Characterization of transition-metal oxides promoted with oxoanions by means test reactions

VIVIANA MARÍA BENÍTEZ; JUAN CARLOS YORI; CARLOS ROMÁN VERA; CARLOS LUIS PIECK; JAVIER MARIO GRAU; JOSÉ MIGUEL PARERA

INDUSTRIAL & ENGINEERING CHEMICAL RESEARCH

Americam Chemical Society

Lugar: Columbus OH; Año: 2005 vol. 44 p. 1716 - 1722

0888-5885

The catalytic activity of some transition metal oxides known to develop “superacidity” by promotion with 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 thermal programmed desorption of pyridine and 2,4,6-trimethyl-pyridine, X-ray diffraction and sortometry.  SO42--ZrO2, SO42--TiO2, SO42--Fe2O3, WO3-ZrO2, WO3-TiO2, WO3-Fe2O3, B2O3-ZrO2, B2O3-TiO2 and B2O3-Fe2O3 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 follows the order:  S, W > B.  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 catalysts are the least active.