Ce金属改性对Cu-SAPO-34催化剂水热稳定性能的影响

采用浸渍法制备系列铜铈复合氧化物分子筛催化剂（Cu-Ce/SAPO-34）,探讨了Ce负载量对Cu/SAPO-34催化剂的水热稳定性的影响,通过XRD、SEM、H₂-TPR、XPS和NH₃-TPD等表征手段分析不同催化剂活性和稳定性差异的原因。研究表明,750℃水热老化未造成Cu-Ce/SAPO-34催化剂菱沸石（chabazite,CHA）骨架坍塌,但破坏了部分孔结构和酸性位点,使催化剂表面结晶度下降。水热老化促使催化剂晶格发生拉伸畸变,使Cu²⁺迁移到催化剂表面,Cu²⁺和Ce⁴⁺团簇形成CuO和CeO₂,造成催化剂的Cu活性物种减少和氧空穴浓度降低,所以Cu-Ce/SAPO-34的NH₃选择性催化还原（NH₃-Selective Catalytic Reduction,NH₃-SCR）性能下降。掺杂Ce能提高Cu/SAPO-34催化剂表面的Cu²⁺和Cu⁺活性物种量,减少Cu物种团簇形成CuO,改善催化剂表面活性Cu物种分布性。提高Ce的负载量能稳固Cu-Ce/SAPO-34催化剂的结构,使中、弱强度酸位点得以维持,从而提高其水热稳定性。结果表明,在研究的系列Cu-Ce/SAPO-34催化剂中,Cu/Ce质量比为4：5时具有最佳的水热稳定性。

Effect of Ce metal modification on the hydrothermal stability of Cu-SAPO-34 catalyst

A series of copper-cerium composite oxide molecular sieve catalysts (Cu-Ce/SAPO-34) were prepared by impregnation method, and the effects of Ce loading on the hydrothermal stability of Cu/SAPO-34 catalyst were discussed. The reasons for the difference in activity and stability of different catalysts were analyzed by XRD, SEM, H₂-TPR, XPS, and NH₃-TPD. The present study showed that hydrothermal aging at 750 ℃ did not cause the chabazite (CHA) framework of Cu-Ce/SAPO-34 catalyst to collapse, but destroyed part of the pore structure and acid sites, and reduced the crystallinity of the catalyst surface. Hydrothermal aging promoted tensile distortion of the catalyst lattice, causing Cu²⁺ to migrate to the catalyst surface, and Cu²⁺ and Ce⁴⁺ clustered to form CuO and CeO₂, which resulted in the reduction of the Cu active species and the decrease of the oxygen hole concentration of the catalyst. Therefore, the performance of Cu-Ce/SAPO-34 for the selective catalytic reduction of NO_x by NH₃ (NH₃-SCR) decreased. Ce doping could increase the amount of Cu²⁺ and Cu⁺ active species on the surface of Cu/SAPO-34 catalyst, reduce Cu species clusters to form CuO, and improve the distribution of active Cu species on the catalyst surface. Increasing the loading of Ce could stabilize the structure of Cu-Ce/SAPO-34 catalyst and maintain the medium and weak acid sites, thereby improving its hydrothermal stability. The results indicated that the Cu/Ce mass ratio of 4∶5 had the best hydrothermal stability among the series of Cu-Ce/SAPO-34 catalysts in this study.