Probing toluene catalytic removal mechanism over supported Pt nano- and single-atom-catalyst

Commercial TiO₂ supported 0.20 wt% Pt catalyst is obtained via the molten salt method, and both Pt nanoparticles and single atom Pt sites are observed. It exhibits high catalytic performance for toluene oxidation, with T₅₀ and T₉₀ being 173 and 183 °C, respectively. Reaction intermediates including benzene, p-xylene, o-xylene, benzaldehyde, phthalic acid, maleic anhydride, itaconic anhydride, acetone, and acetic acid, are detected during toluene oxidation. On this basis, likely toluene combustion reaction pathway is provided. Benzaldehyde is the most stable surface intermediate, and its oxidation can be rate-limiting for the entire toluene oxidation reaction. 2-10.0 vol% H₂O slightly inhibits the reaction by competing surface sites with the reactant, while it does not poison the catalyst. 2.5-10.0 vol% CO₂ slightly poisons the catalyst by surface carbonate formation, whereas 50 ppm SO₂ severely poisons the catalyst by sulfite/sulfate formation.

TiO2 Nanotubes with Pt and Pd Nanoparticles as Catalysts for Electro-Oxidation of Formic Acid

In the present work, the magnetron sputtering technique was used to prepare new catalysts of formic acid electrooxidation based on TiO₂ nanotubes decorated with Pt (platinum), Pd (palladium) or Pd + Pt nanoparticles. TiO₂ nanotubes (TiO₂ NTs) with strictly defined geometry were produced by anodization of Ti foil and Ti mesh in a mixture of glycerol and water with ammonium fluoride electrolyte. The above mentioned catalytically active metal nanoparticles (NPs) were located mainly on the top of the TiO₂ NTs, forming 'rings' and agglomerates. A part of metal nanoparticles decorated also TiO₂ NTs walls, thus providing sufficient electronic conductivity for electron transportation between the metal nanoparticle rings and Ti current collector. The electrocatalytic activity of the TiO₂ NTs/Ti foil, decorated by Pt, Pd and/or Pd + Pt NPs was investigated by cyclic voltammetry (CV) and new Pd/TiO₂ NTs/Ti mesh catalyst was additionally tested in a direct formic acid fuel cell (DFAFC). The results so obtained were compared with commercial catalyst-Pd/Vulcan. CV tests have shown for carbon supported catalysts, that the activity of TiO₂ NTs decorated with Pd was considerably higher than that one decorated with Pt. Moreover, for TiO₂ NTs supported Pd catalyst specific activity (per mg of metal) was higher than that for well dispersed carbon supported commercial catalyst. The tests at DFAFC have revealed also that the maximum of specific power for 0.2 Pd/TiO₂ catalyst was 70% higher than that of the commercial one, Pd/Vulcan. Morphological features, and/or peculiarities, as well as surface composition of the resulting catalysts have been studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and chemical surface analytical methods (X-ray photoelectron spectroscopy-XPS; Auger electron spectroscopy-AES).

Vertically aligned Pt/TiO2 nanobelt films on Ti sheets for efficient degradation of a refractory ethyl thionocarbamate collector

Vertically aligned Pt/TiO₂ nanobelt films (Pt/TNFs) on Ti sheets are fabricated to effectively degrade a refractory ethyl thionocarbamate flotation collector.

Micelle-Assisted Electrodeposition of Mesoporous Fe-Pt Smooth Thin Films and their Electrocatalytic Activity towards the Hydrogen Evolution Reaction

Mesoporous Fe-Pt thin films are obtained by micelle-assisted electrodeposition onto metallic substrates with dissimilar activity (namely, gold, copper, and aluminum seed layers evaporated on Si/Ti) under constant applied potential (E=-1.1 V vs. Ag/AgCl) and deposition time (600 s). The amphiphilic triblock copolymer Pluronic P-123 is used as a soft template to guide the formation of mesopores. The occurrence of pores (ca. 7 nm in diameter) with narrow size distribution, distributed evenly over the surface, is observed in all cases. Despite the applied conditions being the same, the roughness and the amount of Fe incorporated in the films are influenced by the nature of the substrate. In particular, ultra-smooth films containing a larger amount of Fe (21 wt %) are obtained when deposition takes place on the Au surface. X-ray diffraction analyses reveal that Pt and Fe are alloyed to a certain extent, although some iron oxides/hydroxides also unavoidably form. The resulting films have been tested as electrocatalysts in the hydrogen evolution reaction (HER) in alkaline media. The mesoporous Fe-rich Fe-Pt films on Au show excellent HER activity and cyclability.

Controllable hydrothermal synthesis of Ni/H-BEA with a hierarchical core-shell structure and highly enhanced biomass hydrodeoxygenation performance

Ni based catalysts are wildly used in catalytic industrial processes due to their low costs and high activities. The design of highly hierarchical core-shell structured Ni/HBEA is achieved using a sustainable, simple, and easy-tunable hydrothermal synthesis approach using combined NH₄Cl and NH₃·H₂O as a co-precipitation agent at 120 °C. Starting from a single-crystalline hierarchical H⁺-exchanged beta polymorph zeolite (HBEA), the adjustment of the precipitate conditions shows that mixed NH₄Cl and NH₃·H₂O precipitates with proper concentrations are vital in the hydrothermal synthesis for preserving a good crystalline morphology of HBEA and generating abundant highly-dispersed Ni nanoparticles (loading: 41 wt%, 5.9 ± 0.7 nm) encapsulated onto/into the support. NH₄Cl solution without an alkali is unable to generate abundant Ni nanoparticles from Ni salts under the hydrothermal conditions, whereas NH₃·H₂O seriously damages the pore structure. After studying the in situ changes in infrared, X-ray diffractometry, temperature-programmed reduction, and scanning electron microscopy measurements, as well as variations in the filtrate pH, Si/Al ratios, and solid sample Ni loading, a two-step dissolution-recrystallization process is proposed. The process consists of Si dissolution and no change in elemental Al, and after the dissolved Si(iv) concentrations have promoted Ni phyllosilicate nanosheet solubility, further growth of multilayered Ni phyllosilicate nanosheets commences. The precursor Ni phyllosilicate is changeable between Ni₃Si₂O₅(OH)₄ and Ni₃Si₄O₁₀(OH)₂, because of competition in kinetically-favored and thermodynamically-controlled species caused by different basic agents. The superior catalytic performance is demonstrated in the metal/acid catalyzed biomass derived bulky stearic acid hydrodeoxygenation with 90% octadecane selectivity and a promising rate of 54 g g^-1 h^-1, which highly excels the reported rates catalyzed by Ni catalysts. Significant improvements in activity and selectivity are related to the highly dispersive Ni nanoparticles onto/into intra-mesopores of hierarchical HBEA, hence enhance the accessibility of bulky substrates to metal sites and mass transfer capacity.

NiCo nanotubes plated on Pd seeds as a designed magnetically recollectable catalyst with high noble metal utilisation

The tailored structure of a bifunctional, semi-homogeneous NiCo-nanotube catalyst system with embedded Pd nanoparticles, is synthesised by electroless plating.