化工进展 ›› 2022, Vol. 41 ›› Issue (11): 5879-5886.DOI: 10.16085/j.issn.1000-6613.2022-0169

• 工业催化 • 上一篇    下一篇

CrO x /Ti-Al2O3催化剂结构及其催化丙烷脱氢性能

张永祥1(), 王德龙1, 郭晓燕2, 邵怀启1()   

  1. 1.天津科技大学化工与材料学院,天津 300457
    2.南开大学环境科学与工程学院,天津 300350
  • 收稿日期:2022-01-26 修回日期:2022-06-01 出版日期:2022-11-25 发布日期:2022-11-28
  • 通讯作者: 邵怀启
  • 作者简介:张永祥(1998—),男,硕士研究生,研究方向为低碳烷烃脱氢。E-mail:3284299579@qq.com
  • 基金资助:
    国家重点研发计划(2019YFC1804105);中国石油科技创新基金(2017D-5007-0504)

Structure and performance of CrO x /Ti-Al2O3 catalysts for propane dehydrogenation

ZHANG Yongxiang1(), WANG Delong1, GUO Xiaoyan2, SHAO Huaiqi1()   

  1. 1.College of Chemical Engineering and Materials Science, Tianjin University of Science & Technology, Tianjin 300457, China
    2.College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
  • Received:2022-01-26 Revised:2022-06-01 Online:2022-11-25 Published:2022-11-28
  • Contact: SHAO Huaiqi

摘要:

以模板法制备的Ti改性Al2O3为载体制备了CrO x /nTi-Al2O3催化剂,考察了Ti含量对催化剂的结构及其催化丙烷脱氢性能的影响。采用X射线衍射(XRD)、N2吸附-脱附、透射电子显微镜(TEM)、傅里叶变换红外光谱(FTIR)、拉曼光谱、X射线光电子能谱(XPS)、氨气程序升温脱附(NH3-TPD)、吡啶红外吸附(Py-IR)等方法对催化剂的结构进行了表征。结果表明,CrO x /nTi-Al2O3催化剂具有均匀的泡沫状介孔结构并含有少量微孔,表面积在180~195m2/g;铬主要以Cr6+和Cr3+形式存在,其中Cr6+主要以单铬酸盐和双铬酸盐形式存在,Cr3+以α-Cr2O3晶体和高分散Cr2O3形式存在,Ti的加入降低了催化剂表面Cr6+含量,增加了孔道内高分散Cr3+含量;Ti的加入降低了弱酸的强度,生成了少量中强酸,并使催化剂中B酸和L酸中心数量明显减少。少量的Ti(0.5%~1.0%TiO2,质量分数)可明显提高丙烷转化率和丙烯收率,但过多的Ti(>2%TiO2)则明显降低丙烯选择性而使丙烯收率降低。CrO x /nTi-Al2O3催化剂表面Cr6+物种可催化丙烷氧化脱氢,本身还原成Cr3+后继续催化丙烷直接脱氢,孔道内部的高分散Cr3+可催化丙烷直接脱氢反应,二者结合使催化剂保持了较高的催化活性和较好的稳定性。

关键词: 丙烷脱氢, 氧化铝, 氧化铬, 催化剂载体, 钛改性, 稳定性

Abstract:

The Ti-modified alumina was obtained by template method and used as support to prepare CrO x /nTi-Al2O3 catalysts, and the influences of Ti loading on the catalyst structure and catalytic performance for propane dehydrogenation were investigated. X-ray diffraction(XRD), N2 adsorption-desorption, transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FTIR), UV-Raman spectroscopy, X-ray photoelectron spectroscopy(XPS), NH3-temperature-programmed desorption(NH3-TPD) and pyridine-infrared spectroscopy(Py-IR) characterizations were carried out to elucidate the catalyst properties. The results showed that CrO x /nTi-Al2O3 catalysts possessed uniform foam-like mesoporous structure with micropore and high specific surface area of 180—195m2/g. The main chromium species on the catalysts were Cr6+ and Cr3+. Among them, the Cr6+ species existed in the form of monochromate and bichromate, and Cr3+ species existed in the form of crystalline α-Cr2O3 and high-dispersive non-redox Cr2O3. The Ti loading decreased Cr6+ content on the catalyst surface and increased high-dispersive Cr3+ content in the pore channel. The Ti loading decreased weak acid intensity and promoted the formation of medium acid sites, meanwhile the amounts of Brönsted and Lewis acid sites were obviously decreased. The propane conversion and propylene yield on CrO x /nTi-Al2O3 were obviously improved by adding 0.5%—1.0% TiO2(mass), but excess Ti (>2%TiO2) could decrease the propylene selectivity and yield. The oxidation dehydrogenation of propane took places on Cr6+ species, which were reduced to redox Cr3+ species, and then the redox Cr3+ species continuously catalyzed the propane dehydrogenation. Meanwhile, the high-dispersive non-redox Cr3+ species in the pore channel directly catalyzed propane dehydrogenation to produce propylene. The aboved-mentioned Cr active sites provided both high catalytic activity and good stability.

Key words: propane dehydrogenation, alumina, chromia, catalyst support, titanium-modification, stability

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