for2h showed excellent low temperature activity,wide active temperature window, larger pore structure parameters andrelatively stable molecular sieve frame structure. Prolonging ammoniumexchange time debased low temperature activity of fresh samples andimproved anti-aging ability obviously. When Cu-SSZ-13samples wereprepared with Cu(NO3)2as copper source and different ion-exchange method,samples with ammonium exchange for12h showed outstanding NOxreduction rate,wide active temperature window and steady skeleton structurebefore and after hydrothermal aging. Under the same ion-exchange method,the performance of Cu-SSZ-13samples prepared with CuCl2as copper sourceis similar to the sample made by CuSO4. But its sample with ammoniumexchange for24h showed higher catalytic activity and good hydrothermalstability. Through the modulation of TMAda-OH dosage and its crystallizationtime, Cu-SZZ-13samples were successfully prepared by in-situ hydrothermalsynthesis method. In crystallization process, dual template agents have theeffect of the mutual promotion. When nTMAda-OH/nSi=0.15and crystallizationfor96h, the silica alumina ratio increased and uniform crystal shape kept neat.Thus the sample displayed good catalytic deNOxactivity and aging resistance(NOxconversion rate of samples crystallized for four days can reach43%at100°C).