Wei-Lin Dai

XPS studies on surface electronic characteristics of Ni–B and Ni–P amorphous alloy and its correlation to their catalytic properties

Abstract The Ni–B, Ni–P, Ni–B/SiO2 and Ni–P/SiO2 amorphous alloy samples were prepared by chemical reduction with BH4− or H2PO2−. Their amorphous structures were verified by X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). Transmission electron microscopy (TEM) was used to determine their morphology and particle size. XPS experiments have been carefully designed to characterize the surface electronic state of the as-prepared samples. By comparing with electron binding energies of the pure Ni, B and P, the XPS spectra demonstrated that boron donated electron to nickel in Ni–B alloy, resulting in electron-enrichment of elemental Ni, while no significant electron transfer between Ni and P in Ni–P alloy was observed. Those results seem reasonable to elucidate the different catalytic behaviors of Ni–P and Ni–B amorphous alloy catalysts, such as the hydrogenation activity and sulfur resistance ability.

Liquid phase hydrogenation of furfural to furfuryl alcohol over the Fe-promoted Ni-B amorphous alloy catalysts

Abstract The ultrafine Fe-doped Ni-B amorphous catalyst (Ni-Fe-B) was prepared by reducing mixed FeCl3 and NiCl2 with KBH4 in aqueous solution. At suitable Fe-content (χFe), the Ni-Fe-B amorphous catalyst exhibited much higher activity than the corresponding undoped Ni-B in the liquid phase hydrogenation of furfural (FFR) to furfuryl alcohol (FFA). With the increase of χFe, the activity first increased and then decreased while the selectivity to FFA changed in a contrast way. The Fe-B amorphous alloy itself was inactive for the FFR hydrogenation. The optimum χFe was determined as 0.51, at which the FFA yield reached 100% after reaction for 4xa0h. Based on various characterizations, the promoting effect of the Fe-dopant was discussed by considering (1) the increase in the surface area, more highly unsaturated Ni active sites, and the more homogeneous distribution of the Ni active sites owing to the presence of Fe2O3 as a dopant; (2) the affinity of the Fe3+ for the oxygen in the carbonyl group which strengthened the adsorption of the Cue605O bond by the catalyst and thus facilitated its hydrogenation; (3) the electron donation of the metallic Fe to the metallic Ni, making Fe electron-deficient while Ni electron-enriched which activated the Cue605O bond towards the hydrogenation.

Preparation of the Ni-B amorphous alloys with variable boron content and its correlation to the hydrogenation activity

Some ultrafine Ni-B amorphous alloys with variable B contents were prepared by chemical reduction under different conditions. The effect of the B content on their activities was evaluated by using the liquid phase cyclohexene hydrogenation as a probe. Both the specific activity and the TOF value increased with the increase of the B content, showing the promoting effect of the alloying B on the hydrogenation activity, which was mainly attributed to its modification of the nature of the Ni active sites. Concerning the structural effect, the XRD patterns revealed that the amorphous degree of the as-prepared Ni-B alloy increased with the increase of the B content. Meanwhile, the DSC analysis demonstrated that increase of the B content could increase the thermal stability of the Ni-B amorphous alloy and in turn, delay its crystallization during the cyclohexene hydrogenation. Furthermore, the EXAFS also demonstrated that the Ni active sites became more highly unsaturated at higher B content. These structural modifications were favorable for the hydrogenation activity. Concerning the electronic effect, the XPS spectra demonstrated the electronic interaction between Ni and B in the Ni-B amorphous alloy, making Ni electron-enriched while B became electron-deficient. According to the DFT calculations, more electrons may transfer from the alloying B to Ni with the increase of the B content. Such electronic modifications may also facilitate the cyclohexene hydrogenation.

XPS studies on a novel amorphous Ni–Co–W–B alloy powder

Abstract A novel amorphous Ni–Co–W–B alloy powder, which showed higher catalytic activity than Ni–Co–B for the hydrogenation of benzene, was prepared by chemical reduction and characterized by TEM and XRD. The surface composition and the interactions between the components on the surface were studied by XPS. The measurement detected the presence of some oxides and hydroxides, such as NiO, Ni(OH) 2 , Co(OH) 2 , B 2 O 3 and WO 3 associated with their elemental states of Ni, Co, B and W, respectively. The presence of a few number of tungsten atoms leads to more metallic nickel on the surface.

XPS studies of Cu/ZnO/Al2O3 ultra-fine catalysts derived by a novel gel oxalate co-precipitation for methanol synthesis by CO2+H2

Abstract The chemical states of Cu and Zn in an ultra-fine high performance Cu/ZnO/Al2O3 catalyst at various preparation stages for the methanol synthesis by CO2/H2 were investigated by X-ray photoelectron spectroscopy. It was found that copper was presented as metallic state and zinc still as ZnO during reaction or reduction. Moreover, it shows that the metallic Cu can be partially oxidized to Cuδ+ species by pure CO2. The active center of the Cu/ZnO/Al2O3 catalyst for methanol synthesis was discussed.

Highly Effective Oxidative Dehydrogenation of Propane Over Vanadia Supported on Mesoporous SBA-15 Silica

Vanadia-containing mesoporous SBA-15 catalysts were prepared and characterized for the oxidative dehydrogenation (ODH) of propane. It is demonstrated that the vanadia-supported SBA-15 catalysts exhibit a much higher catalytic activity than those reported in the literature obtained over vanadium-supported mesoporous MCM-41 catalysts in the ODH of propane. The high catalytic performance of the mesoporous SBA-15 catalysts is attributed to the particularly large pore diameters and low surface acidity.

Study on the deactivation of amorphous NiB/SiO2 catalyst during the selective hydrogenation of cyclopentadiene to cyclopentene

The deactivation of the silica supported NiB amorphous catalyst during the selective hydrogenation of cyclopentadiene (CPD) to cyclopentene (CPE) in a fixed-bed reactor was studied. According to the characterizations of the initial and used catalysts by ICP, BET, SEM, XRD and XPS, no significant sintering of the active component or crystallization of the amorphous structure was observed, while severe surface oxidation occurred after the deactivation of the catalyst. Those results demonstrated that such a deactivation should mainly be attributed to the oxidation of the active component. Water promoted the deactivation because the surface oxidation of elemental Ni was accelerated by forming Ni(OH)2 in the presence of water. The deactivation resulted from sulfication and carboneous species deposition was not observed in the present conditions, although it really occurred at high sulfur concentration and low CPD conversion.

Influence of calcination and pretreatment temperature on the activity of Ni–B/SiO2 amorphous catalyst in acrylonitrile hydrogenation

Abstract The Ni–B/SiO 2 amorphous catalyst was prepared by impregnation of silica support with NiCl 2 aqueous solution following the chemical reduction with KBH 4 . The influence of calcination and pretreatment temperature on its activity was investigated by using acrylonitrile hydrogenation as a probe. On the one hand, it was found that the activity of the Ni–B/SiO 2 amorphous catalyst first increased and then decreased when the precursor (Ni 2+ /SiO 2 ) was calcined at the temperature from 273 to 773xa0K in Ar flow. The optimum calcination temperature was then determined as 473xa0K. On the other hand, when the as-prepared Ni–B/SiO 2 amorphous catalyst was pretreated at the temperature from 273 to 873xa0K in Ar flow, the activity of the catalyst first remained almost unchanged up to 573xa0K and then decreased abruptly with the further increase of temperature. According to various characterizations, such as inductively coupled plasma (ICP), differential scanning calorimetry (DSC), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS), it was concluded that the effect of the calcination temperature on the activity should mainly be attributed to the surface density of metallic nickel; while the effect of the pretreatment temperature on the activity was caused by the transformation from amorphous structure to crystalline structure.

Mesoporous bimetallic PdCl2-CuCl2 catalysts for dimethyl carbonate synthesis by vapor phase oxidative carbonylation of methanol

Dimethyl carbonate (DMC) synthesis reaction by oxidative carbonylation of methanol has been studied in a flow reaction system at atmospheric pressure in the presence of quaternary ammonium salt (QAS)-promoted bimetallic PdCl2-CuCl2 catalyst system supported on mesoporous HMS silica. The effects of the various QAS promoters, the promoter doping level and the Cu/Pd mole ratio were investigated, as well as the reaction conditions on the catalytic reactivates. The results showed that the tetrabutylammonium bromide (TBAB) promoted PdCl2-CuCl2/HMS catalyst system has the best catalytic performance. The characterization of PdCl2-CuCl2-TBAB/HMS catalysts was performed by means of BET, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The essential role of TBAB promoter is to facilitate the Pd(0)/Pd(II) and Cu(II)/Cu(I) redox processes. The formation of substantial amounts of surface stabilized cuprous species on the bimetallic HMS catalysts may account for the significant enhancement of the catalytic performance in DMC synthesis.

Liquid phase glucose hydrogenation to d-glucitol over an ultrafine Ru-B amorphous alloy catalyst

Abstract A Ru-B amorphous alloy catalyst in the form of ultrafine particles was prepared by chemical reduction of RuCl 3 with borohydride in aqueous solution, whose amorphous structure was confirmed by XRD, DSC, and SAED. Heating pretreatment resulted in the rapid crystallization and the deep decomposition of the Ru-B amorphous alloy as well as the abrupt decrease in the surface area due to the gathering of small particles at high temperature. XPS spectra revealed that partial electrons transferred from the alloying B to the metallic Ru in the as-prepared Ru-B sample. In comparison with other catalysts, the as-prepared Ru-B amorphous catalyst exhibited excellent activity and perfect selectivity to d -glucitol as well as superior lifetime during the liquid phase glucose hydrogenation, showing its potential application in industrial process. The higher activity of the Ru-based catalysts than that of other metal catalysts, such as Co-B and Ni-B amorphous catalysts as well as Raney Ni catalysts, demonstrated that the metallic Ru was more active than both metallic Ni and Co for the glucose hydrogenation. Meanwhile, the Ru-B amorphous catalyst exhibited higher activity than its corresponding crystallized Ru-B and pure Ru powder catalysts, showing the promoting effects of both the amorphous structure and the electronic interaction between the metallic Ru and the alloying B, which was briefly discussed based on the kinetic studies and various characterizations.