Studies on product distribution of nanostructured iron catalyst in Fischer–Tropsch synthesis: Effect of catalyst particle size

The dependencies of hydrocarbon product distributions of Fischer–Tropsch synthesis by iron catalysts on catalysts particle size are studied. The concept of two superimposed Anderson–Schulz–Flory distributions applied for represent size dependency of product distributions. A series of catalysts with different particle size are prepared by microemulsion method. It is found that the carbon number of produced hydrocarbon decreased with decreasing the catalyst particle size. These results indicate the H₂ concentration on catalyst surface decreased by increasing the catalyst particle size. Thus the concentration of monomers that exhibited higher degree of hydrogenation (like CH₂ species) on the surface of catalyst increased with decreasing the catalyst particle size.     

Platinum impregnated zeolite β as a reforming catalyst

It is shown that Pt impregnated zeolite has a high reforming capability for naphthenic feeds such as methylcyclopentane and methylcyclohexane, which are transformed in aromatic and cyclic saturated multibranched molecules with higher octane numbers. The temperature plays a major role in these reactions. The cycloolefinic intermediates produced by the dehydrogenation of the feed molecules are alkylated with the carbonium ions produced by the ring opening of other feed molecules. The disproportionation of the alkylated compounds is suggested to be responsible for the enlargement of the feed molecules. This disproportionation, the isomerization of the cycloolefinic intermediates, and some cracking particularly for methylcyclohexane, are proposed to be responsible for the product distribution under the present conditions.     

Influence of alkylaluminium on TiClx/ MgCl2/ THF catalyst——Effect of Al-alkyl on chemical structure and catalyst performance

研究了一系列不同烷基铝处理的TiCl_x/MgCl₂/THF体系Ziegler-Natta催化剂,并采用XPS、EPR对其化学结构进行表征,初步探讨了烷基铝变化对催化剂化学结构的影响,特别是对Ti价态的影响。研究结果表明,由于烷基铝的作用,催化剂中活性组分Ti的结构发生了明显的改变,而其中烷基铝预还原过程对催化剂的结构影响较大。借助催化剂的这些结构上的变化引起其催化性能的显著提高,对比评价结果表明,小试催化剂的乙烯均聚活性从预还原前的4890 gPE/gcat提高到9300 g PE/gcat,工业生产催化剂从8400 g PE/gcat提高到11000 g PE/gcat。     

Environmental high resolution electron microscopy of gas‐catalyst reactions

Environmental electron microscopy has become an important scientific method for fundamental studies of dynamic chemical reaction processes in heterogeneous catalysis and of catalytic growth of carbon nanotubes. Outstanding contributions are resulting from the ability to observe gas‐catalyst surface reactions in situ, on the atomic scale. A great deal of structural and chemical information including lattice modification of working catalysts is possible. This is key to understanding novel reaction processes, including release mechanism of structural oxygen in oxide catalysts in selective oxidation of hydrocarbons and to designing improved catalysts. This brief survey of the recent spectacular developments in environmental high resolution electron microscopy shows that new opportunities are being opened up in catalysis. This revised version was published online in August 2006 with corrections to the Cover Date.     

Highly effective molybdena–manganese catalyst for propane oxidative dehydrogenation

A manganese oxide catalyst impregnated with molybdenum exhibits high yield, productivity and stability in the oxidative dehydrogenation of propane to propene. This catalyst exhibits catalytic activity and yield to propene at temperatures as low as 623 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ring-opening polymerization of γ-glycidoxypropyltrimethoxysilane catalyzed by multi-metal cyanide catalyst

Ring-opening polymerizations of γ-glycidoxypropyltrimethoxysilane (GPTMS) were carried out by using multi-metal cyanide (MMC) catalyst and the synthesized homopolymer was a comb-shaped polymer with regular structure. The structure of the polymer obtained (P-GPTMS) was characterized by FTIR, ¹H-NMR, and ²⁹Si-NMR spectroscopy, and the molecular weight and its distribution were analyzed by size-exclusion chromatography with multi-angle laser light scattering (SEC-MALLS). The thermal behavior of P-GPTMS was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). P-GPTMS with high molecular weight (M _n = 18,000–80,000) and narrow molecular weight distribution (1.10–1.35) were synthesized when the dosage of MMC catalyst was 0.1% and polymerization temperature was 130 °C. The molecular weight of the product could be adjusted by controlling the polymerization time. The T _g of P-GPTMS is in the range of −34 to −30 °C. On the basis of the TGA data, the decomposition rate of P-GPTMS reached its peak at 374.14 °C and the entire decomposition stopped at 600 °C.     

Vapor phase carbonylation of ethanol with Ni-Zn/c catalyst

Vapor phase carbonylation of ethanol with Ni/C and Ni-Zn/C catalyst was investigatedunder atmospheric pressure.Ni-Zn/C was found to have a significantly higher activity andselectivity than Ni/C.Effects of Zn and Ni loading on ethanol conversion and productdistributions were also investigated,and the sequence of metal loading was compared.The cata-lyst was characterized by XRD(X-ray diffraction)and SEM-EDS.The spectra of XRDdemonstrated that the catalyst structure was changed from crystalline to non-crystalline in theprocess of carbonylation.Stable iodide compound was formed due to the interaction betweenC_2H_5I and active metals.The authors believe that the active phase of carbonylation might havebeen non-crystalline.     

A designed organic–zeolite hybrid acid–base catalyst

An organic–zeolite hybrid catalyst was synthesised via solid-state impregnation of the zeolite with an amount of melamine corresponding to 20 mol% of the aluminium content. A high density of basic sites is formed in the zeolite. From infrared spectroscopy and TGA measurements we infer that melaminium cations are formed in the zeolite which are highly thermally stable. IR spectroscopic and TGA measurements showed the presence of melaminium after pre-treatment in vacuum at 450 °C. The catalyst exhibited activity in the Knoevenagel condensation reaction between benzaldehyde and ethyl cyanoacetate which is suggested to be promoted by the presence of acid and base sites. The catalyst activity was compared with other known base catalysts including hydrotalcites and magnesium oxide on alumina support.     

Boron-doped lamellar porous carbon supported copper catalyst for dimethyl oxalate hydrogenation

Doping heteroatoms on carbon materials could bring some special advantages for using as catalyst support.In this work, a boron doped lamellar porous carbon(B-LPC) was prepared facilely and utilized as carbonbased support to construct Cu/B-LPC catalyst for dimethyl oxalate(DMO) hydrogenation. Doping boron could make the B-LPC own more defects on surface and bigger pore size than B-free LPC, which were beneficial to disperse and anchor Cu nanoparticles. Moreover, the interaction between Cu species...     

LLDPE synthesis via SiO2–Ga-supported zirconocene/MMAO catalyst

In this present study, the linear low-density polyethylene (LLDPE) was synthesized via ethylene/1-octene copolymerization with the zirconocene/MMAO catalyst by in situ impregnation of different silica (SiO₂) supports. The SiO₂ supports used were small-pored (SP) and large-pored (LP) sizes with and without Ga modification. It was found that the SP-SiO₂ support exhibited higher polymerization activity (～1.5 times) than that obtained from the LP-SiO₂ one. This can be attributed to the lower amount of MMAO being present inside the SP-SiO₂ support resulting in higher content of MMAO at the external surface. The higher activity in ethylene/1-octene copolymerization was also found with the supported catalyst having Ga modification onto both SP-and LP-SiO₂ supports_. The results demonstrated that the introduction of Ga may improve ability of supports to immobilize metallocene catalyst. Based on ¹³C NMR measurement, it indicated that all synthesized polymers were typical LLDPE having random distribution of comonomer.     

Kinetic study of CO hydrogenation over co-precipitated iron–nickel catalyst

The kinetic of the Fischer–Tropsch synthesis over a Fe–Ni/Al₂O₃ catalyst was investigated in a fixed bed micro reactor. Experimental conditions were varied as follow: reaction pressure 2–10 bar, H₂/CO feed ratio of 2/1 and space velocity of 96–450 cm³(STP)/h/gram_catalyst at the temperature range 523–573 K. On the basis of carbide-enol mechanism and Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate equations, seventeen kinetic expressions for CO consumption were tested and interaction between adsorption HCO and dissociated adsorption hydrogen as the controlling step gave the most plausible kinetic model. The activation energy was 46.5 kJ/mole for optimal kinetic model.     

Acetone conversion to isobutene in high selectivity using zeolite β catalyst

The catalytic activity of the proton forms of zeolite and ZSM-5 are compared for the conversion of acetone. Zeolite demonstrates markedly enhanced selectivity to isobutene and selectivities of >80% can be achieved for conversions up to 65%. In contrast high selectivities to isobutene with ZSM-5 can be attained only at very low conversions (5%).     

NiMoNx/γ-Al2O3 catalyst for HDN of pyridine

A series of NiMoN_x/γ-Al₂O₃ catalysts with various Ni contents were prepared by a topotactic reaction between their corresponding precursors NiO·MoO₃/γ-Al₂O₃ and NH₃. The catalysts were characterized using BET, XRD, and H₂-TPR techniques, and the HDN activity of pyridine over these catalysts was tested. XRD patterns show that metallic Ni, Mo₂N and a new phase of Ni₃Mo₃N exist in NiMoN_x/γ-Al₂O₃ catalyst. H₂-TPR studies indicate that the presence of Ni lowers the reduction temperature of the passivated surface layer of nitrided Mo/γ-Al₂O₃. The HDN activity for NiMoN_x/γ-Al₂O₃ is much higher than that for NiMoS_x/γ-Al₂O₃. The nitride catalyst with about 5.0 wt% NiO and 15.0 wt% MoO₃ in its precursor has the highest specific denitrogenation activity. The appearance of Ni₃Mo₃N and the synergy between metallic Ni and nitrided Mo are probably responsible for the high activity of NiMoN_x/γ-Al₂O₃ catalyst. The role of Ni in HDN reaction was also investigated. The activities decrease in the order: reduced Ni/γ-Al₂O₃≥nitrided Ni/γ-Al₂O₃>partially reduced Ni/γ-Al₂O₃ and sulfided Ni/γ-Al₂O₃.     

Development of a CH4 dehydroaromatization–catalyst regeneration fluidized bed system

A pilot-scale methane dehydroaromatization–H₂ regeneration fluidized bed system (MDARS) was developed. In the MDARS, the catalyst circulation between a fluidized bed reactor and a fluidized bed regenerator with the help of a catalyst feeder allowed methane dehydroaromatization (MDA) and H₂ regeneration to be carried out simultaneously, which is good for maintaining a stable MDA catalytic activity. A fixed bed reactor (FB) and a single fluidized bed reactor (SFB) were also used for a comparative study. The experimental results showed that the catalytic activity in the MDARS was more stable than that in the FB and SFB reactors. The effects of some parameters of MDARS on the CH₄ conversion and product selectivity were investigated. To verify the feasibility and reliability of the MDARS, an eight-hour long-term test was carried out, which demonstrated that the operation of the MDARS was stable and that the catalytic activity remained stable throughout the entire experimental period.     

The biomimetic catalytic synthesis of acetal compounds using β-cyclodextrin as catalyst

Based on the principle of biomimetic catalysis, β-cyclodextrin was applied to the acetalation reaction as a facile and efficient catalyst, and the synthesis was environmentally friendly with atomic economy. The influencing factors of the acetalation reaction e.g. the reaction time, the volume of water-carrying agent,the molar ratio of catalyst to benzaldehyde and the molar ratio of glycol to benzaldehyde had been studied.The yield of benzaldehyde glycol acetal would reach a maximum of 81.3% under the conditions approached.Six of other acetals were also synthesized. Moreover, a plausible reaction mechanism for the formation of acetal had been proposed.     

Oxidation of isobutane over Mo–V–Sb mixed oxide catalyst

The catalytic performances of Mo–V–Sb mixed oxide catalysts have been studied in the selective oxidation of isobutane into methacrolein. V–Sb mixed oxide showed the activity for oxidative dehydrogenation of isobutane to isobutene. The selectivity to methacrolein increased by the addition of molybdenum species to the V–Sb mixed oxide catalyst. In a series of Mo–V–Sb oxide catalysts, Mo₁V₁Sb₁₀O_x exhibited the highest selectivity to methacrolein at 440°C. The structure analyses by XRD, laser Raman spectroscopy and XPS showed the coexistence of highly dispersed molybdenum suboxide, VSbO₄ and -Sb₂O₄ phases in the Mo₁V₁Sb₁₀O_x. The high catalytic activity of Mo₁V₁Sb₁₀O_x can be explained by the bifunctional mechanism of highly dispersed molybdenum suboxide and VSbO₄ phases. It is likely that the oxidative dehydrogenation of isobutane proceeds on the VSbO₄ phase followed by the oxidation of isobutene into methacrolein on the molybdenum suboxide phase.     

Dry reforming of methane over palladium–platinum on carbon nanotube catalyst

A dry reforming (DR) catalyst based on bimetallic Pd–Pt supported on carbon nanotubes is presented. The catalyst was prepared using a microwave-induced synthesis. It showed enhanced DR activity in the 773–923?K temperature range at 3 atm. Observed carbon balances between the reactant and product gases imply minimal carbon deposition. A global three-reaction (reversible) kinetic model—consisting of DR, reverse water gas shift, and CH₄ decomposition (MD)—adequately simulates the observed concentrations, product H₂/CO ratios, and reactant conversions. Analysis shows that, under the conditions of this study, the DR and MD reactions are net forward and far from equilibrium, while the RWGS is near equilibrium.     

Study on a new iron catalyst for slurry Fischer–Tropsch synthesis

A novel spherical-shaped iron catalyst (100Fe/5Cu/6K/16SiO₂) with 0.24 wt% of SO₄²⁻ loading for slurry Fischer–Tropsch synthesis (FTS) was prepared by spray-drying using cheap industrial iron resource FeSO₄ · 7H₂O. The characterization results from BET, X-ray diffraction and temperature-programmed-reduction (H₂-TPR) show that the sulfate-containing catalyst exhibited higher surface area, more dispersed α-Fe₂O₃ phase and more facility of reduction than a sulfate-free catalyst. The FTS performance in a fixed bed reactor and in a continuous stirred tank reactor indicates that SO₄²⁻ species acts as a promoter by increasing catalyst activity and modifying hydrocarbon selectivity to heavier products.     

Benzylacetate synthesis by oxyacetoxylation of toluene on Pd–Bi binary catalyst

Benzylacetate synthesis from toluene, acetic acid and oxygen on Pd–Bi binary catalyst was studied in the liquid phase. By incorporation of Bi with Pd, both the activity and selectivity were improved. Especially better stability was obtained with the catalyst having Pd/Bi = 3. Deactivation of the catalyst was investigated in detail by XRD, XPS, TEM, elemental analysis, EPMA and so on. Comparing the used catalyst with the fresh one, it was indicated that the main cause of deactivation was the dissolution of Pd into the reaction mixture from the most outer surface of the catalyst. By adopting proper reaction conditions to prevent the Pd dissolution, the catalyst having Pd/Bi = 3 was suggested to be used as an industrial catalyst. This revised version was published online in June 2006 with corrections to the Cover Date.     

Pd oxidation under UHV in a model Pd/ceria–zirconia catalyst

A model planar catalyst was prepared by depositing Pd onto a thick (few m) film of ceria–zirconia in ultrahigh vacuum (UHV), and the oxidation state of Pd and its support was determined by X-ray photoelectron spectroscopy, following thermal treatments in UHV, oxygen, or carbon monoxide. It was found that Pd could be oxidized simply by heating the catalyst in UHV, indicating that transfer of oxygen from the support to the metal is both thermodynamically favorable and facile.