Platinum-based
supported catalysts for hydrocarbon conversion are
among the most effective for selective dehydrogenation and isomerization
processes. However, high process temperatures and the possibility
of coke formation require catalyst modifications to mitigate such
effects. One of the emerging approaches to prevent platinum catalyst
deactivation is the use of boron additives that have been proposed
to prevent coking. Despite such a valuable property of boron, the
mechanisms for extending the catalyst lifetime and the decrease in
coke formation based on this method are still poorly understood. The
type and transformations of boron species on silica surface were investigated
as a function of boron introduction, platinum addition, catalyst activation,
and catalytic reactivity by a combination of X-ray photoelectron spectroscopy,
electron microscopy, solid-state nuclear magnetic resonance spectroscopy,
and density functional theory calculations to uncover the possible
role of boron modification in improving the catalytic performance.
Catalytic nonoxidative dehydrogenation of n-butane
revealed that incorporation of boron improved the catalytic activity
(∼3×) and stability of Pt/SiO2. The role of
boron in enhancing catalytic performance was attributed to facilitating
the migration of alkyl groups from platinum catalytic centers to tetrahedrally
coordinated boron sites.
Isolated Pd atoms supported on high surface area MnO2, prepared by the oxidative grafting of (bis(tricyclohexylphosphine-palladium(0)), catalyze (> 50 turnovers, 17 h) the low temperature (≤ 325 K) oxidation of...
The coverage-dependent behaviour of p-methoxyacetophenone on the clean Si(001) surface was followed using X-ray photoelectron spectroscopy and supporting density functional theory calculations. Unlike other multifunctional organic molecules, this compound exhibits a high selectivity of adsorbate species formation by forming only two distinct adsorbate structures at low coverage, with a third configuration forming at high coverages. At low coverage, surface chemisorption is driven by methoxy group dissociation. However, at high coverage, the surface footprint required for this process is no longer available, leading to the formation of less thermodynamically stable adsorbates that are datively bonded to the surface with a smaller footprint. This coverage-dependent but well-defined behaviour is promising in designing functional organic-inorganic interfaces on silicon.
Preparation of supported metal nanoparticles for catalytic applications often relies on an assumption that the initially prepared wet-impregnated support material is covered with approximately a monolayer of adsorbed species that are shaped into the target nanoparticulate material with a desired size distribution by utilizing appropriate post-treatments that often include calcination and reduction schemes. Here, the formation and evolution of surface nanoparticles were investigated for wet-chemistry deposition of platinum from trimethyl(methylcyclopentadienyl)platinum (IV) precursor onto flat silica supports to interrogate the factors influencing the initial stages of nanoparticle formation. The deposition was performed on silicon-based substrates, including hydroxylated silica (SiO2) and boron-impregnated hydroxylated silica (B/SiO2) surfaces. The deposition resulted in the immediate formation of Pt-containing nanoparticles, as confirmed by atomic force microscopy and x-ray photoelectron spectroscopy. The prepared substrates were later reduced at 550 °C under H2 gas environment. This reduction procedure resulted in the formation of metallic Pt particles. The reactivity of the precursor and dispersion of Pt nanoparticles on the OH-terminated silica surface were compared to those on the B-impregnated surface. The size distribution of the resulting nanoparticles as a function of surface preparation was evaluated, and density functional theory calculations were used to explain the differences between the two types of surfaces investigated.
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