Effect of catalyst confinement and pore size on Fischer-Tropsch synthesis over cobalt supported on carbon nanotubes

This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes(CNT) on the activity and product selectivity of Fischer-Tropsch synthesis(FTS) reaction.Three types of CNT with average pore sizes of 5,11,and 17 nm were used as the supports.The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT.The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT,and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing.The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT.Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.     

Additive effects of alkaline-earth metals and nickel on the performance of Co/γ-Al_2O_3 in methane catalytic partial oxidation

Nano-sized γ-alumina (γ-Al2O3) was first prepared by a precipitation method. Then, active component of cobalt and a series of alkaline- earth metal promoters or nickel (Ni) with different contents were loaded on the γ-Al2O3 support. The catalysts were characterized by N2 adsorption-desorption, X-ray diffraction (XRD) and thermogravimetry analysis (TGA). The activity and selectivity of the catalysts in catalytic partial oxidation (CPO) of methane have been compared with Co/γ-Al2O3, and it is found that the catalytic activity, selectivity, and stability are enhanced by the addition of alkaline-earth metals and nickel. The optimal loadings of strontium (Sr) and Ni were 6 and 4 wt%, respectively. This finding will be helpful in designing the trimetallic Co-Ni-Sr/γ-Al2O3 catalysts with high performance in CPO of methane.     

Reforming of CH4 with CO2 over Co/Mγ-Al oxide catalyst

A series of Co/Mg–Al oxide samples,CoMgAl-x(x=(Mg+Co)/Al molar ratio of 1–5),were prepared by the self-combustion method followed by H2reduction.The catalytic performance and stability of the samples were studied in dry reforming of CH4.XRD and H2-TPR characterization results showed that the reduced CoMgAl-x samples mainly consisted of solid solution and spinel phases with cobalt particles.The spinel phases contained Co3O4 and Con Mg1-n Al2O4(0≦n≦1)varying with the(Mg+Co)/Al ratio.The effect of (Mg+Co)/Al molar ratio on the catalytic behavior was investigated in detail and CoMgAl-3 exhibited the highest catalytic activity and stability among the catalysts studied.     

纯相和镍取代的Co_3O_4尖晶石催化剂用于N_2O直接分解(英文)

A series of NixCo1-xCo2O4(0 ≤ x ≤ 1) spinel catalysts were prepared by the co-precipitation method and used for direct N2O decomposition. The decomposition pathway of the parent precipitates was characterized by thermal analysis. The catalysts were calcined at 500 °C for 3 h and characterized by powder X-ray diffraction, Fourier transform infrared, and N2 adsorption-desorption. Nickel cobaltite spinel was formed in the solid state reaction between NiO and Co3O4. The N2O decomposition measurement revealed significant increase in the activity of Co3O4 spinel oxide catalyst with the partial replacement of Co2+ by Ni2+. The activity of this series of catalysts was controlled by the degree of Co2+ substitution by Ni2+, spinel crystallite size, catalyst surface area, presence of residual K+, and calcination temperature.     

States of Carbon Nanotube Supported Mo-Based HDS Catalysts

The dispersion of the active phase and loading capacity of the Mo species on carbon nanotube (CNT) was studied by the XRD technique. The reducibility properties of Co-Mo catalysts in the oxide state over CNTs were investigated by TPR, while the sulfided Co-Mo/CNT catalysts were characterized by means of the XRD and LRS techniques. The activity and selectivity with respect to the hydrodesulfurization (HDS) performances on carbon nanotube supported Co-Mo catalysts were evaluated. It was found that the main active molybdenum species in the oxide state MoO3/CNT catalysts were MoO2, but not MoO3, as generally expected. The maximum loading before the formation of the bulk phase was lower than 6% (percent by mass, based on MoO3). TPR studies revealed that the active species in the oxide state Co-Mo/CNT catalysts were reduced more easily at relatively lower temperatures in comparison to those of the Co-Mo/γ-Al2O3 catalysts, indicating that the CNT support promoted or favored the reduction of the active species. The active species of a Co-Mo-0.7/CNT catalyst were more easily reduced than those of the Co-Mo/CNT catalysts with Co/Mo atomic ratios of 0.2, 0.35, and 0.5, respectively, suggesting that the Co/Mo atomic ratio has a great effect on the reducibility of the active species. It was found that the incorporation of cobalt improved the dispersion of the molybdenum species on the support, and a phenomenon of mobilization and re-dispersion had occurred during the sulfurization process, resulting in low valence state Mo3S4 and Co-MoS2.17 active phases. HDS measurements showed that the Co-Mo/CNT catalysts were more active than the Co-Mo/γ-Al2O3 ones for the desulfurization of DBT, and the hydrogenolysis/hydrogenation selectivity of the Co-Mo/CNT catalysts was also much higher than those of the Co-Mo/γ-Al2O3. The Co-Mo/CNT catalyst with a Co/Mo atomic ratio of 0.7 showed the highest activity, whereas the catalyst with a Co/Mo atomic ratio of 0.35 had the highest selectivity.     

Complete Oxidation of Methane over Palladium Supported on Alumina Modified with Calcium,Lanthanum,and Cerium Ions

The activity and thermal stability of Pd/Al_2O_3 and Pd/(Al_2O_3 MO_x)(M=Ca,La,Ce) palladium catalysts in the reaction of complete oxidation of methane are presented in this study.The catalyst supports were prepared by sol-gel method and they were dried either conventionally or with supercritical carbon dioxide.Then they were impregnated with palladium nitrate solution.The catalysts with unmodified alumina had a high surface area.The activity and thermal stability of the alumina- supported catalyst was also very high.The introduction of calcium,lanthanum,or cerium oxide into alumina support caused a decrease of the surface area in the way dependent on the support precursor drying method.These modifiers decreased the activity of palladium catalysts,and they required higher temperatures for the complete oxidation of methane than unmodified Pd/Al_2O_3.The improvement of the palladium activity by lanthanum and cerium support modifier was observed only at low temperatures of the reaction.     

Comparing the deactivation behaviour of Co/CNT and Co/γ-Al2O3 nano catalysts in Fischer-Tropsch synthesis

An extensive study of Fischer-Tropsch (FT) synthesis on cobalt nano particles supported on γ-alumina and carbon nanotubes (CNTs) catalysts is reported.20 wt% of cobalt is loaded on the supports by impregnation method.The deactivation of the two catalysts was studied at 220 C,2 MPa and 2.7 L/h feed flow rate using a fixed bed micro-reactor.The calcined fresh and used catalysts were characterized extensively and different sources of catalyst deactivation were identified.Formation of cobalt-support mixed oxides in the form of xCoO yAl2O3 and cobalt aluminates formation were the main sources of the Co/γ-Al2O3 catalyst deactivation.However sintering and cluster growth of cobalt nano particles are the main sources of the Co/CNTs catalyst deactivation.In the case of the Co/γ-Al2O3 catalyst,after 720 h on stream of continuous FT synthesis the average cobalt nano particles diameter increased from 15.9 to 18.4 nm,whereas,under the same reaction conditions the average cobalt nano particles diameter of the Co/CNTs increased from 11.2 to 17.8 nm.Although,the initial FT activity of the Co/CNTs was 26% higher than that of the Co/γ-Al2O3,the FT activity over the Co/CNTs after 720 h on stream decreased by 49% and that over the Co/γ-Al2O3 by 32%.For the Co/γ-Al2O3 catalyst 6.7% of total activity loss and for the Co/CNTs catalyst 11.6% of total activity loss cannot be recovered after regeneration of the catalyst at the same conditions of the first regeneration step.It is concluded that using CNTs as cobalt catalyst support is beneficial in carbon utilization as compared to γ-Al2O3 support,but the Co/CNTs catalyst is more susceptible for deactivation.     

Ti-Si composite oxide-supported cobalt catalysts for CO2 hydrogenation

In the present work, different silica-based supported cobalt (Co) catalysts were synthesized and used for CO2 hydrogenation for methanation. Different supports, such as SSP, MCM-41, TiSSP and TiMCM were used to prepare Co catalysts with 20 wt% Co loading. The supports and catalysts were characterized by means of N2 physisorption, XRD, SEM/EDX, XPS, TPR and CO chemisorption. It is found that after calcination of catalysts, Ti is present in the form of anatase. The introduction of Ti plays important roles in the properties of Co catalysts by:(i) facilitating the reduction of Co oxides species which are strongly interacted with support, (ii) preventing the formation of silicate compounds, and (iii) inhibiting the RWGS reaction. Based on CO2 hydrogenation, the CoTiMCM catalyst exhibites the highest activity and stability.     

氧化钴和氮掺杂碳纳米管纳米复合物的催化与容量性质(英文)

The nanocomposites based on cobalt oxide and nitrogen-doped carbon nanofibers (N-CNFs) with cobalt oxide contents of 10–90 wt% were examined as catalysts in the CO oxidation and supercapacity electrodes. Depending on Со3О4 content, such nanocomposites have different morphologies of cobalt oxide nanoparticles, distributions over the bulk, and ratios of Со3+/Co2+ cations. The 90%Со3О4-N-CNFs nanocomposite showed the best activity because of the increased concentration of defects in N-CNFs. The capacitance of electrodes containing 10%Со3О4-N-CNFs was 95 F/g, which is 1.7 times higher than electrodes made from N-CNFs.     

Complete Oxidation of Methane Alumina Modified with Calcium, over Palladium Supported on Lanthanum, and Cerium Ions

The activity and thermal stability of Pd/Al2O3 and Pd/（Al2O3＋MOx） （M=Ca, La, Ce） palladium catalysts in the reaction of complete oxidation of methane are presented in this study. The catalyst supports were prepared by sol-gel method and they were dried either conventionally or with supercritical carbon dioxide. Then they were impregnated with palladium nitrate solution. The catalysts with unmodified alumina had a high surface area. The activity and thermal stability of the aluminasupported catalyst was also very high. The introduction of calcium, lanthanum, or cerium oxide into alumina support caused a decrease of the surface area in the way dependent on the support precursor drying method. These modifiers decreased the activity of palladium catalysts, and they required higher temperatures for the complete oxidation of methane than unmodified Pd/Al2O3. The improvement of the palladium activity by lanthanum and cerium support modifier was observed only at low temperatures of the reaction.     

La掺杂Bi2O3的制备、表征与可见光催化活性

采用浸渍法制备了La掺杂Bi2O3(La-Bi2O3)光催化剂,利用X射线荧光光谱(XRF)、X射线衍射(XRD)、扫描电子显微镜(SEM)、傅立叶变换红外光谱(FT-IR)、X射线光电子能谱(XPS)、紫外-可见吸收光谱(UV-Vis)和光致发光谱(PL)等分析测试手段对样品的La掺杂量、晶体结构和光谱特征等进行了表征,并以2,4-二氯苯酚(2,4-DCP)水溶液的降解作为探针反应,考察了样品的可见光催化性能.结果表明,适量的La掺杂能有效抑制Bi2O3由四方相向单斜相转变,并将光吸收范围拓展到550 nm以上.掺杂的La可取代Bi2O3晶格中部分Bi,形成Bi—O—La键,并生成了少量镧铋复合氧化物(La0.176Bi0.824O1.5),它们的存在能有效抑制光生电子-空穴对的复合,从而提高光催化量子产率.可见光照射下2,4-DCP的光催化降解实验表明,La-Bi2O3具有良好的可见光催化性能,并且当La的掺杂量为3%(摩尔分数)时,催化剂的可见光催化效率最高.     

Preparation and Characterization of Bismuth Doped TiO2 Thin Films

A series of Bismuth-doped titanium oxide (Bi-doped TiO₂) thin films on glass substrates have been prepared by sol-gel dip coating process. The prepared catalysts were characterized by XRD and XPS. The photocatlytic activity of the thin film catalysts was evaluated through the photodegradation of aqueous methyl orange under UV illumination. The experiments demonstrated that the Bi-doped TiO₂ prepared was anatase phase. The doped bismuth was in the 3⁺ oxidation state. The presence of Bi significantly enhanced the photocatalytic activity of TiO₂ films. At calcination temperature of 500°C, with doping concentration of 2 wt %, Bi-doped TiO₂ thin film showed the highest photocatalyic activity.     

铋、氧化铋、硫化铋在醋酸-硫脲中的溶解性研究

通过研究铋(Ⅲ)与硫脲络合染色,测得络合物最大吸收峰位于460nm波长处,Bi(Ⅲ)含量在0.059～5.7μg/mL范围内符合比尔定律,回归方程Y=0.0117+0.17319 X;相关系数R=0.9999;相对标准偏差RSD为2.66%;检出限为0.013μg/mL;摩尔吸光系数为3.72×104 L.mol-1.cm-1。实验结果表明,铋、氧化铋和硫化铋在醋酸-硫脲中的溶解度分别是0.077、1.347、1.245μg/mL。经比较发现铋、氧化铋和硫化铋在醋酸-硫脲中的溶解性大小是:氧化铋>硫化铋>铋。铋、氧化铋和硫化铋的回收率分别是97.4%、98.1%、96.6%。     

Synthesis of complex hydroxo salts of magnesium, nickel, cobalt, aluminum, and bismuth and oxide catalysts on their base

Synthesis methods have been developed for the precursors of oxide catalysts that include the combination of magnesium nickel cobalt aluminum hydroxocarbonate, with a layered hydrotalcite-type structure and decavanadate and paramolybdate ions in the anion layers, and bismuth hydroxocarbonate. On the base of these precursors, multicomponent oxide catalysts have been manufactured for the oxidative dehydrogenation (OD) of light alkanes. Some of these catalysts showed high selectivities and high product yields in the conversion of ethane to ethylene.     

Improved performance of Bi2O3-doped MnO2 cathode on rechargeability in LiOH aqueous cell

Many attempts have been made to make the zinc-manganese dioxide (Zn-MnO₂) alkaline cell rechargeable, but all investigations are pertained to the proton insertion mechanism into MnO₂. In this paper, a new class of rechargeable bismuth oxide-doped MnO₂ electrode in lithium hydroxide (LiOH) electrolyte is described. The doping and the appropriate pH selection of the aqueous electrolyte improved the electrochemical performance of the aqueous cell. Hence, with an aim to understand the role of bismuth oxide (Bi₂O₃) during the discharge process, doped MnO₂ cathodes are characterized by various techniques like secondary ion mass spectrometry, X-ray diffraction, Fourier transform infra-red spectroscopy, and transmission electron microscopy analysis. The results suggest that the influence of the large radius of the cation (Bi₂O₃; Bi (III) ion (0.96 Å)) cannot be integrated into the spinel structure, thereby, improving the rechargeability. The electrode reaction of doped MnO₂ in LiOH electrolyte is shown to be lithium insertion while preventing the formation of a spinel structure that leads to a major formation of manganese oxy hydroxides.     

Spectrophotometric determination of traces of metallic ions and their mixtures with 3-methyl-1,2-cyclopentanodione dithiosemicarbazone: II. Bismuth,copper, and cobalt

The properties of bismuth, copper, and cobalt complexes of 3-methyl-1,2-cyclopentanodione dithiosemicarbazone and the optimal conditions for their formation are described. The complexes were used with success in the photometric determination of traces of bismuth, copper, and cobalt. Nine procedures are proposed for the accurate analysis of Bi(III)-Cu(II), Bi(III)-Co(II), Zn(II)-Cu(II), Cd(II)-Cu(II), Hg(II)-Cu(II), Zn(II)-Co(II), Cd(II)-Co(II), Hg(II)-Co(II), and Cu(II)-Co(II) mixtures. Satisfactory results were obtained.     

Covalent hybrid of spinel manganese-cobalt oxide and graphene as advanced oxygen reduction electrocatalysts

Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co(3)O(4) nanoparticles, a manganese-cobalt spinel MnCo(2)O(4)/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near-edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrids results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edge and nitrogen K-edge XANES showed strongly perturbed C-O and C-N bonding in the N-rmGO sheet, suggesting the formation of C-O-metal and C-N-metal bonds between N-doped graphene oxide and spinel oxide nanoparticles. Co L-edge and Mn L-edge XANES suggested substitution of Co(3+) sites by Mn(3+), which increased the activity of the catalytic sites in the hybrid materials, further boosting the ORR activity compared with the pure cobalt oxide hybrid. The covalently bonded hybrid afforded much greater activity and durability than the physical mixture of nanoparticles and carbon materials including N-rmGO. At the same mass loading, the MnCo(2)O(4)/N-graphene hybrid can outperform Pt/C in ORR current density at medium overpotentials with stability superior to Pt/C in alkaline solutions.     

The role of bismuth as promoter in Pd–Bi catalysts for the selective oxidation of glucose to gluconate

Bismuth is a well-established promoter of noble metal-based catalysts for the selective liquid phase oxidation of alcohols, aldehydes and carbohydrates with molecular oxygen. Experiments were carried out to improve the understanding of the promoting role of bismuth in bimetallic Pd–Bi catalysts used for the selective oxidation of glucose to gluconate. In relationship with the fact that these catalysts undergo substantial bismuth leaching under the reaction conditions, particular attention was paid to the possible role played by the soluble fraction of bismuth in the oxidative process. Carbon-supported Pd–Bi/C catalysts characterized by various Bi–Pd compositions (0.33≤Bi/Pd≤3.0,10 wt.%Pd+Bi) were prepared from acetate-type precursors, tested under various experimental conditions and analyzed by X-ray diffractometry and X-ray photoelectron spectroscopy (XPS). Whatever the initial catalyst composition, the surface intensity ratio measured by XPS in used catalysts lies in the range 0.4–0.6, suggesting that the dynamic state of the catalyst involves the association of one Bi and two to three Pd atoms. The leaching process and the promoting effect itself are discussed in line with the formation of Bi–glucose and Bi–gluconate complexes present in solution but also as adsorbed species at the catalyst surface. The performances of a monometallic Pd/C catalyst are significantly improved in the presence of adequate amounts of soluble Bi. The involvement of the soluble fraction of bismuth in the overall mechanistic scheme of glucose oxidative dehydrogenation is suggested. The detrimental effect of large amounts of soluble bismuth is attributed to a too extensive adsorption of Bi–glucose complexes on the surface Pd atoms.     

Cobalt promoted copper manganese oxide catalysts for ambient temperature carbon monoxide oxidation

Low levels of cobalt doping (1 wt%) of copper manganese oxide enhances its activity for carbon monoxide oxidation under ambient conditions and the doped catalyst can display higher activity than current commercial catalysts.     

In situ transmission electron microscopy observation of the growth of bismuth oxide whiskers.

Growth of bismuth oxide (most probably Bi2O3) was observed in situ in a transmission electron microscope. Bi liquid particles were dispersed on the substrates of diamond or SiO2. Introduction of oxygen up to 5 x 10-4 Pa resulted in formation of bismuth oxide (most probably Bi2O3) whiskers. The growth mechanism of the whisker was discussed in terms of a vapor-liquid-solid (VLS) mechanism. It is suggested that the liquid droplet of Bi acts as a physical catalyst for growth of bismuth oxide (most probably Bi2O3) whiskers.