Kan Zhang

Effects of surface states over core-shell Ni @SiO2 catalysts on catalytic partial oxidation of methane to synthesis gas

Abstract In the present work, core-shell Ni@SiO2 catalysts were investigated in order to evaluate the relevance of catalytic activity and surface states of Ni core as well as Ni nanoparticles size to catalytic partial oxidation of methane (POM). The catalysts were characterized by N2 adsorption, H2-TPR, XRD, TEM and XPS techniques. The catalytic performance of the core-shell catalysts was found to be dependent on the surface states of catalyst, which influenced the formation of products. It was considered that carbon dioxide formed on the oxidized nickel sites (NiO) and carbon monoxide produced on the reduced sites (Ni). The surface states of active metal in the dynamic were influenced both by the size of Ni core and the porosity of silica shell. However, the catalytic activity would be debased when the size of Ni core was under a certain extent, which can be ascribed to the fact the carbon deposition increased with the increasing content of NiO. The effects of surface states of Ni@SiO2 catalyst on the catalytic performance were discussed and the reaction pathway over Ni core encapsulated inside silica shell was proposed.

Efficient removal of phosphate from aqueous solution using novel magnetic nanocomposites with Fe 3 O 4 @SiO 2 core and mesoporous CeO 2 shell

Abstract Fe 3 O 4 @SiO 2 magnetic nanoparticles functionalized with mesoporous cerium oxide (Fe 3 O 4 @SiO 2 @ m CeO 2 ) was fabricated as a novel adsorbent to remove phosphate from water. The prepared adsorbent was characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption and vibrating sample magnetometry (VSM), and its phosphate removal performance was investigated through the batch adsorption studies. Characterization results confirmed that mesoporous cerium oxide was successfully assembled on the surface of Fe 3 O 4 @SiO 2 nanoparticles, and the synthesized adsorbent possessed a typical core-shell structure with a BET surface area of 195 m 2 /g, accessible mesopores of 2.6 nm, and the saturation magnetization of 21.11 emu/g. The newly developed adsorbent had an excellent performance in adsorbing phosphate, and its maximum adsorption capacity calculated from the Langmuir model was 64.07 mg/g. The adsorption was fast, and the kinetic data could be best fitted with the pseudo-second-order kinetic model. The phosphate removal decreased with the increase of solution pH (2 to 10), while the higher ionic strength slightly promoted the phosphate adsorption. The presence of Cl − and SO 4 2− could enhance the adsorption of phosphate whereas HCO 3 − had interfering effect on the phosphate adsorption. The adsorption mechanism was studied by analyzing Zeta potential and FTIR spectroscopy, and the results indicated that the replacement of the surface hydroxyl groups by phosphate ions with the formation of inner-sphere complex played a key role in the phosphate adsorption. The spent adsorbent could be quickly separated from aqueous solution with the assistance of the external magnetic field, and the adsorbed phosphate could be effectively desorbed using a 1 mol/L NaOH solution.

Catalytic conversion of methanol to aromatics over nano-sized HZSM-5 zeolite modified by ZnSiF6·6H2O

ZnSiF6-modified nano-sized HZSM-5 zeolites (NZ2, NZ3 and NZ4 catalysts) were prepared and investigated as catalysts for the conversion of methanol to aromatics. Moreover, the ZnNZ1 catalyst, prepared by ion exchange using zinc nitrate, was also introduced as a reference sample. The effects of modification on the framework, textural properties and acidity of the parent nano-sized HZSM-5 zeolite (NZ1) were investigated by XRD, FT-IR, 29Si MAS-NMR, SEM, N2 adsorption–desorption, ICP, NH3-TPD, infrared spectroscopy of adsorbed pyridine (Py-IR), UV-vis spectra, X-ray photoelectron spectroscopy (XPS) and n-butylamine and tert-butylamine titration. The results showed that the amount of total acid sites, especially the external surface acid sites of the NZ2, NZ3 and NZ4 catalysts, significantly decreased, which may largely be attributed to the passivation effect of SiF62− on the surface acidity of the parent NZ1 catalyst. Moreover, the amount of Lewis acid sites (L acid sites) increased, whereas the amount of Bronsted acid sites (B acid sites) obviously decreased with the introduction of zinc species. The emergence of new Zn-Lewis acid sites (⊖ZO⋯H⋯O–Zn⊕ species) was beneficial to improving the selectivity to BTX (benzene (B), toluene (T) and xylene (X)) due to their high activity for dehydroaromatization. The FT-IR spectra in the OH− vibration region and the 29Si MAS-NMR spectra show that the treatment of ZnSiF6 could effectively repair partial lattice defects of zeolite and could thus improve the catalyst stability. TG analysis of all the deactivated catalysts showed that the coke amount and the average rate of coke formation decreased over NZ2, NZ3 and NZ4 catalysts, and this may largely be ascribed to their lower surface acidity. The catalytic performance of these materials on the conversion of methanol to aromatics showed that the NZ3 catalyst had the highest selectivity to BTX of about 51.3% and the longest catalytic lifetime of about 234 h under the operating conditions of T = 425 °C, p = 0.1 MPa and WHSV = 0.8 h−1. The improvement in the selectivity to BTX and the catalyst lifetime of the NZ3 catalyst could be ascribed to the synergistic effect among the Zn-Lewis acid sites (⊖ZO⋯H⋯O–Zn⊕ species), external surface acidity and intact framework structure.

Synthesis and Application of Ni-M@Silica Yolk-Shell Nanostructures as Versatile Catalytic Materials

Recent developments in nanochemistry offer precise morphology control of nanomaterials, which has significant impacts in the field of heterogeneous catalysis. Rational design of bifunctional catalysts can influence various aspects of catalytic properties. In the present work, a new type of Ni-M(Co, Zr, Ce)@SiO2 yolk-shell nanoreactor framework comprising Ni-M cores inside hollow silica shells has been prepared through direct silica coating. The Ni-M@SiO2 nanoreactor structure is employed as a model catalyst for the partial oxidation of methane reaction. The Ni/ZrO2@SiO2 catalyst proved to be more active and possessed less carbon deposition reduced effectively by movable lattice oxygen. This nanoreactor framework is remarkably stable at high temperatures up to 750 °C, because the silica hollow shells around the cores essentially block particle sintering. The catalyst exhibited a continuous conversion rate of methane and significantly enhanced stability at high temperatures.

Intrinsic Kinetics of Coking Crude Benzene Hydrodesulfurization on a Ti Modified Co-Mo-P/γ-Al2O3 Catalyst

With different content of thiophene in coking crude benzene, the Orthogonal design experiments of thiophene hydrodesulfurization on a Ti modified Co-Mo-P/γ-Al2O3 catalyst were carried out in a micro-reactor under the reaction conditions of 2.3~2.7MPa,275~335°C, 0.5h-1LHSV and H2/Oil 600~750. The kinetic parameters and the intrinsic kinetics were acquired by 4-order Runge-Kutta method and the modified Simplex method. The power-law type kinetic model was established and consistent with the experiment data and highly acceptable and reliable.