CrOx/SiO2催化剂上丙烷在CO2气氛中脱氢反应的研究

采用XRD、UV-vis DRS、ESR和微分吸附量热等技术,考察了铬担载量分别为2.5、5和10wt%的CrO_x/SiO₂催化剂的结构、表面性质和氧化还原性能。结果表明,催化剂表面上存在多种Cr的氧化态和聚集形式。随着Cr担载量从2.5wt%到10wt%的逐渐增大,催化剂表面占主导地位的Cr物种由CrO₃单体转为多聚CrO₃和Cr₂O₃晶相。在CO₂气氛中催化剂对丙烷转化率和丙烯选择性的大小顺序为2.5wt%CrO_x/SiO₂>5wt%CrO_x/SiO₂>10wt%CrO_x/SiO₂,反应过程中的原位ESR和UV-visDRS测定结果表明,催化剂表面的反应活性中心为Cr⁵⁺,Cr⁵⁺可由催化剂预处理过程中Cr³⁺的氧化及丙烷反应过程中CrO₃单体的还原产生,在反应中CO₂可使Cr³⁺重新氧化为Cr⁵⁺.

Dehydrogenation of Propane over CrOx/SiO2 Catalysts under CO2 Atmosphere

The surface structure and redox properties of CrO_x/SiO₂ catalysts with various Cr loadings of 2.5, 5 and 10wt% have been investigated by XRD, UV-vis DRS, ESR and microcalorimetric adsorption methods.It was found that chronia occurs with different oxidation states and different coordination numbers on the surface of the catalysts.With Cr loadings increasing from 2.5wt% to 10wt%, the dominant surface Cr species change from chromate to polychromate and Cr₂O₃ cluster.The order of propane conversion and selectivity to propane for the propane dehydrogenation reaction under CO₂ atmosphere over CrO_x/SiO₂ catalysts is 2.5wt%CrO_x/SiO₂ > 5wt%CrO_x/SiO₂ > 10wt% CiOx/SiO₂. The results of ESR and UV-vis DRS measured during reaction process indicate that the active center of CrO_x/SiO₂ catalysts for the reaction is Cr⁵⁺ species, which is probablely generated from Cr³⁺ species oxidizing during the calcination and chromate reducting during the reaction.The role of CO₂ is to reoxidize Cr³⁺ to Cr⁵⁺ in the reaction.