Wet milling of H-ZSM-5 zeolite and its effects on direct oxidation of benzene to phenol

The direct oxidation of benzene to phenol with N2O over ZSM-5 catalysts suffers from the problem of rapid catalyst deactivation mainly due to the secondary transformation of phenol into heavier hydrocarbon compounds leading to the catalyst coking. In order to investigate the deactivation behavior of the ZSM-5 catalysts during this reaction, a comparative study was performed over ZSM-5 catalysts having different crystal sizes. The original catalyst was milled to two different periods of time to obtain catalysts having various crystal sizes. The original and the milled catalysts were tested for the benzene to phenol reaction to get an insight into the effect of crystal size on the catalyst deactivation. There was a decrease in catalyst deactivation with a decrease in crystal size. An indirect dependence of catalyst deactivation with total acidity was observed.

Graphical abstractZSM-5 catalyst (original; crystal size −5.5 μm) was wet milled for 30 min and 3 h to obtain catalysts of different crystal sizes (crystal sizes −440 nm and 220 nm). The original and milled catalysts were subjected to benzene to phenol oxidation. The smaller the crystals the lesser the catalyst deactivation. Figure optionsDownload full-size imageDownload as PowerPoint slide