Abstract
Substitution of transition metals for either aluminum and/or phosphorus in the AIPO 4-11 framework is found to afford novel heterogeneous catalysts for liquid phase hydroxylation of phenol with hydrogen peroxide. AlPO 4-11 is more active than SAPO-11 and MgAPO-11 for phenol conversion to hydroquinone. Substitution of transition metal cations, such as Fe, Co and Mn significantly improves the conversion of phenol. The activity follows the order of FeAPO-11 > CoAPO-11 > FeMnAPO-11 > MnAPO-11 ≫ AlPO 4-11. FeAPO-11, FeMnAPO-11 and CoAPO-11 give similar product selectivities of about 1:1 hydroquinone (HQ) to catechol (CT) whereas MnAPO-11 favors the production of catechol. FeAPO-11 show comparable performance to TS-1 (titanium silicate with MFI topology) for phenol conversion, with TS-1 giving higher selectivities toward hydroquinone. Medium pore size CoAPO-11 was more active than larger pore CoAPO-50, -36 and -5. The external surfaces of the catalysts play a significant role in these oxidation reactions.
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