Catalyst Development for HCl Oxidation to Cl2 in the Fluorochemical Industry

Abstract

The catalytic oxidation of gaseous HCl (containing a small amount of HF) to Cl2 is important and highly desired for chlorine recycling in the fluorochemical industry. In the present work, a series of Al-doped MgF2 (Al–MgF2) materials were synthesized via a sol–gel method, followed by calcination at different temperatures and then these synthesized Al–MgF2 materials were used as supports to prepare RuO2/Al–MgF2 catalysts by an incipient impregnation method. These developed catalysts were evaluated in the oxidation of HCl with an upper-bound HF concentration of 400 ppm, as is common in the fluorochemical industry. Specific attention was paid to investigating the effects of calcination temperature for preparing Al–MgF2 supports on the activity and stability of the resultant catalysts. It is found that at an optimal calcination temperature, Al can be incorporated into the framework of rutile structure MgF2, which can further modify the cell parameters of MgF2 close to those of RuO2, modulate the interactions between RuO2 and the support, and yet affect the chemical environment of RuO2 to enhance the catalytic activity and stability. The study on the catalytic kinetics reveals that the estimated apparent activation energy is in line with the incorporated amount of Al into the framework of MgF2 and shows an inverted volcano relationship with the calcination temperature for preparing Al–MgF2 supports. The lowest apparent activation energy of RuO2/Al–MgF2 can be achieved when the Al–MgF2 composite is calcined at 400 °C, and the resultant catalyst shows long-term stability with high activity for the oxidation of HCl containing a small amount of HF.