Oxoanion promoted transicion metal oxides for hydrocarbon isomerization

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

Paris, Francia

Congreso; 13th International Congress on Catalysis; 2004

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.  They were further characterized by pyridine TPD, XRD and sortometry.  SO42--ZrO2 (SZ), SO42--TiO2 (STi), SO42--Fe2O3 (SFe), WO3-ZrO2 (WZ), WO3-TiO2 (WTi), WO3-Fe2O3 (WFe), BO33--ZrO2 (BZ), BO33--TiO2 (BTi) and BO33--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:  (i) number of acid sites generated by promotion:  S > B > W; (ii) fraction of sites desorbing at high temperature:  S,B > W.  (iii) n-butane conversion B, S > W.  (iv) selectivity to isobutane:  W > B,S.  (v) iso-butene conversion: S > B,W. (vi) C5-C6 conversion: S > B,W. (vii) selectivity to isohexanes S,B > W.  When comparing different supports promoted with the same anion, most results indicate that ZrO2 yields the most active ones while Fe2O3 the least.  With respect to the selectivity there is no definite trend and the pattern seems to be linked only to the kind of anion involved.  S and B have similar features with both skeletal branching and cracking contributions while W promoted catalysts have mainly mild isomerization features.