Metal-Support Interactions in Hydrous Titanium Oxide-Supported Nickel Catalysts

Abstract

A combination of techniques, including AES, SIMS, FTIR, and hydrogen chemisorption, has been used to investigate the activation of nickel ions supported on hydrous titanium oxide (HTO) ion-exchange materials.H T O supports allow metal ions to be loaded via ionvexchange such that atomic dispersion is attained in the as-prepared material, even for high metal loadings. The results presented here support earlier work indicating that nickel forms large, 10-20-nm particles during hydrogen reduction of N i / H T O at temperatures of 300 "C or greater. During reduction, these particles become covered by an amorphous film which inhibits catalytic activity. Evidence is presented which supports the theory that this film is composed of carbonaceous residue which originates from the organometallic precursors and organic solvents used to synthesize the H T O support. Reduction/oxidation cycles result in oscillations in the nickel surface concentration which are attributed to decoration of the particles by partially reduced TiO, species, in a manner similar to a strong metal-support interaction (SMSI). This SMSI occurs at temperatures as low as 300 O C , well below the temperatures typically required to induce SMSI on crystalline titania supports. This low onset temperature appears to be related to the amorphous nature of the H T O support, which may be more easily reduced than crystalline titania. Mild oxidation.(300 "C) of N i / H T O prior to reduction increases the amount of metal surface area which is formed during reduction by altering the interaction of the nickel ions with the support such that smaller nickel particles are formed. More severe oxidation treatments (>400 "C) lead to a decrease in active surface area by increasing the interaction of nickel ions with the support such that a smaller fraction of the nickel ions can be reduced and participate in particle formation.

Importance of Size and Distribution of Ni Nanoparticles for the Hydrodeoxygenation of Microalgae Oil

“…In the spectra with adsorbed CO under equilibrium pressure, bands above 2100 cm À1 were detected, which are typical for carbonyls formed with Ni cations. [20][21][22][23] The reduction temperature at 460 8C was lower than the maxima of reduction in the TPR profiles for the latter three samples ( Figure 2). This led to the presence of cationic Ni.…”

Determination of Polycarbonyl Species on Nickel-Containing Catalysts by Adsorption of CO Isotopic Mixtures

“…Generally, CO is adsorbed on flat nickel surfaces in linear and bridged forms [32]. When the surfaces are rough (usually when the metal particles are small) nickel tetracarbonyl is formed [33][34][35].…”

A radium assay technique using hydrous titanium oxide adsorbent for the Sudbury Neutrino Observatory

“…(Hydrous titanium oxide is a non-stoichiometric compound so the chemical formula HTiO is only representational.) Hydrous titanium oxide is an inorganic ion-exchanger [3,4] that has been used in the nuclear industry for the extraction of heavy ions. It is formed as a white colloidal suspension by the hydrolysis of titanium salts [5], which forms particles of sizes ranging from 1 to 100 microns, with a mode at around 10 microns.…”

“…The HTiO is produced by adding 400 ml of 15% w/v Ti(SO 4 ) 2 to 3 l of ultrapure water (UPW) and then adjusting to pH 12 with 3.5 l of 0.5 M NaOH. After allowing the solution to sit in a cool dark area for one week, it is rinsed with UPW to reduce the Na + and SO 4 2− contaminants. The first step in rinsing the HTiO involves reducing the volume of the undisturbed HTiO solution to ∼5 l by aspirating the supernatant.…”