ABSTIWCTWe report propane dehydrogenation behavior of catalysts prepared using two novel synthesis strategies that combine inverse micelle Pt nanocluster technology with silica and alumina sol-gel processing. Unlike some other sol-gel catalyst preparations. Pt particles in these catalysts are not encapsulated in the support structure and the entire Pt particle surface is accessible for reaction. Turnover frequencies (TOF) for these catalysts are comparable to those obtained over Pt catalysts prepared by traditional techniques such as impregnation, yet the resistance to deactivation by carbon poisoning is much greater in our catalysts. The deactivation behavior is more typical of traditionally prepared PtSn catalysts than of pure Pt catalysts.
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.
XRD analysis of plasma-vapor-deposited
ErT2 films during aging (T decay to
3He) reveals an hkl-dependent unit-cell expansion in which (200) grains expand out-of-plane as much as 0.01 Å more than (111) out-of-plane grains. Texture analysis of an aged
ErT2 film reveals a bimodal (111)/(200) out-of-plane preferred orientation. sin2 ψ analysis reveals significant in-plane macro-strain due to
3He
bubble formation/growth. The mechanistic origins regarding these observations are also discussed.
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