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Influence of La2O3 Promoter on the Structure of MnOx/SiO2 Catalysts

Domenii publicaţii > Stiinte ingineresti + Tipuri publicaţii > Articol în revistã ştiinţificã

Autori: Radu Craciun, Nicu Dulamita

Editorial: Catalysis Letters, 46(3-4), p.229-234, 1997.


X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis have been used to characterize the structure of a La2O3 promoted MnOx/SiO2 catalyst, before and after its utilization in ethylbenzene (EB) oxidative dehydrogenation. MnOx/SiO2 and MnOx/La2O3/SiO2 catalysts were prepared by pore volume impregnation, using aqueous solutions of i) La3+-nitrate at an atomic ration of La/Si = 0.08, and ii) Mn2+-nitrate at an atomic ratio of Mn/Si = 0.10, followed by drying and calcination at 500C in air. XRD data show no diffraction patters specific to MnOx on the La2O3 promoted MnOx/SiO2 catalyst, after calcination. Thus, the presence of La2O3 apparently favors the dispersion of manganese oxides during calcination, presumbly by forming mixed Mn-La oxides. On the fresh promoted and unpromoted catalysts, after calcination, XRD and XPS analyses indicated that Mn was present mostly as MnO2 and Mn2O3. Manganese in the unpromoted catalyst has degenerated from Mn4+ to Mn2+, resulting in formation of Mn3O4 species whereas in the case of La promoted catalyst Mn remains well dispersed as MnO2 and Mn2O3. It appears that La2O3 precludes the formation of Mn3O4 during the EB dehydrogenation, conserving Mn structure and oxidation state.

Cuvinte cheie: La2O3/MnO2/SiO2 catalyst, XRD,TPR, XRD, ethylbenzene oxidative dehydrogenation