Competitive Adsorption and Interaction of Benzene and Oxygen on Cu/HZSM5 Zeolites

The competitive adsorption of benzene and oxygen on Cu/HZSM5 zeolites has been studied by FTIR and EPR to understand the gas-phase oxidation of benzene to phenol using molecular oxygen. Benzene proved to be the stronger adsorbate on copper, leading to a poisoning of the catalyst. Phenol, water, and deep combustion products could be detected. The evolution of the benzene radical cation was observed in situ, while benzene and oxygen were adsorbed on the sample either simultaneously or alternatingly. At the same time, the total spin density of the sample and thus the oxidation state of copper were monitored. A new reaction path based on the interplay of the zeolitic hydroxyl groups and the exchanged copper ions was proposed. The benzene resides inside the zeolites channel intersections, but due to benzene molecules blocking the channels, the products are hardly able to diffuse out and thus have to be extracted.