Uniform 3D NiMoS nanoflowers with self-assembled nanosheets were successfully synthesized via a simple hydrothermal growth method using cheap and nontoxic elemental sulfur as sulfur sources. The structure and morphology of the nanomaterials were characterized by SEM, TEM, XRD, Raman and XPS analyses, revealing that the NiMoS nanoflowers were composed of ultrathin nanosheets with a thickness of approximately 6–12 nm. The HRTEM results indicate that the curve/short MoS2 slabs on the nanosheets possess the characteristics of dislocations, distortions and discontinuity, which suggests a defect-rich structure, resulting in the exposure of additional Ni–Mo–S edge sites. The obtained NiMoS nanoflowers exhibited an excellent activity for thiophene hydrodesulfurization (HDS) and 4,6-dimethyldibenzothiophene deep HDS due to their high density of active sites. The outstanding HDS performance suggests that these NiMoS composites with a unique flower-like nanostructure could be useful as promising catalysts for deep desulfurization of fuel oils.

The findings in this study provide new insight into the NiMoS model, revealing that there is a sulfur dynamic equilibrium between the NiMoS edge and the gas phase. Since the evolution of non-stoichiometric sulfur proceeds rapidly at the initial stage of hydrodesulfurization reaction, the sulfur dynamic equilibrium does not draw so much attention. The results indicate that excess sulfur on the Ni–Mo–S edge can be reduced by hydrogen to form SH groups and release H2S, which lead to a low sulfur-covered NiMoS edge and a significant increase in coordinatively unsaturated sites (CUS), resulting in an outstanding HDS activity. Apart from elucidating the effect of non-stoichiometric sulfur on the NiMoS structure, the relationship among H2S partial pressure, Sx and HDS activity has been quantitatively studied. It is expected that these results will be used to deepen the understanding of HDS reaction over promoted MoS2 catalysts, as well as to guide the research on ultra-deep HDS of fuel oils.

•A controllable copper species (Cu0 and Cu+) supported on LaFeO3 was synthesized.•Hydrogen-treatment was used to control copper species and content on the surface.•Photocatalyst with optimized copper showed hydrogen evolution of 343 μmol h−1 g−1.•The high activity was attributed to better charge separation on the surface.LaFeO3 has been reported to have excellent optoelectronic properties and a narrow bandgap, which make it a promising candidate for photocatalytic reactions. In this work, to further improve the photocatalytic water-splitting performance by enhancing the separation of photo-excited carriers and providing active sites for H2 production, cocatalysts (copper species) supported on the perovskite-type oxide LaFeO3 was obtained by a citrate complexation and reduction treatment. Copper ions in the perovskite lattice are easily reduced and LaFeO3 possesses good stability in reducing atmospheres; thus, a series of stable LaFeO3 with a controllable copper species were synthesized and characterized by XRD, DRS, XPS and PL. The results showed that copper species (Cu0 and Cu+) supported on the LaFeO3 surface brought about a significant enhancement of photocatalytic activity. The LaFe0.8 + LaCu0.2 treated at 300 °C exhibited the highest photocatalytic activity, with a H2 evolution rate of 343 μmol g−1 h−1, which was attributed to the fact that a proper Cu0 to Cu+ ratio (Cu0/Cu+ = 1.34) could serve as a cocatalyst for photocatalytic hydrogen evolution, providing accelerated electron–hole separation and proton-reduction sites.

A kinetic model has been developed for the sulfidation of NiMo/Al2O3 hydrodesulfurization (HDS) catalyst, which quantitatively establishes a relationship between the HDS activity and sulfidation conditions. The model parameters were estimated by fitting a series of experimental thiophene HDS conversion data over the catalysts sulfurized under different operations. The results show that the developed model satisfactorily predicts the HDS conversion with a total average relative deviation of less than 4 %. Moreover, parametric studies were made to validate the accuracy of the model. The comparison results show that the proposed model is fairly effective in simulating the sulfidation process. It is expected that the model will be used to guide the sulfidation research of supported Mo-based catalysts and to optimize laboratory/pilot-plant sulfiding procedures.

Alkali-treated HZSM-5 zeolite (AT) was modified with Mg species to produce combined modified HZSM-5 catalyst (Mg-AT) for alkylation of benzene with ethanol to ethylbenzene. The catalysts were tested and characterized by X-ray diffraction (XRD), NH3-Temperature Programmed Desorption (NH3-TPD), Nitrogen adsorption–desorption, Magic angle spinning nuclear magnetic resonance (MAS NMR) and Scanning Electron Microscope (SEM) techniques. The characterization results showed that for the combined modified HZSM-5 sample, the ratio of surface area of mesopores to the total surface area was the highest. The Mg (1 wt%)-AT catalyst was found to exhibit the highest activity (30% of the conversion of benzene) and selectivity to EB (92%) for the reaction, which was confirmed to be due to the proper L/B acid proportion (3.79) and the improvement of the mesopores of the catalyst.

Small amounts of Cu–Zn binary precursor were introduced into traditional ternary Cu–Zn–Al catalysts to produce a series of modified ternary Cu–Zn–Al catalysts for the synthesis of methanol from synthesis gas with high CO content. 2 wt% Cu–Zn (Cu–Zn = 3:1 atomic ratio) binary precursor was found to have the most significant improvement for the catalytic performances. Physicochemical characterization of the as-prepared catalysts by TPR, in situ XRD and in situ XAES techniques indicated that the addition of a suitable amount of binary Cu–Zn precursor partially modified the structure of the catalyst, changed the particle size of Cu, copper surface area and the ratio of Cu+/Cu0, and thus effectively improved the catalytic performances of the catalyst.

•Ni–CsxH3−xPW12O40/SiO2 catalysts for hydrocracking were prepared by direct synthesis.•The addition of Cs enhances the resistance to the sulfur and nitrogen compounds.•The direct synthesized catalyst had better dispersion than impregnated catalyst.•The catalysts achieve the good balance between acidity and hydrogenation function.A series of Ni–CsxH3−xPW12O40/SiO2 catalysts were prepared by direct synthesis method and characterized by BET, XRD, in situ XRD, FT-IR, NH3-TPD, H2-TPR, and H2-TPD. The catalytic performance of the catalysts for the hydrocracking of n-decane with various concentrations of thiophene and pyridine was studied. The best result was obtained on direct synthesized 8%Ni–50%Cs1.5H1.5PW/SiO2 catalyst which has shown the highest activity for the hydrocracking of n-decane and excellent tolerance to the sulfur and nitrogen compounds in the feedstock, superior to the impregnated catalyst and the industrial catalyst. The highest catalytic performance of the catalyst may be due to that the direct synthesized catalysts had better dispersion, higher numbers of acid sites and stronger hydrogenation-dehydrogenation function than that of the impregnated catalyst.

The effect of Cs content in CsxH3-xPW12O40 on the catalytic performance of the reduced Ni-CsxH3-xPW12O40/Al2O3 catalysts for hydrocracking of n-decane with the presence of thiophene and pyridine is studied. The catalysts were characterized by BET, XRD, in situ XRD, Raman, H2-TPR, H2-TPD, NH3-TPD and FT-IR of pyridine adsorption. The best result was obtained on 8%Ni-50%CsH2PW12O40/Al2O3 catalyst which shows the highest catalytic activity and with tolerance to 525 ppm of thiophene and 170 ppm of pyridine (the reaction conditions: 2.0 MPa, LHSV = 2.92 h− 1, H2/n-decane 1500 vol/vol at 300 °C). The high catalytic performance of the catalyst may be due to the proper balance between metal and acid functions by adding a certain proportion of Cs to the system.Highlights►Effect of Cs in Ni-CsxH3-xPW12O40/Al2O3 for hydrocracking of n-decane is studied. ►Proper balance between metal and acid functions is established by adding Cs. ►The highest catalytic activity is obtained on 8% Ni-50% CsH2PW12O40/Al2O3.

In this work, a series of NiMo/γ-Al2O3 catalysts is prepared by one-pot method with controlled precipitation of AlCl3·6H2O, (NH4)6Mo7O24·4H2O and NiCO3·2Ni(OH)2·4H2O using urea and ammonium carbonate as additives. The molar ratio of urea to Al varied from 4.1 to 17.2 and the influence of this parameter on the surface and structural properties of the catalysts and HDM activity was studied. HDM of Ni-TPP was carried out in a batch reactor. The catalysts were characterized by BET, XRD, H2-TPR, DRS, XPS, EDS, FT-IR, TG–DTA and NH3-TPD. The results show that urea employed as additive not only improves the solubility of Mo and Ni salt, but also adjusts the hydroxyl concentration and facilitates the formation of molybdate and polymolybdate. The existence of residual chlorine may improve the dispersion of the particles containing Ni and Mo on the surface of porous Al2O3, enhance hydrogen spillover and the acidity of the catalyst. HDM activity varied with the amount of urea to a maximum at urea/Al of 12.3 with activity of 98%. The highest activity occurred at this ratio is mainly due to better porosity, well dispersed active particles, increased octahedral molybdenum/nickel oxides and proper acidity.Highlights► NiMo/Al2O3 catalysts were prepared by one-pot method using urea as additive. ► NiMo/Al2O3 possessed better porosity and well dispersed active particles. ► The effect of urea concentrations on HDM activity of NiMo/Al2O3 is investigated. ► The HDM activity varied with the amount of urea to maximum at urea/Al of 12.3.

Hydrogen spillover on Ni–CsxH3−xPW12O40 (x = 0, 1, 2) double-function hydrocracking catalyst was studied by temperature-programmed desorption (H2-TPD and NH3/H2-TPD) and thermodynamic calculations. The results of H2-TPD show that the hydrogen adsorption amount on the two-component Ni–CsxH3−xPW12O40 (x = 0, 1, 2) catalysts is much greater than that on single-component catalysts, such as nickel, tungstophosphoric acid and its cesium salts. Moreover, the H+ content is related to the content of Ni–CsxH3−xPW12O40. The above phenomena can be explained by the spillover hydrogen H combining with H+ to form Hn+ (n = 2, 3). The results of NH3/H2-TPD can also indirectly prove the existence of Hn+. It is demonstrated by the theoretical calculation that the formation of Hn+ (n = 2, 3) from H and H+ is favorable in energy, and NH3 may combine with H3+ to form NH6+.

Perovskite-like oxides LaNi1−xCuxO3 (x = 0.1, 0.4, 0.5) were prepared by means of the citric acid complexing method. TPR revealed the incorporation of Cu into the perovskite lattice increased the reducibility of the catalyst. After LaNi1−xCuxO3 were pretreated in H2 for 2 h at certain low temperature, the material still retained its perovskite structure and oxygen vacancies were generated in the lattice. DRS showed that narrowing of band-gap of reduced LaNi1−xCuxO3 was governed by the crystalline structure and the defect in the catalyst. In the photocatalytic water splitting experiment, 200 and 250°C-reduced LaNi0.6Cu0.4O3, 200°C-reduced LaNi0.5Cu0.5O3 possessed the high and colse catalytic activity. XPS showed that the molar ratio of Cu2+/Cu1≈1 and lattice oxygen/adsorb oxygen ≈ 0.2 in the catalysts had high catalytic activity. According to the outcome of our experiments, we conclude that there is a balance relation either between oxygen vacancies and catalytic activity or between Cu2+/Cu1+ redox couples and catalytic performance of these materials for hydrogen production from photocatalytic water splitting. Enhancement of hydrogen yield can be attributed to the small band-gap and the lowering the recombination probability for electron-hole pairs.

Nano Ni–W catalysts with different tungsten contents prepared by mixing alkaline nickel carbonate with ammonium tungstate show high activity and good sulfur tolerance for hydrogenation of thiophene-containing ethylbenzene. The catalysts were characterized by XRD, TPR, SEM, Raman and BET. The results show that the activity of the catalysts for ethylbenzene hydrogenation is affected profoundly by W loading and the best result was obtained on catalyst with W/Ni ratio equal to 0.16. The increase of activity of the catalyst can be attributed to the interaction between Ni and W doped and the increase of the surface area of the catalyst.

Different nickel precursors, i.e., nickel nitrate, nickel acetate and nickel acetate plus citric acid, were used to prepare supported Ni/γ-Al2O3 catalysts for naphthalene hydrogenation to decalin. The catalysts thus prepared were reduced without calcination and after calcination, respectively. The physicochemical characterization and activity testing results show that the catalyst prepared with nickel acetate as precursor and reduced without calcination possesses modest reduction character, higher adsorption and desorption abilities of H2, and exhibits most excellent catalytic performance for the reaction with 99.1% selectivity of decalin at the naphthalene conversion of 100%.

•NiMo–Al2O3 catalysts were prepared by combustion synthesis using starch as fuel.•The textural properties of the catalysts depended strongly on the starch addition.•Starch addition markedly improved the sulfidity and generated Ni–Mo–S Type II phase.•TOF increased with increasing starch addition.•A starch addition ratio of 2.5 exhibited the best hydrodesulfurization performance.The effect of starch addition on the precursor combustion reaction, physicochemical properties, active phase, and intrinsic hydrodesulfurization activity of Al2O3-supported Ni–Mo catalysts prepared by combustion synthesis in a one-pot process has been studied. The results show that the increase in starch addition markedly enhances the molar enthalpy of the combustion reaction, develops the porosity of the catalysts, and improves the reducibility and sulfidability by reducing the interaction of Mo and Ni with the Al2O3 support. Thus, the total number of Ni–Mo–S active sites increases, and substantial amounts of the Ni–Mo–S Type II phase forms, leading to an increase in the turnover frequency (TOF) for the catalysts. However, excess starch will lead to a large agglomeration of Mo particles, resulting in high MoS2 stacking and low MoS2 dispersion. As a result, the specific activities of hydrodesulfurization over NiMoAl-x catalysts peak at a starch addition ratio (x) of 2.5 ((C6H10O5):2Al).Graphical abstractDownload high-res image (70KB)Download full-size image

A series of bifunctional Ni-H3PW12O40/SiO2 catalysts for the hydrocracking of n-decane were designed and prepared. The evaluation results of the catalysts show that Ni-H3PW12O40/SiO2 catalysts possess a high activity for hydrocracking of n-decane and an excellent tolerance to the sulfur and nitrogen compounds in the feedstock. Under the reaction conditions: reaction temperature 300 °C; H2/n-decane volume ratio of 1500; total pressure of 2 Mpa and the LHSV 2 h−1, the conversion of n-decane over reduced 5%Ni-50%H3PW12O40/SiO2 catalysts is as high as 90%, the C5+ selectivity equal to 70%. In order to reveal the structure and nature of the catalysts, a number of characterizations including XRD, Raman, H2-TPD, NH3-TPD, XPS and FT-IR of pyridine adsorption were carried out. The characteristic results show that the high activity of the catalysts and high C5+ selectivity can be related to the unique structure of the H3PW12O40 and its suitable acidity.

The findings in this study provide new insight into the NiMoS model, revealing that there is a sulfur dynamic equilibrium between the NiMoS edge and the gas phase. Since the evolution of non-stoichiometric sulfur proceeds rapidly at the initial stage of hydrodesulfurization reaction, the sulfur dynamic equilibrium does not draw so much attention. The results indicate that excess sulfur on the Ni–Mo–S edge can be reduced by hydrogen to form SH groups and release H2S, which lead to a low sulfur-covered NiMoS edge and a significant increase in coordinatively unsaturated sites (CUS), resulting in an outstanding HDS activity. Apart from elucidating the effect of non-stoichiometric sulfur on the NiMoS structure, the relationship among H2S partial pressure, Sx and HDS activity has been quantitatively studied. It is expected that these results will be used to deepen the understanding of HDS reaction over promoted MoS2 catalysts, as well as to guide the research on ultra-deep HDS of fuel oils.