Wei-Jiang Wang

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.

Progress in design of new amorphous alloy catalysts

Three new kinds of Ni-based amorphous alloy catalysts, Raney type Ni–P(R–Ni–P), Ni–Co–B, and Ni–B(P)/SiO2, have been prepared by modification of either the rapid quenching method or chemical reduction. Their amorphous structures have been determined by XRD, EXAFS, and DSC. Their catalytic activities and selectivities have been measured during the hydrogenation of various organic compounds, which demonstrate the great improvement on the catalytic properties in comparison with the corresponding amorphous alloy catalysts prepared by the rapid quenching method or chemical reduction previously reported. These new amorphous catalysts also exhibit superior catalytic properties over the traditional catalysts, such as Raney Ni, Ni/SiO2, and Pd/C, making them possible to be used in real industrial catalysis. The relationship between the catalytic properties and the structural properties has been discussed according to various characterizations, including ICP, XPS, EXAFS, XRD, TPD, TPR, hydrogen adsorption, IR, SEM, and TEM, etc. The higher hydrogenation activity of R–Ni–P than the Ni–P amorphous catalyst obtained by rapid quenching is mainly ascribed to the increase of the surface area due to the skeleton structure; the higher activity of Ni–Co–B than the Ni–B amorphous catalyst demonstrates a promoting effect of the additive metal(s); while the higher thermal stability of supported Ni–P(B) than the corresponding unsupported catalysts can be explained by considering the stabilizing effect of the silica support on the amorphous structure.

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.

Selective hydrogenation of cyclopentadiene to cyclopentene over an amorphous NiB/SiO2 catalyst

Abstract An amorphous NiB/SiO 2 catalyst, with a large specific surface area, was prepared by a reductive-impregnation method. The selective hydrogenation of cyclopentadiene to cyclopentene was carried out in a continuos flow fix-bed reactor at atmospheric pressure and with 10 g g cat −1 h −1 of cyclopentadiene feed. The catalyst showed high selectivity and stability. Cyclopentene was obtained in 96–100% yield at complete conversion of cyclopentadiene at temperatures ranging from 80°C to 200°C and no significant decrease of the activity was observed during the reaction period of 500 h. The catalyst sample was characterized by ICP, XRD, DSC, SEM, XPS, BET and O 2 adsorption. XRD measurement revealed that the amorphous state was kept after catalytic reaction. Differential kinetic study showed that the hydrogenation proceeded according to a Rideal-Eley mechanism.

Amorphous NiP/SiO2 aerogel: Its preparation, its high thermal stability and its activity during the selective hydrogenation of cyclopentadiene to cyclopentene

Abstract An amorphous NiP/SiO 2 aerogel catalyst, prepared by a sol-gel method, showed extremely high thermal stability up to 500°C as determined by DSC. Its catalytic activity was also much higher than Ni/SiO 2 and amorphous NiP/SiO 2 (prepared by chemical deposition) catalysts for selective hydrogenation of cyclopentadiene to cyclopentene in a continuous flow fixed-bed reactor under atmospheric pressure at 150°C. The experimental results were discussed according to the catalyst characterizations, including XRD, BET, oxygen uptake, EXAFS, and TEM.

Surface morphology and electronic state characterization of Ni-P amorphous alloy films

Abstract Thin films of Ni–P amorphous alloy were deposited by electroless plating onto a p-type silicon substrate. The films underwent a cyclic oxidation–reduction or a crystallization treatments, respectively. The amorphous structure and its crystallization were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), extended X-ray absorption fine structure (EXAFS), scanning electron microscopy (SEM), atomic force microscopy (AFM), scanning tunneling microscopy (STM). The change in the surface composition and surface electronic state were investigated by X-ray photoelectron spectroscopy (XPS).

Regeneration at room temperature for amorphous NiB/SiO2 catalyst deactivated in cyclopentadiene hydrogenation

Abstract The deactivated amorphous NiB/SiO 2 catalyst in the selective hydrogenation of cyclopentadiene (CPD) to cyclopentene (CPE) was regenerated by a new method, base-wash method at room temperature. The base was alkaline-ethanol solution. After regeneration, the activity and selectivity were completely recovered. The results of XRD and DSC measurements showed that the amorphous structure of the regenerated amorphous catalyst is almost the same as that of the original counterpart. STEM-EDAX analysis revealed that the surface of the deactivated catalyst was covered by carbon. After regeneration, the carbon was removed. BET, H 2 chemisorption and XPS tests indicated that the surface areas and chemical state were held on the renewal catalyst. Such regeneration operation can be repeated several times without significant changes in the structural and chemical properties.

Partial hydrogenation of cyclopentadiene over amorphous NiB alloy on α-alumina and titania-modified α-alumina

Amorphous nickel-boron alloys supported on α-alumina (NiB/Al 2 O 3 ) and on titania-modified α-alumina (NiB/TMA) with titania loadings ranging from 1.25 to 10 wt% were prepared by a reductive impregnation method, which resulted in a highly dispersed NiB amorphous alloy on the support. When used as catalysts for partial hydrogenation of cyclopentadiene to cyclopentene in a flow fixed-bed reactor at atmospheric pressure, the NiB/Al 2 O 3 showed higher activity than Ni/Al 2 O 3 and Pd/Al 2 O 3 but the NiB/TMA with 5 wt% of titania loading (NiB/TMA5) showed the highest activity of all for the production of cyclopentene in a temperature range of 80-200°C with 10 g/gcat.h of cyclopentadiene feed. The maximum yield of cyclopentene was 97% on NiB/TMA5, 92% on NiB/Al 2 O 3 , 60% on Ni/Al 2 O 3 and 23% on Pd/Al 2 O 3 , respectively. The catalytic stability of the amorphous NiB/TMA5 was also excellent with time on stream. The catalyst samples were characterized by ICP, XRD, XPS, BET, TEM and O 2 adsorption. The probable modification mechanism is discussed.

Regeneration of amorphous NiB/SiO2 catalysts deactivated in cyclopentadiene hydrogenation

An amorphous NiB/SiO 2 catalyst, deactivated in the partial hydrogenation of cyclopentadiene to cyclopentene, was regenerated by an oxidation-reduction method. After regeneration, the activity was recovered and the selectivity almost recovered. The data of BET, H 2 uptake and XPS measurements on the regenerated catalyst are almost the same as the original counterpart. XRD and DSC tests revealed that some crystallization had occurred over the regenerated catalyst, which led to the selectivity decreasing slightly. This regeneration was repeated several times, but the structural and chemical properties were nearly the same as after the first operation.