Au/LaVO_(4)Nanocomposite:Preparation,Characterization,and Catalytic Activity for CO Oxidation

The size of the gold particles is a very important parameter to get active catalysts.This paper reports a novel colloidal deposition method to prepare Au/LaVO_(4)nanocomposite catalyst with monodispersed Au colloids and uniform LaVO_(4)nanoplates in nonpolar solvent.Monodispersed Au colloids with tunable size(such as 2,5,7,11,13,and 16 nm)and LaVO_(4)nanocrystals with well-defi ned shapes were pre-synthesized assisted with oleic acid/amine.During the following immobilization process,the particle size and shape of Au and LaVO_(4)were nearly preserved.As-prepared Au/LaVO_(4)nanocomposite showed high catalytic activity for CO oxidation at room temperature.Since sizes of gold particles were well-defi ned before the immobilization process,size effect of gold particles was easy to be investigated and the results show that 5-nm Au/LaVO_(4)nanocomposite has the highest activity for CO oxidation.This synthetic method can be extended further for the preparation of other composite nanomaterials.

Ordered two-dimensional porous Co3O4 nanosheets as electrocatalysts for rechargeable Li-O2 batteries

Lithium-oxygen batteries have attracted considerable interest in the past a few years, because they have higher theoretical specific energy than Li-ion batteries. However, the available en ergy den sities of the Li-O2 batteries are much less than expected. It is particularly urgent to find catalyst with high activity. Herein, a series of Co3O4 with differe nt morphologies (ordered two-dimensio nal porous nano sheets, flowerlike and cuboidlike) were successfully prepared through facile hydrothermal and calcinatio n methods. Ordered two-dime nsional Co3O4 nano sheets show the best cycling stability. Detailed experimental results reveal that the superiority of the unique two-dimensional uniform porous structures is vital for Li-O2 batteries cathode catalysts. Due to the ordered structures with high surface areas and active sites, the catalysts indicate a high specific discharge capacity of about 10,417 mAh/g at a current density of 200 mA/g, and steadily cycle for more than 50 times with a limited capacity of 1,000 mAh/g.

Effect of SiO_(2)/Al_(2)O_(3)ratio on the conversion of methanol to olefins over molecular sieve catalysts

A series of SAPO-34 molecular sieves with different SiO_(2)/Al_(2)O_(3)ratios have been synthesized for the methanol-to-olefin(MTO)reaction.Their physico-chemical properties are characterized by various techniques such as X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),Fourier transform infrared spectroscopy(FT-IR)and N2 adsorption-desorption.The results are compared with those of the commercial HZSM-5,which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO_(2)/Al_(2)O_(3)ratio.The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO_(2)/Al_(2)O_(3)ratio of 0.4 exhibits the highest BET surface area.FT-IR spectra indicate that HZSM-5 has both Brǿnsted and Lewis acid sites and Brǿnsted acid sites are stronger,whereas SAPO-34 samples are dominated only by Lewis acid sites.When the SiO_(2)/Al_(2)O_(3)ratio increases,propylene and butylenes become the predominant product of the MTO reaction over HZSM-5.In contrast,the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene.According to the product distribution,the reaction mechanism over HZSM-5 catalysts is proposed.