The modification and stability of γ-Al2O3 based catalysts for hydrolytic decomposition of CF4

Abstract

Al2O3 of different phases were applied in the hydrolytic decomposition of CF4 with water into CO2 and HF at 750°C. It was found that γ-Al2O3 was an active catalytic phase, but it deactivated rapidly due to the transformation into a catalytically inactive α-Al2O3 affected by the HF produced in the reaction. To increase catalytic stability, the γ-Al2O3 was modified with various types of metals such as Zn, Ni, Mg, Sr and Ba. When the γ-Al2O3 was modified with Zn and Ni, the catalytic stability was enhanced remarkably, which was mainly due to the formation of Zn or Ni aluminates resistant to the HF on catalyst surface during the reaction. Mg, Sr and Ba were also good structural stabilizers for γ-Al2O3, but the catalytic activity for the CF4 decomposition decreased due to their neutralizing effect on acid sites of γ-Al2O3. The FTIR spectra of adsorbed pyridine revealed that Lewis acidity of γ-Al2O3 based catalysts played an important role and the efficient structure modifier can preserve the Lewis acid sites on the catalysts in the CF4 hydrolysis process.