Caracterización de óxidos de metales de transición promovidos con oxoaniones por medio de reacciones test

V.M. BENÍTEZ; J.C. YORI; C.R. VERA; C.L. PIECK; J.M. GRAU; J.M. PARERA

Mérida, Yucatán, México

Simposio; XIX Simposio Iberoamericano de Catálisis; 2004

Instituto Mexicano del Petróleo - UNAM

The catalytic activity of some transition metal oxides known to develop “superacidity” by promotion with certain oxoanions was compared with a set of acid-catalyzed test reactions (isomerization of n-butane, isobutene, n-hexane and cyclohexane). They were further characterized by pyridine thermal programmed desorption, X-ray diffraction and sortometry. SO42--ZrO2, SO42--TiO2, SO42--Fe2O3, WO3-ZrO2, WO3-TiO2, WO3-Fe2O3, B2O3-ZrO2, B2O3-TiO2 (BTi) and B2O3-Fe2O3 (BFe) were synthesized by impregnation of the oxoanion over a fresh xerogel of the transition metal hydroxide. Certain promoter-dependent orders, irrespective of the support, could be elucidated, mainly that the number of acid sites generated by promotion is highest for S, W and B following. The proportion of strong acid sites is most important for S and B. The most active catalyst are always the zirconia ones while the Fe2O3 are the less active. The acidity and activity patterns are rationalized with known models of acidity generation and carbenium ion chemistry. Key words: superacids, test reactions, titania, zirconia, iron, tungsten, boron, sulfate.