CrO_(x)/Ti-Al_(2)O_(3)催化剂结构及其催化丙烷脱氢性能  

Structure and performance of CrO_(x)/Ti-Al_(2)O_(3) catalysts for propane dehydrogenation

作　　者：张永祥 王德龙 郭晓燕[2] 邵怀启 ZHANG Yongxiang;WANG Delong;GUO Xiaoyan;SHAO Huaiqi(College of Chemical Engineering and Materials Science,Tianjin University of Science&Technology,Tianjin 300457,China;College of Environmental Science and Engineering,Nankai University,Tianjin 300350,China)

机构地区：[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

出　　处：《化工进展》2022年第11期5879-5886,共8页Chemical Industry and Engineering Progress

基　　金：国家重点研发计划(2019YFC1804105);中国石油科技创新基金(2017D-5007-0504)。

摘　　要：以模板法制备的Ti改性Al_(2)O_(3)为载体制备了CrO_(x)/nTi-Al_(2)O_(3)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)、N_(2)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(NH_(3)-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-Al_(2)O_(3)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180~195m^(2)/g;铬主要以Cr^(6+)和Cr^(3+)形式存在,其中Cr^(6+)主要以单铬酸盐和双铬酸盐形式存在,Cr^(3+)以α-Cr_(2)O_(3)晶体和高分散Cr_(2)O_(3)形式存在,Ti的加入降低了催化剂表面Cr^(6+)含量,增加了孔道内高分散Cr^(3+)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%TiO_(2),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%TiO_(2))则明显降低丙烯选择性而使丙烯收率降低。CrO_(x)/nTi-Al_(2)O_(3)催化剂表面Cr^(6+)物种可催化丙烷氧化脱氢,本身还原成Cr^(3+)后继续催化丙烷直接脱氢,孔道内部的高分散Cr^(3+)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。The Ti-modified alumina was obtained by template method and used as support to prepare CrO_(x)/nTi-Al_(2)O_(3) catalysts,and the influences of Ti loading on the catalyst structure and catalytic performance for propane dehydrogenation were investigated.X-ray diffraction(XRD),N_(2) adsorptiondesorption,transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FTIR),UVRaman spectroscopy,X-ray photoelectron spectroscopy(XPS),NH_(3)-temperature-programmed desorption(NH_(3)-TPD)and pyridine-infrared spectroscopy(Py-IR)characterizations were carried out to elucidate the catalyst properties.The results showed that CrO_(x)/nTi-Al_(2)O_(3) catalysts possessed uniform foam-like mesoporous structure with micropore and high specific surface area of 180—195m^(2)/g.The main chromium species on the catalysts were Cr^(6+)and Cr^(3+).Among them,the Cr^(6+)species existed in the form of monochromate and bichromate,and Cr^(3+)species existed in the form of crystallineα-Cr_(2)O_(3) and high-dispersive non-redox Cr_(2)O_(3).The Ti loading decreased Cr^(6+)content on the catalyst surface and increased high-dispersive Cr^(3+)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-Al_(2)O_(3) were obviously improved by adding 0.5%—1.0%TiO_(2)(mass),but excess Ti(>2%TiO_(2))could decrease the propylene selectivity and yield.The oxidation dehydrogenation of propane took places on Cr^(6+)species,which were reduced to redox Cr^(3+)species,and then the redox Cr^(3+)species continuously catalyzed the propane dehydrogenation.Meanwhile,the high-dispersive non-redox Cr^(3+)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.

关 键 词：丙烷脱氢 氧化铝 氧化铬 催化剂载体 钛改性 稳定性 

分 类 号：TQ031.4[化学工程]