DEACTIVATION OF NACL B2O3/FE2O3 CATALYSTS AND THEIR IMPROVEMENT FOR THE OXIDATIVE COUPLING OF METHANE/

In the present work, the deactivation of the NaCl/B2O3/Fe2O3 catalysts was studied for the oxidative coupling of methane. Several techniques , such as XPS, XRD, SEM, H-2-TPR, and flow-reaction, were employed to examine the function of each catalyst component, and its change during the catalytic reaction. NaCl and B2O3 show a synergistic effect on th e Fe2O3 surface. B2O3 modifies the oxidative activity of Fe2O3 and mak es the first reduction peak of Fe2O3 shift from 490 to 750 degrees C. The NaCl modified B2O3/Fe2O3 catalyst has high reduction rate, high ac tivity and selectivity at about 750 degrees C. It is demonstrated that the deactivation of the NaCl/B2O3/Fe2O3 catalysts is a complicated pr ocess, consisting of chloride loss, sodium change, B2O3 loss, silica d eposition and catalyst sintering. The chloride loss enhances the surfa ce basicity, which causes the silica deposition and sodium change, and aggravates the catalyst sintering. The silica deposition and catalyst sintering cause permanent deactivation. The B2O3 loss is not a direct reason for catalyst deactivation. NaCl crystal diluted NaCl/B2O3/Fe2O 3 catalysts have a better stability. The deactivated catalyst has a mo re stable structure. When it is regenerated by impregnating with NaCl again, a more stable catalyst can be obtained.