Search

Strontium titanate (STO) photocatalysts were prepared via a slightly modified Pechini sol–gel method. A unique rapid calcination technique with a short exposure time was used to obtain crystalline products. The samples were characterized by X-ray diffractometry, scanning electron microscopy, diffuse reflectance spectroscopy, infrared spectroscopy, nitrogen adsorption–desorption measurements, and X-ray photoelectron spectroscopy. Their photocatalytic activity was evaluated by the photocatalytic oxidation of phenol, oxalic acid, and chlorophenol under UV light irradiation using commercial STO as a reference. These pollutants, together with glucose and propanol, were used to investigate the stability of the samples against various functional groups. All our samples exhibited higher photocatalytic activity than the commercial STO reference. With increasing calcination temperature, the crystallinity and primary crystallite sizes increased while the band gaps and specific surface areas decreased. The photocatalytic activity of the most efficient sample was explained by the presence of SrCO3 on its surface. The STO catalysts were highly stable as they largely retained their crystalline composition after exposure to chemicals with different functional groups. Finally, we compared the costs associated with the unique calcination technique with a more conventional one and found that our method is ~35% more cost-effective. [ABSTRACT FROM AUTHOR]

Strontium titanates were prepared with different morphologies by varying the ratio of solvents used during the synthesis. The effects of morphology and solvent (ethylene glycol to water) ratio were investigated both on the structure and photocatalytic activity of the samples. Structural properties were determined by X-ray diffraction, scanning electron microscopy, diffuse reflectance spectroscopy, and nitrogen adsorption measurements. The photocatalytic activity of the samples was evaluated by the photocatalytic oxidation of phenol and by the photocatalytic reduction of carbon dioxide. The ratio of solvents notably influenced the morphology, strontium carbonate content, primary crystallite size, and specific surface area of the samples. Samples prepared at low ethylene glycol to water ratios were spherical, while the ones prepared at high ethylene glycol to water ratios could be characterized predominantly by lamellar morphology. The former samples were found to have the highest efficiency for phenol degradation, while the sample with the most well-defined lamellar morphology proved to be the best for CO2 reduction. [ABSTRACT FROM AUTHOR]

Pt nanoparticles with controlled sizes between 1.6-7.0 nm were anchored onto the surface and pores of SBA-15 silica support. The catalysts were characterized by TEM-ED, BET, XRD, and ICP-MS techniques and were tested in liquid phase hydrosilylation of phenylacetylene with triethylsilane. The activity of the 7.0 nm Pt nanoparticles anchored onto the surface of SBA-15 in hydrosilylation (TOF = 0.107 molecules·site-1·s-1) was ~2 times higher compared to the 5.0 nm Pt/SBA-15 (TOF = 0.049 molecules·site-1·s-1) catalyst and ~10 times higher compared to the 1.6 nm Pt/SBA-15 (TOF = 0.017 molecules·site-1·s-1) catalyst. Regarding the selectivity, bigger nanoparticles produced more vinylsilane-type products (α- and β-(E)-products) and less side products (mainly ditriethylsilane, triethyl(1-phenylethyl)silane and triethyl(phenethyl)silane derived likely from the reduction of the vinylsilane products). However, the selectivity towards the β-(E)-triethyl(styryl)silane was higher in the case of 1.6 nm Pt/SBA-15 catalyst compared to 5.0 nm Pt/SBA-15 and 7.0 nm Pt/SBA-15, respectively, which can be attributed to the beneficial effect of the size differences of the Pt nanoparticles as well as the differences of the quality and quantity of Pt/SiO2 interfaces. [ABSTRACT FROM AUTHOR]

Direct liquid fuel cells are very appealing alternatives for fighting climate change, particularly in the field of personal mobility solutions. This is especially true for direct methanol fuel cells (DMFCs) that use and burn safe fuels that are readily available from sustainable sources using well-established C1 chemistry. However, DMFCs also have some serious competitive disadvantages, like the high cost of the noble metal catalysts, the difficulties of the catalyst application, and the poisoning of the catalyst due to carbon monoxide formation. Here we demonstrate that depositing platinum on TiO2 by atomic layer deposition (ALD) is an easy, reproducible method for the synthesis of TiO2-supported platinum catalyst for methanol oxidation with superior anti-poisoning properties. [ABSTRACT FROM AUTHOR]

Formic acid (FA) can be considered both a CO and a H2 carrier via selective dehydration and dehydrogenation pathways, respectively. The two processes can be influenced by the modification of the active components of the catalysts used. In the present study the adsorption of FA and the decomposition of the formed formate intermediate were investigated on potassium promoted Rh(111) surfaces. The preadsorbed potassium markedly increased the uptake of FA at 300 K, and influenced the decomposition of formate depending on the potassium coverage. The work function (Δϕ) is increased by the adsorption of FA on K/Rh(111) at 300 K suggesting a large negative charge on the chemisorbed molecule, which could be probably due to the enhanced back-donation of electrons from the K-promoted Rh into an empty π orbital of HCOOH. The binding energy of the formate species is therefore increased resulting in a greater concentration of irreversibly adsorbed formate species. Decomposition of the formate species led to the formation of H2, CO2, H2O, and CO, which desorbed at significantly higher temperatures from the K-promoted surface than from the K-free one as it was proven by thermal desorption studies. Transformation of surface formate to carbonate (evidenced by UPS) and its decomposition and desorption is responsible for the high temperature CO and CO2 formation. [ABSTRACT FROM AUTHOR]

Rh is one of the most effective metals in several technologically important heterogeneous catalytic reactions, like the hydrogenation of CO2, and CO, the CO+H2O reaction, and methane and ethanol transformations. Titania and titanates are among the most frequently studied supports for Rh nanoparticles. The present study demonstrates that the nature of the support has a marked influence on the specific activity. For comparison, the catalytic activity of TiO2 P25 is also presented. It is pointed out that a certain amount of Rh can be stabilized as cation (Rh+) in ion-exchange positions (i.e., in atomic scale distribution) of the titanate framework. This ionic form does not exists on TiO2. We pay distinguished attention not only to the electronic interaction between Rh metal and the titania/titanate support, but also to the Rh-induced phase transitions of one-dimensional titanate nanowires (TiONW) and nanotubes (TiONT). Support transformation phenomena can be observed in Rh-loaded titanates. Rh decorated nanowires transform into the TiO2(B) phase, whereas their pristine counterparts recrystallize into anatase. The formation of anatase is dominant during the thermal annealing process in both acid-treated and Rh-decorated nanotubes; Rh catalysis this transformation. We demonstrate that the phase transformations and the formation of Rh nanoclusters and incorporated Rh ions affect the conversion and the selectivity of the reactions. The following initial activity order was found in the CO2 + H2, CO + H2O and C2H5OH decomposition reactions: Rh/TiO2 (Degussa P25) ≥ Rh/TiONW > Rh/TiONT. On the other hand it is remarkable that the hydrogen selectivity in ethanol decomposition was two times higher on Rh/TiONW and Rh/TiO(NT) catalysts than on Rh/TiO2 due to the presence of Rh+ cations incorporated into the framework of the titanate structures. [ABSTRACT FROM AUTHOR]