Ultrastable nanogold catalyst—on the way going to practical application

The catalytic performance of gold nanoparticles （NPs） can be dramatically changed by choosing support materials and by designing the fine architecture of contact structure between gold NPs and the supports. So far many kinds of base metal oxides including acidic metal oxides such as Nb2O5 , carbon materials, organic polymers have been reported as effective support for gold NPs.

Correlation between catalytic activity of supported gold catalysts for carbon monoxide oxidation and metal–oxygen binding energy of the support metal oxides

The effect of a wide variety of metal oxide （MOx） supports has been discussed for CO oxidation on nanoparticulate gold catalysts. By using typical co‐precipitation and deposition–precipitation methods and under identical calcination conditions, supported gold catalysts were prepared on a wide variety of MOx supports, and the temperature for 50%conversion was measured to qualita‐tively evaluate the catalytic activities of these simple MOx and supported Au catalysts. Furthermore, the difference in these temperatures for the simple MOx compared to the supported Au catalysts is plotted against the metal–oxygen binding energies of the support MOx. A clear volcano‐like correla‐tion between the temperature difference and the metal–oxygen binding energies is observed. This correlation suggests that the use of MOx with appropriate metal–oxygen binding energies （300–500 kJ/atom O） greatly improves the catalytic activity of MOx by the deposition of Au NPs.

Preparation of gold nanoparticles supported on Nb_2O_5 by deposition precipitation and deposition reduction methods and their catalytic activity for CO oxidation

Nanoparticulate gold catalysts supported on niobium oxides （Nb2O5） were prepared by different deposition methods. The deposition precipitation （DP） method, DP method with urea, deposition reduction （DR） method and one‐pot method were used to prepare a 1 wt%Au/Nb2O5 catalyst. Lay‐ered‐type Nb2O5 synthesized by a hydrothermal method （Nb2O5（HT）） was the most suitable as a support among various types of Nb2O5 including commercially available Nb2O5 samples. It appeared that the large BET surface area of Nb2O5（HT） enabled the dispersion of gold as nanoparticles （NPs）. Gold NPs with a mean diameter of about 5 nm were deposited by both the DP method and DR method on Nb2O5（HT） under an optimized condition. The temperature for 50%CO conversion for Au/Nb2O5（HT） prepared by the DR method was 73 ＆#176;C. Without deposition of gold, Nb2O5（HT） showed no catalytic activity for CO oxidation even at 250 ＆#176;C. Therefore, the enhancement of the activity by deposition of gold was remarkable. This simple Au/Nb2O5 catalyst will expand the types of gold catalysts to acidic supports, giving rise to new applications.

Preparation of gold clusters on metal oxides by deposition-precipitation with microwave drying and their catalytic performance for CO and sulfide oxidation

Gold clusters and small nanoparticles supported on metal oxides could be prepared by deposition‐precipitation followed by microwave irradiation as a drying method and then calcination.The drying method influenced the size of the Au particles.Au(III)was partly reduced during conventional oven drying,resulting in Au aggregates.In contrast,Au(III)was preserved during microwave drying owing to rapid and uniform heating,and the Au diameter was minimized to1.4nm on Al2O3.This method can be applied to several metal oxide supports having different microwave absorption efficiencies,such as MnO2,Al2O3,and TiO2.These catalysts exhibited higher catalytic activities for CO oxidation at low temperature and for selective aerobic oxidation of sulfide than those prepared by conventional methods.

Highly efficient base-free aerobic oxidation of alcohols over gold nanoparticles supported on ZnO-CuO mixed oxides

The design and preparation of suitable supports are of great importance for gold catalysts to attain excellent catalytic performance for alcohol oxidation.In this work,we found that ZnO-CuO mixed oxides supported gold catalysts showed much better catalytic activity for base-free aerobic oxidation of benzyl alcohol than Au/ZnO and Au/CuO catalysts,and among them Au/Zn0.7Cu0.3O displayed the best catalytic performance.In addition,the Au/Zn0.7Cu0.3O catalyst could selectively catalyze the aerobic oxidation of a wide range of alcohols to produce the corresponding carbonyl compounds with high yields under mild conditions without base.Further characterizations indicated that the outstanding catalytic performance of Au/Zn0.7Cu0.3O was correlated with the small size of Au nanoparticles(NPs),good low-temperature reducibility,high concentration of surface oxygen species,and collaborative interaction between Au NPs and mixed oxide.

One-Step Synthesis of Magnetically Recyclable Au/Co/Fe Triple- Layered Core-Shell Nanoparticles as Highly Efficient Catalysts for the Hydrolytic Dehydrogenation of Ammonia Borane

Magnetically recyclable Au/Co/Fe core-shell nanoparticles （NPs） have been successfully synthesized via a one-step in situ procedure. Transmission electron microscope （TEM）, energy dispersive X-ray spectroscopic （EDS）, and electron energy-loss spectroscopic （EELS） measurements revealed that the trimetallic Au/Co/Fe NPs have a triple-layered core-shell structure composed of a Au core, a Co-rich inter-layer, and a Fe-rich shell. The Au/Co/Fe core-shell NPs exhibit much higher catalytic activities for hydrolytic dehydrogenation of ammonia borane （NHBBH3, AB） than the monometallic （Au, Co, Fe） or bimetallic （AuCo, AuFe, CoFe） counterparts.