•Metal promoters promoted reduction of phosphate precursor and dispersion of MoP.•Noble phosphides formed in Mo40MP catalysts (M = Ru, Pd and Pt).•Metal promoters enhanced activity of MoP catalyst for hydroconversion.•Ru was an optimum promoter for hydroconversion on MoP catalyst.•Ru prevented sintering of MoP particles and suppressed coke during hydroconversion.SiO2 supported bifunctional MoP catalysts modified with different metal promoters (Ni, Ru, Pd, Pt), where Mo/Ni and Mo/M(M = Ru, Pd and Pt) atomic ratios was respectively 10 and 40, were prepared by TPR method from the phosphate precursors. It was found that the introduction of metal promoters facilitated the reduction of phosphate precursor and enhanced the dispersion of MoP. However, the MoP catalyst acidity was scarcely influenced by the small amount of metal promoters. In the hydroconversion of methyl laurate, the promoters enhanced the MoP catalyst activity for conversion of methyl laurate and hydrogenation of alkenes (intermediate), but reduced isomerization ability. Among the promoters, Ru was an optimum to decrease selectivity to alkenes while maintain high selectivity to iso-alkanes, and Mo40RuP showed better stability than MoP. At 380 °C and 3.0 MPa, the conversion of methyl laurate, the total selectivity to C11 and C12 hydrocarbons and the selectivity to iso-alkanes maintained at 100%, ∼94% and ∼30% on Mo40RuP during 102 h, respectively. The good stability of Mo40RuP is ascribed to that the presence of Ru prevented the sintering of MoP particles and suppressed carbon deposition.Download high-res image (162KB)Download full-size image

Ni2P/SiO2 was in situ prepared from Ni/SiO2via a phosphorization process using a dodecane solution containing triphenylphosphine (TPP) as the phosphorus source on a fixed-bed reactor. The influence of the phosphorization condition (nominal P/Ni molar ratio, temperature, WHSV of TPP and atmosphere) on the structure of the phosphorized samples was investigated. The sample structure was characterized by means of XRD, TEM, ICP-AES, TGA, N2 sorption, and FT-IR and magnetic property. It was found that the phosphorization of metallic Ni to Ni2P was promoted by increasing the phosphorization temperature and nominal P/Ni molar ratio and decreasing the WHSV of TPP. The phosphorization rate was much faster in the H2 atmosphere than the N2 one, ascribed to the formation of reactive H atoms on the Ni atoms that facilitated the cleavage of the P–C bond in PPT releasing more reactive PH3/P. To prepare the well-crystallized Ni2P/SiO2 in the H2 atmosphere, the minimum temperature (250 °C) and nominal P/Ni ratio (0.67) were necessary. Also, the Ni2P crystallite size in Ni2P/SiO2 was determined by the Ni one in Ni/SiO2, and no sintering took place during the phosphorization even at 400 °C. It is worth stating that there was a carbonaceous deposit formed on the in situ prepared catalysts, which was harmful for the catalyst activity for the deoxygenation of methyl laurate to hydrocarbons. The phosphorization condition greatly affected the performance of the resulting catalysts. On the whole, the Ni2P/SiO2 catalyst with good performance was prepared under a suitable phosphorization condition (i.e., 300 °C, nominal P/Ni ratio of 0.75, TPP WHSV of 0.5 h−1, and H2 atmosphere). Under the reaction conditions of 340 °C, 3.0 MPa, methyl laurate WHSV of 5 h−1 and H2/methyl laurate molar ratio of 25, it gave the conversion of methyl laurate and the total selectivity for C11 and C12 hydrocarbons higher than 98% and 96% during 100 h, respectively, exhibiting good stability. Finally, we propose a mechanism for the phosphorization of Ni/SiO2.

An effective approach to enhancing the activity of the Ni2P/SiO2 catalyst for the hydrodechlorination of chlorobenzene (CB) was reported. At atmospheric pressure, 513 K, a CB WHSV of 4.1 h−1 and a H2/CB molar ratio of 9.0, Ni2P/SiO2 gave a chlorobenzene conversion of 5.6%. Surprisingly, after Ni2P/SiO2 was pretreated with a 0.8–3.0% H2O/H2 flow below 543 K, the conversion reached as high as 99%. As the pretreatment temperature increased, the conversion tended to decrease; however, a conversion of 42.6% was still obtained even at the pretreatment temperature of 673 K. The activity of Ni2P/SiO2 was also improved when 0.8% H2O or 0.5% O2 was introduced into the reaction system. In addition, the passivation of Ni2P/SiO2 followed by the reduction led to a conversion of 33%. The Ni2P/SiO2 catalysts before and after the pretreatment were characterized by N2-sorption, XRD, ICP-AES, XPS, in situ DRIFT, and H2- and NH3-TPD. The results show that the pretreatment did not obviously influence specific surface area, pore structure, Ni2P crystallite size, the electron density of Ni in Ni2P, and the Ni and P contents, while it created new P–OH groups and reduced the amount of surface Ni sites. We propose a surface model of Ni2P/SiO2 containing the Ni sites and the P–OH groups and consider that the synergism between the Ni site and the P–OH group can explain the promoting effect due to H2O and O2 on the activity of Ni2P/SiO2, and the synergism mainly took place on the Ni2P particles and at the interface between the Ni2P particles and SiO2.

•The presence of CS2 enhanced the stability of Ni2P/SiO2 after induction period.•The presence of CS2 led to transition from Ni2P to Ni12P5 during induction period.•Decarbonylation and formation of alkenes were promoted by the presence of CS2.•Ni2P/SiO2 deactivation in the absence of CS2 is mainly due to coking.The effect of CS2 on the performance of Ni2P/SiO2 for the deoxygenation of methyl laurate as a model compound to hydrocarbons was investigated. To explore the catalyst deactivation, the fresh and used catalysts were characterized by N2 sorption, XRD, HRTEM, 31P MAS NMR, XPS, ICP-AES and TG-DTA. For comparison, we also investigated the performance of Ni12P5/SiO2 and the effects of H2O and CO on the property of Ni2P/SiO2. At 300 °C, 3.0 MPa and WHSV of 5 h− 1, Ni2P/SiO2 continuously deactivated during 28 h in the absence of CS2, which is mainly ascribed to the carbonaceous deposit as well as the surface restructuring of Ni2P due to H2O. The presence of CS2 accelerated the deactivation of Ni2P/SiO2 in the initial stage (about first 10 h), whereas the catalyst activity did not change obviously in the latter 18 h. Also, the presence of CS2 remarkably promoted the decarbonylation reaction and the formations of undecene and dodecene, which were more obvious with higher CS2 concentration. Interestingly, the Ni2P phase was transformed to Ni12P5 in the presence of CS2, which did not take place in the absence of CS2. We propose that the effect of CS2 on the performance of Ni2P/SiO2 is mainly ascribed to the formation of the surface nickel phosphosulfide phase on bulk Ni12P5. In addition, water was detrimental to the catalyst stability.

•SAPO-11 supported nickel phosphide catalysts were used for hydroisomerization.•Nickel phosphide/SAPO-11 showed higher isomerization selectivity than Ni/SAPO-11.•The roles of P in nickel phosphide contribute to high isomerization selectivity.•A balance between the acid and Ni sites was required.•Isododecane yield reached 65% on Ni2P/SAPO-11 containing 3 wt.% Ni.A new type of nickel phosphide catalysts supported on SAPO-11 was used for the hydroisomerization of n-dodecane. Their properties were characterized by means of N2-sorption, H2-TPR, XRD, XPS, DRIFTS of adsorbed pyridine, CO chemisorption, and NH3-TPD and H2-TPD. The effects of the Ni/P ratio and the nickel content on catalyst performance were investigated. For comparison, the property and performance of Ni/SAPO-11 were also considered. Compared to Ni/SAPO-11, SAPO-11 supported nickel phosphides had higher isomerization selectivity due to their lower hydrogenolysis activity. As the Ni/P ratio deceased, the n-dodecane conversion decreased, while the isododecane selectivity reached its maximum at the Ni/P ratio of 1. As the nickel content increased, the n-dodecane conversion and isododecane selectivity reached their maximum. In short, a balance between medium strength acid sites and Ni sites was required for obtaining high n-dodecane conversion and isododecane selectivity. Moreover, there was a synergism between the Ni sites and the medium strength acid site. Under suitable conditions, the isododecane yield reached about 65% on Ni2P/SAPO-11 containing 3 wt% Ni.

The bifunctional Ni2P/SAPO-11 was tested for the hydroconversion (involving deoxygenation and hydroisomerization) of methyl laurate as a model compound to hydrocarbons. The influences of reaction conditions, catalyst stability, and catalyst deactivation were investigated. For comparison, the performance of Ni/SAPO-11 was also examined. The result shows that the increase of temperature and the deceases of weight hourly space velocity (WHSV) and H2 pressure favored the conversion of methyl laurate meanwhile promoted the decarbonylation and hydroisomerization as well as cracking reactions. Apart from the Ni sites that were dominating for deoxygenation, the acid sites also affected the deoxygenation pathway. Due to more medium strength acid sites, Ni/SAPO-11 gave higher selectivity to isoalkanes and more preferentially catalyzed the hydrodeoxygenation pathway to produce the C12 hydrocarbons than Ni2P/SAPO-11. During the test for 101 h, Ni2P/SAPO-11 exhibited greatly superior stability to Ni/SAPO-11 for the deoxygenation of methyl laurate, while both Ni2P/SAPO-11 and Ni/SAPO-11 were deactivated for the hydroisomerization. Under the condition of 360 °C, 3.0 MPa, WHSV of 2 h–1, and H2/methyl laurate molar ratio of 25, the conversion of methyl laurate was close to 100% and the total selectivity to isoundecane and isododecane decreased from 36.9% to 28.6% on Ni2P/SAPO-11. To explore the catalyst deactivation, the fresh and the used catalysts were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy, and N2 adsorption–desorption. The sintering of Ni particles and carbonaceous deposit contribute to inferior stability of Ni/SAPO-11 for both deoxygenation and hydroisomerization, while no obvious sintering of Ni2P particles took place and the carbonaceous deposit mainly led to the loss of the activity for hydroisomerization on Ni2P/SAPO-11. We propose that carbonaceous deposit mostly formed on the acid sites that are indispensible for hydroisomerization.

Ni/SiO2, Fe/SiO2 and bimetallic FeNi/SiO2 catalysts with different Fe/Ni weight ratios were prepared by incipient-wetness impregnation method for the deoxygenation of methyl laurate to hydrocarbons. It was found that a suitable amount of Fe enhanced the activity of Ni/SiO2 for the deoxygenation of methyl laurate, and FeNi(0.25)/SiO2 with a Fe/Ni weight ratio of 0.25 showed the best activity. Moreover, the addition of Fe to Ni/SiO2 significantly promoted the hydrodeoxygenation pathway to produce more C12 hydrocarbon and suppressed the activity for C–C hydrogenolysis. The effect of Fe on the performance of Ni/SiO2 is ascribed the formation of the NiFe alloy particles, particularly with the Fe-enriched surface at low Fe content, and the existence of oxygen vacancies in Fe oxides. A mechanism is proposed to explain the promoting effect of Fe, which involves the synergism between iron sites with strong oxophilicity and nickel sites with high ability to activate hydrogen. Besides, the effect of reaction conditions and catalyst stability were also investigated.

•Ni/Mo ratio determines acidity, dispersion and phosphide phase.•There is an electron transfer from Ni to Mo.•Catalyst activity and product distribution can be tuned by altering Ni/Mo ratio.•Catalyst with Ni/Mo ratio of 1 shows particular performance.SiO2-supported Ni2P, MoP and Ni–Mo bimetallic phosphides with different Ni/Mo ratios were investigated for the deoxygenation of methyl laurate to C11 and C12 hydrocarbons. They were characterized by means of N2 sorption, X-ray diffraction, transmission electron microscope, CO chemisorption, X-ray photoelectron spectroscopy and NH3 temperature-programmed desorption. In the Ni–Mo bimetallic phosphide, the NiMoP2 phase was formed apart from Ni2P and MoP, and the incorporation of Mo into Ni2P took place. These led to an interaction between Ni and Mo via the electron transfer from Ni to Mo. In addition, the increase in the Ni/Mo ratio tended to reduce the phosphide dispersion and catalyst acidity. In the deoxygenation, the turnover frequency of methyl laurate and the C11/C12 ratio tended to increase as the Ni/Mo ratio increased (apart from Ni/Mo ratio of 1). This is related to not only the different catalytic roles of Ni and Mo sites but also the interaction between Ni and Mo and the phosphide dispersion. In all, the C11/C12 ratio can be regulated by altering the Ni/Mo ratio. The catalyst acidity obviously affected the distributions of the oxygenated intermediates.

The deoxygenation of methyl laurate as a model compound to diesel-like hydrocarbons was performed on Ni2P/SiO2, Ni2P/MCM-41, and Ni2P/SBA-15 catalysts. The effect of Ni2P dispersion on the catalyst structure and performance was investigated. The average Ni2P crystallite sizes varying from 3 to 12 nm were obtained. In correlation with the Ni/P ratio, the catalyst acid amount was mainly determined by the surplus P species. The deoxygenation was tested at 300–340 °C, 2.0 MPa, weight hourly space velocity of 10 h–1, and H2/methyl laurate ratio of 50. For different catalysts, the conversion of methyl laurate followed the different sequence from the turnover frequency (TOF). The TOF increased with the Ni2P crystallite size. The lower TOF on smaller crystallites can be attributed to the stronger interaction between Ni and P. Both hydrodeoxygenation and decarbonylation pathways occurred on the Ni2P catalysts. As indicated by the ratio between n-undecane (n-C11) and n-dodecane (n-C12) being larger than 1.0, the main deoxygenation pathway was decarbonylation. We suggested that the deoxygenation pathway was affected by Brönsted acidity and Ni2P crystallite size (i.e., the interaction between the Ni and P atoms). The Brönsted acid sites because of P–OH groups and the Ni sites having less interaction with P favored the decarbonylation pathway. With an increasing reaction temperature, the conversion, the selectivity to n-C11 and n-C12, and the n-C11/n-C12 ratio increased. At 340 °C, the conversion and the selectivity to n-C11 and n-C12 on all Ni2P catalysts exceeded 97 and 99%, respectively.

Ni2P/SiO2, MoP/SiO2, and NiMoP/SiO2 with different Ni/Mo molar ratios were prepared by temperature-programmed reduction (TPR). Their structural properties were characterized by N2 sorption, X-ray diffraction (XRD), CO chemisorption, X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed desorption (H2-TPD), and NH3 temperature-programmed desorption (NH3-TPD). Their performances for the hydrodeoxygenation (HDO) of anisole were tested in a fixed-bed reactor. It was found that there were mainly three reactions that occurred during the HDO, i.e., the demethylation of anisole, the hydrogenolysis of phenol, and the hydrogenation of benzene. The HDO activities decreased in the sequence of Ni2P/SiO2 > NiMoP/SiO2 > MoP/SiO2. The NiMoP/SiO2 catalysts with larger Ni/Mo ratios had higher activities. In the phosphides, the Niδ+ and Moδ+ sites bearing small positive charges acted not only as Lewis acid sites for the demethylation but also as metal sites for the hydrogenolysis and hydrogenation. The Niδ+ site was more active than the Moδ+ site, and there was no synergy between the Niδ+ and Moδ+ sites. The superior activity of Ni2P to that of MoP is attributed to the higher d electron density in Ni2P. PO−H groups, which acted as Brønsted sites and provided active hydrogen species, had less activity for the three reactions compared to the metal sites. In comparison to a conventional NiMo/γ-Al2O3 catalyst, the Ni phosphide-containing catalysts had much higher activities. The catalyst deactivation due to water was preliminarily discussed. The oxidation of phosphide by water might lead to the formation of metal oxide and/or phosphate, leading to the catalyst deactivation. The high stability of Ni2P/SiO2 may be related to the ligand effect of P that lowers the electron density of Ni and inhibits the Ni−O combination.

Ce0.75Zr0.25O2 solid solution supported Ru catalysts were prepared and tested for CH4–CO2 reforming. The effect of Ru content on the properties of the catalysts was investigated by means of N2 adsorption–desorption, H2-TPR/MS, XRD, XPS, CO chemisorption and H2-TPD/MS. It was found that the highly dispersed Ru species favored the interaction between Ru and Ce0.75Zr0.25O2. The reduced Ce0.75Zr0.25O2 was able to store hydrogen, while Ru promoted the reduction of Ce0.75Zr0.25O2. Under the identical conditions, the CH4 and CO2 conversions of the catalysts increased with the increase of Ru content, however, the turnover frequencies of CH4 and CO2 were higher for the catalysts with lower Ru contents, which may be resulted from the strong interaction between Ru and Ce0.75Zr0.25O2. The Ru catalyst exhibited good stability and excellent resistance to carbon deposition. Remarkably, zirconium and cerium hydrides were detected in the used catalyst, which may participate in the elimination of the carbon deposit. Apart from the nature of metallic Ru and the redox property of Ce0.75Zr0.25O2, we suggest that the excellent resistance of the catalyst to carbon deposition is also attributed to the hydrogen storage of the reduced Ce0.75Zr0.25O2.

HMS-supported Ni catalysts were prepared by the direct synthesis and the impregnation method. In the direct synthesis, the effect of nickel content and pH value of the preparation system on the catalyst structure and hydrodechlorination performance was systematically investigated. The physicochemical properties of the catalysts were characterized by means of N2 adsorption, hydrogen temperature-programmed reduction, low- and wide-angle X-ray diffraction, hydrogen chemisorption, hydrogen temperature-programmed desorption, transmission electron microscope, and atomic absorption spectroscopy. The catalyst activity in the hydrodechlorination of chlorobenzene was evaluated in a fixed-bed reactor at atmospheric pressure. For the n%Ni(m%)-HMS samples prepared by the direct synthesis method, BET surface area, pore volume, and the pore (2∼5 nm) diameter decrease with increasing Ni content, and the mesostructures becomes worse. When the nickel content exceeds 7.0 wt%, the sample with mesostructures cannot be prepared. This is attributed to the decrease of pH value in the preparation system and the embedment of Ni2+ in the SiO2 matrix. Ni2+ ions highly disperse in the n%Ni(m%)-HMS samples and mainly exist as nickel silicate. After reduction at 450∼650 °C, the metallic nickel particles in n%Ni(m%)-HMS uniformly distribute at about 3 nm. However, for the im−4.1%Ni/HMS sample prepared by the impregnation method, the metallic nickel particles are much larger than those of n%Ni(m%)-HMS. In the hydrodechlorination of chlorobenzene, the n%Ni(m%)-HMS samples show higher activities than im−4.1%Ni/HMS, which can be attributed to the strong interaction between small metallic nickel particles and the support, a greater amount of spilt-over hydrogen, and the acidity of nickel silicate. When the nickel content exceeds 5.9 wt % and the reduction temperature is above 450 °C, there is no remarkable difference in chlorobenzene conversion for n%Ni(m%)-HMS samples. This is perhaps related to the intraparticle mass transfer limitation.

SiO2, TiO2, γ-Al2O3, and HY zeolite supported phosphide catalysts were prepared by the hydrogen temperature-programmed reduction method from phosphate precursors. The physicochemical properties of the catalysts were characterized by means of N2 adsorption−desorption, hydrogen temperature-programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed desorption, inductively coupled plasma atomic emission spectroscopy, energy-dispersion X-ray spectroscopy, and thermal gravimetric analysis. The catalyst performance in the hydrodechlorination of chlorobenzene was evaluated in a fixed-bed reactor at atmospheric pressure. It has been found that the support property remarkably affects the formation of nickel phosphides. With the same Ni/P molar ratio (about 0.7) in the precursors, Ni2P is prepared on SiO2 and TiO2; however, Ni and Ni3P form on γ-Al2O3 and Ni and Ni12P5 form on HY. This phenomenon is attributed to some phosphorus reacting with γ-Al2O3 and HY to form AlPO4, and the phosphorus reacting with nickel is scarce. Under identical reaction conditions, the hydrodechlorination performance of the catalysts decrease in the order of SiO2-supported N2P, γ-Al2O3-supported Ni−Ni3P, TiO2-supported N2P, and HY-supported Ni−Ni12P5. The catalyst performance is closely related to the properties of active phases and hydrogen species. Nickel phosphides have better performance than metallic nickel due to the electron deficiency of nickel, and the spilt-over hydrogen species also contribute to the hydrogenolysis of C−Cl bond. The chlorobenzene conversion exceeds 99% over SiO2-supported Ni2P during 130 h at 573 K. The excellent performance is ascribed to the strong poison resistance of Ni2P to chlorine and the abundant hydrogen species. TiO2-supported N2P and HY-supported Ni−Ni12P5 have good initial activities; however, their deactivation is remarkable, especially HY-supported Ni−Ni12P5. Their deactivation is mainly owing to the carbonous deposition.

The influence of Ni2P loading on the properties of Ni2P/SiO2 catalysts was investigated by means of N2 adsorption–desorption, X-ray diffraction, H2 and NH3 temperature-programmed desorption, CO chemisorption, inductively coupled plasma atomic emission spectroscopy and activity evaluation for the hydrodechlorization of chlorobenzene. It was found that increasing Ni2P loading results in the decrease of Ni2P dispersion. Higher P/Ni ratio occurs in the catalysts with lower Ni2P loadings, indicating that smaller Ni2P crystallites may more strongly interact with surplus P. We suggest that the acid amount of the Ni2P/SiO2 catalyst is related to the exposed Ni sites and P-OH groups, while Brönsted acidity of P-OH groups facilitates hydrogen spillover. Increasing Ni2P loading is favorable to the catalyst activity, while this effect is not obvious when the Ni2P loading is greater than 9.6 wt%. Apart from the metallic property of Ni2P phase and spilt-over hydrogen species, we propose that the acidity and the role of P in activating reactants should be considered for the catalyst performance.

The effect of calcination temperature on the properties of eggshell Ni/MgO–Al2O3 catalysts was studied. Catalyst deactivation was also investigated. It is found that higher calcination temperature contributes to lower surface area, wider pore, and larger Ni crystallites. Small Ni crystallites and large pores favor the catalyst performance. Catalyst deactivation is due to the formation of NiO–MgO solid solution and/or NiAl2O4, phase transformation, and sintering.

Ce0.75Zr0.25O2 solid solutions doped with Y3+ or Pr4+/Pr3+ were prepared by the co-precipitation method, and their physicochemical properties were characterized by means of N2 adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, FT-Raman, and H2 temperature-programmed reduction and thermogravimetric analysis. Their performance in CH4–CO2 reforming was also tested in an atmospheric fixed-bed reactor. Ce0.75Zr0.25O2 and Y3+ or Pr4+/Pr3+ doped Ce0.75Zr0.25O2 solid solutions are of CaF2 structure, and the thermal stability of Ce0.75Zr0.25O2 is enhanced by doping Y3+ or Pr4+/Pr3+. Comparing with Ce0.75Zr0.25O2, the migration of bulk lattice oxygen species become easier and the content of surface oxygen species is higher in the doped Ce0.75Zr0.25O2, which is due to either oxygen vacancies or/and structural distortion resulted from the doping. The activity of the solid solutions in CH4–CO2 reforming is closely related to the surface oxygen species. Y3+ or Pr4+/Pr3+ doped Ce0.75Zr0.25O2, especially the former, show higher activity than Ce0.75Zr0.25O2, and Y3+ doped Ce0.75Zr0.25O2 possesses better stability. All of the catalysts have good coke resistance. The catalyst deactivation is mainly due to the catalyst sintering.

Silica-supported Ni3P, Ni12P5, and Ni2P catalysts were prepared by the temperature-programmed reduction method from nickel phosphate precursors. A Ni/SiO2 catalyst was also prepared as a reference. The effect of the initial Ni/P molar ratio in the precursor on the catalyst structure and hydrodechlorination performance was investigated. The physicochemical properties of the catalysts were characterized by means of N2 adsorption, hydrogen temperature-programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet and visible spectroscopy, hydrogen temperature-programmed desorption, and inductively coupled plasma spectroscopy. The catalyst activities in the hydrodechlorination of chlorobenzene were evaluated in a fixed-bed reactor at atmospheric pressure. The silica-supported nickel phosphides exhibited superior hydrodechlorination activities to that of supported nickel. This can be attributed to the special physicochemical properties of nickel phosphides and a great amount of spillover hydrogen species. In nickel phosphides, there is a small amount of electron transfer from Ni to P, leading to a small positive charge on Ni. This favors a weakening of the interaction between chlorine and nickel sites, as well as between adsorbed hydrogen species and nickel phosphides. The “ensemble effect” of P is also beneficial in decreasing the coverage of chlorine on nickel sites. Because of the reduced interaction between adsorbed hydrogen species and nickel phosphides, the energy barrier of the hydrogen spillover on the silica-supported nickel phosphide catalysts decreases, which accounts for the increased amount of spillover hydrogen species on the catalyst surface. Spillover hydrogen species not only promote the hydrogenolysis of the C−Cl bond, but also favor the removal of chlorine ions from the surface of the catalysts. Hydrodechlorination over the nickel phosphide catalysts is characterized by a reaction induction period that becomes longer with increasing phosphorus content in the catalyst precursor. This is related to the blocking of active sites by excess phosphorus.

A simple method to prepare eggshell Ni/MgO-Al2O3 catalyst was developed. In partial oxidation of methane, eggshell Ni/MgO-Al2O3 showed better reactivity and stability than the uniform one, even than eggshell Ni/Al2O3.

The effects of CeO2 and CaO composite promoters on the properties of eggshell Ni/MgO-Al2O3 catalysts of 1.5 mm diameter for the partial oxidation of methane to syngas were investigated. The addition of 1wt.% promoters could enhance the catalytic performance of the Ni/MgO-Al2O3 catalyst, while further increasing the promoter content to 4wt.% results in the decrease of reactivity. The catalytic property is related to the oxidizability of surface nickel species.

The impregnated Ni/Ce0.75Zr0.25O2 catalysts were prepared with the supports synthesized by the co-precipitation involving the surfactant or not, and the co-precipitated Ni/Ce0.75Zr0.25O2 catalysts were also prepared with or without the surfactant assistance. In the co-precipitated catalysts, Ni2+ entered the lattice of Ce0.75Zr0.25O2 solid solution, which led to a better nickel dispersion and a stronger interaction between nickel species and the solid solution in comparison with the impregnated catalysts. With the surfactant assistance, the catalysts had larger surface area and pore volume than the ones without the surfactant. Among the prepared catalysts, the co-precipitated one with the surfactant assistance showed the highest activity in CH4–CO2 reforming. Under the conditions of 0.1 MPa, 1123 K, nCH4/nCO2=1nCH4/nCO2=1 and space velocity of 1.2 × 104 h−1, the CH4 and CO2 conversions were about 92% and 94% over the catalyst, respectively. It is revealed that the catalysts performance is related to the textural properties, the support activity, and the nickel dispersion and the interaction between nickel species and the support.

The effects of MgO promoter on the physicochemical properties and catalytic performance of Ni/Al2O3 catalysts for the partial oxidation of methane to syngas were studied by means of BET, XRD, H2-TPR, TEM and performance evaluation. It was found that the MgO promoter benefited from the uniformity of nickel species in the catalysts, inhibited the formation of NiAl2O4 spinel and improved the interaction between nickel species and support. These results were related to the formation of NiO-MgO solid solution and MgAl2O4 spinel. Moreover, for the catalysts with a proper amount of MgO promoter, the nickel dispersiveness was enhanced, therefore making their catalytic performance in methane partial oxidation improved. However, the excessive MgO promoter exerted a negative effect on the catalytic performance. Meanwhile, the basicity of MgO promoted the reversed water-gas shift reaction, which led to an increase in CO selectivity and a decrease in H2 selectivity. The suitable content of MgO promoter in Ni/Al2O3 catalyst was ∼7 wt-%.

Xerogel and aerogel catalysts have been prepared via a sol–gel process followed by conventional drying and supercritical drying, respectively. The catalysts were characterized by means of XRD, XPS, H2-TPR, TPD, TEM, TGA and N2 adsorption–desorption. The catalytic performance of the catalysts in CH4 reforming with CO2 was evaluated. The results indicate that the method for the preparation of the aerogel leads to higher specific surface area, larger pore size, lower bulk density, higher thermal stability, and higher dispersivity and homogeneity of nickel species than that of the xerogel. The aerogel catalyst shows high catalytic activity, good resistance to sintering at high reaction temperature and prolonged stability.Nickel-based xerogel and aerogel catalysts have been prepared, and the method for the preparation of the aerogel leads to a higher specific surface area and higher dispersivity and homogeneity of nickel species than that of the xerogel.

AbstractThe effect of CeO2 and CaO promoters on the ignition performance over Ni/MgO-Al2O3 catalyst for the partial oxidation of methane (POM) to synthesis gas was investigated. It was found that the POM reaction could not be ignited over lwt%Ni/MgO-Al2O3 catalyst without the promoters in the temperature range from 773 K to 1073 K. CeO2 and CaO promoters enhanced the ignition performance and the POM reactivity of lwt%Ni/MgO-Al2Oa catalyst remarkably. Moreover, the improving effect became greater with the increase of the promoter content under the investigated reaction conditions. The modification effects of CeO2 and CaO promoters were closely related to the concentration and reducibility of the surface and bulk oxygen species.

SiO2-supported Ni-Mo bimetallic phosphides were prepared by temperature-programmed reduction (TPR) method from the phosphate precursors calcined at different temperatures. Their properties were characterized by means of ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), H2 temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD), transmission electron microscopy (TEM), CO chemisorption, H2 and NH3 temperature-programmed desorptions (H2-TPD and NH3-TPD). Their catalytic performances for the deoxygenation of methyl laurate were tested in a fixed-bed reactor. When the precursors were calcined at 400 and 500 °C, respectively, NiMoP2 phase could be formed apart from Ni2P and MoP phases in the prepared C400 and C500 catalysts. However, when the precursors were calcined at 600, 700 and 800 °C, respectively, only Ni2P and MoP phases could be detected in the prepared C600, C700 and C800 catalysts. Also, in C400, C500 and C600 catalysts, Mo atoms were found to be entered in the lattice of Ni2P phase, but the entering extent became less with the increase of calcination temperature. As the calcination temperature of the precursor increased, the interaction between Ni and Mo in the prepared catalysts decreased, and the phosphide crystallite size tended to increase, subsequently leading to the decrease in the surface metal site density and the acid amount. C600 catalyst showed the highest activity among the tested ones for the deoxygenation of methyl laurate. As the calcination temperature of the precursor increased, the selectivity to C12 hydrocarbons decreased while the selectivity to C11 hydrocarbons tended to increase. This can be mainly attributed to the decreased Ni-Mo interaction and the increased phosphide particle size. In sum, the structure and performance of Ni-Mo bimetallic phosphide catalyst can be tuned by the calcination temperature of precursor.The increase in the calcination temperature of NiMo bimetallic phosphate precursor made the Ni-Mo interaction weak and the phosphide particle sinter, which is favorable for the decarbonylation reaction of methyl laurate to form the C11 hydrocarbon.Download full-size image

Ni2P/SiO2 catalyst with high dispersion was obtained by temperature-programmedly reducing the precursor that was prepared via a new approach. In this approach, nickel-containing silica was firstly synthesized via a sol–gel process, and phosphorus species were then supported on it through impregnation. In the precursor, the nickel species highly dispersed and the interaction between nickel and support was strong. This contributed to the resistance of Ni2P to sintering, and the resulting Ni2P particles were very small and uniform. The Ni2P/SiO2 catalyst proved to be very active and stable in the hydrodechlorination of chlorobenzene.

•Bifunctional Ni2P/AlMCM-41 was prepared by in situ phosphorization at 300 °C.•There were similar Ni2P particle sizes in Ni2P/AlMCM-41 with different Si/Al ratios.•The acid amount of Ni2P/AlMCM-41 increased with decreasing the Si/Al ratio.•Ni2P/AlMCM-41 with the Si/Al ratio of 5 had the highest activity for isomerization.•Ni2P/AlMCM-41 had very low activity for methanation and CC bond hydrogenolysis.A series of Ni2P/AlMCM-41-x bifunctional catalysts with different Si/Al ratios (x) were synthesized by in situ phosphorization of Ni/AlMCM-41-x with triphenylphosphine (nominal Ni/P ratio of 0.75) at 300 °C on a fixed-bed reactor. For comparison, NiP/AlMCM-41-5-TPR was also prepared by the TPR method from the supported nickel phosphate with the Ni/P ratio of 1.0, during which metallic Ni rather than Ni2P formed. TEM images show that Ni and Ni2P particles uniformly distributed in Ni2P/AlMCM-41-x and NiP/AlMCM-41-5-TPR. The Ni2P/AlMCM-41-x acidity increased with decreasing the Si/Al ratio. In the hydroconversion of methyl laurate, the conversions were close to 100% on all catalysts at 360 °C, 3.0 MPa, methyl laurate WHSV of 2 h−1 and H2/methyl laurate ratio of 25. As to Ni2P/AlMCM-41-x, with decreasing the Si/Al ratio, the total selectivity to C11 and C12 hydrocarbons decreased, while the total selectivity to isoundecane and isododecane (Si-C11+i-C12) firstly increased and then decreased. Ni2P/AlMCM-41-5 gave the largest Si-C11+i-C12 of 43.2%. While NiP/AlMCM-41-5-TPR gave higher Si-C11+i-C12 than Ni2P/AlMCM-41-5, it was more active for the undesired CC bond cleavage and methanation. We propose that the in-situ phosphorization adopted here is a promising approach to preparing Ni2P-based bifunctional catalysts.

An effective approach to enhancing the activity of the Ni2P/SiO2 catalyst for the hydrodechlorination of chlorobenzene (CB) was reported. At atmospheric pressure, 513 K, a CB WHSV of 4.1 h−1 and a H2/CB molar ratio of 9.0, Ni2P/SiO2 gave a chlorobenzene conversion of 5.6%. Surprisingly, after Ni2P/SiO2 was pretreated with a 0.8–3.0% H2O/H2 flow below 543 K, the conversion reached as high as 99%. As the pretreatment temperature increased, the conversion tended to decrease; however, a conversion of 42.6% was still obtained even at the pretreatment temperature of 673 K. The activity of Ni2P/SiO2 was also improved when 0.8% H2O or 0.5% O2 was introduced into the reaction system. In addition, the passivation of Ni2P/SiO2 followed by the reduction led to a conversion of 33%. The Ni2P/SiO2 catalysts before and after the pretreatment were characterized by N2-sorption, XRD, ICP-AES, XPS, in situ DRIFT, and H2- and NH3-TPD. The results show that the pretreatment did not obviously influence specific surface area, pore structure, Ni2P crystallite size, the electron density of Ni in Ni2P, and the Ni and P contents, while it created new P–OH groups and reduced the amount of surface Ni sites. We propose a surface model of Ni2P/SiO2 containing the Ni sites and the P–OH groups and consider that the synergism between the Ni site and the P–OH group can explain the promoting effect due to H2O and O2 on the activity of Ni2P/SiO2, and the synergism mainly took place on the Ni2P particles and at the interface between the Ni2P particles and SiO2.

Ni2P/SiO2 was in situ prepared from Ni/SiO2via a phosphorization process using a dodecane solution containing triphenylphosphine (TPP) as the phosphorus source on a fixed-bed reactor. The influence of the phosphorization condition (nominal P/Ni molar ratio, temperature, WHSV of TPP and atmosphere) on the structure of the phosphorized samples was investigated. The sample structure was characterized by means of XRD, TEM, ICP-AES, TGA, N2 sorption, and FT-IR and magnetic property. It was found that the phosphorization of metallic Ni to Ni2P was promoted by increasing the phosphorization temperature and nominal P/Ni molar ratio and decreasing the WHSV of TPP. The phosphorization rate was much faster in the H2 atmosphere than the N2 one, ascribed to the formation of reactive H atoms on the Ni atoms that facilitated the cleavage of the P–C bond in PPT releasing more reactive PH3/P. To prepare the well-crystallized Ni2P/SiO2 in the H2 atmosphere, the minimum temperature (250 °C) and nominal P/Ni ratio (0.67) were necessary. Also, the Ni2P crystallite size in Ni2P/SiO2 was determined by the Ni one in Ni/SiO2, and no sintering took place during the phosphorization even at 400 °C. It is worth stating that there was a carbonaceous deposit formed on the in situ prepared catalysts, which was harmful for the catalyst activity for the deoxygenation of methyl laurate to hydrocarbons. The phosphorization condition greatly affected the performance of the resulting catalysts. On the whole, the Ni2P/SiO2 catalyst with good performance was prepared under a suitable phosphorization condition (i.e., 300 °C, nominal P/Ni ratio of 0.75, TPP WHSV of 0.5 h−1, and H2 atmosphere). Under the reaction conditions of 340 °C, 3.0 MPa, methyl laurate WHSV of 5 h−1 and H2/methyl laurate molar ratio of 25, it gave the conversion of methyl laurate and the total selectivity for C11 and C12 hydrocarbons higher than 98% and 96% during 100 h, respectively, exhibiting good stability. Finally, we propose a mechanism for the phosphorization of Ni/SiO2.