Engineering Research Center of Ministry of Education for Fine Chemicals, Shanxi University
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences

本研究采用一锅式共沉淀法制备了xZn-CaZr固溶体催化剂并将其应用于CO2-BDH反应，通过多种手段探明该系列催化剂的理化性质并结合催化性能阐述其构效关系及表面氧化还原机制。研究表明，xZn-CaZr催化剂在Zn含量为6%−12%的情况下形成了Zn物种高度分散的固溶体结构，且氧缺陷的数量与Zn的含量成正比。在xZn-CaZr催化剂上，晶格氧的数量和氧迁移率是决定催化性能的关键因素，其中，0.4Zn-CaZr催化剂展示出最佳的催化活性，而0.2Zn-CaZr催化剂展示出最佳的反应稳定性。该研究为进一步开发绿色高性能的CO2-BDH催化剂提供了参考价值。

CO2-assisted oxidative dehydrogenation of isobutane to isobutene (CO2-BDH) is an environmentally friendly low-carbon dehydrogenation process, which can effectively utilize greenhouse gas CO2 while producing value-added product isobutylene. Besides, the soft oxidizing property of CO2 can break the thermodynamic limitation of dehydrogenation reaction and avoid the problem of deep oxidation, which makes isobutylene highly selective. However, its industrialization is still challenged by the lack of green and efficient catalysts. In this work, xZn-CaZr solid solution catalysts was prepared by one-pot co-precipitation method and applied to CO2-BDH reaction. The physicochemical properties of all catalysts were investigated by various means, and the structure-activity relationship and surface redox mechanism were described in combination with catalytic performance. The results show that xZn-CaZr catalysts formed solid solution structure with Zn species (6%−12%) existing in highly dispersion state, and the "confinement effect" given by mesoporous skeleton and strong metal-support interactions contributes to the stable distribution of nanoscale sites and generates more Zn-O-Zr interfaces. When excessive Zn species (16%) is added, the ZnO crystal will have obvious phase separation from the solid solution phase. The surface chemical states of different catalysts were analyzed by XPS, and it was found that the relative content of Oβ increased first and then decreased with the increase of Zn content. In addition, the surface reduction characteristics of the catalyst indicated that the promotion of an appropriate amount of Zn species can improve the mobility of lattice oxygen, thus 0.4Zn-CaZr catalyst showing the highest relative content of Oβ and the best oxygen conductivity. In the activity evaluation of different xZn-CaZr catalyst, 0.4Zn-CaZr catalyst shows the best catalytic dehydrogenation activity but its stability is poor, while 0.2Zn-CaZr catalyst has the best reaction stability. Moreover, the catalytic performance of ZnCaZr catalyst under different C4H10-CO2 ratios was also investigated, which indicated that the higher CO2 content in the feed gas was helpful to improve the catalytic stability and isobutene selectivity. Combined with the surface chemical state and carbon deposition information of the spent catalyst, it was found that the relative content of Oβ on the surface of 0.4Zn-CaZr catalyst decreases obviously, but the carbon deposition rate was slow. On the contrary, the relative content of Oβ for 0.2Zn-CaZr catalyst decreased less, but its carbon deposition rate was faster. We believe that the amount and mobility of lattice oxygen over xZn-CaZr catalysts were revealed as key factors in determining the catalytic performance. Notably, higher content and superior mobility of lattice oxygen can enhance the redox function of the solid solution catalyst itself and improve the activation performance of CO2. The strong oxygen supply capacity can ensure the continuous MvK catalytic cycle on the Zn-O-Zr interface, and avoid the deep accumulation of inert carbon deposits while improving the dehydrogenation activity of isobutane and selectivity of isobutene. This study shed lights on the further design and development of green and efficient CO2-BDH catalysts.

国家自然科学基金 (22178202, 21603127), 山西省科技创新团队项目(202204051001012), 煤炭高效低碳利用全国重点实验室开放课题基金(J23-24-609-2), 天津市科技计划项目(22YFYSHZ00290)和中国科学院山西煤炭化学研究所自主创新项目(SCJC-DT-2023-03)资助

刘玉鹏, 刘玲技, 蔚晓盛, 王永钊, 李国强, 李磊, 王长真. ZnCaZr固溶体催化异丁烷-CO2氧化脱氢制异丁烯的研究[J]. 燃料化学学报（中英文）, 2024, 52(8): 1103-1114.

LIU Yupeng, LIU Lingji, YU Xiaosheng, WANG Yongzhao, LI Guoqiang, LI Lei, WANG Changzhen. CO2 assistant oxidative dehydrogenation of isobutane to isobutene catalyzed by ZnCaZr solid solution[J]. Journal of Fuel Chemistry and Technology, 2024, 52(8): 1103-1114.