Research Of PILCs Supported Catalysts For Selective Catalytic Reduction Of NO_x With NH₃at Low Temperature

The selective catalytic reduction of NOxwith NH₃（NH₃-SCR） as reductant atlow temperature has drawn much attraction as a promising technology to remove NOxfrom stationary sources. There is much interest in developing such a technologybecause of its low cost and industrial application demand. The key of the technologyis the catalyst. In this study, in order to develop economical catalysts with goodactivity, the MnO_x-based metal oxides has been supported over pillared interlayeredclays arosed from the economical and easy obtained clays, then the catalysts wereused for SCR of NO with NH₃at low temperature. The preparation and NH₃-SCRactiveity at low temperature of MnO_x/Ti-PILC, the promotion of its catalyticactivities （including the activie components and the pillars） were studed. The reactionkinetics and SO₂posioning mechanism have been systermaticly investigated. Besides,N2absorption/desorption, XRD, FT-IR, TG, NH₃-TPD, H₂-TPR, XPS characterisionmethods were also used to study the property-activity relationship of the catalysts.1. It was found that preparation factors of Ti-PILC（including Ti/clay, H/clay, thepillaring temperature, solvent, concentration of the clays and the thermal treatmenttemperature）, the MnO_xloadings and the cacinating temperatures all had greatinfluence on the SCR activity of MnO_x/Ti-PILC. Under the conditions of Ti/clay of15mmol/g, H/Ti of1.2,1:1weight ratio of H₂O and actone,1%clay suspention andthermal-treated at500℃, proper Ti-PILC support could be obtained for MnO_x,MnO_x/Ti-PILC with10%MnO_xloadings and cacainated at300℃exhibited superioractivity which was better than MnO_x/TiO2（P25）, even at high space velocity of65000h-1, nearly100%NO conversion cold be obtained at180℃. This catalystshowed good resistance to H₂O, however, its resistance ability to SO₂need to befurther studied.2. For the study of the active componts, different kinds of metal （M=Bi、La、Fe、Sn、W、V、Ce） has been doped to MnO_x/Ti-PILC to investigate their effect on theactivity, the results showed that both Ce and La were very helpful for the enhancement of the activity in absence of H₂O and SO₂. For the addition of Ce andLa, there was a best doped amout. the resultant Mn-CeO_x/Ti-PILC was enhanced inredox properties and surface ative absorbed O; Mn-LaO_x/Ti-PILC was also promotedin redox charactors and surface acidity concentration. These two catalysts displayedhiger activity than MnO_x/Ti-PILC, besids, the resistance to SO₂and H₂O was alsoheightened.It has been found that the preparation method of Ti-PILCs can influence the lowtemperature-SCR activity of Mn-CeO_x/Ti-PILCs, the catasyt with titania formTiOSO₄（Mn-CeO_x/Ti-PILC（S）） rewealed much higher activity compared to thoseform both Ti（OC₄H₉）₄and TiCl₄（Mn-CeO_x/Ti-PILC（O） and Mn-CeO_x/Ti-PILC（Cl））,due to its higher acidity concentration, extra-lattice TiO2, along with the large surfacearea and pore volume, all of which could be attributed to the effective pillaringprocess. Mn-CeO_x/Ti-PILC（S） could keep its high activity in presence of low amoutof SO₂（100ppm） at200℃, while deactived quickly when200ppm SO₂wasintroduced to the gas.In order to study the SO₂deactivation machanism on Mn-CeO_x/Ti-PILC, N2absorption/desorption、XRD、FT-IR、TG、NH₃-TPD、H₂-TPR methods were usedto investigeate and compare samples before/after SO₂posioned and heat-regenerated.It was assumed that the sulfates saltes deposited over the catalysts account for thedeactivation. Based on the experimental data at100℃and200℃, the kineticsexperiment was carried with the E-R and L-H mechanism, the results showed that theSCR tend to follow the L-H mechanism under the conditions in this study.3. Impacts of various pillars were also studied, the results displayed that thekinds of pillars had great influence on the activity of PILC supported MnO_xandMn-CeO_xcatalysts, Ti and Zr tend to be better for the activity than Fe and Al. On thebasis of the results, two MnO_xbased catalysts supported over PILC with mixedpillars（MnO_x/Zr-Ce-PILC and Mn-CeO_x/Ti-Zr-PILC） has been investigated. Theresults showed that the simple one-step method to introduce Zr and Ce pillars intoclays proved sucssesful to enhance the surface area and the pores, strengthen theintereaction between MnO_xand the support and improve the redox properties, thusthe activity was greatly promoted even in presence of H₂O and SO₂. For Mn-CeO_x/Ti-Zr-PILC catalysts, it could be concluded that organ-modification of theclays could contribute to better the pillaring process with Ti-Zr mixed pillars and thenenhanced the SCR activity of supported Mn-CeO_xcatalysts.