No abstract

No abstract

The gas-phase catalytic oxidation of benzene was carried out using molecular oxygen as an oxidant over Cu-supported catalysts. Phenol was formed only when using Cu-supported high-silica-type zeolites as catalysts. The Cu-supported H-ZSM-5 zeolite (CuH-ZSM-5) was the most active among those tested. Deep oxidation products (CO and CO 2 ) were also produced together with phenol and they were suggested to form either via phenol or directly from benzene, based on the activity test experiments by varying the contact time. The yield and selectivity of phenol had a maximum with respect to the Cu contents in the CuH-ZSM-5, and were optimized with ca. a 0.77 wt.% Cu loading (phenol yield $4.9%). The calcination of the CuH-ZSM-5 at the higher temperature of around 1123 K was found to be effective for the phenol formation. The H-ZSM-5 with lower Si/Al atomic ratios was an effective support for the phenol formation. The EPR study revealed that the increase in the square-pyramidal Cu 2+ species was brought about when the CuH-ZSM-5 was calcined at higher temperatures or when HZSM-5 with lower Si/Al atomic ratios was used as a support. The isolated squarepyramidal Cu 2+ species was suggested to be the active species for the phenol formation.

No abstract

The liquid-phase oxidation of benzene was carried out in aqueous acetic acid solvent over V-substituted heteropolyacids (V−HPAs) using molecular O2 and ascorbic acid as the oxidant and reducing reagent, respectively. Phenol was exclusively obtained as the oxygenation product. The elimination of the V species from the V−HPA (Keggin structure) catalyst into the reaction solvent during the benzene oxidation reaction was largely inhibited by ion-exchanging the proton of the V−HPA catalyst with Cs+. The main active species were assumed to be the V species anchored in the HPA. The influences of the reaction temperature, the concentration of acetic acid in the aqueous solvent, and the reaction pressure on the yield of phenol were investigated to obtain the optimal reactions condition for phenol formation. The reuse of the V−HPA catalyst caused gradual deactivation for phenol formation, despite the retention of the structure of the V−HPA catalyst. The deactivation was suggested to be due to the reduction of the V species in the V−HPA catalyst on the basis of the diffuse reflection spectra of the used catalysts.