Few-layered graphene networks composed of phosphorus and nitrogen dual-doped porous graphene (PNG) are synthesized via a MgO-templated chemical vapor deposition (CVD) using (NH4)3PO4 as N and P ...source. P and N atoms have been substitutionally doped in graphene networks since the doping takes place at the same time with the graphene growth in the CVD process. Raman spectra show that the amount of defects or disorders increases after P and N atoms are incorporated into graphene frameworks. The doping levels of P and N measured by X-ray photoelectron spectroscopy are 0.6 and 2.6 at %, respectively. As anodes for Li ion batteries (LIBs), the PNG electrode exhibits high reversible capacity (2250 mA h g–1 at the current density of 50 mA g–1), excellent rate capability (750 mA h g–1 at 1000 mA g–1), and satisfactory cycling stability (no capacity decay after 1500 cycles), showing much enhanced electrode performance as compared to the undoped few-layered porous graphene. Our results show that the PNG is a promising candidate for anode materials in high-rate LIBs.
The directly catalytic conversion of C2-C6 alkanes to aromatics has aroused widespread interest from both academia and industry because of the growing demand for aromatics. Compared with pure HZSM-5 ...zeolites, the addition of metal species is required to enhance the selectivity of BTX by inhibiting undesirable side reactions. This paper reviewed the research progress of aromatization for light alkanes on HZSM-5 zeolites and its metal-containing catalysts based on theoretical and experimental research. The chemical states of metal species and dehydrogenation mechanisms of Zn and Ga-containing HZSM-5 catalysts are introduced in detail. The interaction of Zn or Ga with HZSM-5 zeolite produces Zn or Ga-Lewis acid sites that can promote the dehydrogenation of alkanes and intermediate products, thereby increasing the selectivity of BTX. On Zn-containing HZSM-5, only the Zn species were found to be involved in the dehydrogenation activation process of alkanes. In contrast, on Ga-containing HZSM-5, the acid-base pairs composed of Ga species with adjacent basic oxygen ions are responsible for the dehydrogenation of alkanes. However, there is still controversy over the active species of alkanes dehydrogenation, which needs further investigation.
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•A review of the conversion of light alkanes to aromatics.•The mechanism of aromatization over HZSM-5 and its metal modified catalysts.•Systematic studied the effect of metal species on catalyst property and reactivity.•The emphasis on chemical state and catalysis of metal active species.
Engineering metal-organic frameworks (MOF) for heterogeneous catalysts have been of extreme interest since they could bridge the gap between homogeneous and heterogeneous catalysis. We have designed ...and synthesized gold functionalized IRMOF-3 catalysts by post-covalent modification (PM) and one-pot (OP) synthesis methods. The gold functionalized IRMOF-3 catalysts provide an efficient, economic, and novel route for the one-pot synthesis of structurally divergent propargylamines
via
three component coupling of alkyne, amine, and aldehyde (A
3
) without any additives or an inert atmosphere. The catalysts were characterized in depth to understand their structure-property relationship. It was shown that the 4.6%Au/IRMOF-3 catalyst, prepared by the PM method, contains a fraction of cationic gold (Au
3+
/Au
0
= 0.2), which shows much higher catalytic activity than that of 3.2% or 0.6%Au/IRMOF-3 prepared by OP method, although the former exhibits much lower crystallinity than the latter two catalysts. Notably, the catalytic activity of the Au/IRMOF-3 catalysts could be significantly enhanced at a moderate reaction temperature (150 °C). All the Au/IRMOF-3 catalysts can be easily recycled and used repetitively at least 5 times, especially the catalysts prepared by the OP method, which showed no drop in activity for the successive 5 uses. These features render the catalysts particularly attractive in the practice of propargylamines synthesis in an environmentally friendly manner.
Gold functionalized metal-organic frameworks are efficient and recyclable heterogeneous catalysts for the one-pot synthesis of propargylamines.
Three-dimensional (3D) networks composing of S and N dual-doped graphene (SNG) were synthesized by a chemical vapor deposition approach using MgSO4-containing whiskers as templates and S source and ...NH3 as N source. Energy dispersive spectrometer mapping and X-ray photoelectron spectroscopy coupled with Raman analysis have revealed that S and N atoms with concentrations of 5.2 and 1.8atom%, respectively, have been substitutionally incorporated into the graphene networks via covalent bonds. The SNG, as an anode material for lithium ion batteries (LIBs), exhibits extremely high capacity (3525mAh/g at the current density of 50mA/g) and superior rate capability (870mAh/g at 1000mA/g) with excellent cycling stability (remaining a reversible capacity of 400mAh/g at 10A/g after 2500 cycles). The enhanced conductivity, the 3D porous network with many disorders and the intrinsically high Li storage capacity of S and N-doped carbon segments have led to the excellent electrode performance of the SNG networks. The effects of binder content and calendaring pressure on the electrode performance have been investigated. The full LIB with SNG as anode and LiCoO2 as cathode can afford a high reversible capability (164mAh/g at 0.2C) and good cycling stability.
Biochar, a by-product from the fast pyrolysis of pine wood, was used as the support material for the synthesis of carbon-encapsulated iron nanoparticles. The nanoparticles were characterized for ...physicochemical properties by multiple morphological and structural methods (
e.g.
, SEM, TEM, XRD, FTIR, and TPD). The FischerTropsch synthesis (FTS) process was carried out to evaluate the catalytic activity of the nanoparticles on conversion of biomass-derived synthesis gas (bio-syngas) to liquid hydrocarbons. Characterization results revealed that the nanoparticles had coreshell structures with iron
in situ
encapsulated within a graphitic shell. Moreover, significant amounts of iron carbide (mainly Fe
3
C) were formed as an interface between the carbonaceous shell and the iron core. FTS tests indicated that such carbon-encapsulated iron nanoparticles possessed a high activity on conversion of bio-syngas and good selectivity towards liquid hydrocarbons (of which olefins were the dominant product). Over a 1500 h testing period, the nanoparticles showed striking stability against deactivation, with CO conversion maintained at about 95% and liquid hydrocarbon selectivity at about 68%.
The Fe-core/C-shell nanocomposite catalyst was synthesized by self-assembly at high temperature using char. The catalyst proves highly active and stable for upgrading biosyngas to liquid hydrocarbons.
The influence of solid-phase wall boundary condition in terms of specularity coefficient and particle–wall restitution coefficient on the flow behavior of spouted beds was investigated using ...two-fluid model approach in the computational fluid dynamics software FLUENT 6.3. Parametric studies of specularity coefficient and particle–wall restitution coefficient were performed to evaluate their effects on the flow hydrodynamics in terms of fountain height, spout diameter, pressure drop, local voidage and particles velocity. The numerical predictions were compared with available experimental data in the literatures to obtain the suitable values of specularity coefficient and particle–wall restitution coefficient for spouted beds. The simulated results show that the solid-phase wall boundary condition plays an important role in CFD modeling of spouted beds. The specularity coefficient has a pronounced effect on the spouting behavior and a small specularity coefficient (0.05) can give good predictions, while the particle–wall restitution coefficient is not critical for the holistic flow characteristics.
► We used two-fluid model approach to simulate spouted beds hydrodynamics at different solid-phase wall boundary conditions. ► Specularity coefficient affects significantly spouting behavior. ► Small specularity coefficient gives good predictions. ► Particle–wall restitution coefficient plays minor role.
Light cycle oil (LCO) from fluid catalytic cracking (FCC) was treated by selective hydrogenation and then cracked in a FCC apparatus. Compared with LCO, hydrogenated LCO (hydro-LCO) exhibited ...remarkable FCC performance, recording with that 50.83 wt % hydro-LCO was converted into gasoline fraction. This is attributed to the reduction of aromatics in hydro-LCO, especially for the multiring aromatics. After hydrogenation, the amount of multiring aromatics significantly decreased from 63.2 to 9.5 wt %, while naphthenoaromatics (including indans, tetralin, and indenes) increased from 8.8 to 34.2 wt %. In accordance with the experimental results and theoretical analysis of LCO reaction characteristics, a synergistic process for LCO efficient conversion to high octane number gasoline was proposed, and simulation experiments were carried out. The results show that, compared with routine FCC, 20 wt % higher conversion and 16 wt % more gasoline could be obtained. Moreover, gasoline from synergistic process exhibited decreased sulfur and olefins, but increased aromatics, and thereby improved octane number. These findings indicate that the proposed synergistic process could be an effective option for producing gasoline with high octane number.
Industrial CFB risers usually handle polydisperse mixtures with broad size distribution, which significantly influenced the performance of the reactors. However, traditional Computational Fluid ...Dynamics (CFD) models usually assumed that the particle followed the mono-disperse distribution. In the present work, the method of computational particle fluid dynamic (CPFD) was applied for simulating the complex hydrodynamics in the CFB riser with various particle size distributions (PSDs). Two kinds of PSDs, namely Gaussian and Lognormal distribution with various PSD widths, were implemented into the CPFD scheme. With the CPFD method, the present work extensively studied the effects of PSD on the hydrodynamics and on the solids back-mixing. The CPFD results showed that the PSD significantly affected particle's flow behaviors at the lower zone of the riser, while the PSD effects were negligible in the upper part of the riser. This is meaningful for the industrial riser reactors since most of the reaction and transport process occur in this lower zone of the riser. Besides, the simulation results showed that wider PSD dramatically weaken the particle's back-mixing behaviors in the riser. The significant effects of PSD predicted by the CPFD method imply that large errors will be introduced if the mono-disperse assumption is adopted to simulate the experimental CFB riser handling particles with broad size distribution.
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•We used the CPFD method to study the effects of particle size distribution (PSD).•The PSD significantly affects the particle flow behaviors.•Wider PSD is helpful to reduce the extent of solids back-mixing.
Four kinds of ZSM-5 zeolites with different SiO2/Al2O3 ratios are alkali-treated in 0.2M NaOH solution for 300min at 363K. Changes to the compositions, morphologies, pore sizes, and distributions of ...the zeolites are compared before and after alkali-treatment. The changes observed are largely influenced by the SiO2/Al2O3 ratios with which the zeolites are synthesized. A possible mechanism of desilication during alkali-treatment is proposed. The SiO2/Al2O3 ratio of zeolites is found to influence the yield of light olefins that use heavy oil as feedstock. Alkali-treated ZSM-5 zeolites produce higher yields of light olefins compared to either untreated zeolites or the industry catalyst CEP-1. It is believed that alkali-treatment introduces mesopores to the zeolites and improves their catalytic cracking ability. ZSM-5 zeolites with SiO2/Al2O3 ratios of 50 also present superior selectivity toward light olefins because of their optimized hierarchical pores.
