Zn/ZSM-5 (NZ2) and Zn/Ni/ZSM-5 (NZ3) as the catalysts for methanol to aromatics (MTA) were synthesized by a simple ultrasonic impregnation. The textural and acid properties of all catalysts were characterized using XRD, HRTEM, NH3-TPD, Py-IR, XPS, XRF and TG techniques. The XRD and HRTEM results showed that the basic zeolite structures were not affected much with the incorporation of Zn and Ni species. However, great changes have taken place in acid properties. The Py-IR and XPS results indicated that the Zn-Lewis acid sites (ZnOH+ species), which have stronger interaction with the zeolite framework compared with ZnO species, were generated at the expense of B acid sites with the incorporation of zinc species. Moreover, the product analysis results showed that the incorporation of zinc species promoted the primary aromatization by enhancing the dehydroaromatization and suppressing the cracking and subsequent H-transfer reaction. Furthermore, the addition of Ni species well inhibited the loss of zinc species by converting partial ZnO species to ZnOH+ species, and thus improved the aromatization activity and catalyst stability. The catalytic performance results showed that the NZ3 possess higher conversion of methanol in a longer time and lower average rate of coke formation compared with NZ2. In addition, the NZ3 also exhibited the highest yield of BTX as the reaction proceeds.ZnOH+ species: enhance dehydrogenation and aromatization; Ni species: inhibit the outflow of Zn species by converting the ZnO species to ZnOH+ species, and thus improve the selectivity of BTX. Download high-res image (127KB)Download full-size image

•Nanocrystallite self-assembled hierarchical ZSM-5 zeolite microspheres (NSHZ) were prepared for methanol to aromatics.•Addition of KH-560 effectively decreased crystal size.•Large amount of intercrystalline mesopores were introduced by accumulation of nanocrystals.•Plenty of strong acid sites and proper B/L were indispensible for improving the selectivity of BTX.•Small crystal size and large number of mesopores significantly increased the catalytic lifetime.Nanocrystallite self-assembled hierarchical ZSM-5 zeolite microspheres (NSHZ) were prepared by a simple hydrothermal synthesis procedure in the presence of 3-glycidoxypropyltrimethoxysilane (KH-560). Moreover, the HZSM-5 zeolite (Commercial ZSM-5) and MSHZ zeolite (Mesoporous HZSM-5 synthesized without addition of KH-560) were also introduced as reference samples. The textural and acid properties of all fresh catalysts (HZSM-5, MSHZ, NSHZ) were characterized using XRD, SEM, TEM, ICP, N2 adsorption-desorption, NH3-TPD, Pyridine adsorption IR spectra (Py-IR) and FT-IR techniques. The results showed that uniform NSHZ zeolite microspheres possessed higher crystallinity, smaller crystal size, higher BET surface and pore volume. At the same time, the NSHZ zeolite also had more strong acid sites and proper B/L ratio (The ratio of the amount of Bronsted acid sites to that of Lewis acid sites). Benefiting from these merits, the NSHZ zeolite exhibited higher catalytic lifetime and selectivity of light aromatics (benzene (B), toluene (T) and xylene (X)). The desorption measurements of isooctane showed that NSHZ zeolite had superior diffusion performance, which could effectively promote the fast removal of heavier molecules. In addition, TG analysis of all used catalysts confirmed that NSHZ zeolite had higher coke capability and lower average rate of coke formation.Download high-res image (292KB)Download full-size image

ZnSiF6-modified nano-sized HZSM-5 zeolites (NZ2, NZ3 and NZ4 catalysts) were prepared and investigated as catalysts for the conversion of methanol to aromatics. Moreover, the ZnNZ1 catalyst, prepared by ion exchange using zinc nitrate, was also introduced as a reference sample. The effects of modification on the framework, textural properties and acidity of the parent nano-sized HZSM-5 zeolite (NZ1) were investigated by XRD, FT-IR, 29Si MAS-NMR, SEM, N2 adsorption–desorption, ICP, NH3-TPD, infrared spectroscopy of adsorbed pyridine (Py-IR), UV-vis spectra, X-ray photoelectron spectroscopy (XPS) and n-butylamine and tert-butylamine titration. The results showed that the amount of total acid sites, especially the external surface acid sites of the NZ2, NZ3 and NZ4 catalysts, significantly decreased, which may largely be attributed to the passivation effect of SiF62− on the surface acidity of the parent NZ1 catalyst. Moreover, the amount of Lewis acid sites (L acid sites) increased, whereas the amount of Brønsted acid sites (B acid sites) obviously decreased with the introduction of zinc species. The emergence of new Zn-Lewis acid sites (⊖ZO⋯H⋯O–Zn⊕ species) was beneficial to improving the selectivity to BTX (benzene (B), toluene (T) and xylene (X)) due to their high activity for dehydroaromatization. The FT-IR spectra in the OH− vibration region and the 29Si MAS-NMR spectra show that the treatment of ZnSiF6 could effectively repair partial lattice defects of zeolite and could thus improve the catalyst stability. TG analysis of all the deactivated catalysts showed that the coke amount and the average rate of coke formation decreased over NZ2, NZ3 and NZ4 catalysts, and this may largely be ascribed to their lower surface acidity. The catalytic performance of these materials on the conversion of methanol to aromatics showed that the NZ3 catalyst had the highest selectivity to BTX of about 51.3% and the longest catalytic lifetime of about 234 h under the operating conditions of T = 425 °C, p = 0.1 MPa and WHSV = 0.8 h−1. The improvement in the selectivity to BTX and the catalyst lifetime of the NZ3 catalyst could be ascribed to the synergistic effect among the Zn-Lewis acid sites (⊖ZO⋯H⋯O–Zn⊕ species), external surface acidity and intact framework structure.

•Three pyrrolidinium-based ILs as electrolytes for Li–O2 batteries are investigated.•The oxygen diffusion coefficient and pivotal properties of these ILs are measured.•The battery performances with three IL electrolytes are analyzed and compared.•The correlation of the IL properties with these performances is analyzed and explored.Pyrrolidinium-based ionic liquids (ILs), such as PYR13TFSI, PYR14TFSI, and PYR1(2O1)TFSI, exhibit high thermal and electrochemical stability with wide electrochemical windows as electrolytes for application to rechargeable Li–O2 batteries. In this work, several fundamental properties of three ILs are measured: the ionic conductivity, oxygen solubility, and oxygen diffusion coefficient. The oxygen electro-reduction kinetics is characterized using cyclic voltammetry. The performances of Li–O2 batteries with these IL electrolytes are also investigated using electrochemical impedance spectroscopy and galvanostatic discharge–charge tests. The results demonstrate that the PYR1(2O1)TFSI electrolyte battery has a higher first-discharge voltage than the PYR13TFSI electrolyte and PYR14TFSI electrolyte batteries. Both PYR13TFSI- and PYR1(2O1)TFSI-based batteries exhibit higher first-discharge capacities and better cycling stabilities than the PYR14TFSI-based battery for 30 cycles. A theoretical analysis of the experimental results shows that the diffusion coefficient and solubility of oxygen in the electrolyte remarkably affect the discharge capacity and cycling stability of the batteries. Particularly, the oxygen diffusion coefficient of the IL electrolyte can effectively facilitate the electrochemical oxygen electro-reduction reaction and oxygen concentration distribution in the catalyst layers of air electrodes. The oxygen diffusion coefficient and oxygen solubility improvements of IL electrolytes can enhance the discharge–charge performances of Li–O2 batteries.

•Ni–Yb/Al2O3 catalysts with different Ni/Yb ratios were prepared.•The Yb-doping increased metal-support interaction and prevented growth of Ni particles.•The reduced acidity of Ni catalyst by Yb-doping contributed to inhibiting coking.•The addition of Yb facilitated adsorption of CO2 and catalyzed methane combustion.Carbon deposition is urgent issue for the partial oxidation of methane to synthesis gas (POM). To figure out this problem, Ni–Yb/Al2O3 catalysts with different Ni/Yb ratios were prepared. The structural properties and carbon deposition of catalysts were characterized by XRD, TEM, N2 adsorption, H2-TPR, NH3-TPD and TG techniques. The addition of Yb increased the dispersibility of Ni species and improved the interaction with support, thus preventing the growth of Ni nanoparticles, which was favorable to reduce coking. More importantly, the acidity of Ni/Al2O3 catalyst was reduced due to addition of Yb, which contributes to improving the carbon balance and inhibiting carbon deposition. The Ni–Yb/Al2O3 catalyst (Ni/Yb = 1) proved to be more active, giving CH4 conversion of 98%, CO selectivity of 98% and H2 selectivity of 83% (800 °C and space velocity of 5 × 104 mL g−1 h−1). In addition, the addition of Yb was deduced to facilitate adsorption of CO2 and catalyze methane combustion, which was the first step of POM reaction, thus reducing carbon deposition and improving methane conversion.

•The Ni particles supported on silica were prepared using different alkanol solvents.•The size of Ni particles was tuned by confinement of carbon templates.•The Ni/SiO2 catalyst prepared by glycerol solvent was proved to be more active.•The scheme of POM was determined by surface states of nickel particles.The Ni nanoparticles of narrow size distribution supported on silica were prepared using different alkanol solvents (ethanol, ethylene glycol and glycerol) by wet impregnation method. The mean size of Ni nanoparticles can be tuned using alkanol as delivery conveyors and removable carbon templates. Compared with conventional catalysts prepared using aqueous solution, the as-obtained catalysts owned smaller and uniform size of metal particle due to confinement effect of carbon templates, especially ethylene glycol and glycerol as solvent (6–8 nm). It was found catalytic activity was dependent on the size of the metal particles. The overall scheme of POM was determined by surface valence states of nickel particles which were affected by nanoparticles size. Inspiringly, the Ni/SiO2 catalyst prepared by glycerol solvent was proved to be more active, giving CH4 conversion of 94%, CO selectivity of 88% due to the higher reducibility, higher metal dispersion and more unsaturated surface atoms contributed by smaller metal nanoparticles.The sizes of Ni particles were controlled by carbon templates derived from carbonization of alkanol solvent.Download high-res image (133KB)Download full-size image

•The Ni/ZrO2@SiO2 catalysts with mesoporous silica shell were synthesized.•The formation routes of carbon deposition were discussed in detail.•The Ni/ZrO2@SiO2 catalyst showed effective resistance to carbon deposition.•Silica shell inhibited coke by blocking selectively the edge and corner atoms.Carbon deposition, which may reduce the number of active sites or remove metal particles from the catalyst surface, is an urgent issue for the partial oxidation of methane (POM) to synthesis gas. To solve this problem, Ni/ZrO2@SiO2 catalysts were prepared by a modified Stöber method. The investigation was focused mainly on the role of ZrO2 addition and mesopore silica shell in preventing carbon deposition. The structural properties and carbon deposition of catalysts were characterized by XRD, TEM, N2 adsorption and TG techniques. The oxygen transfer capacity and reducibility of catalysts were evaluated by oxygen storage capacity (OSC) and temperature programmed reduction (TPR). Inspiringly, the Ni/ZrO2@SiO2 catalyst was proved to be more active and possessed less carbon deposition due to the higher reducibility and oxygen storage/release capacity. Importantly, compared with the support catalysts, the catalysts coated by mesopore silica shell showed exceptional resistance to coking, because the edge and corner atoms favor to carbon deposition were selectively blocked by silica shell, in addition, the size of the pore channel prevented growth up of carbon filament.The silica shell inhibited coking by blocking selectively the edge and corner atoms.

•Mesoporous NiO–Al2O3 catalysts were prepared by sol–gel method.•Calcination temperature exhibited great effect on physicochemical properties.•NiO–Al2O3-600 showed the highest catalytic reactivity and stability.A series of mesoporous NiO–Al2O3 catalysts were prepared by sol–gel method with calcination temperature increasing from 400 °C to 800 °C. The effect of calcination temperature on the texture property and catalytic performance of NiO–Al2O3 catalysts for partial oxidation of methane (POM) was investigated. These catalysts were evaluated by X-ray diffraction (XRD), transmission electronic microscopy (TEM), N2 adsorption–desorption method and temperature programmed reduction (TPR) techniques and tested in a fixed bed reactor at 550 °C. The meso-NiO–Al2O3 catalyst with low carbon deposition prepared at 600 °C was proved to be more active, stable. After 40 h reaction at 550 °C, the Ni–Al2O3-600 sample still maintained relatively high CH4 conversion and CO yield indicating high activity and stable structure of obtained sample.The mesoporous NiO–Al2O3 catalyst was prepared by modified sol–gel method via an improved one pot evaporation-induced self-assembly (EISA) to control the volatile process.

•Core–shell Fe2O3/Pt nanoparticles with amorphous iron oxide cores are synthesized.•The influences of the amorphous iron oxide cores on Pt shells are discussed.•The catalytic properties of the nanoparticles for methanol oxidation are studied.•The catalytic properties of Pt shell can be tuned by varying its surface coverage.Core–shell Fe2O3/Pt nanoparticles with amorphous iron oxide cores are successfully synthesized by a two-step chemical reduction strategy. The Pt loading can be adjusted using this preparation technique to obtain a series of chemical compositions with varying amounts of Pt precursors. The morphology, structure, and composition of the as-prepared nanoparticles are characterized by transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. Electrocatalytic characteristics are systematically investigated by electrochemical techniques, such as cyclic voltammetry, chronoamperometry, and in situ Fourier transform infrared spectroscopy. Compared with the E-TEK 40 wt% Pt/C catalyst, the as-made Fe2O3/Pt nanoparticles exhibit superior catalytic activity with lower peak potential and enhanced CO2 selectivity toward methanol electrooxidation in acidic medium. The highest activity is achieved by core–shell Fe2O3/Pt nanoparticles with a Fe/Pt atomic ratio of 2:1 (A g−1 of Pt) or 3:1 (mA cm−2). These nanomaterials also show much higher structural stability and tolerance to the intermediates of methanol oxidation. Methanol electrooxidation reactions with higher performance can be achieved using core–shell nanoparticles with an amorphous iron oxide core and minimum Pt loading.

In the present work, core-shell Ni@SiO2 catalysts were investigated in order to evaluate the relevance of catalytic activity and surface states of Ni core as well as Ni nanoparticles size to catalytic partial oxidation of methane (POM). The catalysts were characterized by N2 adsorption, H2-TPR, XRD, TEM and XPS techniques. The catalytic performance of the core-shell catalysts was found to be dependent on the surface states of catalyst, which influenced the formation of products. It was considered that carbon dioxide formed on the oxidized nickel sites (NiO) and carbon monoxide produced on the reduced sites (Ni). The surface states of active metal in the dynamic were influenced both by the size of Ni core and the porosity of silica shell. However, the catalytic activity would be debased when the size of Ni core was under a certain extent, which can be ascribed to the fact the carbon deposition increased with the increasing content of NiO. The effects of surface states of Ni@SiO2 catalyst on the catalytic performance were discussed and the reaction pathway over Ni core encapsulated inside silica shell was proposed.For NiO@SiO2 catalyst, complete oxidation of methane occurs on the NiO part, accompanied with the formation of carbon, whereas the reforming of CH4 with H2O or CO2 appears on the Ni portion.Download full-size image

ZnSiF6-modified nano-sized HZSM-5 zeolites (NZ2, NZ3 and NZ4 catalysts) were prepared and investigated as catalysts for the conversion of methanol to aromatics. Moreover, the ZnNZ1 catalyst, prepared by ion exchange using zinc nitrate, was also introduced as a reference sample. The effects of modification on the framework, textural properties and acidity of the parent nano-sized HZSM-5 zeolite (NZ1) were investigated by XRD, FT-IR, 29Si MAS-NMR, SEM, N2 adsorption–desorption, ICP, NH3-TPD, infrared spectroscopy of adsorbed pyridine (Py-IR), UV-vis spectra, X-ray photoelectron spectroscopy (XPS) and n-butylamine and tert-butylamine titration. The results showed that the amount of total acid sites, especially the external surface acid sites of the NZ2, NZ3 and NZ4 catalysts, significantly decreased, which may largely be attributed to the passivation effect of SiF62− on the surface acidity of the parent NZ1 catalyst. Moreover, the amount of Lewis acid sites (L acid sites) increased, whereas the amount of Brønsted acid sites (B acid sites) obviously decreased with the introduction of zinc species. The emergence of new Zn-Lewis acid sites (⊖ZO⋯H⋯O–Zn⊕ species) was beneficial to improving the selectivity to BTX (benzene (B), toluene (T) and xylene (X)) due to their high activity for dehydroaromatization. The FT-IR spectra in the OH− vibration region and the 29Si MAS-NMR spectra show that the treatment of ZnSiF6 could effectively repair partial lattice defects of zeolite and could thus improve the catalyst stability. TG analysis of all the deactivated catalysts showed that the coke amount and the average rate of coke formation decreased over NZ2, NZ3 and NZ4 catalysts, and this may largely be ascribed to their lower surface acidity. The catalytic performance of these materials on the conversion of methanol to aromatics showed that the NZ3 catalyst had the highest selectivity to BTX of about 51.3% and the longest catalytic lifetime of about 234 h under the operating conditions of T = 425 °C, p = 0.1 MPa and WHSV = 0.8 h−1. The improvement in the selectivity to BTX and the catalyst lifetime of the NZ3 catalyst could be ascribed to the synergistic effect among the Zn-Lewis acid sites (⊖ZO⋯H⋯O–Zn⊕ species), external surface acidity and intact framework structure.