Yong-Ming Chai

Two-step synthesis of binary Ni–Fe sulfides supported on nickel foam as highly efficient electrocatalysts for the oxygen evolution reaction

A facile two-step method has been used to synthesize binary Ni–Fe sulfides supported on nickel foam (NF) as electrocatalysts for the oxygen evolution reaction (OER). Firstly, NiFe hydroxide nanosheets have been electrodeposited on NF (NiFe/NF) as a precursor with a large surface area. Secondly, the as-prepared NiFe/NF has been subjected to a hydrothermal sulfuration process in order to prepare NiFeS/NF as an efficient electrocatalyst for the OER. The as-prepared samples have been characterized by XRD, XPS and SEM. The SEM images show that the NiFeS film was composed of needle-like nanostructures covering the surface of the NF. The corresponding OER performances in alkaline media have been systematically investigated. NiFeS/NF shows a superior overpotential of 65 mV at 10 mA cm−2, which is much lower than most Ni-based electrocatalysts. The overpotential of 189 mV at 100 mA cm−2 of NiFeS/NF suggests very promising OER activity for industrial applications. The electrochemically active surface area (251.25 cm2) of NiFeS/NF is obviously larger than that of NiFeS/NF (173.75 cm2) and NiFeS/NF (205.00 cm2). However, the stability of NiFeS/NF is not very good due to the intrinsic nature of metal sulfides in alkaline solution. An approach of electrodeposition of Fe hydroxide film on NiFeS/NF (NiFeS–Fe/NF) has been used to protect NiFeS/NF for better stability for the OER. The OER performances of NiFeS–Fe/NF demonstrate enhanced stability but lower activity with 101.6 mV at 10 mA cm−2. Therefore, there may be an optimal balance between activity and stability of transition metal sulfides for the OER.

Reactive adsorption of thiophene on Ni/ZnO adsorbent：Effect of ZnO textural structure on the desulfurization activity

Abstract To better understand the nature of reactive adsorption of thiophene on Ni/ZnO adsorbent, the effect of ZnO textural structure on the desulfurization activity was investigated. ZnO materials were synthesized by low-temperature solid-state reaction and the corresponding Ni/ZnO adsorbents were prepared by incipient impregnation method. The analysis results showed that the crystalline sizes of ZnO as-synthesized as well as the BET surface areas varied obviously with the calcination temperature. The activity evaluations indicated that the Ni/ZnO adsorbents prepared with ZnO possessed a favorable textural structure as active component exhibited good activity of removing thiophene. The evolutions of the main crystalline phases of Ni/ZnO adsorbents before and after reaction confirmed that ZnO played a crucial role in taking up S element and converting it into ZnS in the reactive adsorption process. It was concluded that ZnO with larger surface area and smaller crystal particles resulted in better desulfurization activity, which may be the main reason for the different activities of the Ni/ZnO adsorbents prepared with ZnO calcined at different temperatures.

In situ sulfurized CoMoS/CoMoO4 shell–core nanorods supported on N-doped reduced graphene oxide (NRGO) as efficient electrocatalyst for hydrogen evolution reaction

Many strategies, such as doping metal, designing low-dimensional nanostructures, and enhancing the utilization of active sites based on a conductive support, have been intensively pursued to improve the intrinsic activity of transition metal chalcogenides for the hydrogen evolution reaction (HER). However, integrating all the above-mentioned merits into one electrocatalyst is still a significant challenge. Herein, we have successfully prepared uniform CoMoS/CoMoO4 (CMS) shell–core nanorods, with a diameter of 60 nm and a length of 800 nm, supported on N-doped reduced graphene oxide (NRGO). The obtained CMS/NRGO can combine many advantages, including transition metal doping, one-dimensional nanorods, and the superior conductivity of NRGO, resulting in very promising HER properties and excellent stability. The optimum sulfurization temperature for unsupported CMS nanorods has been explored using uniform CoMoO4 nanorods as a precursor. Although CMS-3 prepared with a sulfurization temperature of 300 °C has been found to possess the optimum activity for the HER, when adopting NRGO as a support, CMS-3/NRGO exhibits an impressive enhancement in HER performances with a low overpotential of 80 mV, a small Tafel slope of 58 mV dec−1, and a large exchange current density of 428 μA cm−2. In addition, the electrocatalytic activity of CMS-3/NRGO shows a negligible delay after 1000 cycles, indicating its robust electrochemical stability in acid electrolyte solution. Therefore, adopting low-temperature sulfurization of one-dimensional metal oxide precursors supported on NRGO may be a promising strategy for obtaining excellent electrocatalysts for the HER.

NiMo/Al2O3 catalyst containing nano-sized zeolite Y for deep hydrodesulfurization and hydrodenitrogenation of diesel

Abstract Two mixed-matrix NiMo/Al 2 O 3 catalysts containing nano- and micro-sized zeolite Y have been prepared to explore the size effect of zeolite Y particle on the hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of fluid catalytic cracking (FCC) diesel. They were characterized by SEM, BET, XRD, H 2 -TPR, NH 3 -TPD and HRTEM. The results show that the catalyst containing nano-sized zeolite Y possesses larger average pore diameter, higher pore volume, weaker and lesser acid sites, more easily reducible metal phases, shorter MoS 2 slabs and more slab layers than the catalyst containing micro-sized zeolite Y. The catalysts were also evaluated with a high-pressure fixed-bed reactor using real FCC diesel as feed. The results display that the catalyst containing nano-sized zeolite Y bears higher HDS and HDN activities and exhibits higher relative rate constant for the removal of total sulfur or nitrogen than the one containing micro-sized zeolite.

Influences of different phosphorus contents on NiMoP/Al2O3 hydrotreating catalysts

Abstract NiMoP/Al2O3 hydrotreating catalysts with different phosphorus contents were prepared by impregnating NiMoP aqueous solution into γ-Al2O3. The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) performances of the catalysts were evaluated using the model compounds dibenzothiophene and quinoline in toluene. The results show that the HDS and HDN performances of the catalysts can be improved by adding appropriate quantities of phosphorus in the catalysts, and its performance can be decreased markedly when the catalysts have high phosphorus content. The catalysts were investigated by means of XRD and high-resolution transmission electron microscopy (HRTEM) to get a better understanding of the nature of active phases. The results of XRD and HRTEM characterizations indicate that the stacked layers number of active component MoS2 nanoparticles increases with the increase of the phosphorus content. Because the interaction between active component and γ-Al2O3 carrier is weakened by adding phosphorus into the catalysts, the relative content of type-II “Ni-Mo-S” phase is increased.

Controllable synthesis of three dimensional electrodeposited Co–P nanosphere arrays as efficient electrocatalysts for overall water splitting

Novel three dimensional (3D) electrodeposited Co–P nanosphere arrays on FTO (Co–P/FTO) have been successfully prepared as efficient bifunctional electrocatalysts for overall water splitting in alkaline media. The morphologies and properties of the 3D Co–P nanosphere arrays can be controlled by the electrolyte concentration. At the middle concentration, Co–P nanospheres have a more homogeneous size and array distribution and a rough surface, implying a larger surface area and an increased number of active sites for water splitting. The electrochemical measurements confirm the best electrocatalytic performances of Co–P/FTO at the middle concentration. They show excellent activity, with an overpotential of 125 mV for HER, 420 mV for OER and Tafel slopes of 54 mV dec−1 and 83 mV dec−1, respectively. The fabricated bifunctional systems of Co–P/Co–P can efficiently catalyse HER and OER at the same time, solving the incompatible problem of different media between HER and OER. Therefore, controlling the synthesis of 3D Co–P/FTO nanosphere arrays through electrodeposition can provide a facile way for the bifunctional electrocatalysis of both HER and OER.

Effect of phosphorus content on the active phase structure of NiMoP/Al2O3 catalyst

Abstract NiMoP/Al2O3 catalysts with different phosphorus contents were prepared by co-impregnation method and are characterized by temperature-programmed reduction (TPR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) tests. The effect of phosphorus content on the active phase structure of these catalysts was investigated. The TPR results indicated that with the increase of the phosphorus content in the catalysts, the amount of tetrahedral Mo species was decreased, while that of octahedral Mo species was increased. The HRTEM results showed that the number of stacking layers of MoS2 nanoparticles increased with the phosphorus content, which was effective in enhancing the hydrogenation selectivity of the catalysts. The fraction of available Mo dispersion (fMo) and the number of active phases in the catalysts increased with increasing phosphorus content to P/MoO3 = 0.09; beyond that, a reverse trend was observed. High HDS and HDN activity were obtained over the catalyst with the phosphorus content of P/MoO3 = 0.09, which could be attributed to its high concentration of Mo atoms on the catalyst surface, high-efficient promotion rate (PR) and high promoter ratio (Ni/Mo). However, excessive phosphorus content may deteriorate the performance of NiMoP/Al2O3 catalysts due to the aggregation of active components.

Synthesis, Characterization and Thermal Decomposition Mechanism of Cetyltrimethyl Ammonium Tetrathiotungstate

Abstract The synthesis, characterization and thermal decomposition mechanism of cetyltrimethyl ammonium tetrathiotungstate (CTriMATT) were studied herein. The as-synthesized CTriMATT was characterized by Elemental analysis, X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Ultraviolet visible (UV-Vis) spectra. The results showed that the as-synthesized CTriMATT had high purity and good crystallinity. The introduction of alkyl groups induced a shift of the stretching vibration band of W-S bond to lower wavenumber, while it had no influence on the position of WS 2− . Thermogravimetric analysis (TG), differential thermal analysis (DTA) and in situ XRD characterizations revealed that CTriMATT began to decompose at 423 K in nitrogen and was converted to WS 2 eventually. In addition, the decomposition product of CTriMATT at 673 K in nitrogen was characterized by N 2 adsorption (BET) and scanning electron microscopy (SEM). The results demonstrated that WS 2 with higher specific surface area, and pore volume could be obtained from the thermal decomposition of CTriMATT in nitrogen.

Synergetic effect between sulfurized Mo/γ-Al2O3 and Ni/γ-Al2O3 catalysts in hydrodenitrogenation of quinoline

Abstract An evidence for the synergetic effect between the stacked bed of Mo/γ-Al 2 O 3 and Ni/γ-Al 2 O 3 in the hydrodenitrogenation (HDN) reaction of quinoline has been provided in this paper. The synergism factor decreases when the reaction temperature increases (280–340°C). The synergetic effect leads to improve the hydrogenation activity for the stacked bed compared with the single Mo/γ-Al 2 O 3 bed, which may be attributed to the generation of hydrogen spillover on the Ni/γ-Al 2 O 3 catalyst.

Study on the structure of active phase in NiMoP impregnation solution using Laser Raman spectroscopy II.Effect of organic additives

Abstract Laser Raman spectroscopy (LRS) was used to characterize the NiMoP impregnant with different contents of glycol and citric acid as well as dried Al 2 O 3 impregnated with this NiMoP impregnant. The effect of glycol and citric acid on the structure of active phases in NiMoP impregnant and during the impregnation process was investigated. The results indicated that with glycol as the additive in the NiMoP(0.063) impregnant, the active phases like H x [PMo 11 O 39 ] (7− x )− or H x [PMo 9 O 31 ] (3− x )− ) and H x [PMo 12 O 40 ] (3− x )− are converted to H x [P 2 Mo 5 O 23 ] (6− x )− . With citric acid as the additive, H x [P 2 Mo 5 O 23 ] (6− x )− , (H x [PMo 11 O 39 ] (7− x )− or H x [PMo 9 O 31 ] (3− x )− ) and H x [PMo 12 O 40 ] (3− x )− are present together in the NiMoP(0.063) impregnant; however, citric acid leads a decrease of H x [P 2 Mo 5 O 23 ] (6− x )− content but an increase of H x [PMo 12 O 40 ] (3− x )− . Compared with glycol, during the impregnation of alumina with the NiMoP impregnant, citric acid is more effective in preventing the active phases from being decomposed in the cavities of alumina.