Oxidation of dichloromethane over Pt, Pd, Rh, and V2O5 catalysts supported on Al2O3, Al2O3–TiO2 and Al2O3–CeO2

Pt, Pd, Rh and V2O5 metallic monolith catalysts supported on Al2O3, Al2O3–TiO2 and Al2O3–CeO2 were examined in the oxidation of dichloromethane (DCM). To improve the selectivity towards HCl and to prevent catalysts’ deactivation, the water amount in the feed gas mixture was adjusted to 1.5 wt.%. All tested catalysts showed high activity in DCM oxidation and high selectivity towards HCl formation. Over Pt/Al2O3 and Rh/Al2O3, the 100% DCM conversions were reached at 420 °C and 440 °C and the maximum HCl yields detected were 92% and 93%, respectively. Addition of CeO2 to the Al2O3 support affected the activity only a little, while somewhat more visible enhancement was seen with the addition of Pt, Pd, Rh and V2O5. However, more positive effect on the HCl and/or CO2 yield was observed. Results showed that high acidity together with increased reducibility leads to an active catalyst for DCM oxidation. After the 40.3 h stability test no obvious change in the Pt/Al2O3 catalysts’ performance was seen. Characterization showed no carbonaceous species on the catalyst's surface, but instead, some chlorine was detected on the surface that at this point did not affect the catalyst's activity or selectivity. The DCM decomposition seems to proceed on the catalyst surface via detaching the chlorine atoms before the breakage of the hydrogen bonds, hence following the order of the lowest bond energy in each step.

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► All tested catalysts showed high activity in DCM oxidation.
► DCM oxidation was affected the most by GHSV, then with DCM and water concentration.
► Acidity and reducibility were key features when activity and selectivity are considered.
► After 40.3 h in DCM oxidation the Pt/Al2O3 catalyst proved to be stable.
► DCM decomposed by detaching the chlorine prior to breakage of hydrogen.