Haiqin Wan

TiO2 supported Pd@Ag as highly selective catalysts for hydrogenation of acetylene in excess ethylene

A novel TiO2 supported core-shell (Pd@Ag) bimetallic catalyst was fabricated via the sequential photodeposition method. The Ag shell effectively blocks the high coordination sites on the Pd core, and therefore pronouncedly enhances the ethylene selectivity for the catalytic hydrogenation of acetylene in excess ethylene.

Effect of cobalt precursors on the dispersion, reduction, and CO oxidation of CoOx/γ-Al2O3 catalysts calcined in N2

The present work tentatively investigated the effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the physicochemical properties of CoO(x)/γ-Al(2)O(3) catalysts calcined in N(2). XRD, Raman, XPS, FTIR, and UV-vis DRS results suggested that CoO/γ-Al(2)O(3) was obtained from cobalt acetate precursors and CoO was dispersed on γ-Al(2)O(3) below its dispersion capacity of 1.50 mmol/(100 m(2) γ-Al(2)O(3)), whereas Co(3)O(4)/γ-Al(2)O(3) was obtained from cobalt nitrate precursors and Co(3)O(4) preferred to agglomerate above the dispersion capacity of 0.15 mmol/(100m(2) γ-Al(2)O(3)). Compared with Co(3)O(4)/γ-Al(2)O(3), CoO/γ-Al(2)O(3) catalysts were difficult to be reduced and easy to desorb oxygen species at low temperatures and presented high activities for CO oxidation as proved by H(2)-TPR, O(2)-TPD, and CO oxidation model reaction results. A surface incorporation model was proposed to explain the dispersion and reduction properties of CoO/γ-Al(2)O(3) catalysts.

Influence of ZrO2 properties on catalytic hydrodechlorination of chlorobenzene over Pd/ZrO2 catalysts

Pd/ZrO(2) catalysts using different ZrO(2) as supports were prepared using the deposition-precipitation method and were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N(2) adsorption, temperature programmed reduction, H(2) chemisorption and measurement of surface hydroxyl group. Catalytic hydrodechlorination (HDC) of chlorobenzene was used to evaluate the activity and stability of the catalyst. The results showed that ZrO(2) support calcined at 300 degrees C was amorphous in nature, whereas ZrO(2) supports calcined at 500 and 600 degrees C consisted of both monoclinic and tetragonal phases. In addition, increasing calcination temperature led to the decrease of specific surface area and surface hydroxyl group content of the ZrO(2) support. For temperature programmed reduction of PdO/ZrO(2) samples, two H(2) consumption peaks with varied reduction temperature were distinctly observed, implying the existence of different Pd species in Pd/ZrO(2) catalysts. In addition, Pd/ZrO(2) catalyst with ZrO(2) calcined at 500 degrees C had a relatively higher content of Pd species with strong metal-support interaction than other catalysts. For catalytic HDC of chlorobenzene, Pd/ZrO(2) catalyst with ZrO(2) support calcined at 500 degrees C exhibited a higher initial activity and stability as compared to other catalysts, indicative of a strong dependence of the catalytic behavior of the Pd/ZrO(2) catalyst on the support properties for catalytic HDC of chlorobenzene.

Influence of magnesia modification on the properties of copper oxide supported on γ-alumina

XRD, BET, TPR, UV-vis DRS and in situ FT-IR were employed to investigate the dispersion, reduction and CO(2)-adsorption behaviors of copper oxide supported on magnesia modified gamma-Al(2)O(3) (Mg-Al) samples. The results indicate that magnesia could be highly dispersed on the surface of gamma-Al(2)O(3) to form a monolayer and the dispersion capacity is about 1.55 mmol/(100 m(2)gamma-Al(2)O(3)). For copper oxide supported on Mg-Al samples, both the dispersion capacity and the reduction temperature of surface CuO decrease with the MgO loading. CO(2)-adsorption IR results show that the surface strong basic amount for the catalysts increases with the dispersed MgO loading. In addition, the activity of CO oxidation suggests that the main active species in this system should be small CuO cluster and the existence of dispersed MgO enhances the activity of CO oxidation. The catalysts might be applied in pollution control devices for vehicle exhaust, CO gas sensors, catalytic combustion and gas purification of CO(2) lasers. All the results have been discussed by the consideration of the variation of gamma-Al(2)O(3) surface structure before and after magnesia modification.

ZrO2-functionalized magnetic mesoporous SiO2 as effective phosphate adsorbent.

Phosphate pollution may cause eutrophication of the aquatic environment. In the present study, magnetic mesoporous SiO2 (denoted as MMS) and ZrO2-functionalized magnetic mesoporous SiO2 (denoted as ZrO2-MMS) were prepared and phosphate adsorption over the materials was investigated. The adsorbents were characterized by X-ray diffraction, transition electron microscopy, vibration sample magnetometer, N2 adsorption/desorption, zeta-potential measurement, and X-ray photoelectron spectroscopy. The results showed that MMS consisted of magnetite with particle sizes of 10-20 nm and ordered mesoporous SiO2 with the most probable pore diameter of 2.0 nm. The adsorbents could be readily separated and recovered under external magnetic field. The surface grafting of ZrO2 onto MMS led to an increase in surface zeta potential due to the formation of covalently linked ZrO2 functionality on the surface of MMS. Moreover, ZrO2 functionalization resulted in enhanced phosphate adsorption. Phosphate adsorption isotherms over the adsorbents could be well described by the Freundlich model. Phosphate adsorption kinetics followed the pseudo-second-order kinetics and the adsorption rate decreased with initial phosphate concentration. Additionally, increasing pH led to suppressed phosphate adsorption, and phosphate adsorption slightly increased with ionic strength.

Effect of MnOx modification on the activity and adsorption of CuO/Ce0.67Zr0.33O2 catalyst for NO reduction

The present work explored the effect of MnO(x) modification on the activity and adsorption of CuO/Ce(0.67)Zr(0.33)O(2) catalyst for NO reduction by CO. XRD, Raman, UV, XPS, H(2)-TPR, and in situ FT-IR were used to characterize these catalysts. Results suggested that the incorporation of copper and manganese species resulted in the lattice expansion and the decease of microstrain of ceria-zirconia, thus inducing the formation of oxygen vacancies. There was a strong interaction between surface copper, manganese, and the support via charge transfer. The addition of manganese species could promote the reduction of the resultant catalysts and assist copper oxide in changing the valence and the support in supplying oxygen. These reduction behaviors were dependent on the loading amounts of MnO(x) and the impregnation procedure. In addition, the introduction of MnO(x) cannot change the adsorption type of NO, but readily helped to activate the adsorbed NO species. As a result, these factors were responsible for the enhancement of activity and selectivity through MnO(x) modification.

Enhanced adsorption of humic acids on ordered mesoporous carbon compared with microporous activated carbon

Humic acids are ubiquitous in surface and underground waters and may pose potential risk to human health when present in drinking water sources. In this study, ordered mesoporous carbon was synthesized by means of a hard template method and further characterized by X-ray diffraction, N2 adsorption, transition electron microscopy, elemental analysis, and zeta-potential measurement. Batch experiments were conducted to evaluate adsorption of two humic acids from coal and soil, respectively, on the synthesized carbon. For comparison, a commercial microporous activated carbon and nonporous graphite were included as additional adsorbents; moreover, phenol was adopted as a small probe adsorbate. Pore size distribution characterization showed that the synthesized carbon had ordered mesoporous structure, whereas the activated carbon was composed mainly of micropores with a much broader pore size distribution. Accordingly, adsorption of the two humic acids was substantially lower on the activated carbon than on the synthesized carbon, because of the size-exclusion effect. In contrast, the synthesized carbon and activated carbon showed comparable adsorption for phenol when the size-exclusion effect was not in operation. Additionally, we verified by size-exclusion chromatography studies that the synthesized carbon exhibited greater adsorption for the large humic acid fraction than the activated carbon. The pH dependence of adsorption on the three carbonaceous adsorbents was also compared between the two test humic acids. The findings highlight the potential of using ordered mesoporous carbon as a superior adsorbent for the removal of humic acids.

Enhanced photocatalytic reduction of aqueous Pb(II) over Ag loaded TiO2 with formic acid as hole scavenger

In the present study, photocatalytic Pb(II) reduction over TiO2 and Ag/TiO2 catalysts in the presence of formic acid was explored to eliminate Pb(II) pollution in water. Ag/TiO2 catalysts were prepared by the photo-deposition method and characterized using UV-Vis diffuse reflectance spectra, X-ray reflection diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Ag deposition on TiO2 led to enhanced photocatalytic Pb(II) reduction and the Ag/TiO2 catalyst with a Ag loading amount of 0.99 wt.% exhibited the optimum photocatalytic activity. For Pb(II) reduction over Ag/TiO2 with a Ag loading amount of 0.99 wt.%, initial Pb(II) reduction rate was found to be dependent on the initial concentrations of formic acid and Pb(II). Increasing initial Pb(II) concentration led to linearly increased initial Pb(II) reduction rate. At low formic acid concentration, in parallel, initial Pb(II) reduction rates increased with formic concentration, but remained nearly identical at high formic acid concentration. Solution pH impacted the photocatalytic Pb(II) reduction and after irradiation for 100 min Pb(II) was removed by 11.8%, 91.2% and 98.6% at pH of 0.8, 2.0 and 3.5, respectively, indicative of enhanced Pb(II) reduction with pH in the tested pH range. The results showed that Ag/TiO2 displayed superior catalytic activity to TiO2, highlighting the potential of using Ag/TiO2 as a more effective catalyst for photocatalytic Pb(II) reduction.

A comparative study on the dispersion behaviors and surface acid properties of molybdena on CeO2 and ZrO2 (Tet).

Dispersion of molybdena on CeO(2), ZrO(2) (Tet), and a mixture of CeO(2) and ZrO(2) (Tet), was investigated by using laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and temperature programmed reduction (TPR). The results indicate that molybdena is dispersed on both individual oxide support and mixed oxide support at the adopted molybdena loadings (0.2 and 0.8 mmol Mo(6+)/100 m(2)) and the structure of the supported molybdena species is intimate association with its loading amount. Two molybdena species are identified by Raman results, i.e. isolated MoO(4)(2-) species at 0.2 mmol Mo(6+)/100 m(2) and polymolybdate species at 0.8 mmol Mo(6+)/100 m(2). IR spectra of ammonia adsorption prove that isolated MoO(4)(2-) species are Lewis acid sites on the Mo/Ce and/or Zr samples, and the polymolybdate species are Brönsted acid sites on the Mo/Ce and/or Zr samples. Moreover, a combination of the Raman, IR and TPR results confirms that at 0.2 mmol Mo(6+)/100 m(2) Ce+Zr, molybdena is preferentially dispersed on the surface of CeO(2) when a mixed oxide support (CeO(2) and ZrO(2)) is present, which was explained in term of the difference of the surface basicity between CeO(2) and ZrO(2) (Tet). Surface structures of the oxide supports were also taken into consideration.

Highly effective catalytic peroxymonosulfate activation on N-doped mesoporous carbon for o -phenylphenol degradation

As a broad-spectrum preservative, toxic o-phenylphenol (OPP) was frequently detected in aquatic environments. In this study, N-doped mesoporous carbon was prepared by a hard template method using different nitrogen precursors and carbonization temperatures (i.e., 700, 850 and 1000 °C), and was used to activate peroxymonosulfate (PMS) for OPP degradation. For comparison, mesoporous carbon (CMK-3) was also prepared. Characterization results showed that the N-doped mesoporous carbon samples prepared under different conditions were perfect replica of their template. In comparison with ethylenediamine (EDA) and dicyandiamide (DCDA) as the precursors, N-doped mesoporous carbon prepared using EDA and carbon tetrachloride as the precursors displayed a higher catalytic activity for OPP degradation. Increasing carbonization temperature of N-doped mesoporous carbon led to decreased N content and increased graphitic N content at the expense of pyridinic and pyrrolic N. Electron paramagnetic resonance (EPR) analysis showed that PMS activation on N-doped mesoporous carbon resulted in highly active species and singlet oxygen, and catalytic PMS activation for OPP degradation followed a combined radical and nonradical reaction mechanism. Increasing PMS concentration enhanced OPP degradation, while OPP degradation rate was independent on initial OPP concentration. Furthermore, the dependency of OPP degradation on PMS concentration followed the Langmuir-Hinshelwood model, reflecting that the activation of adsorbed PMS was the rate controlling step. Based on the analysis by time-of-flight mass spectrometry, the degradation pathway of OPP was proposed.