Kunlun Ding

Identification of active sites in CO oxidation and water-gas shift over supported Pt catalysts

Comparing active site reactivity Noble metal nanoparticles often exhibit behaviors distinct from atomic and bulk versions of the same material. Gold and platinum dispersed on metal oxide supports, for example, show remarkable low-temperature reactivity for carbon monoxide (CO) oxidation by oxygen or water. Ding et al. used infrared spectroscopy to identify CO adsorbed on isolated platinum atoms or nanoparticles dispersed on zeolite and oxide supports. Temperature-programmed desorption studies showed that CO reacted at much lower temperatures when adsorbed on nanoparticles versus on isolated metal atoms. Science, this issue p. 189 Infrared spectroscopy reveals that carbon monoxide oxidizes more readily on supported noble metal nanoparticles than on isolated atoms. [Also see Perspective by Stephens et al.] Identification and characterization of catalytic active sites are the prerequisites for an atomic-level understanding of the catalytic mechanism and rational design of high-performance heterogeneous catalysts. Indirect evidence in recent reports suggests that platinum (Pt) single atoms are exceptionally active catalytic sites. We demonstrate that infrared spectroscopy can be a fast and convenient characterization method with which to directly distinguish and quantify Pt single atoms from nanoparticles. In addition, we directly observe that only Pt nanoparticles show activity for carbon monoxide (CO) oxidation and water-gas shift at low temperatures, whereas Pt single atoms behave as spectators. The lack of catalytic activity of Pt single atoms can be partly attributed to the strong binding of CO molecules.

Fluorescence Upconversion Microbarcodes for Multiplexed Biological Detection: Nucleic Acid Encoding

Fluoride rare-earth-doped upconversion microbarcodes have been successfully developed for multiplexed signaling and nucleic-acid encoding. This kind of novel barcode material can be used for rapid and sensitive analysis of nucleic acids and antigens, which would have many potential applications in clinical, food, and environment detection.

In Situ Controllable Loading of Ultrafine Noble Metal Particles on Titania

Herein we present a novel and facile approach to controllably load ultrafine noble metal nanoparticles on titania through in situ redox reaction between the reductive titanium(III) oxide support and metal salt precursors in aqueous solution. A series of noble metal/TiO(2) nanocomposites with uniform metal dispersion, tunable metal particle size, and narrow metal particle size distribution were obtained.

SnO2/carbon nanotube nanocomposites synthesized in supercritical fluids: highly efficient materials for use as a chemical sensor and as the anode of a lithium-ion battery

SnO2/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared via oxidation of SnCl2 in a supercritical CO2?methanol mixture containing MWCNTs. The as-prepared nanocomposites were characterized by means of x-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy. It was indicated that SnO2 nanoparticles with size of 3?5?nm were uniformly and tightly decorated on the MWCNTs. The chemiluminescence characteristic to H2S and electrochemical performance of the as-prepared SnO2/MWCNT composites were investigated. The SnO2/MWCNT composites exhibited extremely high efficiency for detecting H2S, and also displayed good electrochemical performance as the anode material in a lithium-ion battery.

Rare‐Earth Upconverting Nanobarcodes for Multiplexed Biological Detection

Since the decoding of the human genome, the need to obtain more and more molecular information from smaller and smaller samples is intensifying. Biosystem-analysis, disease diagnosis, and biomedical studies all require the tracking of spatio-temporal information from multiple targets, involving proteins, genes, lipids and glycans for target pattern recognition and system definition. Multiplexed assays are therefore required in order to complement advances in genomics and proteomics, and to allow a large number of nucleic acids and proteins to be rapidly screened.[1–4]

Pd nanoparticles immobilized on sepiolite by ionic liquids: efficient catalysts for hydrogenation of alkenes and Heck reactions

Palladium-sepiolite catalysts were prepared by immobilizing Pd2+ on sepiolite using an ionic liquid containing a guanidine cation, followed by reduction with hydrogen at 150 °C. The resulting composites were characterized by different techniques. X-Ray photoelectron spectroscopy analysis showed that the loaded Pd existed mainly in the form of Pd0, with a small amount of its oxides, and distributed uniformly on sepiolite with particle size about 5 nm, as confirmed by transmission electron microscopy examination. X-Ray diffraction analysis indicated that the sepiolite retained its original structure after deposition of Pd nanoparticles. The activities of the Pd-sepiolite catalysts for hydrogenations of some alkenes (e.g., cyclohexene and 1,3-cyclohexdiene) and Heck reactions were investigated. It was demonstrated that the as-prepared catalysts exhibited very high efficiency for these reactions.

Study on the Anatase to Rutile Phase Transformation and Controlled Synthesis of Rutile Nanocrystals with the Assistance of Ionic Liquid

We developed a route to synthesize rutile TiO(2) nanocrystals (NCs) with the assistance of 1-butyl-3-methylimidazolium chloride (bmim(+)Cl(-)). The phase transformation from anatase to rutile phase was investigated, and a simple model to describe the phase transformation process was proposed considering that the nucleation and growth of rutile phase were determined by the aggregation manner of anatase NCs and Ostwald ripening process, respectively. It was demonstrated that the surfactant-like nature of the IL used was crucial for controlling the crystallization process via controlling the aggregation manner of the NCs. The phase, shape, and size of TiO(2) NCs could be tuned by the controlling the operating conditions, such as temperature, solution acidity, and reactant concentration of the bmim(+)Cl(-)/TiCl(4)/H(2)O reaction system. Phase-pure rutile multipods and 1D nanorods with different sizes were controllably obtained.

A simple route to coat mesoporous SiO2 layer on carbon nanotubes

Herein we present a simple method to coat a porous SiO2 layer on carbon nanotubes (CNTs) with the aid of the cationic surfactant cetyltrimethyl ammonium bromide (CTAB). The coating process was studied systematically, and a possible coating mechanism was proposed. Temperature and the ratio of CTAB/CNTs/H2O were found to play key role in the coating process. This method can be applied to both multiwalled carbon nanotubes (MWNTs) and single walled carbon nanotubes (SWNTs). The individualized nature of the CNTs (both MWNTs and SWNTs) was maintained during the coating process. Furthermore, Raman spectroscopy showed that this method is nondestructive to the electronic structure of CNTs. The CNT/porous SiO2 core/shell structure will serve as a platform for further surface functionalization of CNTs.

Large-scale production of self-assembled SnO2 nanospheres and their application in high-performance chemiluminescence sensors for hydrogen sulfide gas

Mesoporous SnO2 nanospheres with high thermal stability have been fabricated via reaction of sodium stannate with CO2 controllably released from urea under hydrothermal conditions. The resultant products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen sorption and FTIR analysis. It was indicated that the products exhibited nearly monodisperse mesoporous or hollow spherical nanostructures with sizes in the range of ca. 25–50 nm, which were composed of nanocrystals with sizes of less than 10 nm. The formation mechnism of SnO2 nanospheres was also discussed. Urea not only acted as the CO2 resource for the formation of SnO2 primary nanocrystals, but also played an important role in their self-assembly into nanospheres. The as-prepared SnO2 nanospheres exhibited superior sensitivity, high selectivity, and extremely rapid response for detecting H2S gas based on catalytic chemiluminescence (CL) characteristics.

Adhesion and Atomic Structures of Gold on Ceria Nanostructures:The Role of Surface Structure and Oxidation State of Ceria Supports

We report an aberration-corrected electron microscopy analysis of the adhesion and atomic structures of gold nanoparticle catalysts supported on ceria nanocubes and nanorods. Under oxidative conditions, the as-prepared gold nanoparticles on the ceria nanocubes have extended atom layers at the metal-support interface. In contrast, regular gold nanoparticles and rafts are present on the ceria nanorod supports. Under the reducing conditions of water-gas shift reaction, the extended gold atom layers and rafts vanish. In addition, the gold particles on the nanocubes change in morphology and increase in size while those on the nanorods are almost unchanged. The size, morphology, and atomic interface structures of gold strongly depend on the surface structures of ceria supports ((100) surface versus (111) surface) and the reaction environment (reductive versus oxidative). These findings provide insights into the deactivation mechanisms and the shape-dependent catalysis of oxide supported metal catalysts.