Abstract
Ru/TiO2 are promising heterogeneous catalysts in different key-reactions taking place in the catalytic conversion of biomass towards fuel additives, biofuels, or biochemicals. TiO2 supported highly dispersed nanometric-size metallic Ru catalysts were prepared at room temperature via a solar light induced photon-assisted one-step synthesis in liquid phase, far smaller Ru nanoparticles with sharper size distribution being synthesized when compared to the catalysts that were prepared by impregnation with thermal reduction in hydrogen. The underlying strategy is based on the redox photoactivity of the TiO2 semi-conductor support under solar light for allowing the reduction of metal ions pre-adsorbed at the host surface by photogenerated electrons from the conduction band of the semi-conductor in order to get a fine control in terms of size distribution and dispersion, with no need of chemical reductant, final thermal treatment, or external hydrogen. Whether acetylacetonate or chloride was used as precursor, 0.6 nm sub-nanometric metallic Ru particles were synthesized on TiO2 with a sharp size distribution at a low loading of 0.5 wt.%. Using the chloride precursor was necessary for preparing Ru/TiO2 catalysts with a 0.8 nm sub-nanometric mean particle size at 5 wt.% loading, achieved in basic conditions for benefitting from the enhanced adsorption between the positively-charged chloro-complexes and the negatively-charged TiO2 surface. Remarkably, within the 0.5–5 wt.% range, the Ru content had only a slight influence on the sub-nanometric particle size distribution, thanks to the implementation of suitable photo-assisted synthesis conditions. We demonstrated further that a fine control of the metal Ru nanoparticle size on the TiO2 support was possible via a controlled nanocluster growth under irradiation, while the nanoparticles revealed a good resistance to thermal sintering.
Highlights
The crucial role that is played by heterogeneous catalysis in industrial chemical processes usually requires the engineering of tailored supported metal nanoparticles as catalysts, since the catalytic activity and the reaction rates can be strongly influenced by both the shape and the size of supported metallic nanoparticles [1,2,3]
Photolysis of the ruthenium precursors could be neglected under solar light in our experimental conditions, since no disappearance of the main absorption peaks that were assigned to both precursors was observed whatever the precursor used
We proved the effectiveness of an elegant low-temperature one-step photon-assisted synthesis method taking advantage of the redox photoactivity of the TiO2 semi-conductor support under solar light, for preparing highly dispersed TiO2 supported metallic Ru catalysts that are promising heterogeneous catalysts in different key-reactions that are involved in the catalytic biomass conversion into fuel additives, biofuels, or biochemicals
Summary
The crucial role that is played by heterogeneous catalysis in industrial chemical processes usually requires the engineering of tailored supported metal nanoparticles as catalysts, since the catalytic activity and the reaction rates can be strongly influenced by both the shape and the size of supported metallic nanoparticles [1,2,3]. The low-temperature and one-step photon-assisted synthesis method differs from the most widely used preparation methods, for which a final post-deposition reduction/activation/ step is required to form the supported metallic particles after the metal precursor has been introduced onto the support carrier, and usually consisting either in a thermal treatment with the use of external hydrogen, or in a chemical reduction in solution with external reducing agent [8]. The influence of the synthesis parameters on the deposition rate and on the metallic nanoparticle shape and it was investigated in some early studies [9], the photodeposition synthesis method has been mainly used for preparing catalytic and photocatalytic materials consisting in monometallic and more scarcely bimetallic particles being dispersed on a medium or high surface area support. TiO2 was the main semi-conductor support used, other materials, such as
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