Xuzhuang Yang

Reduction of Nitroaromatic Compounds on Supported Gold Nanoparticles by Visible and Ultraviolet Light

Shedding light: Nitroaromatic compounds on gold nanoparticles (3 wt %) supported on ZrO2 can be reduced directly to the corresponding azo compounds when illuminated with visible light or ultraviolet light at 40 °C (see picture). The process occurs with high selectivity and at ambient temperature and pressure, and enables the selection of intermediates that are unstable in thermal reactions.

Selective oxidation of methanol to methyl formate on catalysts of Au–Ag alloy nanoparticles supported on titania under UV irradiation

We find that the Au–Ag alloy nanoparticles supported on titania exhibit superior methanol conversion and methyl formate selectivity for selective oxidation of methanol by low partial pressure oxygen in air under UV irradiation in the 15 °C–45 °C temperature range, with the highest methanol conversion above 90% and the highest selectivity towards methyl formate above 85%. The only by-product definitely detected is CO2. The superior photocatalytic performance of the catalyst is closely related to the special structure of the catalyst and the electronic properties of the alloy, which reduce the recombination of the photo-excited electron–hole pairs by transferring the photo-excited electrons in time from the conduction band of titania to the alloy on the one hand, and elevate the negative charge level of the alloy surface by the spd hybridization, the formation of Schottky barriers, the electron transfer from the conduction band of titania to the metal as well as the interband and intraband electron transitions under UV irradiation on the other hand. The photo-generated holes are responsible for the oxidation from methanol to coordinated methoxy, from coordinated methoxy to coordinated formaldehyde and finally to carbon dioxide. The methyl formate selectivity is dependent on the density of the surface methoxy. To enhance the efficiency of electron–hole separation is beneficial to the formation of the coordinated methoxy and coordinated formaldehyde and thus the selectivity to methyl formate. The negative charges on the surface of the metal are responsible for the dissociation of oxygen, which is the rate-determining step in the reaction. The dissociative oxygen repels the water molecules formed from the surface hydroxyls and refills the oxygen vacancies on the surface of titania. The surface oxygen is the acceptor of the hydrogen dissociated from methanol and/or methoxy and thus is beneficial for the formation of the coordinated methoxy and coordinated formaldehyde. The oxygen partial pressure remarkably influences the methanol conversion and the methyl formate selectivity. The light intensity has a remarkable impact on the methanol conversion but not on the methyl formate selectivity. These findings provide useful insight into the design of catalysts for selective oxidation of methanol to methyl formate in a more green way.

Trapping the catalyst working state by amber-inspired hybrid material to reveal the cobalt nanostructure evolution in clean liquid fuel synthesis

It has been a long-term dream for scientists working in the field of catalysis to characterize the catalyst details at any state during the course of reaction under actual working conditions. Here, an amber-inspired hybrid material was designed to trap the catalyst working state generated during the reaction process of cobalt-based Fischer–Tropsch synthesis (FTS), which made the unavailable information for the catalytic clean liquid fuel synthesis processes obtainable via current ex situ characterization techniques. The trapped states were used to study the nanostructure evolution of the air-sensitive active species. In the experiments, the thin films of organic modifier anchored onto the montmorillonite (MMT) supports were designed to prevent the active Co components and phases generated during catalytic reaction from being oxidized when they are exposed to air. Consequently, the changes of the active species such as e-Co to hcp Co and e-Co to fcc Co phase transformation, Co nanoparticle growth, reoxidation during reaction, and the structure–property relationship of FTS catalysts were revealed clearly for the first time.

Visible Light Promoted Hydrochlorination of Olefin Over Pt, Au and Pd Supported on Zirconia

Abstract The Pt, Au and Pd catalysts supported on zirconia were prepared by the colloid deposition method. The catalytic activities of the catalysts for the hydrochlorination of 4-phenyl-1-butene were investigated under the irradiation of visible light, taking hydrochloric acid as the sources of chloride and hydrogen. The catalysts exhibited superior activities under the irradiation, giving rise to 4-phenylbutyl chloride and 4-phenyl-2-butenol, but they were almost inactive without the irradiation. Ethanol was unfavorable to the reaction. In addition to 4-phenylbutyl chloride, 2,3-dimethylstyrene was the by-product on the Pt and Au catalysts, and the isomerization from 4-phenyl-1-butene to benzene-1-butenyl occurred on the Pd/ZrO2 catalyst in ethanol solution.Graphical Abstract