Catalytic Decomposition of Methane Over M–Co–Al Catalysts (M = Mg,Ni, Zn,Cu)

Abstract  

The catalytic decomposition of methane over M–Co–Al (M = Mg, Ni, Zn, Cu) was studied. The samples were prepared by co-precipitation and characterized by S_BET, TGA, DTA, TPR and XRD. The carbon produced in the reaction was characterized by SEM and TPO. Activity tests were carried out in a thermobalance between 500 and 750 °C. The results show that the textural properties of the calcined samples did not change significantly with the partial substitution of Co by Mg, Ni, Zn or Cu. On the other hand, there were marked differences in the reduced samples. There was a strong influence on the reducibility of cobalt oxides in the presence of Ni or Cu. Nickel promoted the reduction of Co₃O₄ at the same temperature as the NiO phase, whereas copper strongly decreased the reduction temperature of both Co₃O₄ and CoAl₂O₄ due to a synergistic effect between Cu and Co. The sample containing Cu resulted in low catalytic activity in the whole temperature range because the reduction conditions promoted the formation of a Cu–Co alloy. In the reaction carried out at 700 °C, the observed activity was Co–Al > Mg–Co–Al > Ni–Co–Al. All the samples were deactivated by encapsulation under these conditions due to high rates of carbon deposition. The carbon produced was mainly carbon nanotubes, except for the Cu–Co–Al sample, which produced mostly amorphous carbon.     

Solvo-displacement route to ternary compounds Ag–M–S (M=Ga,Cu or Hg)

Ternary compounds AgGaS₂, Cu_0.8Ag_1.2S and Ag₂HgS₂ were prepared at 200 °C via a solvo-displacement route. The products were characterized with X-ray powder diffraction patterns, X-ray photoelectron spectra and transmission electron microscope images. A possible formation mechanism of solvo-displacement reaction was proposed.     

M1 to M2 Phase Transformation and Phase Cooperation in Bulk Mixed Metal Mo–V–M–O (M=Te, Nb) Catalysts for Selective Ammoxidation of Propane

In the present study we systematically explored hydrothermal synthesis of bulk mixed metal Mo–V–(Te–Nb)–O catalysts and investigated the bulk characteristics of the resulting M1 and M2 phases as well as their roles in the selective ammoxidation of propane. It was found that unlike Mo–V–Te–Nb–O M1 phases, the Mo–V–Te–O M1 phases may be quantitatively transformed into M2 phases of the same chemical composition indicating that Nb stabilizes the M1 structure. The stabilizing role of Nb and Te was further observed in high resolution TEM studies of Mo–V–(Te–Nb)–O catalysts which indicated that structural order and the M1 phase domain size progressively decreased in this order: Mo–V–Te–Nb–O > Mo–V–Te–O > Mo–V–O. The cooperation between the M1 and M2 phases in propane ammoxidation to acrylonitrile was observed only at low propane conversions suggesting that the M1 phase is the only crystalline phase required for the activity and selectivity of the Mo–V–Te–Nb–O catalysts in propane ammoxidation to acrylonitrile at practical propane conversions.     

土法2M～4X

1.序言 2M～4X与2,4～D同是属于氯代苯氧乙酸类化合物,囚此二者的效果是极其相似的,2M～4X其主要是用于谷物,亚麻仁、亚麻类化合物,作选择性除草剂。 2M～4X,是利用煤焦油副产～磷甲酚与一氯醋酸先缩合后氯化的方法制得的。如果磷甲酚与一氯     

Comparison of the Activity of Pd–M (M: Ag,Co, Cu,Fe, Ni,Zn) Bimetallic Electrocatalysts for Oxygen Reduction Reaction

Topics in Catalysis - Carbon-supported 7.5 wt% Pd–2.5 wt% M (M: Ag, Co, Cu, Fe, Ni, Zn) bimetallic catalysts were synthesized via wet impregnation and assessed as...     

Ceramic monolith supported Mn–Ce–M ternary mixed-oxide (M=Cu,Ni or Co) catalyst for VOCs catalytic oxidation

The MO_x (M=Cu, Ni or Co) modified manganese-cerium mixed-oxide catalysts supported on ceramic monolith were prepared by sol-gel method and examined for the catalytic combustion of o-xylene. Results show that the addition of CuO_x could significantly enhance the catalytic properties of the monolithic catalysts, which may be correlated with the Mn-Cu synergistic interaction. The effects of the preparation parameters including the Cu content, the total amount of active phase and the calcination temperature and time, as well as the reaction conditions, i.e., the space velocity and concentration of o-xylene, on the catalytic performance for the combustion of o-xylene were also investigated. It is shown that the MnCeCu_0.4/monolith catalyst with the active phase loading of 11.4 wt% and calcined at 500 °C for 3 h displays the highest catalytic activity. When the concentration of o-xylene is 1000 ppm and the space velocity is 10,000 h⁻¹, the temperature at which 90% o-xylene conversion is reached is 277 °C. It is also seen that the optimum catalyst has a good catalytic stability and exhibits an excellent activity not only at a rather high space velocity but also within a wide range of o-xylene concentration. Furthermore, the optimum catalyst also show the high combustion performance for other hydrocarbons, e.g., n-butanol and styrene.     

Microwave dielectric properties of ceramics based on CaTiO3–LnMO3 System (Ln–La,Nd; M–Al,Ga)

Structural features and microwave dielectric properties of LnMO₃–CaTiO₃ samples (where Ln stands for La or Nd, M stands for Al or Ga) are studied. Solid solutions with the rhombic perovskite structure are shown to be formed with increasing molar concentration of LnMO₃ up to ∼35% (for Ln–Nd, M–Al) or ∼40% (for Ln–La, M–Ga). Further increase of the neodymium aluminate or lanthanum gallate molar content in the solid solution up to 70% leads to formation of solid solutions with the tetragonal perovskite structure. A family of promising ceramics for application in the microwave technology with dielectric permittivity lying within the range from 43 to 48, the dielectric permittivity temperature coefficient being near to zero, and heightened quality factor (Q·f ⩾40,000 GHz) are obtained.     

Universal Brønsted-Evans-Polanyi Relations for C–C,C–O,C–N,N–O,N–N,and O–O Dissociation Reactions

Abstract  

It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals.     

Catalytic combustion of methane over M (Ni,Co, Cu) supported on ceria–magnesia

The catalytic activity of a series of M(= Ni, Co, Cu)/(CeO₂)_x–(MgO)_1 − x catalysts for methane combustion was investigated. (CeO₂)_x–(MgO)_1 − x supports were prepared by a sol-gel method. The influence of CeO₂ content and active components such as Ni, Co and Cu are discussed. The results indicate that the activity of the catalysts depends strongly on CeO₂ content. The Ni/(CeO₂)_0.1 − (MgO)_0.9 catalyst showed the highest catalytic activity and good thermal stability for methane combustion. The highly dispersed NiO is the main active site for methane combustion. Fresh M (Ni, Co and Cu)/(CeO₂)_0.1–(MgO)_0.9 catalysts showed that the activity of CuO for methane combustion was slightly higher than that of NiO and CoO, while the thermal stability increased in the order Cu < Co < Ni. Cu/(CeO₂)_0.1–(MgO)_0.9 catalyst was sintered after a second evaluation. Consequently, (CeO₂)_0.1–(MgO)_0.9 is deemed to be a good support for Ni.     

Microstructure and electrical properties of ZnO–ZrO2–Bi2O3–M3O4 (MCo,Mn) varistors

Phase evolution, microstructure and the electrical properties of ZrO₂-added pyrochlore-free ZnO–Bi₂O₃–M₃O₄ (MCo, Mn) varistors have been studied as functions of ZrO₂ content up to 10 vol% and the sintering temperature between 900 and 1300 °C. Zirconia remained as intergranular second phase particles up to 1100 °C, which retarded densification and inhibited the grain growth of ZnO. At higher temperatures, on the contrary, ZrO₂ particles began to be entrapped in ZnO grains and irreversibly transform from monoclinic to stable cubic phase dissolving transition metal ions. The grain size of ZnO decreased with increasing ZrO₂ content, and increased with the increase of the sintering temperature. Accordingly breakdown voltage changed with both ZrO₂ content and the sintering temperature as was expected. Nonlinear coefficient (α) depended primarily on the sintering temperature: it increased to >40 up to 1000 °C, and significantly decreased to <30 at higher temperatures probably due to the volatilization of Bi₂O₃. While the specimens sintered at 1200 °C or above had relatively high leakage current (I_L) and large clamping ratio (C_R), those with ZrO₂ content of 0.5–5.0 vol% and sintered below 1200 °C revealed low I_L of ⩽20 μA/cm² and C_R well below 2.0. In spite that varistor characteristics of ZrO₂-added system could not match those of commercial ZnO varistors, its low temperature sinterability and ease of breakdown voltage control via ZrO₂ content without a serious loss of its figures of merit are worth noticing, particularly for multi-layered chip varistor (MLV) application.     

Flame sprayed tri-metallic Pt–Sn–X/Al2O3 catalysts (X = Ce,Zn, and K) for propane dehydration

Trimetallic nanocrystalline Pt–Sn–X/Al₂O₃ catalysts (X = Ce, Zn, and K) consisting of 0.3 wt.% Pt, 1 wt.% Sn, and 0.5 wt.% X have been prepared by one-step flame spray pyrolysis (FSP). As shown by the X-ray diffraction (XRD) and the transmission electron microscopy (TEM) results, the as-synthesized FSP-made catalysts were consisted of single-crystalline γ-alumina particles with average primary particle sizes 8 to 9 nm. The N₂ physisorption results revealed that all the catalysts contained only the macropore structure. The catalytic properties of the FSP-made catalysts were investigated in the dehydration of propane. Addition of Ce during FSP synthesis resulted in higher Pt dispersion as well as improved catalytic activity and stability than the non-promoted Pt–Sn/Al₂O₃. An opposite trend was found with the ones doped with Zn and K in which high surface coverage of Zn and K resulted in a significant loss of Pt active sites. The mechanism for the formation of the trimetallic nanoparticles during one-step FSP synthesis appeared to depend strongly on the differences in the vapor pressure of the metals and the alumina support in flame.     

无铅或少铅钙钛矿CH3NH3M1-xPbxX3(M=Sn,Sr;X=Cl,Br,I)太阳能电池的研究进展

本文综述了Sn2+或Sr2+取代的无铅或少铅钙钛矿CH3NH3PbX3 (X=Cl,Br,I)的结构及其主要的制备方法,评述了各种方法的优缺点.简要介绍了无铅或少铅钙钛矿材料的能隙以及材料的稳定性对太阳能电池的影响,并对其发展前景进行了展望.     

New catalytic functions of Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys in the conversions of methanol

Pd and Pt supported on ZnO, Ga₂O₃ and In₂O₃ exhibit high catalytic performance for the steam reforming of methanol, CH₃OH+H₂OCO₂+3HH₂, and the dehydrogenation of methanol to HCOOCH₃, 2CH₃OHHCOOCH₃+2HH₂. Combined results with temperature-programmed reduction (TPR) and XRD method revealed that Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys were produced upon reduction. Over the catalysts having the alloy phase, the reactions proceeded selectively, whereas the catalysts having metallic phase exhibited poor selectivities.     

Separation of Xenon and Krypton in the Metal–Organic Frameworks M2(m-dobdc) (M=Co,Ni)

The separation of Xe and Kr from air is challenging owing both to the very low atmospheric concentrations of these gases and the need for their distillation at cryogenic temperatures. Alternatively, separation processes based on adsorption could provide a less energy-intensive route to the isolation of these gases. Here, we demonstrate that the metal–organic frameworks M₂(m-dobdc) (M=Co, Ni; m-dobdc⁴⁻=4,6-dioxido-1,3-benzenedicarboxylate) effectively separate Xe and Kr at ambient temperatures based on the different adsorption enthalpies of each gas at the coordinatively-unsaturated M²⁺ sites in each material. In situ Xe- and Kr-dosed powder X-ray diffraction studies further reveal key differences in the binding of Xe and Kr within the materials. In particular, while both gases adsorb near the framework open metal sites at 200 K, much higher Xe occupancies are observed at these sites relative to Kr, corroborating a stronger interaction of the polarizing M²⁺ cations with Xe. Further, while krypton is only found located above the open metal sites, two additional adsorption sites are observed for xenon, correlating with the stronger adsorption of Xe over Kr in these materials. These results suggest the possible utility of employing M₂(m-dobdc) materials in the adsorptive separation of Xe and Kr.     

X油田M区精细地震构造解释技术探讨

X油田M区断层广泛发育,构造复杂,是典型的复杂断块油藏。该区开发程度已经进入中后期,构造的刻画精度在一定程度上影响着该区的开发水平。为了提高该区的构造认识精度,通过研究总结出以断层解释技术和构造成图技术为核心的地震精细构造解释技术,其中包括层位精细标定技术、三维断层解释、沿层相干体切片、井控变速成图等。这些技术在该区广泛运用,并根据认识成果指导实际生产,取得了良好效果。     

Chemistry of soluble β-diketiminatoalkaline-earth metal complexes with M-X bonds (M=Mg, Ca, Sr; X=OH, Halides, H)

Victor Grignard's Nobel Prize-winning preparation of organomagnesium halides (Grignard reagents) marked the formal beginning of organometallic chemistry with alkaline earth metals. Further development of this invaluable synthetic route, RX+Mg→RMgX, with the heavier alkaline earth metals (Ca and Sr) was hampered by limitations in synthetic methodologies. Moreover, the lack of suitable ligands for stabilizing the reactive target molecules, particularly with the more electropositive Ca and Sr, was another obstacle. The absence in the literature, until just recently, of fundamental alkaline earth metal complexes with M-H, M-F, and M-OH (where M is the Group 2 metal Mg, Ca, or Sr) bonds amenable for organometallic reactions is remarkable. The progress in isolating various unstable compounds of p-block elements with β-diketiminate ligands was recently applied to Group 2 chemistry. The monoanionic β-diketiminate ligands are versatile tools for addressing synthetic challenges, as amply demonstrated with alkaline earth complexes: the synthesis and structural characterization of soluble β-diketiminatocalcium hydroxide, β-diketiminatostrontium hydroxide, and β-diketiminatocalcium fluoride are just a few examples of our contribution to this area of research. To advance the chemistry beyond synthesis, we have investigated the reactivity and potential for applications of these species, for example, through the demonstration of dip coating surfaces with CaCO(3) and CaF(2) with solutions of the calcium hydroxide and calcium fluoride complexes, respectively. In this Account, we summarize some recent developments in alkaline earth metal complex chemistry, particularly of Mg, Ca, and Sr, through the utilization of β-diketiminate ligands. We focus on results generated in our laboratory but give due mention to work from other groups as well. We also highlight the closely related chemistry of the Group 12 element Zn, as well as the important chemistry developed by other groups using the complexes we have reported. Although Mg and Ca are more abundant in living organisms, no other metal has as many biological functions as Zn. Thus Zn, the nontoxic alternative to the heavier Group 12 elements Cd and Hg, occupies a unique position ripe for further exploration.