自然科学版
陕西师范大学学报(自然科学版)
双碳背景下的稀土催化专刊
V2O5-Al2O3催化CO2氧化乙苯脱氢的稀土氧化物助剂效应
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王欢1,2,杨国庆2,宋永红2,赵永华1,刘昭铁2,刘忠文2*
(1 辽宁工业大学 化学与环境工程学院,辽宁 锦州 121001; 2002372 陕西省合成气转化重点实验室,陕西师范大学 化学化工学院,陕西 西安 710119)
刘忠文,男,教授,博士生导师,研究方向为C1化学化工。E-mail:zwliu@snnu.edu.cn
摘要:
结合尿素辅助水热和蒸发诱导自组装方法,制备了一系列V2O5-LnO-Al2O3(LnO分别为La2O3、CeO2、Pr6O11、Nd2O3或Yb2O3)钒基复合氧化物催化剂,其中V2O5质量分数为9%,助剂质量分数为7%。采用N2吸脱附、X射线衍射(XRD)、拉曼光谱(Raman)、H2程序升温还原(H2-TPR)、X射线光电子能谱(XPS)以及热分析(TG-DSC)等技术对催化剂的织构、结构、还原性能等进行了表征分析。在常压、550 ℃、n(CO2)∶n(乙苯)=20∶1和接触时间为0.17 h的条件下,考察了上述钒基复合氧化物催化剂催化CO2氧化乙苯脱氢(CO2-ODEB)反应的性能,探讨了不同稀土氧化物的助剂效应及其作用机制,分析了催化剂的失活原因。结果表明:稀土氧化物对V2O5-Al2O3催化剂的织构性质、结构特征、还原性能、表面可还原钒物种数量、氧缺陷含量及积炭行为有不同程度的影响。其中, V2O5-Pr6O11-Al2O3催化剂的比表面积最大,孔道规整度较高,可还原的表面钒物种最多,表现出最高的初始乙苯转化率;V2O5-CeO2-Al2O3催化剂不仅具有较好的还原性能和较多的表面可还原钒物种,且其氧缺陷含量最高,能够较好地维持CO2-ODEB反应过程中V5+与V4+之间的氧化还原循环稳定性,表现出较高的初始活性和最佳的长周期稳定性。催化剂的失活分析结果表明:虽然加入不同稀土氧化物能够在一定程度上影响催化剂的抗积炭能力,但与V5+的不可逆还原相比,积炭并不是催化剂失活的主要原因。
关键词:
乙苯脱氢;苯乙烯;二氧化碳;稀土氧化物;钒氧化物
收稿日期:
2021-10-20
中图分类号:
TQ426;TQ241.21bility
文献标识码:
A
文章编号:
1672-4291(2022)02-0121-10
基金项目:
国家自然科学基金(21636006);中央高校基本科研业务费专项资金(GK201901001)
Doi:
10.15983/j.cnki.jsnu.2022015
Promotional effects of rare earth oxides on V2O5-Al2O3 for the oxidative dehydrogenation of ethylbenzene with CO2
WANG Huan1, 2, YANG Guoqing2, SONG Yonghong2, Zhaotie2ZHAO Yonghua1, LIU Zhaotie2, LIU Zhongwen2*
(1 School of Chemical and Environmental Engineering, Liaoning University of Technology,Jinzhou 121001, Liaoning, China;2 Shaanxi Key Laboratory of Syngas Conversion, School of Chemistry & Chemical Engineering,Shaanxi Normal University, Xi′an 710119, Shaanxi, China)
Abstract:
The V2O5-LnO-Al2O3 catalysts(LnO: La2O3, CeO2, Pr6O11, Nd2O3, Yb2O3) were synthesized via the route by combining the urea-hydrolysis assisted hydrothermal and evaporation-induced self-assembly methods. For all the catalysts,the V2O5 and LnO loading were fixed to 9% and 7%(mass fraction), respectively.The catalysts were characterized by the N2 adsorption/desorption, XRD, Raman, H2-TPR, XPS and TG-DSC techniques. Under the conditions of 0.1 MPa, 550 ℃, CO2/ethylbenzene (EB) of 20(molar radio)and contact time of 0.17 h, the promotional effects of rare earth oxides on the catalytic performance of V2O5-Al2O3 for the oxidative dehydrogenation of ethylbenzene with CO2 (CO2-ODEB) were investigated.Results indicate that the addition of rare earth oxide into V2O5-Al2O3 had clear impacts on the textural, structural and reduction properties of the catalysts, the extent of which is strongly dependent on the specific LnO. Among the investigated catalysts,V2O5-Pr6O11-Al2O3 catalyst showed the highest initial EB conversion, which is mainly attributed to the more ordered mesostructure, the largest specific surface area and the most abundant reducible VOx species on the surface of the catalyst. In contrast,V2O5-CeO2-Al2O3 catalyst showed the best stability for CO2-ODEB.This is well explained as the stable redox recycle of V5+/V4+ due to the highest amount of the oxygen defects, a higher amount of reducible VOx species and the higher reducibility of the catalyst. Although the coke deposition over the catalyst for CO2-ODEB was alleviated by adding LnO into V2O5-Al2O3, the catalyst deactivation caused by the irreversible reduction of V5+ was more significant,revealing the critical role of the irreversibly reduced V5+ for the deactivation of the catalyst.
KeyWords:
dehydrogenation of ethylbenzene;styrene;carbon dioxide;rare earth oxides;vanadium oxide