Probing the effect of spatial morphology of catalyst on its photothermal catalytic performance is crucial for solar-driven renewable catalytic reforming of hydrogen production . In this study, Au nanoparticles loaded on various morphologies of TiO 2 nanoparticles were synthesized and characterized. The experimental results indicated that decorating TiO 2 with Au nanoparticles could dramatically increase its photocatalytic activities by 20–40 times. The photothermal conversion efficiency of Au/TiO 2 (12.74%–25.54%) was higher than those of TiO 2 due to the introduction of LSPR of Au nanoparticles could effectively improve the utilization of solar spectrum. Titania nanoflower (TNF) nanoparticles with high light absorption capacity , better colloidal dispersion stability , porous properties and narrow band gap represented the highest H 2 productivity (144.13 μmol·g −1 ·h −1 ). The coarse surface structure was also conducive to the dispersion of gold particles on the surface of the carrier and the growth rate of Au/TNF hydrogen production (40 times) which was higher than that of other morphology within 2 h. The results of glycerol photothermal hydrogen generation highlighted the effect of temperature on colloidal dispersion stability and hydrogen production capability of nanoparticle suspension. It demonstrated that the photothermal effect aroused a temperature rise that would deteriorate the dispersion stability of the suspension although a local entropy increase in the catalyst nanoparticles might occur. At the same time, the temperature rise caused by the photothermal effect efficiently produces hydrogen in the reaction temperature range. Therefore, an ideal temperature setting for maximal hydrogen generation could be validated and improved the photothermal synergistic impact on biomass-reformed hydrogen generation.
The 5-hydroxymethylfurfural oxidation reaction (HMFOR) is regarded as a promising approach to produce biomass-derived highly valuable chemical products. 5-Hydroxymethyl-2-furancarboxylic acid (HMFCA) as a typical product via selective oxidation of the aldehyde group in HMF was obtained on Au/anatase and Au/rutile catalysts under photoexcited and dark states. The results show that the HMF oxidation reactivities of Au/rutile and Au/anatase were improved under visible light irradiation compared with those under dark conditions, and the increase of the activity is more obvious as the reaction temperature decreases. The kinetic studies showed that visible light irradiation reduced the energy barrier of the HMF oxidation reaction and promoted the reaction activities. The radical capture and EPR experiments were further used to explore the mechanisms of the HMF oxidation reaction under both conditions over Au/TiO2 catalysts. The evidence indicated that the main active species were 1O2 and trace amounts of •O2– under dark conditions, while the main active species were •O2–, 1O2, and h+ under visible light irradiation conditions for both Au/rutile and Au/anatase catalysts.
Transfer hydrogenation of unsaturated nitro compounds by NH 3 BH 3 is an important hydrogenation reaction. Among them, Au/TiO 2 catalysts could achieve good activity for this reaction, but often have problem such as the selectivity decline. In this study, we prepare PVA-wrapped Au nanoparticles, and then load them onto TiO 2 support to obtain Au/TiO 2 catalyst. We demonstrate that the prepared catalyst after calcination has achieved high activity (>99 %) and high selectivity (99 %) in the transfer hydrogenation of 4-nitrostyrene (4-NS) within 30 min by NH 3 BH 3 under ambient temperature and pressure. In addition, the catalyst can still maintain high selectivity (>97 %) after being recycled for 5 times, showing its remarkable stability and reusability. Characterization results and density functional theory (DFT) calculations showed that the presence of Au-OH species accelerates the dehydrogenation of NH 3 BH 3 and thus enhances the catalytic activity. Meanwhile, Au-OH species and low-coordinated Au are beneficial to enhance nitro adsorption and improve the selectivity of transfer hydrogenation reaction. This study provides new ideas for the rational design of high-performance green gold catalytic transfer hydrogenation reactions.
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