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

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 37 nm. 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 SO₄^2-. 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 24 h. The activation energy of the AZS catalyst in catalytic hydrolysis of C₄F₈ is 60.49 kJ/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.