Hydroxylation/oxidation of benzene over Cu-ZSM-5 systems: Optimization of the one-step route to phenol

Aerobic one-step oxidation of benzene to phenol on copper exchanged HZSM5 zeolites: A mechanistic study

“…less polar zeolites, permit faster desorption. A preliminary study carried out with reduced O 2 /N 2 ratio to suppress the total oxidation and stepping up the temperature from 723 K to 823 K resulted in a clear rise of the total phenol yield (not shown here), which is in agreement with the findings in literature [4,5] and demonstrates the complexity of this multi-parameter system. To increase the selectivity to phenol, all side reactions including total oxidation and especially the formation of coke have to be suppressed.…”

“…It is obvious that a high copper loading promotes the formation of the deep oxidation products. These results correspond with the result of oxygen activation on the copper centers and with the observation that was made previously in literature [3][4][5]. The more copper centers are available in the zeolite the more oxygen molecules can be activated.…”

“…The catalysts which provide the best yields of phenol can be identified from figure 4. Obviously, the obtained amounts of phenol were not as high as it has been reported in literature [3][4][5]. However the main aim of this study is to understand the reaction mechanism on a molecular scale, so the small yields of phenol did not diminish our results.…”

“…Interestingly, other oxygenated products like benzoquinone and benzofuran were observed also in the absence of BrØnsted acid sites. Earlier gas phase work did not pay specific attention to the BrØnsted acid sites [2][3][4][5]. Ø On zeolites with a high affinity for the total oxidation, the formation of deep oxidation products (CO, CO 2 ) can be decreased by reducing the O 2 flow.…”

“…Hamada et al explored the gas-phase reaction on several Cu/HZM5-zeolites under different reaction conditions and reported a phenol yield up to 5% with a selectivity of nearly 30% [2][3][4]. Meanwhile phenol yields up to 10% have been reported [5], but the detailed reaction mechanism for the phenol formation is still unknown. Knowledge of the reaction mechanism would allow the modification of the catalysts and to increase the phenol yields.…”