【作者】 李云辉；

【导师】 张新艳；

【作者基本信息】 长春理工大学 ， 环境科学与工程， 2023， 硕士

【摘要】 柴油车是重要的NO_x排放源,氨选择性催化还原（NH₃-SCR）是柴油车尾气NO_x去除中应用最广泛的技术。在NH₃-SCR领域的催化剂中,铜基小孔分子筛催化剂因具备优异的催化活性、N₂选择性和水热稳定性,受到研究人员的青睐。其中,CHA构型的Cu-SSZ-13分子筛拥有优异的催化活性、N₂选择性和抗HCs中毒能力,但高温水热环境中存在催化性能下降的问题;AEI构型的Cu-SSZ-39分子筛拥有优异的中高温活性和水热稳定性,但低温SCR活性相对较差。基于此,本文探索在SSZ-13的合成过程中添加葡萄糖,调变分子筛的生长过程和晶粒尺寸,提升Cu-SSZ-13分子筛的水热稳定性;将具有优异氧化能力的Ce Zr O_x与Cu-SSZ-39分子筛复合,制备Ce Zr O_x/Cu-SSZ-39复合催化剂,提高Cu-SSZ-39分子筛的低温NH₃-SCR活性。主要研究结果如下:（1）在SSZ-13分子筛的合成过程中添加葡萄糖,降低了SSZ-13分子筛的晶粒尺寸（约10μm减小到约3μm）,并且由粗糙不规则球形形貌变成光滑均匀的立方体形貌。采用葡萄糖调节制备的催化剂Cu-SSZ-13-Glu表现出优于传统Cu-SSZ-13的NH₃-SCR催化性能,表征结果发现其结晶度提高、酸性位点增加及氧化还原性有所提高。同时,Cu-SSZ-13-Glu具有优异的水热稳定性,相比传统Cu-SSZ-13显著提升。相比传统Cu-SSZ-13,Cu-SSZ-13-Glu分子筛结构更加稳定,水热老化后能够保持更高的结晶度和更多的比表面积和微孔体积。并且Cu-SSZ-13-Glu分子筛中Cu²⁺离子更稳定,水热老化后生成的Cu O_x物种更少,保留了更多的Cu（OH）⁺-Z物种和酸性位点。（2）将优异氧化能力的CeZrO_x与Cu-SSZ-39分子筛复合,提升了Cu-SSZ-39的低温NH₃-SCR活性。Ce Zr O_x/Cu-SSZ-39在125-200℃的低温度范围内的NO转化率比Cu-SSZ-39平均高出近18%。表征结果发现,Ce Zr O_x/Cu-SSZ-39催化剂上具有更多活跃Cu（OH）⁺-Z物种,氧化还原性提高,促进了NH₃-SCR反应的进行。并且Ce Zr O_x/Cu-SSZ-39催化剂含有表面化学吸附氧,有利于NO氧化成NO₂,进而促进快速SCR反应的发生。同时,Ce Zr O_x/Cu-SSZ-39水热老化处理后依然保持更好的催化剂活性,水热稳定性比Cu-SSZ-39有所提高。Ce Zr O_x复合削弱了水热条件对Cu-SSZ-39的影响,复合催化剂在水热老化后保持了较好的比表面积和孔结构,降低了水热老化过程中酸性位点和可还原性物种的损失。更多还原

【Abstract】 Diesel vehicles are an important source of NO_x emissions,and ammonia selective catalytic reduction（NH₃-SCR）is the most widely used technology for diesel exhaust NO_x removal.Among the catalysts in the field of NH₃-SCR,Cu Based Small-pore Zeolite catalysts are favored by researchers for their excellent catalytic activity,N₂ selectivity and hydrothermal stability.Among them,Cu-SSZ-13 with the CHA structure has excellent catalytic activity,N₂ selectivity and resistance to HCs poisoning,but there is a problem of catalytic performance degradation in high-temperature hydrothermal environment;Cu-SSZ-39 with the AEI structure has excellent medium and high temperature activity and hydrothermal stability,but the low-temperature SCR activity is relatively poor.Based on this,this paper explores the addition of glucose in the synthesis of SSZ-13,to modulate the grain size and enhance the hydrothermal stability of Cu-SSZ-13;the Ce Zr O_x with excellent oxidation ability is compounded with Cu-SSZ-39,to prepare Ce Zr O_x/Cu-SSZ-39 composite catalyst to improve the low-temperature NH₃-SCR activity of Cu-SSZ-39.The main findings were as follows:（1）The addition of the glucose during the synthesis of SSZ-13,reduced the grain size of SSZ-13（about 10μm to about 3μm）,and changed the rough and irregular spherical shape to a smooth and uniform cubic shape.The catalyst Cu-SSZ-13-Glu prepared by glucose conditioning exhibited better NH₃-SCR catalytic performance than conventional Cu-SSZ-13,and the characterization results revealed improved crystallinity,increased acidic sites and improved redox properties.Meanwhile,Cu-SSZ-13-Glu has excellent hydrothermal stability,which is significantly improved compared with conventional Cu-SSZ-13.Compared with traditional Cu-SSZ-13,Cu-SSZ-13-Glu has a more stable structure and can maintain higher crystallinity and more specific surface area and microporous volume after hydrothermal aging.Moreover,the Cu²⁺ions in Cu-SSZ-13-Glu are more stable and generate less Cu O_x species after hydrothermal aging,retaining more Cu（OH）⁺-Z species and acidic sites.（2）The low-temperature NH₃-SCR activity of Cu-SSZ-39 was enhanced by compounding Ce Zr O_x,which has excellent oxidation capacity,with Cu-SSZ-39.The NO conversion of Ce Zr O_x/Cu-SSZ-39 is on average nearly 18%higher than that of Cu-SSZ-39 in the low temperature range of 125-200℃.The characterization results revealed that the Ce Zr O_x/Cu-SSZ-39 catalyst has more active Cu（OH）⁺-Z species on it with improved redox properties,which promotes the NH₃-SCR reaction.And the Ce Zr O_x/Cu-SSZ-39 catalyst contains surface chemisorbed oxygen,which facilitates the oxidation of NO to NO₂ and thus promotes the fast SCR reaction.Meanwhile,Ce Zr O_x/Cu-SSZ-39 still maintained better catalyst activity after hydrothermal aging treatment and improved hydrothermal stability compared with Cu-SSZ-39.The Ce Zr O_x composite weakened the effect of hydrothermal conditions on Cu-SSZ-39,and the composite catalyst maintained better specific surface area and pore structure after hydrothermal aging,reducing the acidic sites and reducible species during hydrothermal aging.The loss of acidic sites and reducible species during hydrothermal aging was reduced.更多还原