Cu-SAPO-18催化剂氨选择性催化还原NO_(x)钾中毒机理的研究

Potassium Poisoning Mechanism of Cu-SAPO-18 Catalyst for Selective Catalytic Reduction of NO_(x) by Ammonia

研究了不同水热老化温度对钾(K)中毒0.4K-Cu-SAPO-18样品的结构及其NH_(3)-SCR(NH_(3)作为还原剂的选择性还原技术)催化活性的影响.结果表明,K中毒对样品结构影响较小,但明显降低了其NH_(3)-SCR性能,在350℃时,K中毒样品0.4K-Cu-SAPO-18的NO转化率为65.88%,明显低于未中毒Cu-SAPO-18样品的90.85%.水热老化温度明显影响催化剂的结构,减少了活性位点,降低了表面酸性.随着水热老化温度升高,催化剂的AEI结构被破坏,活性物种数量降低,催化活性明显下降.氢气程序升温还原(H_(2)-TPR)结果表明,孤立的Cu^(2+)和Cu^(+)的总量分别从未中毒Cu-SAPO-18样品的66.61和1.32μmol/g变化到K中毒0.4K-Cu-SAPO-18样品的39.52和101.96μmol/g,表明K中毒样品中孤立Cu^(2+)容易转化为Cu2O.K中毒后,样品的弱酸、中强酸、强酸性位点的数量降低,分别从未中毒Cu-SAPO-18样品的0.201,0.103和0.302 mmol/g降低到中毒0.4K-Cu-SAPO-18样品的0.102,0.086和0.071 mmol/g.氨气程序升温脱附(NH_(3)-TPD)和原位红外结果表明,K竞争性地取代了催化剂中孤立的Cu^(2+)和H+,使K中毒0.4K-Cu-SAPO-18样品的活性位和酸性位减少,导致催化活性下降.在低温NH_(3)-SCR反应中,K中毒和未中毒样品均以Eley-Rideal(E-R)和Langmuir-Hinshelwood(L-H)机理进行,而L-H机理占主导地位,但K中毒样品的反应速率明显降低.

The effects of different hydrothermal aging temperatures on the structure and catalytic activity of NH_(3)-SCR of K poisoned 0.4K-Cu-SAPO-18 samples were studied.The results showed that K poisoning had little effect on the structure of the samples,but the NH_(3)-SCR performance was significantly reduced.At 350℃,the NO conversion rate of 0.4K-Cu-SAPO-18 was 65.88%,which was significantly lower than 90.85%of the unpoisoned Cu-SAPO-18 sample.The hydrothermal aging temperature obviously affected the structure of the catalyst,reducing active sites and surface acidity.As the hydrothermal aging temperature increases,the AEI structure of the catalyst was destroyed,the active species decreased,and the catalytic activity decreased significantly.H_(2)-TPR results showed that the total amount of isolated Cu^(2+)and Cu^(+)varied from 66.61 and 1.32μmol/g for unpoisoned Cu-SAPO-18 samples to 39.52 and 101.96μmol/g for K poisoned 0.4K-Cu-SAPO-18 samples,respectively,indicating that isolated Cu^(2+)was easily converted to Cu2O in K poisoned samples.After K poisoning,the number of weak acid sites,medium strong acid sites and strong acid sites decreased,from 0.201,0.103 and 0.302 mmol/g for unpoisoned Cu-SAPO-18 sample to 0.102,0.086 and 0.071 mmol/g for poisoned 0.4K-Cu-SAPO-18 sample,respectively.The results of NH_(3)-TPD and in situ IR showed that K competitively replaced isolated Cu^(2+)and H+in the catalyst[K^(+)+Si-O(Cu^(2+))-Al→Si-O(K^(+))-Al+Cu^(2+),K^(+)+Si-O(H+)-Al→Si-O(K^(+))-Al+H+],and decreased the active and acidic sites of 0.4K-Cu-SAPO-18 sample,which resulted in the decrease of its catalytic activity.In the low temperature NH_(3)-SCR reaction,Elye-rideal(E-R)and Langmuir-Hinshelwood(L-H)mechanisms were performed for both K poisoned and unpoisoned samples,and the Langmuir-Hinshelwood mechanism was dominant.However,the reaction rate of K poisoning samples decreased significantly.