气相氟化CCl_2F_2制备CF_4的催化剂研究

CCl2F2(CFC-12)曾广泛用作制冷剂和推进剂,是消耗臭氧层的罪魁祸首,选取何种温度将CCl2F2转化为高附加值的四氟甲烷(CF4)是本研究的目标。通过沉积沉淀法制备了一系列不同温度焙烧的CrAlF催化剂,并用于气相氟化CCl2F2反应合成CF4,600℃焙烧的催化剂活性最好,400℃反应温度下合成CF4的生成产率约为92%。XRD、Raman和UV-Vis分析结果表明随着焙烧温度升高,催化剂表面的晶相Cr2O3的含量增加。晶相Cr2O3很难被活化而形成活性物种,因而催化剂活性与CrAlF催化剂表面Cr2O3的含量有关。CrAlF-6催化剂活性最高归因于其表面相对最低的Cr2O3含量。研究发现载体Al2O3经氟化后生成AlF3,并且形成的小晶粒AlF3载体有利于获得较高的催化活性。催化剂失活的主要原因可能与催化剂表面CrO的含量增加以及晶粒增大有关。

Study on Catalysts for Vapor Fluorination CCl2F2 to Synthesize CF4

CCl2F2（CFC-12） has extensive use of refrigerant and propellant,and as the culprit of depleting the ozone layer,one promise to transform CCl2F2 into carbon tetrafluoride（CF4）.In this paper,a series of catalysts under different calcination temperature were preparated by deposition precipitation method for vapor fluorination CCl2F2 to synthesize CF4.It is found that the catalytic activity is best when the calcination temperature is 600 ℃,the yeild of CF4 is about 92% as fluorination of CFC-12 at the 400 ℃.XRD,Raman and UV-Vis analysis results showed that with the roasting temperature on the surface of the catalyst,Cr2O3 crystalling phase of content.Cr2O3 crystalling phase to activate,thus formed active catalyst activeness and species CrAlF Cr2O3 content of catalyst on the surface.CrAlF-6 catalyst activity due to its lowest Cr2O3 surface relative content.The study found that after Al2O3 carrier AlF3 generated fluorine,and the formation of small grain AlF3 carrier to obtain higher catalytic activity.The catalyst deactivation of the main reason may be Cr2O3 surface with catalyst of content and increase grain.