Preparation of porous hollow silica spheres via a layer-by- layer process and the chromatographic performance

Hollow silica spheres possessing excellent mechanical properties were successfully prepared through a layer-by-layer process using uniform polystyrene （PS） latex fabricated by dispersion polymerization as template. The formation of hollow SiO2 micro-spheres, structures and properties were observed in detail by zeta potential, SEM, TEM, FTIR, TGA and nitrogen sorption porosimetry. The results indicated that the hollow spheres were uniform with particle diameter of 1.6 μm and shell thickness of 150 nm. The surface area was 511 m2/g and the pore diameter was 8.36 nm. A new stationary phase for HPLC was obtained by using C18-derivatized hollow SiO2 micro-spheres as packing materials and the chromatographic properties were evaluated for the separation of some regular small molecules. The packed column showed low column pressure, high values of efficiency （up to about 43 000 plates/m） and appropriate asymmetry factors.

In-situ generation of platinum nanoparticles on LaCoO_(3) matrix for soot oxidation

The LaCo_(0.94)Pt_(0.06)O_(3) catalyst is reduced under 5% H_(2)/Ar at different temperatures to get Pt/LaCoO_(3) with high catalytic activity for soot oxidation.Transmission electron microscopy(TEM),scanning electron microscopy(SEM),X-ray diffraction(XRD),Brunauer-Emmett-Teller method(BET),X-ray photoelectron spectroscopy(XPS),H_(2)-temperature programmed reduction(H_(2)-TPR),O_(2)-temperature programmed desorption(O_(2)-TPD) and thermogravimetric analysis(TGA) were used to study the physicochemical properties of the catalyst.SEM and TEM results indicate that Pt nanoparticles(<10 nm) are grown homogeneously on the surface of the LaCoO_(3) matrix after in-situ reduction.XRD shows that the reduced catalyst has a high symmetrical structure.TGA results indicate that all reduced catalysts exhibit an excellent activity,especially the catalyst reduced at 350℃(T_(10)=338℃,T_(50)=393℃,T_(90)=427℃).And perovskite is the primary active component.According to XPS study,the high symmetrical structure benefits the mobility of oxygen vacancy,and Pt nanoparticles induce the oxygen vacancy to move to its adjacent situation,resulting in more adsorbed oxygen on the surface of the reduced catalyst and increasing the activity.The possible reaction principle is also proposed.

Ag-assisted CeO2 catalyst for soot oxidation

In this work,the Ag loaded Ce-based catalyst was synthesized(by the sol-gel method)and its performance was studied by TG,H2-TPR,XRD,SEM,TEM,BET and XPS.The results show that Ag nanoparticles be successfully loaded onto the CeO2 surface and the relative content of Ag nanoparticles is about 10.22 wt.%close to the theoretical value(10%).XPS shows that Ag nanoparticles induce a great number of oxygen vacancies in the CeO2 lattice through the electronic transfer,and H2-TPR indicates that the Ag-assisted CeO2 catalyst exhibits a better reduction performance and Ag nanoparticles can promote O^- transform into O2^-.The catalytic activity for soot oxidation was studied by TG under air atmosphere and the activity was found to be obviously enhanced when Ag nanoparticles be load on the surface of CeO2(T10=386℃,79o=472.5℃,Tm=431℃).The reaction mechanism was also presented and Oi species is regarded as the determinant factor for the catalytic activity.

Study on the mechanism of NH3-selective catalytic reduction over CuCexZr1-x/TiO2

Copper-cerium-zirconium catalysts loaded on Ti02 prepared by a wet impregnation method were investigated for NHz-selective catalytic reduction （SCR） of NOx. The reaction mechanism was proposed on the basis of results from in situ diffuse reflectance infrared transform spectroscopy （DRIFT）. When NH3 is introduced, ammonia bonded to Lewis acid sites is more stable over CuCe0.25Zr0.75/TiO2 at high temperature, while Brensted acid sites are more important than Lewis acid sites at low temperature. For the NH3＋NO＋O2 co-adsorption, NH3 species occupy most of activity sites on CuCe0.25Zr0.75/TiO2 catalyst, and mainly exist in the forms of NH4＋ （at low temperature） and NH3 coordinated （at high temperature）, playing a crucial role in the NHz-SCR process. Two different reaction routes, the L-H mechanism at low temperature （〈 200℃） and the E-R mechanism at high temperature （〉200℃）, are presented for the SCR reaction over C uCe0.25Zr0.75/TiO2 catalyst.