Direct hydroxylation of benzene to phenol by nitrous oxide on amorphous aluminium-iron binary phosphates

• The iron content has a decisive influence on the catalytic behaviour of the amorphous iron aluminium phosphates.
• Aluminium iron phosphates with iron contents ≤1 wt% provided optimum yields to phenol.
• Isolated iron species as active sites in the benzene hydroxylation.

The effect of iron content (Fe/Al molar ratio = 0.01–1 equivalent to the iron percentages from 0.5 to 20.5 wt%) and thermal treatment (450–650 °C) of aluminium-iron phosphates, prepared by an ammonia gelation method, on their catalytic performances in the one-step hydroxylation of benzene to phenol by N2O, has been investigated. The solids have been characterized by ICP-MS, EDX, XRD, DRIFT, DR UV–V, XPS, and N2 adsorption techniques. The results obtained showed the critical role of iron content in the catalytic behaviour of binary phosphates while thermal treatment hardly had effect. Phosphates with a lower amount of iron exhibited the best yield to phenol that was similar to those reported in the literature for Fe-MFI type catalysts. Thus, yield to phenol of 22% (0.7 gPhe/gcat h) at 350 °C has been achieved on the binary phosphate with Fe/Al = 0.02 (1 wt% of iron) calcined a 450 °C, in which highly dispersed iron species exist.

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