高比表面积α-AlF_3的制备和表征

Preparation and Characterization of High Surface Area α-AlF_3

采用炭硬模板法制备了高比表面积的α-AlF3(HS-α-AlF3)。首先,将一定浓度的蔗糖溶液浸渍到γ-Al2O3中,然后经过热处理,使得蔗糖分解为炭。其次,将含炭的γ-Al2O3固体用HF气体进行氟化。最后,再利用燃烧法除去炭硬模板。采用XRD、低温氮吸附-脱附、NH3-TPD、SEM-EDX等技术对样品进行了表征。结果表明,当炭化温度为450℃时,HF-N2混合气体积比为1:4,除碳温度为425℃时,制得的α-AlF3比表面积最大,为66 m2.g-1。此外,HS-α-AlF3催化剂对CCl2F2歧化反应的催化活性也明显高于常规方法制备的低比表面积的α-AlF3,这是因为高比表面积的α-AlF3催化剂具有较大的酸量。

High surface area a-AlF3 （HS-a-AlF3） has been prepared by a carbon hard template method. The synthesis procedure consisted of three steps： （1） the impregnation of a sucrose （C12H22O11） aqueous solution with γ-Al2O3 and subsequent thermal treatment; （2） the thermal treatment of the obtained solid with HF; （3） the removal of the carbon template in C@a-AlF3 upon high temperature combustion. The optimal conditions for the highest surface area of the synthesized a-AlF3 （66 m2·g-1） are obtained based on the results from XRD, low temperature adsorption-desorption, ammonia temperature programmed desorption （NH3-TPD）, SEM, EDX and the FTIR spectra of pyridine adsorption. The temperatures for fluorination, carbon calcinations and carbon removal are 400, 450 and 425℃, respectively, and the HF/N： volume ratio is 1：4, In addition, the HS-a-AlF3 catalyst is more active for the dismutation of CCl2F2 than the catalyst prepared by a direct fluorination of the γ-Al2O3 due to its higher amount of acid sites.