The Investigation Of Catalystic Behaviors Of Cr-Based Catalyst For Gas Phase Fluorination Of 1,1,1-Trifluoro-2-Chloroethane

Fluorine chemistry is a branch of modern chemical industry, in which refrigerants production is an important part. Chromium oxides are the key catalysts for F/1l exchange reaction in the synthesis of new generation refrigerants and thus the core technique in the production of ODS substitutes. However, some issues such as translation of Cr species during the pre-fluorination process and the mechanism of F-C1 exchange reaction still needs further investigation. As chromium oxides mainly consist of amorphous CrO3, amorphous Cr2O3 and crystalline Cr2O3, in this project, we plan to design crystalline Cr2O3, amorphous Cr2O3-crystalline Cr2O3, amorphous Cr2O3-crystalline Cr2O3 as three model catalysts. Translation of these different Cr species during pre-fluorination process could be investigation of by qualitatively estimating the contents of these species. Combined with catalytic performance (activity, selectivity and stability) of F-C1 exchange reaction over these catalysts, contributions of these Cr species and their influence on the catalyst deactivation could be evaluated. These works are helpful in development of highly efficient catalyst systems for F-C1 exchange reaction and production of ODS substitutes.The detailed contents of this work are as follows:1. Two Cr-based model catalysts (Cr2O3 and CrO3/Cr2O3) were prepared and tested for gas phase fluorination of 2-cholo-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 Cr(VI) species in the catalyst had an initial turnover frequency of 1.71×10-4 s-1, which was much higher than that of the Cr(III) species (4.16 ×10-5 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.2. The Cr2O3 catalyst was prepared using a precipitation method, and the Cr2O3 catalyst was impregnated in H2CrO4 solution for preparing the a-Cr2O3/Cr2O3 catalyst.Both of the Cr2O3 and a-Cr2O3/Cr2O3 catalysts were tested for gas phase fluorination of 2-cholo-1,1,1-trifluoroethane to synthesize 1,1,1,2-tetrafluoroethane. The experimental results showed that the activity of the Cr2O3 catalyst was low but very stable during the reaction. On the contrary, as there was high valent Cr species in the a-Cr2O3/Cr2O3 catalyst, it had higher initial activity. However, it deactivated rapidly. The H2-TPR profiles showed that the a-Cr2O3/Cr2O3 catalyst had higher high valent Cr content compared to the Cr2O3 catalyst. The high valence Cr species in the reaction process is easy to loss, which accounts for the catalyst deactivation. Combined with XRD and catalytic behaviors of the Cr2O3 and catalysts, it can be found a-Cr2O3 has higher catalytic activity than the Cr2O3 catalyst.3. CrOxFy species in fluorine chlorine exchange reaction plays a very important role, so finding a high performance and good stability CrOxFy catalyst preparation method is particularly important.So try different methods in this chapter, the preparation of t he same conditions and catalytic fluorination CrOxFy species as HFC-133 a, in order to study the performance of the catalytic species CrOxFy fluorination of HCFC-133a, and further explores the corresponding reaction mechanism according to the results of the experiment.