Modifying α-Al2O3 with cerium, zirconium, and sulfate for catalytic removal of C4F8.

Abstract

Modification of α-Al2O3 (A) with cerium (C), zirconium (Z), and sulfate (S) for effective C4F8 removal is evaluated at temperatures ≤ 650°C. Catalytic hydrolysis of C4F8 is conducted to compare the performance of catalysts prepared (namely, A, AC, AZ, AS, ACS, and AZS). The interplay between rare earth element, acid amount, and surface area is further investigated. An investigation was carried out by characterization of catalysts by using XRD, BET, and NH3-TPD. XRD pattern of the modified α-Al2O3 catalyst shows that the average grain size is 37nm. BET analysis indicates that the surface area increases with the addition of Ce and Zr, while NH3-TPD analysis shows the improvement of acid sites after the addition of Ce, Zr, and SO42-. The experimental results indicate that C4F8 conversion over A catalyst reaches 14.81% at 550°C with the addition of 38% H2O(g). Under the same operating condition, C4F8 conversion efficiencies achieved with AC and AZ catalysts increase to 42.03% and 50.1%, respectively. Furthermore, the efficiencies over AS, ACS, and AZS catalysts increase to 49.85%, 86.94%, and 87.18%, respectively. Stability tests show that the performances of the catalysts for C4F8 conversion are with the order of AZS > ACS > AZ > AC > AS > A at 650°C during 24h. The activation energy of the AZS catalyst in catalytic hydrolysis of C4F8 is 60.49kJ/mol. The products of C4F8 conversion mainly include CO2, CO, and COF2 and small amounts of CHF3 and C2F4. This study has confirmed that the AZS catalyst shows the best activity, acidity, and stability on C4F8 removal.