Effects of calcination and reduction temperature on the performance of Co-Pt-ZrO2/γ-A12O3 catalysts for Fischer-Tropsch synthesis

采用浸渍法制备了Co-Pt-ZrO2/γ-Al2O3催化剂,对其进行了BET、XRD和TPR等表征,并在浆态床反应器上考察了焙烧温度和还原温度对催化剂费托合成反应性能的影响.结果表明,焙烧温度过高,容易造成Co物种和载体间的相互作用增强,使部分氧化钻颗粒聚集或烧结,导致催化剂的F-T合成反应活性和C5+烃选择性降低.还原温度较低时,钴物种不能充分还原,CO加氢活性低,甲烷选择性高,重质烃选择性低;还原温度过高,则可能造成活性物种的烧结,反而降低了催化剂的活性和重质烃选择性.在原料气n(H2)/n( CO)=2.0、483 K、2.4 MPa和空速3.6 L/( gcat·h)的条件下,31.08％ Co～0.11％Pt ～ 7.16％ ZrO2/Al2O3催化剂在673 K焙烧.纯H2下653 K还原后,其费托性能最佳;CO转化率为27.0％,C5+的选择性为83.0％.     

Solid-state synthesis of chiral ferrocenylaldimines from methyl esters of α-amino acid hydrochlorides in the presence of potassium carbonate

The solid-state interaction of the three-component mixtures (ferrocenylcarbaldehyde: methyl ester of amino acid hydrochloride: K₂CO₃) afforded new optically active Schiff bases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 583–586, March, 1999.     

Synthesis of methyl N-phenyl carbamate from dimethyl carbonate and 1,3-diphenyl urea under mild conditions

Synthesis of methyl N-phenyl carbamate from dimethyl carbonate and 1,3-diphenyl urea was investigated under atmospheric pressure. The results showed that homogenous catalyst sodium methoxide had the excellent activity to efficiently catalyze the synthesis of methyl N-phenyl carbamate under atmospheric pressure.     

Effects of glow discharge plasma on Cu–Co–Al-based supported catalysts for higher alcohol synthesis

The novel plasma assisted Cu–Co/γ-Al₂O₃ catalysts were prepared by incipient impregnation method for CO hydrogenation to higher alcohols and characterized by means of scanning electron microscopy (SEM), N₂ adsorption, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. It was found that introduction of plasma significantly improved the specific surface area, dispersion of catalyst and the enrichment of active species on the surface of catalysts. Under the conditions of P = 5.0 MPa, GHSV = 6,000 h⁻¹, V(H₂)/V(CO) = 2, T = 573 K, the conversion of carbon monoxide over the plasma enhanced catalyst increased by 41.9% compared with that of the conventional sample, and the space time yield reached 337.1 g kg⁻¹ h⁻¹.     

The effects of Te on the performance of Mo-V catalysts prepared by hydrothermal synthesis

Some Mo-V-Te-La catalysts with varied component were prepared by hydrothermal synthesis and dried with microwave method. The component of the catalyst were greatly affected the crystal structure and Raman spectrum. The phase in the catalysts was different when the Mo, V, and Te content varied. When the catalyst containing the same Mo, V content, due to the effect of dopant of Te element (V0.07 Mo0.93)5O14 became the main phase in the catalyst. The catalyst also showed good activity for the reaction of selective oxidation propane to acrolein and acrylic acid.     

Controlled synthesis of cobalt nanocrystals on the carbon spheres for enhancing Fischer–Tropsch synthesis performance

Non-porous carbon sphere was used as support to synthesize supported cobalt Fischer-Tropsch catalysts with high activity and durability. Strong metal-support interaction was avoided and intrinsic activity of pristine cobalt nano-particles was studied. Thermal decomposition synthesis method was applied to obtain cobalt catalysts with high dispersion and narrow particle size distribution. Furthermore the cobalt size can be controlled by the molar ratio of o-dichlorobenzene/benzylamine. Compared with supported cobalt catalysts prepared by incipient wetness impregnation method and ultrasonic impregnation method,the catalyst prepared by thermal decomposition method showed higher catalytic activity, higher long chain hydrocarbons selectivity and lower methane selectivity.     

Systematic variation of the sodium/sulfur promoter content on carbon-supported iron catalysts for the Fischer–Tropsch to olefins reaction

The Fischer–Tropsch to olefins(FTO) process is a method for the direct conversion of synthesis gas to lower C_2–C_4olefins. Carbon-supported iron carbide nanoparticles are attractive catalysts for this reaction.The catalytic activity can be improved and undesired formation of alkanes can be suppressed by the addition of sodium and sulfur as promoters but the influence of their content and ratio remains poorly understood and the promoted catalysts often suffer from rapid deactivation due to particle growth. A series of carbon black-supported iron catalysts with similar iron content and nominal sodium/sulfur loadings of 1–30/0.5–5 wt% with respect to iron are prepared and characterized under FTO conditions at 1and 10 bar syngas pressure to illuminate the influence of the promoter level on the catalytic properties.Iron particles and promoters undergo significant reorganization during FTO operation under industrially relevant conditions. Low sodium content(1–3 wt%) leads to a delay in iron carbide formation. Sodium contents of 15–30 wt% lead to rapid loss of catalytic activity due to the covering of the iron surface with promoters during particle growth under FTO operation. Higher activity and slower loss of activity are observed at low promoter contents(1–3 wt% sodium and 0.5–1 wt% sulfur) but a minimum amount of alkali is required to effectively suppress methane and C_2–C_4paraffin formation. A reference catalyst support(carbide-derived carbon aerogel) shows that the optimum promoter level depends on iron particle size and support pore structure.     

Phase behavior and modeling of the poly(methyl methacrylate)–CO2–methyl methacrylate system

Cloud-point data for the system poly(methyl methacrylate) (PMMA)–CO₂–methyl methacrylate (MMA) are measured in the temperature range of 26 to 170°C, to pressures as high as 2500 bar, and with cosolvent concentrations of 10.4, 28.9, and 48.4 wt.%. PMMA does not dissolve in pure CO₂ to 255°C and 2550 bar. The cloud-point curve for the PMMA–CO₂–10.4 wt.% MMA system exhibits a negative slope that reaches 2500 bar at 105°C. With 28.9 wt.% MMA the cloud-point curve remains relatively flat at ∼900 bar for temperatures between 25 and 170°C. With 48.4 wt.% MMA the cloud-point curve exhibits a positive slope that extends to 20°C and ∼100 bar. Pressure-composition isotherms are also reported for the CO₂–MMA system at 40.0, 80.0, 105.5°C. This system exhibits type-I phase behavior with a continuous mixture–critical curve. The Peng–Robinson (PR) and SAFT equations of state model the CO₂–MMA data reasonably well without any binary interaction parameters, although the PR equation provides a better representation of the mixture-critical region. It is not possible to obtain even a qualitative fit of the PMMA–MMA–CO₂ data with the SAFT equation of state. The SAFT model qualitatively shows that the cloud-point pressure decreases with increasing MMA concentration and that the cloud-point curve exhibits a positive slope for very high concentrations of MMA in solution.     

Nanostructured catalysts for direct electrooxidation of dimethyl ether based on Bi- and trimetallic Pt–Ru and Pt–Ru–Pd alloys prepared from coordination compounds

Bi- and trimetallic platinum–ruthenium and platinum–ruthenium–palladium catalysts with specified atomic ratios Pt: Ru = 1: 1 and Pt: Ru: Pd = 1: 1: 0.1, respectively, were synthesized from the coordination compounds of the metals deposited on highly dispersed carbon black. The catalysts were characterized by powder X-ray diffraction, electron dispersive analysis, and transmission electron microscopy. According to voltammetry data, the highest activity in the dimethyl ether (DME) electrooxidation is exhibited by the catalyst Pt_0.43Ru_0.47Pd_0.1/C; hence, it may be considered as a promising anode material for direct DME fuel cells.     

Synthesis and study of Ru–Ba–Cs/Sibunit ternary catalysts for ammonia synthesis

Ru–Ba–Cs/Sibunit ternary catalysts were synthesized. Their activity in ammonia synthesis and the thermal stability of the support in a reducing atmosphere at elevated temperature depend on the molar ratio of the promoters. The results of studies using physical methods suggest that cesium predominantly interacts with the support, acting as an electronic promoter, whereas barium is a structural promoter. The synergistic action of the promoters at increased barium content of the catalyst was revealed. The highest activity in ammonia synthesis, 34.5 mL_NH3 g_cat ^–1 h^–1, was reached for the 4% Ru–10.8% Ba–2.6% Cs/Sibunit catalyst.     

Heterogeneous synthesis of glycerol carbonate from glycerol and dimethyl carbonate catalyzed by LiCl/CaO

In this article, a CaO-based catalyst was prepared by impregnating chloride salts on CaO to develop a highly efficient heterogeneous catalyst for the synthesis of glycerol carbonate (GC) from glycerol and dimethyl carbonate. LiCl/CaO exhibited a high catalytic activity under moderate reaction conditions. The effects of the LiCl loadings, the amount of catalyst and the calcination temperature on the catalytic activity were investigated. The highest yield of 94.19% glycerol carbonate was obtained at 65 °C on CaO loaded with 10% LiCl after 1 h, and the catalyst had high stability in reusing work. Scanning electron microscopy (SEM), X-ray diffraction (XRD), BET, CO₂-TPD, XPS and thermalgravity (TG) were used to characterize the prepared catalyst. It was found that the high catalytic activity of CaO after modification with LiCl is associated with the structural aspects and the amount of basicity of the catalyst. The Li₂O₂ species, which is a strong basic site that is formed by the substitution of the Ca²⁺ in CaO lattice by Li⁺, has great activity for transesterification.     

An in situ infrared study of dimethyl carbonate synthesis from carbon dioxide and methanol over well-shaped CeO2

The mechanism of dimethyl carbonate(DMC) formation from CO_2 and methanol is investigated using three well-shaped CeO_2 catalysts, nanorod, nanocube and octahedron, which are packed with different crystal planes. In situ Fourier Transform Infrared Spectroscopy(FTIR) is employed to probe each reaction step in the DMC synthesis. The number of –OH groups and the species of CO_2 adsorptions on ceria surface have significant influence on the activity of ceria with different morphologies. Rod-ceria has favorable catalytic activity because of the large amount of –OH groups and the formation of bidentate carbonate species.     

Synthesis of methyl ketones from terminal olefins using PdCl2/CrO3 system mimicking the Wacker process

An efficient synthesis of methyl ketones from terminal olefins using PdCl₂/CrO₃ system mimicking the Wacker process is developed. The method shows good functional groups compatibility, no aldehyde by-products and is operationally simple. CrO₃ is the sole oxidant and replaces both Cu-salts and molecular oxygen, traditionally used in this process. The method holds potential for future applications in organic synthesis.     

Metal-organic frameworks MOF-808-X as highly efficient catalysts for direct synthesis of dimethyl carbonate from CO2 and methanol

A series of metal-organic frameworks MOF-808-X (6-connected) were synthesized by regulating the ZrOCl₂·8H₂O/1,3,5-benzenetricarboxylic acid (BTC) molar ratio (X) and tested for the direct synthesis of dimethyl carbonate (DMC) from CO₂ and CH₃OH with 1,1,1-trimethoxymethane (TMM) as a dehydrating agent. The effect of the ZrOCl₂·8H₂O/BTC molar ratio on the physicochemical properties and catalytic performance of MOF-808-X was investigated. Results showed that a proper ZrOCl₂·8H₂O/BTC molar ratio during MOF-808-X synthesis was fairly important to reduce the redundant BTC or zirconium clusters trapped in the micropores of MOF-808-X. MOF-808-4, with almost no redundant BTC or zirconium clusters trapped in the micropores, exhibited the largest surface area, micropore size, and the number of acidic-basic sites, and consequently showed the best activity among all MOF-808-X, with the highest DMC yield of 21.5% under the optimal reaction conditions. Moreover, benefiting from the larger micropore size, MOF-808-4 outperformed our previously reported UiO-66-24 (12-connected), which had even more acidic-basic sites and larger surface area than MOF-808-4, mainly because the larger micropore size of MOF-808-4 provided higher accessibility for the reactant to the active sites located in the micropores. Furthermore, a possible reaction mechanism over MOF-808-4 was proposed based on the in situ FT-IR results. The effects of different reaction parameters on DMC formation and the reusability of MOF-808-X were also studied.     

Synthesis of dimethyl carbonate from methanol and supercritical carbon dioxide

The synthesis of dimethyl carbonate (DMC) from methanol and supercritical carbon dioxide over various base catalysts has been studied. Compounds of group-I elements (Li, Na and K) were used as base catalysts. The promoter and the dehydrating agent were also used to enhance the yield of DMC. The effects of the catalysts, promoter and dehydrating agent on the yield of DMC were investigated. By-products such as dimethyl ether (DME) and C₁–C₂ hydrocarbons were formed with the DMC as a main product. The yield of DMC with different alkali metal catalysts ranked in the following order: K > Na > Li. The catalysts of the metal-CO₃ compounds were more effective than the metal-OH compounds in DMC synthesis. The maximum DMC yield reached up to about 12 mol% in the presence of K₂CO₃ (catalyst), CH₃I (promoter) and 2,2-dimethoxypropane (dehydrating agent) at 130–140°C and 200 bar. The reaction mechanism of DMC synthesis from methanol and supercritical carbon dioxide was proposed.     

Effects of Mo promoters on the Cu-Fe bimetal catalysts for the DMC formation from CO2 and methanol

The Mo-promoted Cu-Fe bimetal catalysts were prepared and used for the formation of dimethyl carbonate（DMC） from CO₂ and methanol.The catalysts were characterized by X-ray diffraction（XRD）, temperature programmed reduction（TPR）,laser Raman spectra（LRS）,energy dispersive spectroscopy （EDS） and temperature programmed desorption（TPD） techniques.The experimental results demonstrated that the Mo promoters can decrease the reducibility and increase the dispersion of Cu-Fe clusters.The concentration balance of base-acid sites can be readily adjusted by changing the Mo content.The moderate concentration balance of acid and base sites was in favor of the DMC formation. Under optimal experimental conditions,the highest methanol conversion of 6.99%with a DMC selectivity of 87.7%can be obtained when 2.5 wt%of Mo was loaded.     

Effect of calcination conditions on MoO3/SiO2 catalysts for synthesis of methylphenyl carbonate

The effect of calcination conditions on MoO₃/SiO₂ catalysts for the synthesis of methylphenyl carbonate was investigated in terms of catalytic activities and surface properties. The calcination temperature was varied in the range of 300 to 800^oC. These calcination conditions have shown a close relationship with the catalyst activities. The optimal calcination temperature of MoO₃/SiO₂was found to be around 550-600^oC. The catalysts were characterized by XRD, SEM, FT-IR and XPS analysis.     

核壳结构TiO2@SiO2催化碳酸二甲酯与苯酚酯交换合成碳酸二苯酯

以反相微乳液法和沉淀法相结合制备了核壳结构TiO₂@SiO₂,首次用于碳酸二甲酯与苯酚酯交换合成碳酸二苯酯反应,显示较好的催化活性. 采用200 ℃焙烧的TiO₂@SiO₂,用量0.20 g,反应9 h,苯酚转化率达41.8%,酯交换选择性为100%. 透射电镜显示TiO₂@SiO₂核厚壳薄,TiO₂核直径220-300 nm,SiO₂壳厚度40-60 nm,具有介孔结构. TiO₂@SiO₂对碳酸二甲酯与苯酚酯交换反应有好的重复使用性,使用4次苯酚转化率仍保持在40%以上. TiO₂与SiO₂发生相互作用,Ti进入骨架形成Ti-O-Si键,骨架Ti的形成提高了TiO₂@SiO₂的催化性能.     

ZIF-67/CeO2催化CO2和甲醇直接合成碳酸二甲酯

采用沉淀法将ZIF-67负载到CeO₂上,制备了具有多重活性位点的非均相催化剂ZIF-67/CeO₂,并研究其催化CO₂和甲醇直接反应生成碳酸二甲酯(DMC)的性能。采用 X 射线衍射、N2吸附-脱附、傅里叶变换红外光谱和 X 射线光电子能谱研究了ZIF-67/CeO₂的各种理化性质。结果表明,ZIF-67的引入使ZIF-67/CeO₂催化剂产生更多的氧空位。在考察的ZIF-67/CeO₂系列催化剂中,0.3-ZIF-67/CeO₂(0.3为Co、Ce物质的量之比)在具有高的比表面积的同时还能保持介孔结构,具有丰富的酸碱位点,并且具有较高的CO₂吸附容量,表现出最好的催化性能。在反应温度为140℃、压力为4.5 MPa的条件下反应4 h,DMC收率可达到3.79 mmol_DMC·gcat^-1。