Characterization of MnAPO-5 for Ethane Oxydehydrogenation

Manganese-substituted AlPO4-5 molecular sieve (MnAPO-5) was characterized by temperature-programmed reduction (TPR) and diffuse reflectance UV−Vis and electron paramagnetic resonance (EPR) spectroscopies, and the results were compared with those of manganese oxides impregnated on AlPO4-5 (Mn/AlPO4-5). It was found from TPR that the manganese interacted strongly with the aluminophosphate surface in MnAPO-5. Higher temperatures were required to reduce the manganese species on MnAPO-5 by hydrogen than to reduce those on Mn/AlPO4-5. The TPR, UV−Vis, and EPR results indicate that Mn2+ or Mn3+ was the major oxidation state of manganese in MnAPO-5, in which a small amount of MnO2 or Mn2O3 was also found. O2- was observed from AlPO4-5, MnAPO-5, and Mn/AlPO4-5 by EPR at gzz = 2.021, gxx = 2.008, and gyy = 2.003; it existed on the surface of the aluminophosphate rather than being associated with manganese on either MnAPO-5 or Mn/AlPO4-5. A kinetic model involving oxygen and ethane adsorption was proposed for ethane...