Pyrolysis of Trifluoromethane over Activated Carbon: Role of the Surface Oxygen Groups

Abstract

The pyrolysis of CHF3 and CHClF2 over activated carbons was investigated at 823 K, GHSV of 1820 h–1 and pressure of 1 bar. To elucidate the mechanism, activated carbons were treated in H2 at 1123 K, HNO3 solution at 363 K, N2 at 873 K or supported with 4 wt% poly(acrylic acid sodium salt), respectively. The results confirm that following different treatments, the concentration of surface oxygen groups on activated carbons varies dramatically. These surface groups play important roles in the decomposition of CHF3 and the product profiles. It is suggested that carboxylic groups are responsible for the formation of CF3 and ultimately the product C2F6 which results from the coupling of CF3, while the interaction between CHF3 and hydroxyl or lactonic groups leads to the total destruction of CHF3 and production of CO and CO2. Pyrolysis of CHClF2 over activated carbon confirms that surface oxygen groups have no noticeable influence on the reactions of CF2. By contrast, a pure carbon surface is responsible for the disproportionation of CF2 and formation of CF3.