催化学报

催化学报 ›› 2019, Vol. 40 ›› Issue (4): 590-599.DOI: 10.1016/S1872-2067(19)63312-7

• 论文 • 上一篇    下一篇

柴油机尾气中的碱性无机污染物引起Cu-SAPO-18脱硝催化剂的化学失活

明淑君a, 庞磊b, 范驰a, 郭文a, 董亚浩a, 刘鹏a, 陈真a, 李涛a   

  1. a 华中科技大学化学与化工学院, 能量转换存储材料化学教育部重点实验室, 材料化学与服役失效湖北省重点实验室, 湖北武汉 430074;
    b 武汉东风汽车研发中心, 湖北武汉 430056
  • 收稿日期:2018-11-19 修回日期:2019-01-11 出版日期:2019-04-18 发布日期:2019-03-14
  • 通讯作者: 李涛, 陈真
  • 基金资助:

    国家自然科学基金（21473064）.

Chemical deactivation of Cu-SAPO-18 deNOx catalyst caused by basic inorganic contaminants in diesel exhaust

Shujun Minga, Lei Pangb, Chi Fana, Wen Guoa, Yahao Donga, Peng Liua, Zhen Chena, Tao Lia   

  1. a Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Material Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China;
    b DongFeng Trucks R & D Center, Wuhan 430056, Hubei, China
  • Received:2018-11-19 Revised:2019-01-11 Online:2019-04-18 Published:2019-03-14
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21473064).

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摘要：

选择性催化还原NOx（NH3-SCR）已是柴油机尾气处理系统中有效的NOx减排技术.铜基分子筛催化剂作为潜在的NH3-SCR催化剂已被广泛研究，其中具有AEI结构的Cu-SAPO-18分子筛表现出优异的脱硝活性和水热稳定性，成为柴油机尾气后处理系统潜在的替代品.然而在实际的后处理应用中，生物柴油污染物、发动机润滑剂和燃料添加剂中的一些无机组分（K，Na，S，P，Ca和Mg等）可逐渐聚集在催化剂表面，导致催化剂孔道堵塞和活性位点丢失，最终导致SCR催化剂失活.由于碱金属和碱土金属在柴油衍生物中含量较高，因而其对SCR催化剂的影响引起了人们更多的关注.本文采用浸渍法制备了掺杂不同含量碱性无机污染物（K，Na，Ca和Mg）的Cu-SAPO-18催化剂，以阐明这些污染物对Cu-SAPO-18结构、酸性位点和铜物种的影响.
XRD和氮吸附实验结果表明，低含量污染物的掺入造成催化剂孔道堵塞和比表面积下降，而高含量污染物引入导致催化剂部分结构被破坏，其中高含量Na的引入造成催化剂结构破坏最为严重.H2-TPR和EPR结果表明，污染物引入Cu-SAPO-18后，催化剂的Cu2+数目减少，这是由于Cu2+被K+，Na+，Ca2+和Mg2+取代造成的.被取代的Cu2+由于无法位于离子交换位点上会在煅烧过程中转变成CuO和CuAl2O4，CuO的产生会造成催化剂孔道堵塞甚至部分骨架结构坍塌.另外，NH3-TPD结果表明，与新鲜催化剂相比，被污染的Cu-SAPO-18催化剂总酸性位点减少，这是由于H+和Cu2+被K+，Na+，Ca2+和Mg2+取代造成Brönsted酸和Lewis酸减少造成的.催化剂比表面积的降低、Cu2+数目以及酸含量的减少最终造成催化剂失活，且催化剂失活程度随无机污染物含量的增加而增大.但不同无机组分造成催化剂的失活程度不同，其中K，Na，Ca和Mg造成Cu-SAPO-18催化剂失活程度为K > Na > Ca > Mg.此外，K，Na，Ca和Mg造成Cu-SAPO-18催化剂比表面积、Cu2+含量以及酸含量的减少程度分别为Na > K > Ca > Mg，Na > K > Mg > Ca和K > Na > Ca > Mg.其中酸含量下降程度与催化剂失活程度一致，表明在某种程度上，酸含量对催化剂NH3-SCR活性的影响高于催化剂结构和Cu2+对活性的影响.最后，我们还通过NH3-SCR动力学测试研究了K，Na，Ca和Mg对Cu-SAPO-18催化NH3-SCR反应机理的影响，结果显示新鲜催化剂和被污染催化剂具有相近的活化能，表明无机污染物对Cu-SAPO-18催化NH3-SCR反应机理没有影响.

关键词: Cu-SAPO-18催化剂, 碱性无机污染物, NH3选择性催化还原NOx, 酸性位点, 铜离子

Abstract:

Contaminants (K, Na, Ca, and Mg) were introduced into Cu-SAPO-18 via incipient wetness impregnation to investigate their effect on the selective catalytic reduction of NOx with NH3 (NH3-SCR) over Cu-SAPO-18. After the introduction of contaminants into Cu-SAPO-18, the quantity of acidic sites and Cu2+ species in catalyst decreases owing to the replacement of H+ and Cu2+ by K+, Na+, Ca2+, and Mg2+. Furthermore, the loss of isolated Cu2+ induces the generation of CuO and CuAl2O4-like phases, which causes further loss in the Brunauer-Emmett-Teller surface area of the catalyst. Consequently, the deNOx performance of the contaminated Cu-SAPO-18 catalysts drops. Such decline in NH3-SCR performance becomes more pronounced by increasing the contaminant contents from 0.5 to 1.0 mmol/gcatal. In addition, the deactivation influence of the contaminants on Cu-SAPO-18 is presented in the order of K > Na > Ca > Mg, which is consistent with the order of reduction of acidic sites. To a certain degree, the effect of the acidic sites on the deactivation of Cu-SAPO-18 might be more significant than that of isolated Cu2+ and the catalyst framework. Moreover, kinetic analysis of NH3-SCR was conducted, and the results indicate that there is no influence of contaminants on the NH3-SCR mechanism.

Key words: Cu-SAPO-18 catalyst, Basic inorganic contaminant, Selective catalytic reduction of NOx with NH3, Acidic site, Isolated Cu2+