RESUMO
The induction of chemical processes by plasmonic systems is a rapidly growing field with potentially many strategic applications. One of them is the transformation of solar energy into chemical fuel by the association of plasmonic metal nanoparticles (M NPs) and a semi-conductor (SC). When the localized surface plasmon resonance (LSPR) and the SC absorption do not match, one limitation of these systems is the efficiency of hot electron transfer from M NPs to SC through the Schottky barrier formed at the M NP/SC interfaces. Here we show that high surface area 1 wt% Au/TiO2-UV100, prepared by adsorption of a NaBH4-protected 3 nm gold sol, readily catalyzes the photoreduction of carbon dioxide with water into methane under both solar and visible-only irradiation with a CH4vs. H2 selectivity of 63%. Tuning Au NP size and titania surface area, in particular via thermal treatments, highlights the key role of the metal dispersion and of the accessible Au-TiO2 perimeter interface on the direct SC-based solar process. The impact of Au NP density in turn provides evidence for the dual role of gold as co-catalyst and recombination sites for charge carriers. It is shown that the plasmon-induced process contributes up to 20% of the solar activity. The plasmon-based contribution is enhanced by a large Au NP size and a high degree of crystallinity of the SC support. By minimizing surface hydroxylation while retaining a relatively high surface area of 120 m2 g-1, pre-calcining TiO2-UV100 at 450 °C leads to an optimum monometallic system in terms of activity and selectivity under both solar and visible irradiation. A state-of-the-art methane selectivity of 100% is achieved in the hot electron process.
RESUMO
The Fischer-Tropsch synthesis (FTS) is a structure-sensitive exothermic reaction that enables catalytic transformation of syngas to high quality liquid fuels. Now, monolithic cobalt-based heterogeneous catalysts were elaborated through a wet chemistry approach that allows control over nanocrystal shape and crystallographic phase, while at the same time enables heat management. Copper and nickel foams have been employed as supports for the epitaxial growth of hcp-Co nanowires directly from a solution containing a coordination compound of cobalt and stabilizing ligands. The Co/Cufoam catalyst was tested for Fischer-Tropsch synthesis in a fixed-bed reactor, showing stability and significantly superior activity and selectivity towards C5+ compared to a Co/SiO2 -Al2 O3 reference catalyst under the same conditions.
RESUMO
Selective hydrogenation is an important process in petrochemistry to purify feedstock for polymer synthesis. For this process, catalysts containing metallic palladium deposited with an eggshell distribution on porous alumina are usually employed. For this kind of catalyst, the activity is known to be in close relation with the thickness of the palladium crust. As palladium oxide is brown and alumina is white, the palladium distribution in a catalyst bead before the reduction step can be characterized by optical microscopy. We propose an original and automatic procedure of optical image analysis to obtain a fast and robust method to measure the mean crust thickness of a catalyst batch and the corresponding standard deviation. The approach is validated by two different methods. First, we compared the crust thickness with those obtained by electron probe microanalysis. Then, catalytic tests of four samples with varying palladium crust thicknesses were performed and confirmed the expected correlation between activity and crust thickness measured by optical microscopy coupled with image analysis.
RESUMO
A 'co-templating' strategy supported by molecular modelling has been used to prepare, for the first time, silicoaluminophosphates with the SAV and KFI framework topologies, each of which has a three-dimensionally connected pore system with high specific volume.
