Sodium titanate powders, solution

To optimize the use of the amorphous sodium titanate powders as catalyst substrates, it is important to fully characterize the ion-exchange properties of the material. Further, the solution properties of the active metal to be loaded onto the support will be an important parameter in the control of the adsorption process. For example, exposure of sodium titanate to a nickel salt solution does not guarantee that nickel will be loaded onto the sodium titanate, or that the nickel, if loaded, will be dispersed on an atomic level. Sodium titanate only behaves as a cation exchange material under certain pH conditions. The solution pH also influences the hydrolysis and speciation of dissolved nickel ions (3), which can form large polymeric clusters or colloidal particles which are not adsorbed by the sodium titanate via a simple ion-exchange process. 

This paper describes some of our initial studies of the solution properties of sodium titanate powders in order to understand and control the metal-loading process in the preparation of a heterogeneous catalyst from the materials. The purposes of this study are 1) to define the pH and concentration regimes in which nickel is loaded onto sodium titanate as monomeric ions via ion exchange, as polymeric clusters via hydrolysis, or as discrete particles of colloidal nickel hydroxide, and 2) to characterize the catalysts with respect to the dispersion of the active metal under reaction conditions by measuring the activity and selectivity of the catalysts for a known "structure-sensitive" reaction, the hydrogenolysis of n-butane. 

Three different nickel-loaded sodium titanates were prepared by exposing 5 gm of the sodium titanate powder to aqueous solutions of nickel nitrate containing sufficient nickel to incorporate one mole of nickel for every two moles of sodium on the support (corresponding to the stoichiometry associated with complete ion exchange). Each sample was prepared using different pH conditions (and thus, different Ni(II) concentrations) to vary the mechanism of... 

Titanium isopropoxide and NaOH are reacted in a molar ratio of 2 1, respectively, with the titanium isopropoxide added to the NaOH-methanol solution with stirring. Subsequently, hydrolysis is done by pouring the mixture into an acetone-water mixture containing 8.5 vol water one liter of the acetone-water mixture is required for each mole of titanium. The hydrolyzed material is coarse and can be easily and rapidly vacuum filtered through a 50 micrometer frit. After drying at ambient temperature under vacuum, dried titanate powder is then screened with the material which passes a Number bo U. S. Standard sieve and is retained on a Number l i0 U. S. Standard sieve being the desired fraction. Some properties of sodium titanate powder are listed in Table I. 

Titania powders not only with particulate morphology in different nano-sizes but also with fibrous morphology were synthesized. Even synthesis of nanotubes was reported under hydrothermal conditions from NaOH solution [26-30] and also nanofibers from KOH solution [31,32]. Both nanotubes and nanofibers thus prepared were later clarified to be protonated titania (titanate) [33-36]. A comprehensive review was published on protonated titanate nanotubes [37]. Effects of remnant sodium content and annealing temperature were studied on the structure and photoactivity of the nanotubes [38]. Titanate nanowires and nanoribbons were also reportedly formed [39,40]. Nano-sized Ti02 powders were obtained by annealing of titanate nanotubes and nanofibers [41]. Mesoporous anatase-type Ti02 powder was prepared by selective dissolution of silica component in Ti-Si binary oxides [42]. 

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