Cr_2O_3和CrO_3/Cr_2O_3催化剂的2-氯-1,1,1-三氟乙烷气相氟化反应的活性物种和失活（英文）

Catalytic Behaviors of Cr_2O_3 and CrO_3/Cr_2O_3 Catalysts for Gas Phase Fluorination of 2-Chloro-1,1,1-trifluoroethane: Active Species and Catalyst Deactivation

采用沉淀法和浸渍法制备了2种铬基(Cr_2O_3和CrO_3/Cr_2O_3)催化剂,用于气相氟化2-氯-1,1,1-三氟乙烷合成1,1,1,2-四氟乙烷。研究发现含有低价铬(Cr3+)物种的Cr_2O_3催化剂上2-氯-1,1,1-三氟乙烷的稳态转化率为18.5%,而含有高价铬(Cr6+)物种和低价铬(Cr3+)物种的CrO_3/Cr_2O_3催化剂初始转化率达到30.6%,然而存在明显的失活。含有Cr6+物种的CrO_3/Cr_2O_3催化剂的2-氯-1,1,1-三氟乙烷氟化反应初始TOF值为1.71×10-4 molHCFC-133a·molCr髩-1·s-1,高于含有Cr3+物种的Cr_2O_3催化剂(4.16×10-5 molHCFC-133a·molCr髥-1·s-1)。Cr_2O_3催化剂在氟化反应前后催化剂的物相结构保持不变;而含有高价铬物种的CrO_3/Cr_2O_3催化剂经HF反应后生成了CrO_xF_y活性物种。然而,CrO_xF_y物种在反应中挥发或转化成稳定但无活性的CrF_3,从而导致催化剂失活。

Two Cr-based model catalysts （Cr2O3 and CrO3/Cr2O3） were prepared respectively by precipitation and impregnation method and tested for gas phase fluorination of 2-chloro-1,1,1-trifluoroethane to synthesize 1,1,1,2-tetrafluoroethane. It was found that the Cr2O3 catalyst containing low valent Cr species （Cr3＋） was stable during the reaction with a steady state conversion of 18.5%. On the contrary, the CrO3/Cr2O3 catalyst containing both high valent Cr species （Cr6＋） and low valent Cr species （Cr3＋） had higher initial activity （30.6%） but it deactivated rapidly, with the same activity as the Cr2O3 catalyst at steady state. Moreover, quantitative analyses showed that the Cr6＋ species in the CrO3/Cr2O3 catalyst had an initial turnover frequency of 1.71×10-4 molHCFC-133a·molCr（Ⅵ）-1·s-1, which was much higher than that of the Cr3＋ species （4.16×10-5 molHCFC-133a·molCr（Ⅲ）-1·s-1） in the Cr2O3 catalyst. In addition, the characterization results revealed that the Cr2O3 remained its structure while the high valent Cr species in the CrO3/Cr2O3 reacted with HF to form catalytically active CrOxFy species. However, such CrOxFy species could either volatilize during the reaction or transformed to stable but inactive CrF3, which accounted for the catalyst deactivation.