Tandem c-cl cleavage and oxidation over Pt/ZSM-5 catalysts for CH2Cl2 deep oxidation: Acidity - Redox synergy, rate - Limiting step, and catalyst stability

A Pt/ZSM-5-18 catalyst with a Si/Al molar ratio of 18 in the support was highly active for the oxidation of CH2Cl2, exhibiting high selectivity towards CO2 formation. The excellent performance can be attributed to its abundant surface acidity, which facilitates the C-Cl cleavage of CH2Cl2, as well as the strong oxidation ability of the Pt species that promotes the sequential oxidation of intermediates such as CH3Cl and CO. Quantitative analysis of the turnover frequencies (TOFs) further revealed that the C-Cl cleavage of CH2Cl2 is the rate-limiting step, while the oxidation of CH3Cl and CO on the Pt surface is more facile, with TOFs of 10-fold and 50-fold higher than that of the C-Cl cleavage, respectively. However, the rate-limiting step in CH3Cl oxidation is related to the oxidation step, suggesting a reactant-dependent kinetic relevance. The partial deactivation of the catalyst can be attributed to either coke deposition under dry conditions or competitive adsorption of water under wet conditions. Nonetheless, the catalyst's stability is hardly influenced by Pt aggregation through the migration of framework Al sites in the support.

Automated summary

The Pt/ZSM-5-18 catalyst with a Si/Al molar ratio of 18 in the support is highly active for the oxidation of CH2Cl2, showing high selectivity towards CO2 formation. The excellent performance is attributed to abundant surface acidity and strong oxidation ability. The rate-limiting step is the C-Cl cleavage of CH2Cl2, while the oxidation of CH3Cl and CO is more facile. The catalyst's stability is hardly affected by Pt aggregation.