Three-component hybrid catalyst for direct synthesis of isoparaffin via modified Fischer–Tropsch synthesis

Direct isoparaffin synthesis method from syngas was developed by using a hybrid catalyst composed of Fischer–Tropsch synthesis catalyst, ZSM-5 zeolite, and Pd/SiO₂, where normal paraffin from Fischer–Tropsch synthesis was hydrocracked in situ on ZSM-5 and Pd/SiO₂ stabilized zeolite activity effectively even at pressurized steam atmosphere mainly via spillover effect.     

Anionic synthesis of ω-1,1-diphenylethylene-terminated polystyrene macromonomers. Rational synthesis of ABC hetero three-armed-star-branched polymers

Summary Polystyrene macromonomers with terminal 1,1-diphenylethylene functionality were prepared by the reaction of one equivalent of poly(styryl)lithium with 1,4-bis (l-phenylethenyl)benzene (PDDPE). The macromonomer functionalities were determined by ¹H NMR [(vinyl CH₂)=5.4 ppm] and UV spectroscopy (_max=260 nm). The stoichiometric linking reaction of poly(styryl)lithium (M_n=15.3x10³ g/mol) with an -1,1-diphenylethylene-terminated polystyrene macromonomer (M_n=5.4x10³ g/mol) followed by addition of styrene monomer has been used to prepare a hetero three-armed, star-branched polymer with M_n=5.8x10⁴ g/mol (5,400-15,300-37,300). The g value ([]b/[]l) was equal to 0.92.     

MXene:From synthesis to environment remediation

A new burgeoning family of two-dimensional(2D) transition metal carbides/nitrides,better known as MXenes,have received extensive attention because of their distinct properties,such as metallic conductivity,good hydrophilicity,large surface area,good mechanical stability,and biodegradability.About 40 different MXenes have been synthesized,and dozens more structures and properties have been theoretically predicted.However,the recent progress in MXenes development is not well covered in chronologic...     

Selective synthesis of ethylamine over β zeolite

Ethylamine is selectively produced in the amination of ethanol with ammonia over H zeolite.     

Hydrothermal synthesis of single-crystal α-tristrontium phosphate particles

Anisotropic ceramic bodies can be fabricated by a reactive template grain growth method; however, template particles with suitable powder properties are required to create the ceramics with well controlled anisotropy. Therefore, we synthesized well-isolated α-tristrontium phosphate (α-TSP) particles with a hexagonal plate-like shape as template particles for anisotropic strontium apatite ceramics using α-strontium hydrogen phosphate (α-SrHPO₄) precursor particles. Three synthetic parameters were varied: (i) precursor particle size, (ii) stirring rate, and (iii) hydrothermal temperature. Well-isolated hexagonal plate-like α-TSP single-crystal particles were successfully synthesized by hydrothermal treatment at 150 °C for 3 h at a stirring rate of 150 rpm using fine α-SrHPO₄ precursor particles. The developed plane of the hexagonal plate-like α-TSP particles was determined to be the {00l} plane, and the side planes were revealed to be not {h00} planes, but inclined {h0l} planes. The resulting α-TSP particles may provide a promising template for the development of anisotropic apatite-based ceramics.     

New hydroxyapatite–hydrotalcite composites I. synthesis

The synthesis and characterization of original materials, composed by hydrotalcite and hydroxyapatite, is discussed. All the syntheses were carried out in presence of microwave irradiation during the crystallization step. The interactions between the two compounds depend on the synthesis procedure. If hydroxyapatite is incorporated to hydrotalcite, the first compound is encapsulated by hydrotalcite. Instead, if hydroxyapatite is first prepared, the resulting solid is essentially a hydrotalcite with interlayered hydroxyapatite. When the composite material is synthesized by a simultaneous coprecipitation, the small clusters of hydroxyapatite and hydrotalcite are homogeneously dispersed. Consequently, the specific surface area and the particle size vary.     

Hydrothermal synthesis of potassium–sodium niobate powders

Potassium–sodium niobates (K_xNa_1−xNbO₃, 0 < x < 1, KNN) were hydrothermally synthesized under varying alkaline ratios (K⁺/Na⁺), total hydroxide concentration, reaction temperature, and time. Compositional surveys were developed by using Rietveld analyses derived quantitative volume fractions. The data demonstrated that phase pure KNN synthesis can be achieved by reacting the niobium source with the hydroxide solution having 6 M total hydroxide concentration, cation ratio (K⁺/Na⁺) of above 6 at temperatures ≥200°C for 24 h. Dissolution–precipitation events through intermediate products including hexaniobates were postulated as a plausible formation mechanism. It was shown also that the single-phase KNN approaching the morphotropic phase boundary (MPB) could be obtained by further incorporation of sodium ions into the crystal via post-annealing at 800°C/2 h, following the hydrothermal synthesis.     

Application of methanol synthesis reactor to large-scale plants

The developing status of world large-scale methanol production technology is analyzed and Linda's JW low-pressure methanol synthesis reactor with uniform temperature is described. JW serial reactors have been successfully introduced in and applied in Harbin Gasification Plant and the productivity has been increased by 50% and now nine sets of equipments are successfully running in Harbin Gasification Plant,Jiangsu Xinya, Shandong Kenli,Henan Zhongyuan, Handan Xinyangguang,' Shanxi Weihua and Inner Mongolia Tianye. Now it has manufacturing the reactors of 300,000 t/a for Liaoning Dahua. Some solutions for the structure problems of 1000 ～5000 t/d methanol synthesis rectors are put forward.     

Ion-exchange synthesis of α-modification of nickel hydroxide

An anion-exchange method for synthesizing nickel hydroxide using industrial strongly basic AV-17-8 anionite has been proposed. The influence of conditions (concentration and nature of starting salt, amount of the anionite, process duration, etc.) on the precipitate yield has been established. The product has been investigated by scanning electron microscopy, IR and Raman spectroscopy, X-ray phase analysis, and thermal and chemical analyses. It has been established that the product is a disordered layered modification of nickel hydroxide α-Ni(OH)₂, which contains anions and water molecules in the interlayer spacing. Nickel hydroxide particles are needle crystals (40–80 nm) that form agglomerates 0.3–0.5 μm in size.     

Heat exchanger network synthesis with detailed exchanger designs—2. Hybrid optimization strategy for synthesis of heat exchanger networks

We propose a new strategy to synthesize heat exchanger networks with detailed designs of individual heat exchangers. The proposed strategy uses a multistep approach by first obtaining a heat exchanger network topology through solving a modified version of the mixed integer nonlinear programming (MINLP) stage-wise superstructure of Yee and Grossmann, which includes a smoothed LMTD approximation and pressure drops. In a second nonlinear programming (NLP) suboptimization step, we allow for nonisothermal mixing to solve problems with or without exchanger bypasses. The selected heat exchangers along with the mass and energy balances obtained are then used to design the network with detailed exchanger designs through solving a sequence of NLPs for individual heat exchanger designs. The NLPs are based on the detailed discretized optimization models of Kazi et al., which solve quickly and reliably to obtain heat exchangers based on rigorous, first-principles derived coupled differential equations. These models solve a differential algebraic equation system and do not rely on usual assumptions associated with other heuristic-based exchanger design methods, such as log mean temperature difference and F_T correction factors. These detailed exchanger designs are then used to update the network optimization model through sets of correction factors on heat exchanger area, number of shells, heat transfer coefficients, and pressure drops of each exchanger design, in a method based on that of Short et al. The method solves reliably, guaranteeing feasible exchangers for every potential network generated by the shortcut models, through validation with rigorous heat exchanger models at every iteration. In addition, the method does not increase the nonlinearity of the MINLP model, nor does it require any manual intervention or initialization from the user. Three examples are solved and the results are compared to those obtained in the literature.     

Carbothermal synthesis of β-sialon from mechanochemically activated precursors

Reaction mixtures of halloysite clay and fine carbon for carbothermal reduction and nitridation (CRN) synthesis of β-sialon were ground in a planetary ball mill under flowing nitrogen for varying periods before being converted to sialon by heating in nitrogen at 1200–1400 °C. After 4 h grinding the XRD reflections of the halloysite were destroyed and some of the octahedrally-coordinated Al was converted to four- and five-fold coordination. ²⁷Al and ²⁹Si MAS NMR gave no evidence of the formation of AlN or SiN bonds upon grinding. Upon subsequent heating in nitrogen, the ground samples show significant differences from the unground control, the intermediate compound mullite being replaced by β-sialon (z ≈ 2) a temperature at least 100 °C lower, but the formation of corundum (α-Al₂O₃) also occurs at a lower temperature and is more persistent than in the unground control. MAS NMR spectroscopy shows that the products from the ground mixtures contain relatively less AlON units and that the formation of SiC (a transient reaction intermediate) is also facilitated by grinding. The optimum grinding time for this system was found to be 12 h.     

Mechanochemical synthesis of MoSi2–SiC nanocomposite powder

MoSi₂–25 wt.%SiC nanocomposite powder was successfully synthesized by ball milling Mo, Si and graphite powders. The effect of milling time and annealing temperature were investigated. Changes in the crystal structure and powder morphology were monitored by XRD and SEM, respectively. The microstructure of powders was further studied by peak profile analysis and TEM. MoSi₂ and SiC were synthesized after 10 h of milling. Both high and low temperature polymorphs (LTP and HTP) of MoSi₂ were observed at the short milling times. Further milling led to the transformation of LTP to HTP. On the other hands, an inverse HTP to LTP transformation took place during annealing of 20 h milled powder at 900 °C. Results of peak profile analysis showed that the mean grain size and strain of the 20 h milled powder are 31.8 nm and 1.19% that is in consistent with TEM image.     

New bimodal pore catalysts for Fischer–Tropsch synthesis

A simple preparation method of bimodal pore supports was developed by introducing SiO₂ or ZrO₂ sols into large pores of SiO₂ gel pellets directly. The pores of the obtained bimodal pore supports distributed distinctly as two kinds of main pores. On the other hand, the increased BET surface area and decreased pore volume, compared to those of original silica gel, indicated that the obtained bimodal pore supports formed according to the designed route. The obtained bimodal pore supports were applied in liquid-phase Fischer–Tropsch synthesis (FTS) where cobalt was supported. The bimodal pore catalysts presented the best reaction performance in liquid-phase Fischer–Tropsch synthesis (FTS) as higher reaction rate and lower methane selectivities, because the spatial promotional effect of bimodal pore structure and chemical effect of the porous zirconia behaved inside the large pores of original silica gel.     

Selective synthesis of α-olefins on Fe-Zn Fischer-Tropsch catalysts

Fe/Zn oxides promoted with K and Cu selectively produce -olefins at typical Fischer-Tropsch synthesis conditions (2/1 H₂/CO, 1 MPa, and 270°C). The simultaneous presence of K and Cu introduces a synergistic activity enhancement while maintaining the high olefin selectivity obtained by alkali promotion. Structural and morphological differences in Fe-Zn oxides prepared from ammonium glycolate complexes or precipitated from nitrate solutions have only a small influence on catalytic properties. Catalyst behavior is strongly influenced by synergistic promoter effects (Cu, K) and by the controlled in situ conversion of iron oxide precursors to carbides.     

One-pot synthesis of Cu–carbon hybrid hollow spheres

Novel hybrid hollow spheres (HSs) are easily prepared by a combination of hydrothermal carbonization (HTC) and emulsion template method for the first time. The HSs have an average diameter of 3.5 μm and a shell thickness of about 70 nm. The HSs consist of a matrix of hydrothermal carbon, in which Cu nanoparticles of several nanometers in size are imbedded, and exhibit a well-defined shape, a relatively uniform size and high flexibility. With regard to the formation mechanism, trioctylamine (TOA) droplet in the oil-in-water (W/O) emulsion plays the role of a template. Under hydrothermal conditions, TOA in the droplet and Cu²⁺ outside the droplet form the Cu–amine complex, which aggregates at the interface and is then reduced to form Cu nanoparticles by ascorbic acid (VC), and HTC of VC to hydrothermal carbon occurs at the interface. By changing the carbon source into glucose the size of HSs can be tuned down to 1 μm and the bowl-like hollow structure can be obtained by increasing reaction time, indicating the flexibility of this approach. Due to the special structure of these HSs, they can be used as a new ultrasound contrast agent or a template for porous CuO HSs.     

Combustion synthesis of AlN–SiC solid solution particles

The feasibility of synthesising AlN–SiC solid solution ceramics by combustion synthesis (CS) reaction is demonstrated through igniting the mixtures of aluminium, silicon and carbon black under different nitrogen pressure values. The effects of the nitrogen pressure and the atomic ratio of (Si+C)/Al on the crystalline phases formed in the reaction product and on the characteristics of combustion behaviour were investigated. Combining thermodynamic analysis and the combustion characteristics, the reaction sequence and the formation of AlN–SiC solid solution by CS were explained.     

Microwave synthesis of duplexα/β-SiAlON ceramic cutting inserts:Modifying m,n,z values,synthesis temperature,and excess Y2O3 synthesis additive

Duplexα/β-SiAlON ceramic cutting inserts(30α:70β)were synthesized by microwave sintering.The effects of solid solution parameters(m,n,z),synthesis temperature,and amount of excess Y₂O₃ synthesis additive on phase assemblage,microstructure,mechanical properties,and cutting performance were systematically investigated.It was found that increasing m value could improve the formation ofαphase while high z value over 1.0 resulted in the dissolution ofαphase intoβphase and intergranular phase.Increasing the amount of excess Y₂O₃ could promote densification and elongatedβgrain growth;however,the excess Y₂O₃ amount above 4 wt%resulted in substantial crystallization of M'SS phase,thus declining the mechanical properties and wear resistance.The microwave-synthesizedα/β-SiAlON cutting insert with modified parameters(m=1.7,n=1.0,z=0.7,and 3 wt%excess Y₂O₃)was obtained with optimal comprehensive properties,whose tool life was found to increase by approximately 75%in high-speed milling of Inconel 718 superalloy compared to the commercialα/β-SiAlON cutting insert.     

Sol–gel synthesis and catalytic properties of vanadium phosphates

Vanadium phosphates with variable specific surface areas were synthesized from vanadium alkoxides and phosphoric acid by precipitation in various solvents. The catalytic properties were studied in the reaction of methanol oxidation. Although the specific activities increase with the specific surface areas (BET), the intrinsic activities seem to depend on the particle morphology. The selectivities do not vary within a large range. The same method of precipitation was applied to prepare vanadium phosphates on a silica support. It is shown that the supported phase is highly dispersed, and that these supported catalysts are more stable than silica‐supported vanadium oxide for methanol oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structures and performance of Pd–Mo–K/Al2O3 catalysts used for mixed alcohol synthesis from synthesis gas

The structures of the palladium-modified Mo–K/Al₂O₃ catalyst samples were characterized by the XRD, LRS, and EXAFS techniques and correlated to the catalytic properties of the samples for alcohol synthesis from synthesis gas. It is found that in the oxidic palladium-modified samples a strong interaction of the palladium modifier with the supported K–Mo–O species occurs. This interaction leads to a decrease in the size of the molybdenum species and stabilization of the cationic palladium species on the samples during sulfidation. Upon sulfidation, the sulfided molybdenum species in the palladium-free sample is mainly present as large patches of MoS₂-like slabs with their basal sulfur planes interacting with the support surface. With the modification of palladium to the samples, the supported MoS₂-like species becomes highly dispersed as revealed by the decrease in the average size of the sulfided molybdenum species. The interaction of the palladium species with the molybdenum component may cause the basal planes of the MoS₂-like species to become oriented perpendicular to the support surface due to favorable bonding of the MoS₂ edge planes to the support through Mo–O–Al bonds. In comparison with the sulfided Pd-free sample, the properties of the Pd-modified samples for alcohol synthesis from synthesis gas are much improved, which most probably results from the synergic interaction of the palladium with the molybdenum species that gives rise to the appearance of the active sites.