Hydrocarbon oxidation and aldol condensation over basic zeolite catalysts

Ion-exchanged X zeolites, with and without occluded cesium, were tested as catalysts for hydrocarbon oxidation and aldol condensation. Infrared spectroscopy confirmed that combustion products were formed during the oxidation reactions. The reaction profile of 1-butene or butane oxidation over zeolite X in the range of 473-523 K revealed an induction time followed by a maximum in CO2 production. Ion-exchanged NaX and CsX exhibited a higher maximum CO2 production rate than MgX during butene oxidation at 473 K. Addition of Cs to CsX above ion-exchange capacity decreased the CO2 production rate, indicating that basicity was not important for the reaction. Silica, alumina and Cs-doped alumina were several orders of magnitude less active than NaX and CsX for 1-butene oxidation at 523 K. In general, the oxidation of butane was slower than that of 1-butene. The high electric field associated with cations in the zeolite pores is suggested to be important for the oxidation reactions. In contrast to hydrocarbon oxidation, the condensation reaction of propionic acid and formaldehyde to form methacrylic acid at 598 K depended on the basicity of the zeolite, with the activity increasing in the order NaX < KX < CsX. Increasing the basicity of CsX by occluding Cs in the pores beyond ion-exchange capacity further increased the activity. (C) 2006 Elsevier B.V. All rights reserved.