Electrochemical characterization of two different framework Ti(IV) speciesin Ti/Beta zeolites in contact with solvents

Five Ti/Beta zeolites prepared by the conventional hydroxide procedure or b y using fluoride as mineralizer have been studied by cyclic voltammetry and pulse voltammetry. Three peak couples (AA', BB' and CC') were recorded. Th e AA' peak was due to Ti atoms leached to the solution. Peak BB' is relativ ely insensitive to the electrolyte salt, while the reduction potential of C C' decreases progressively from perchlorate or nitrate to chloride and brom ide. This suggests the presence of two framework Ti populations, one less p rone to expand its coordination number (proposed to be Ti(OSi=)(4)) and oth er Ti atoms that coordinate with ligands within the short timescales of the electrochemical measurements (either (=SiO)(3)TiOH or (=SiO)(2)Ti(OH)(2) t itanols).