Low-template Synthesized SSZ-13 And Its Performance In NH₃-Selective Catalytic Reduction Reaction

Massive NO_Xemission will cause serious environmental problems such as acid rain,haze and photochemical smog.Under the strict Limits and Measurement Methods for Emissions from Light-Duty Vehicles（China 6）,the removal of NO_Xis urgent.NH₃-Selective Catalytic Reduction（SCR）technology is considered to be the most efficient NO_Xtreatment technology at present.The key of SCR performance lies in the preparation of catalyst.At present,the Cu modified SSZ-13 catalyst has been widely studied for its excellent performance and high thermal stability.Usually,the preparation of highly crystallized SSZ-13requires a large amount of organic template N,N,N-trimethyl-1-adamantane ammonium hydroxide（TMADa OH）.Moreover,the large amount of waste water with high concentration of alkali causes severe environmental problem.In order to solve above mentioned problems,developing a procedure of synthesizing highly crystallized SSZ-13 at low TMADa OH usage is proposed and applied to NH₃-SCR reaction.The specific contents are as follows:Firstly,SSZ-13 with Si O₂/Al₂O₃of 8,10,15 and 20 are successfully prepared under the condition of n（TMADa OH/Si O₂）=0.1 without adding alkali source and water.The Si O₂/Al₂O₃of 10 is determined as the optimal support for preparing Cu-SSZ-13 catalyst for NH₃-SCR test.Effects of n（TMADa OH/Si O₂）,crystallization time and crystallization temperature on the synthesis of SSZ-13 with Si O₂/Al₂O₃of 10 are well studied.Results show that the highly crystallized SSZ-13 could be synthesized under extremely low TMADa OH usage（n（TMADa OH/Si O₂）=0.096,crystallized at 150℃for 72 h）with excellent catalytic performance in NH₃-SCR reaction after Cu ion exchange.Secondly,futher decreasing n（TMADa OH/Si O₂）to 0.012,auxiliary templates TEAOH and DEA is necessary to maintain the crystallinity of as-synthesized SSZ-13.Effects of the amount of auxiliary template,crystallization temperature,crystallization time and two different aging methods on the product SSZ-13 under the low TMADa OH are systematically investigated.Results show that pretreatment of the mixture of silicon source,aluminum source,TMADa OH and SSZ-13 seed at 30℃for 12 h has great influence on the crystallization of SSZ-13.Highly crystalline pure SSZ-13 is prepared by applying the pretreated mixture at 150℃for 72 h.Its crystallinity is 91.5%higher than that of the product with n（TMADa OH/Si O₂）=0.012.As-prepared SSZ-13 was ion-exchange with Cu obtaining95%NO_Xconversion in the range of 250-600℃.Moreover,the NO_Xconversion in the low temperature section is 25%higher than that of the product before the optimization of synthesis conditions.