CO Hydrogenation over Re-Co Bimetallic Catalysts Supported over SiO2, Al2O3 and NaY Zeolite

The promotion of rhenium on the reduction of Co²⁺ ions in cobalt based samples prepared by various methods, such as, sol/gel technique, incipient wetness impregnationof Al₂O₃ and NaY, has been investigated in the CO hydrogenation. Among the samples the reducibility of the sol/gel, Re-Co/Al₂O₃ and Re-Co/NaY(IM) were the highest compared to Re-Co/NaY (IE) [8]. In addition to facilitating reduction of Co²⁺ ions, the rhenium increased the rate of reaction and the formation ofC₅₊ hydrocarbons at 10 bar pressures. The samples pretreated in various manner, revealed an about five fold increase in activity and an increase in the chain length in the NaYsupported sample while the activity and selectivity changed in various way in the sol/gel prepared samples. Simultaneously, rhenium increased the amount of olefins of low carbon numbers.In the mechanism the rhenium provides an action preventing fast deactivation of cobalt.     

Cu_xCo_(1-x)/Al_2O_3/FeCrAl整体式催化剂上甲苯催化燃烧(英文)

以FeCrAl合金薄片为基底,Al2O3浆料为过渡胶体,不同摩尔比的Cu、Co为催化活性组分,制备了一系列CuxCo1-x/Al2O3/FeCrAl(x=0-1)新型整体式催化剂.采用X射线粉末衍射(XRD),扫描电子显微镜(SEM),X光电子能谱(XPS)和程序升温还原(TPR)等手段对催化剂的结构进行了表征.在微型固定床反应器上评价了催化剂的催化甲苯燃烧性能.研究结果表明:在所制备的整体式催化剂上,当Cu含量比较低时,形成了Cu-Co-O固溶体;当Cu含量比较高时,可以测得CuO的衍射峰.催化剂表面颗粒大小和形貌与Cu、Co摩尔比密切相关.在催化剂表面,Co以Co2+和Co3+价态存在,而Cu主要以Cu2+价态存在.催化剂中的Cu可以改善Co的氧化还原性,从而有利于催化剂活性的提高.在所制备的催化剂中,Cu0.5Co0.5/Al2O3/FeCrAl催化剂具有最好的活性,甲苯在374oC可以完全催化燃烧消除.     

富氧条件下Co/ZSM-5催化剂对C3H8选择还原NOx的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C₃H₈选择性催化还原NO_x性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co³⁺和Co²⁺物种,也有孔内的Co²⁺离子。富氧条件下Co/ZSM-5催化剂上C₃H₈选择性催化还原NO_x的活性主要与ZSM-5载体孔外表面分散的CoO_x物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoO_x物种中钴离子可还原能力增强,C₃H₈选择性催化还原NO_x的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NO_x的转化率和催化剂比速率（k）的下降。孔外表面Co₃O₄晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C₃H₈的氧化燃烧,使C₃H₈选择性催化还原NO_x的活性降低。     

富氧条件下Co/ZSM-5催化剂对C_3H_8选择还原NO_x的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C3H8选择性催化还原NOx性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co3+和Co2+物种,也有孔内的Co2+离子。富氧条件下Co/ZSM-5催化剂上C3H8选择性催化还原NOx的活性主要与ZSM-5载体孔外表面分散的CoOx物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoOx物种中钴离子可还原能力增强,C3H8选择性催化还原NOx的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NOx的转化率和催化剂比速率(k)的下降。孔外表面Co3O4晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C3H8的氧化燃烧,使C3H8选择性催化还原NOx的活性降低。     

Effects of Activation Atmospheres on Structure and Activity of Mo-based Catalyst for Synthesis of Higher Alcohols

Activated carbon supported Mo-based catalysts were prepared and reduced under different activation atmospheres, including pure H₂, syngas (H₂/CO=2/1), and pure CO. The catalysts structures were characterized by X-ray diffraction, X-ray absorption fine structure, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The catalytic performance for the higher alcohol synthesis from syngas was tested. The pure H₂ treatment showed a high reduction capacity. The presence of a large amount of metallic Co⁰. and low valence state Mo^φ+ (0<φ<2) on the surface suggested a super activity for the CO dissociation and hydrogenation, which promoted hydrocarbons formation and reduced the alcohol selectivity. In contrast, the pure CO-reduced catalyst had a low reduction degree. The Mo and Co species at the catalyst mainly existed in the form of Mo⁴⁺ and Co²⁺. The syngas-reduced catalyst showed the highest activity and selectivity for the higher alcohols synthesis. We suggest that the syngas treatment had an appropriate reduction capacity that is between those of pure H₂ and pure CO and led to the coexistence of multivalent Co species as well as the enrichment of Mo^δ+ on the catalyst's surface. The synergistic effects between these active species provided a better cooperativity and equilibrium between the CO dissociation, hydrogenation and CO insertion and thus contributed beneficially to the formation of higher alcohols.     

Synthesis and characterization of La1+xSr2−xCoMnO7−δ (x=0,0.2; δ=0,1)

The n=2 Ruddlesden-Popper phases LaSr₂CoMnO₇ and La_1.2Sr_1.8CoMnO₇ have been synthesized by a sol-gel method. The O6-type phases LaSr₂CoMnO₆ and La_1.2Sr_1.8CoMnO₆ were produced by reduction of the O7 phases under a hydrogen atmosphere. The materials crystallize in the tetragonal I4/mmm space group with no evidence of long-range cation order in the neutron and electron diffraction data. Oxygen vacancies in the reduced materials are located primarily at the common apex of the double perovskite layers giving rise to square pyramidal coordination around cobalt and manganese ions. The oxidation states Co³⁺/Mn⁴⁺ and Co²⁺/Mn³⁺ predominate in the as-prepared and reduced materials, respectively. The materials are spin glasses at low temperature and the dominant magnetic interactions change from ferro- to antiferromagnetic following reduction.     

Cobalt loss from Co-ZrO2 catalyst for Fischer-Tropsch synthesis in continuously stirred tank reactor

The cobalt loss of the co-precipitated Co-ZrO₂ catalyst was investigated during the Fischer-Tropsch synthesis in a continuously stirred tank reactor. The cobalt species in the produced water originating from the transformation of CoO into Co²⁺ ions was tested by TPR, XRD and XPS. Furthermore, reduction at a relatively higher temperature resulted in a lower loss of cobalt.     

Magnetic susceptibility and specific heat of uranium double perovskite oxides Ba2MUO6 (M=Co, Ni)

Double perovskites Ba₂MUO₆ (M=Co, Ni) were prepared by the solid-state reaction. X-ray diffraction measurements show that both cobalt (nickel) and uranium ions are ordered in the NaCl type over the six-coordinate B sites of the perovskite ABO₃. Detailed magnetic susceptibility and specific heat measurements show that Ba₂CoUO₆ and Ba₂NiUO₆ order ferromagnetically at 9.1 and 25 K, respectively. From the analysis of the magnetic specific heat, the ground states of the Co²⁺ and Ni²⁺ ions were determined.     

Effect of copper source on the structure–activity of CuAl2O4 spinel catalysts for CO hydrogenation

Due to the complexity of the structure–activity relationship of the CuAl₂O₄ spinel catalyst, optimization of the catalyst structure is a great challenge. In this paper, three different CuAl₂O₄ spinel catalysts were prepared by the solid-phase method using copper hydroxide, copper nitrate, and copper oxide as the copper source, respectively, to study the difference in the structure of CuAl₂O₄ spinel catalysts induced by the raw materials and the catalytic behavior for CO hydrogenation. The structure of CuAl₂O₄ spinel catalyst was characterized by XRD, BET, SEM, TEM, H₂-TPR and XPS. The activity of CO hydrogenation over the CuAl₂O₄ spinel catalyst without pre-reduction was evaluated in the slurry reactor. The results demonstrated that different copper sources had obvious influence on the CuAl₂O₄ spinel texture properties, surface enrichment degree, as well as decomposition and reduction ability, which further regulated the ratio of Cu⁺/Cu⁰ and thus affected the catalytic performance, especially the alcohol distribution. The CuAl₂O₄ spinel, employing copper hydroxide as the copper source, showed better selectivity of C₂₊OH, which was assigned to a higher ratio of Cu⁺/Cu⁰, along with larger pore size and pore volume. Moreover, the synergistic effect between Cu⁰ and γ-Al₂O₃ improved the selectivity of dimethyl ether.     

Crystal structure, microstructure and reducibility of LaNixCo1−xO3 and LaFexCo1−xO3 Perovskites (0<x≤0.5)

Nickel and iron substituted LaCoO₃ with rhombohedrally distorted perovskite structure were obtained in the temperature range of 600-900 °C by thermal decomposition of freeze-dried citrates and by the Pechini method. The crystal structure, morphology and defective structure of LaCo_1−xNi_xO₃ and LaCo_1−xFe_xO₃ were characterized by X-ray diffraction and neutron powder diffraction, TEM and SEM analyses and electron paramagnetic resonance spectroscopy. The reducibility was tested by temperature programmed reduction with hydrogen. The products of the partial and complete reduction were determined by ex-situ XRD experiments. The replacement of Co by Ni and Fe led to lattice expansion of the perovskite structure. For perovskites annealed at 900 °C, there was a random Ni, Fe and Co distribution. The morphology of the perovskites does not depend on the Ni and Fe content, nor does it depend on the type of the precursor used. LaCo_1−xNi_xO₃ perovskites (x>0.1) annealed at 900 °C are reduced to Co/Ni transition metal and La₂O₃ via the formation of oxygen deficient Brownmillerite-type compositions. For LaCo_1−xNi_xO₃ annealed at 600 °C, Co/Ni metal, in addition to oxygen-deficient perovskites, was formed as an intermediate product at the initial stage of the reduction. The interaction of LaCo_1−xFe_xO₃ with H₂ occurs by reduction of Co³⁺ to Co²⁺ prior to the Fe³⁺ ions. The reducibility of Fe-substituted perovskites is less sensitive towards the synthesis procedure in comparison with that of Ni substituted perovskites.     

Mosaic CuI−CuII−InIII 2D Perovskites: Pressure-Dependence of the Intervalence Charge Transfer and a Mechanochemical Alloying Method

The perovskite (BA)₄[Cu^II(Cu^IIn^III)_0.5]Cl₈ ( 1_BA ; BA⁺=butylammonium) allows us to study the high-pressure structural, optical, and transport properties of a mixed-valence 2D perovskite. Compressing 1_BA reduces the onset energy of Cu^I/II intervalence charge transfer from 1.2 eV at ambient pressure to 0.2 eV at 21 GPa. The electronic conductivity of 1_BA increases by 4 orders of magnitude upon compression to 20 GPa, when the activation energy for conduction decreases to 0.16 eV. In contrast, Cu^II perovskites achieve similar conductivity at ≈50 GPa. The solution-state synthesis of these perovskites is complicated, with more undesirable side products likely from the precursor mixtures containing three different metal ions. To circumvent this problem, we demonstrate an efficient mechanochemical synthesis to expand this family of halide perovskites with complex composition by simply pulverizing together powders of 2D Cu^II single perovskites and Cu^IIn^III double perovskites.     

Effect of the nature of support and Cu precursor on the activity of copper-containing catalysts in CO oxidation

We have studied the catalytic activity of supported copper-containing catalysts based on ZSM-5, Al₂O₃, and SiO₂ in oxidation of CO. We have established that the difference between the activities of systems with 1.8% copper content obtained from different precursors is determined by the different reducibilities of their active sites, the number of such sites, and the distribution of the metal ions. The fact that the activity is highest for 1.8% Cu-ZSM-5 obtained from copper acetate is due to the relatively higher number of associated Cu²⁺ cations in square planar coordination in a non-lattice oxygen environment, which have high reducibility, and the higher overall oxygen content O_ads + O_OH in the surface layer of the catalyst.     

Catalytic performance of Fe modified K/MO2C catalyst for CO hydrogenation

Fe modified and un-modified K/Mo2C were prepared and investigated as catalysts for CO hydrogenation reaction. Compared with K/Mo2C catalyst, the addition of Fe increased the production of alcohols, especially the C2+OH. Meanwhile, considerable amounts of C5+ hydrocar- bons and C2= -C4= were formed, whereas methane selectivity greatly decreased. Also, the activity and selectivity of the catalyst were readily affected by the reaction pressure and temperature employed. According to the XPS results, Mo4+ might be responsible for the production of alcohols, whereas the low valence state of Mo species such as Mo0 and/or Mo2+ might be account for the high activity and selectivity toward hydrocarbons.     

Characteristics of Active Site Formation in Co-Containing Catalysts for CO Oxidation on Chemically Different Supports

We have studied the catalytic activity in CO oxidation for cobalt-containing (1.2 mass % Co) catalysts on different supports: ZSM-5, Al₂O₃, SiO₂, and ERI. Using X-ray photoelectron spectroscopy (XPS), diffuse reflection electronic spectroscopy, and thermal programmed reduction we have established that the differences in the activity of Co-containing catalysts are due to different localization of the cobalt cations, the nature of their distribution in the surface layer of the catalyst, and the presence of cobalt ions Co_Oh in an environment of intralattice oxygen which have high reducibility.     

Alloying a single and a double perovskite: a Cu+/2+ mixed-valence layered halide perovskite with strong optical absorption

Introducing heterovalent cations at the octahedral sites of halide perovskites can substantially change their optoelectronic properties. Yet, in most cases, only small amounts of such metals can be incorporated as impurities into the three-dimensional lattice. Here, we exploit the greater structural flexibility of the two-dimensional (2D) perovskite framework to place three distinct stoichiometric cations in the octahedral sites. The new layered perovskites A^I₄[Cu^II(Cu^IIn^III)_0.5Cl₈] (1, A = organic cation) may be derived from a Cu^I–In^III double perovskite by replacing half of the octahedral metal sites with Cu²⁺. Electron paramagnetic resonance and X-ray absorption spectroscopy confirm the presence of Cu²⁺ in 1. Crystallographic studies demonstrate that 1 represents an averaging of the Cu^I–In^III double perovskite and Cu^II single perovskite structures. However, whereas the highly insulating Cu^I–In^III and Cu^II perovskites are colorless and yellow, respectively, 1 is black, with substantially higher electronic conductivity than that of either endmember. We trace these emergent properties in 1 to intervalence charge transfer between the mixed-valence Cu centers. We further propose a tiling model to describe how the Cu⁺, Cu²⁺, and In³⁺ coordination spheres can pack most favorably into a 2D perovskite lattice, which explains the unusual 1 : 2 : 1 ratio of these cations found in 1. Magnetic susceptibility data of 1 further corroborate this packing model. The emergence of enhanced visible light absorption and electronic conductivity in 1 demonstrates the importance of devising strategies for increasing the compositional complexity of halide perovskites.

A novel 2D halide perovskite with stoichiometric quantities of Cu⁺, Cu²⁺, and In³⁺ in the inorganic slabs shows emergent properties not seen in Cu^II or Cu^I–In^III perovskites, including enhanced visible-light absorption and electronic conductivity.     

IR spectral study of the effect of the reaction medium on the state of cobalt in a 10% Co/Al2O3 catalyst for aliphatic hydrocarbons from CO and H2

Diffuse scattering IR spectroscopy was used to study the 10% Co/Al₂O₃ catalyst for the synthesis of aliphatic hydrocarbons from CO and H₂. Ionic and metallic cobalt forms were identified in the IR spectroscopy. The adsorption of CO on these forms is accompanied by the appearance of linear and bridged complexes. After prolonged treatment of the catalyst by a CO + 2H₂ mixture, the ions and surface of metallic cobalt remain available for the adsorption of CO. Modification of the surface of metallic cobalt occurs upon the action of the reaction medium. This modification is seen in a bathochromic displacement of the IR bands for the adsorbed and linear CO forms. This displacement is accompanied by a reduction in the strength of the metal-carbon bond in the Co^o-CO complex.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2640–2643, November, 1990.     

碳纳米管促进的Co-Mo-K硫化物基催化剂用于合成气制低碳混合醇

 以自行制备的多壁碳纳米管(CNT)作为添加剂,制备共沉淀型CNT促进的Co-Mo-K硫化物基催化剂. 实验发现,与未添加CNT的催化剂相比,添加少量CNT可显著提高CO的加氢转化活性和生成低碳醇的选择性. 在5.0 MPa, 623 K, V(CO)∶V(H2)∶V(N2)=45∶45∶10, GHSV=3600 ml/(g·h)的反应条件下, Co1Mo1K0.3-10%CNT催化剂上CO的转化率达21.6%, 相应的总醇(C1～4醇)时空产率为241.5 mg/(g·h), 产物中C2+醇/C1醇=1.39 (C基选择性比). 添加少量CNT并不会导致Co1Mo1K0.3硫化物基催化剂上CO加氢反应表观活化能发生明显变化,但却导致工作态催化剂表面催化活性Mo物种(Mo4+)的摩尔百分率有所提高; 另一方面, CNT促进的催化剂对H2有更强的吸附活化能力,并能在相当大程度上抑制水煤气变换副反应的发生. 这些因素有利于提高催化剂的活性和选择性.     

Controlling carbon monoxide emissions from automobile vehicle exhaust using copper oxide catalysts in a catalytic converter

Carbon monoxide (CO) is a very poisonous gas present in the atmosphere. It has significant effects on human beings, animals, plants and the climate. Automobile vehicle exhaust contributes 64% of the CO pollution in urban areas. To control this exhaust pollution, various types of catalysts in catalytic converters have been investigated. Increasing costs of noble metals as a catalyst in automobile vehicles motivates the investigation of material that can be substituted for noble metals. Among the non-noble metals, copper (Cu) is found to be the most capable and highly active catalyst for CO oxidation, compared to precious metal catalysts. Lower cost, easy availability and advance preparation conditions with stabilizers, promoters and so on, make Cu a good choice as an auto exhaust purification catalyst. The oxidation of CO proceeds very quickly over Cu°, followed by Cu⁺ and Cu²⁺. The Cu₂O catalyst is more active in an O₂-rich atmosphere than in O₂-lean conditions. The reduced species of copper (Cu⁰, Cu⁺) are essential for better CO oxidation but smaller Cu particles could be less active than the higher ones. There is a great deal of research available on the Cu catalyst for CO oxidation, but there is a gap in the literature for a review article individually applied to the Cu catalyst for CO oxidation. To fill this gap, the present review updates information on Cu catalysts in the purification of exhaust gases.     

Oxo-bridged Tri- and Tetra-nuclear Cobalt Complexes Supported with Amide-Based Nitrogen Donor Ligands

This work presents two mixed-valent μ₃-oxo-bridged trinuclear [(Co²⁺)₂Co³⁺] complexes 1 and 2 and a μ₄-oxo-bridged tetranuclear [Co²⁺₄] complex 3 . Crystal structures of 1 and 2 showed the presence of triangular complexes having two Co²⁺ and one Co³⁺ centers bridged by a μ³-oxo group. In contrast, complex 3 exhibited a tetrahedrally arranged μ₄-oxo-bridged [Co²⁺₄] core. A significant feature is the stabilization of unusual μ-oxo-bridged complexes exclusively supported with all nitrogen donor ligands. The X-ray photoelectron spectroscopy confirmed the multiple oxidation states of cobalt ions in these complexes. Such oxo-bridged cobalt complexes were investigated for their catalytic activity towards H₂O₂-mediated oxidation of assorted benzyl alcohols.     

Co oxidation with oxygen in the presence of hydrogen on CoO/CeO<Subscript>2</Subscript> and CuO/CoO/CeO<Subscript>2</Subscript> catalysts

The catalytic activity of the CoO/CeO₂ and CuO/CoO/CeO₂ systems in selective CO oxidation in the presence of hydrogen at 20–450°C ([CuO] = 1.0–2.5%, [CoO] = 1.0–7.0%) is reported. The maximum CO conversion (X) decreases in the following order: CuO/CoO/CeO₂ (X = 98–99%, T = 140–170°C) > CoO/CeO₂ (X = 67–84%, T = 230–240°C) > CeO₂ (X = 34%, T = 350°C). TPD, TPR, and EPR experiments have demonstrated that the high activity of CuO/CoO/CeO₂ is due to the strong interaction of the supported copper and cobalt oxides with cerium dioxide, which yields Cu-Co-Ce-O clusters on the surface. The carbonyl group in the complexes Co^δ+-CO and Cu⁺-CO is oxidized by oxygen of the Cu-Co-Ce-O clusters at 140–160°C and by oxygen of the Co-Ce-O clusters at 240°C. The decrease in the activity of the catalysts at high temperatures is due to the fact that hydrogen reduces the clusters on which CO oxidation takes place, yielding Co⁰ and Cu⁰ particles, which are inactive in CO oxidation. The hydrogenation of CO into methane at high temperatures is due to the appearance of Co⁰ particles in the catalysts.