Influence of the Co/Al ratio and the temperature of thermal treatment on cobalt speciation and catalytic properties of Co-ZSM-5 prepared by solid-state ion exchange

Physico-chemical and catalytic properties of cobalt-containing ZSM-5 zeolite prepared by solid-state ion exchange were compared as a function of both the Co/Al molar ratio and the temperature of thermal treatment. The catalysts were characterized by chemical analysis, XRD, N2 BET, TEM/EDX, H2 TPR, FTIR, XANES, EXAFS and TPD of NH3. The preparation procedure results in the disappearance of Brønsted acid sites and the creation of new Lewis acid sites, as suggested by TPD of NH3 and FTIR of pyridine adsorption. TEM/EDX shows that for a Co/Al ratio of 1/2, cobalt is present as exchanged ions in the zeolite and as oxide particles on the support; whilst for a Co/Al ratio of 1 or 3/2, a cobalt phyllosilicate phase is present at the outer surface of the zeolite. Catalyst prepared with the Co/Al ratio of 1 at 500 °C exhibits high activity and selectivity toward acetonitrile in the ammoxidation of ethane and ethylene.

Ammoxidation of ethylene was tested over Co-ZSM-5 catalysts. The Co/Al molar ratio and the temperature of thermal treatment had an important influence on the physico-chemical and catalytic properties. The preparation procedure results in the disappearance of Brønsted acid sites and the creation of new Lewis acid sites. Furthermore, TEM/EDX and EXAFS show that for Co/Al = 1 and 3/2, a cobalt phyllosilicate phase is present at the outer surface of the zeolite.Figure optionsDownload as PowerPoint slide