Effects of acid treatment on activated carbon used as a support for Rb and K catalyst for C2F5I synthesis and its mechanism

In the present work, the activated carbon (AC) support was treated with HCl, HNO3 and HF solution. The order of catalyst dispersion was as follows: Rb–K/AC–HNO3 > Rb–K/AC–HF > Rb–K/AC–HCl > Rb–K/AC. The same sequence was also observed for the amount of the acid surface oxygen groups on AC, but not for the basicity of the catalyst. The key role of acid treatment on AC surface chemistry and the basic sites, which are closely related to catalyst dispersion and basicity, is examined to rationalize these findings. On the other hand, a consideration of the reaction mechanism suggests that the reaction proceeds via CF2 carbenes formed on the catalyst surface as intermediates, followed by carbine disproportionation to CF3 radicals and CF3CF2 radicals, followed by reaction with I2 to produce CF3CF2I, and it was also found that the Rb–K/AC–HCl catalyst with a high dispersion and moderate basicity was helpful for the enhancement of catalytic activity for C2F5I synthesis.

The Rb and K dispersion followed a similar sequence of the total amount of the oxygen-containing surface groups on AC. But no unambiguous correlation was found between the dispersion and basicity of catalyst. The reaction mechanism of C2F5I proceeds via CF2 carbene on the surface of the catalyst, and the high dispersion and moderate basicity of the catalyst Rb–K/AC–HCl helped to enhance the catalytic activity for C2F5I synthesis by the reaction of C2HF5, I2 and O2.Figure optionsDownload as PowerPoint slideHighlights
► Modification of the activated carbon (AC) supports with HNO3, HCl and HF solution result in various surface oxygen groups.
► Treatments AC with HNO3, HCl and HF improve the distribution of the active component and change the basicity of carbon-supported Rb–K catalysts.
► The catalytic reaction proceeds via CF2 carbene on the surface of the catalyst.
► The high dispersion and moderate basicity of the catalyst Rb–K/AC–HCl help to enhance the catalytic activity for C2F5I synthesis.