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

No abstract

No abstract

The utilization of copper-impregnated HZSM-5 (Cu/HZSM-5) zeolites as catalysts for the gasphase catalytic oxidation of benzene was attempted. The major products were phenol, carbon dioxide, and carbon monoxide. The Si/Al ratio in the HZSM-5 support of the Cu/HZSM-5 catalyst influenced both the yield of and the selectivity for phenol, both of which increased with a decrease in the Si/Al atomic ratio of the HZSM-5 support with constant Cu loading. The amount of carbon monoxide uptake of the prereduced Cu/HZSM-5 catalysts decreased with a decrease in the Si/ Al atomic ratio of the HZSM-5 support of the Cu/HZSM-5 catalyst. The yield of phenol over the Cu/HZSM-5 catalyst increased, along with both the yield of CO 2 and CO, by adding water vapor in the reaction system. The oxygen species adsorbed on the Cu/HZSM-5 catalyst were suggested to be responsible for the formation of phenol, based on the results of the transition response experiment. The amount of the isolated Cu 2+ species with square-pyramidal configuration on the Cu/HZSM-5 catalyst estimated from the ESR observation was found to have a correlation with the yield of phenol.

The liquid-phase catalytic oxidation of benzene was carried out under mild reaction conditions over Cuimpregnated zeolite catalysts (Cu/NaX, Cu/HX, Cu/NaY, Cu/HY, Cu/NaZSM-5, Cu/HZSM-5, Cu/Namordenite, Cu/Hmordenite, and Cu/Hbeta) using both molecular oxygen and ascorbic acid as the oxidant and the reducing reagents, respectively. Phenol was exclusively produced as the oxidation product and no other product was detected. Among the catalysts tested in this study, the Cu/HY catalyst had the highest activity for phenol formation. H-type zeolites were more effective supports for phenol formation than the corresponding Na-type ones. The yield of phenol was found to increase with the simultaneous increase in the amounts of both the supported Cu and the added ascorbic acid. The Cu species supported on HY began to elute as Cu 2+ species in the solvent from the HY support with the initiation of the oxidation of benzene. The dissolved Cu 2+ species were reduced to form precipitated Cu 1+ species during the benzene oxidation. The homogeneous Cu species dissolved from the Cu/HY catalyst were thus suggested as mainly contributing to the phenol formation. The precipitated Cu 1+ species that had no activity for the benzene oxidation were found to be regenerated in their oxidation activity toward phenol formation by calcination of the Cu 1+ species in flowing air, although parts of the Cu species were found to be converted to aggregated CuO during the calcination.Résumé : On a effectué l'oxydation catalytique du benzène en phase liquide, dans des conditions douces, sur des catalyseurs de zéolite imprégnée de cuivre (Cu/NaX, C/HX, Cu/NaY, Cu/HY, Cu/NaZSM-5, Cu/HZSM-5, Cu/Namordenite, Cu/Hmordenite et Cu/Hbeta), en utilisant de l'oxygène moléculaire et de l'acide ascorbique respectivement comme agents oxydant et réducteur. Le seul produit d'oxydation est le phénol et aucun autre produit n'a été détecté. Parmi les catalyseurs évalués dans cette étude, le catalyseur Cu/HY présente l'activité la plus élevée pour la formation de phénol. Les zéolites du type H sont des supports plus efficaces que les supports correspondants de type Na pour la formation de phénol. On a observé que le rendement en phénol augmente avec une augmentation simultanée dans les quantités à la fois du Cu supporté et de l'acide ascorbique ajouté. Les entités de Cu supportées sur HY commencent à s'éluer du support HY vers le solvant, sous la forme de cations Cu 2+ , dès le début de l'oxydation de benzène. Au cours de l'oxydation du benzène, les cations Cu 2+ sont réduits en espèces Cu 1+ qui précipitent. On suggère donc que les espèces Cu homogènes, dissoutes du catalyseur Cu/HY, sont les principales à contribuer à la formation du phénol. On a observé que, si on soumet les espèces Cu 1+ qui ont précipité à une calcination avec circulation d'air, elles peuvent être partiellement régénérées dans leur activité oxydante conduisant à la formation de phénol, même si une certaine partie de ces entités est transformée en CuO agrégé au cours de cette calcination.

No abstract