Polystyrene Supported Manganese Complexes: Heterogeneous Catalysts for Oxidation Reactions

Divinyl benzene crosslinked polystyrene supported β-diketone linked complexes of Mn(II) have been prepared, characterized and their role as catalysts in the oxidation of alcohols by Cr(VI) have been studied. The catalytic activity is influenced by the degree of crosslinking of the polymer matrix, distance between the polymer matrix and metal complex, structural environment of the ligand and acidity of the medium. A possible mechanism has also been suggested. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular Engineering of Supported Vanadium Oxide Catalysts Through Support Modification

Highly dispersed, multilayered surface metal oxide catalysts (V₂O₅/MO _x /SiO₂, M = Ti(IV), Zr(IV) or Al(III)) were successfully synthesized by taking into account various factors that govern the maximum dispersion of metal oxide species on silica. The characterization results revealed that the molecular structures of the surface vanadium oxide species on the modified supports are a strong function of environmental conditions. The surface vanadium oxide species under dehydrated conditions are predominantly isolated VO₄ units, similar to the dehydrated V₂O₅/SiO₂ catalysts. Upon hydration, the surface vanadium oxide species on the modified supports consist of polymerized VO₅/VO₆ units and/or less polymerized (VO₃) _n species, which depend on the vanadia content and the specific second metal oxide loading. The surface V cations are found to preferentially interact with the surface metal (Ti, Zr or Al) oxide species on silica. The V(V) cations in the dehydrated state appear to possess both oxygenated ligands of Si(IV)–O^– and M–O^–. Consequently, the reducibility and catalytic properties of the surface vanadium oxide species are significantly altered. The turnover frequencies of the surface VO₄ species on these modified supports for methanol oxidation to redox products (predominantly formaldehyde) increase by more than an order of magnitude relative to the unmodified V₂O₅/SiO₂ catalysts. These reactivity enhancements are associated with the substitution of Si(IV)–O^– oxygenated ligands by less electronegative M–O^– ligands in the O=V(–O–support)₃ structure, which strongly suggests that the bridging V–O–support bonds play a key role in determining the reactivity of the surface vanadium oxide species on oxide supports.     

First In Situ Raman Study of Vanadium Oxide Based SO2 Oxidation Supported Molten Salt Catalysts

In situ Raman spectroscopy at temperatures up to 500°C is used for the first time to identify vanadium species on the surface of a vanadium oxide based supported molten salt catalyst during SO₂ oxidation. Vanadia/silica catalysts impregnated with Cs₂SO₄ were exposed to various SO₂/O₂/SO₃ atmospheres and in situ Raman spectra were obtained and compared to Raman spectra of unsupported model V₂O₅–Cs₂SO₄ and V₂O₅–Cs₂S₂O₇ molten salts. The data indicate that (1) the V^V complex V^VO₂(SO₄)₂ ^3– (with characteristic bands at 1034 cm^–1 due to (V=O) and 940 cm^–1 due to sulfate) and Cs₂SO₄ dominate the catalyst surface after calcination; (2) upon admission of SO₃/O₂ the excess sulfate is converted to pyrosulfate and the V^V dimer (V^VO)₂O(SO₄)₄ ^4– (with characteristic bands at 1046 cm^–1 due to (V=O), 830 cm^–1 due to bridging S–O along S–O–V and 770 cm^–1 due to V–O–V) is formed and (3) admission of SO₂ causes reduction of V^V to V^IV (with the (V=O) shifting to 1024 cm^–1) and to V^IV precipitation below 420°C.     

Characterization and Reactivity of TiO2/SiO2 Supported Vanadium Oxide Catalysts

Several TiO₂/SiO₂ supports and supported vanadium oxide (vanadia) catalysts of varying titania and vanadia content are synthesized and characterized. Titania rutile phase is not detected for the TiO₂/SiO₂ supports even up to a calcinations temperature of 1073 K. The supported vanadia catalysts were also studied for the ethane and propane ODH reaction and compared with TiO₂ (Degussa P25) supported catalysts. Surface vanadia species are present on the titania or silica part of the TiO₂/SiO₂ support depending on the titania and vanadia loading of the catalyst. Depending on the vanadia loading in the V₂O₅/TiO₂/SiO₂ catalyst the anatase to rutile phase transformation may occur below 1073 K. Furthermore, the ODH activity is retained or decreases less rapidly compared to the TiO₂ supported catalyst as the calcination temperature is increased. Consequently, the TiO₂/SiO₂ supported vanadia catalysts do provide certain advantages compared to the TiO₂ (Degussa P25) supported system.     

Vanadium Oxide Based Nanostructured Materials: Novel Oxidative Dehydrogenation Catalysts

Novel vanadium oxide based catalyst derived from the open-framework solid, [Co₃V₁₈O₄₂(H₂O)₁₂(XO₄)]·24 H₂O (X = V, S) (1) catalyses oxidative dehydrogenation of propane to propylene. Catalyst activity was evaluated in the temperature range 250–400 °C with varying gas hourly space velocity (GHSV). At 350 °C and GHSV of 9786 h^?1 and at 1.3% propane conversion the selectivity to propylene was 36.8%. The major products obtained were propylene and CO _x (CO₂ and CO). The ratio of the propylene to CO _x depended directly on the catalytic sites present. Thus, as the amount of the catalyst was decreased, the conversion decreased with an increase in the propylene selectivity and a decrease in the selectivity to carbon oxides—CO _x . The catalyst has been characterized by temperature programmed reduction and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).     

固载杂多酸催化剂研究进展

固载型杂多酸作为一类新型固体酸催化材料,与传统的质子酸催化剂相比,其优点突出,已应用于炼油技术、化工和精细化学品的合成领域.文章对固载型杂多酸催化剂的重要性质和近年来的应用研究进展进行综述.     

Role of CO2 During Oxidative Dehydrogenation of Propane Over Bulk and Activated-Carbon Supported Cerium and Vanadium Based Catalysts

Catalysis Letters - CeO2, V2O5 and CeVO4 were synthesised as bulk oxides, or deposited over activated carbon, characterized by XRD, HRTEM, CO2-TPO, C3H8-TPR, DRIFTS and Raman techniques and tested...     

Elimination of Vanadium and Arsenic from VKCs Catalysts

Abstract

Vanadium and arsenic eliminations from an alkaline leaching solution of spent VKCs catalysts were studied. To this end, several commercial resins or polymers synthesized in the laboratory were evaluated in a solid–liquid batch extraction. Conditions for an effective extraction of vanadium and arsenic were determined. An extraction process, using a glass column, is described for the recovery of the vanadium. The elimination of arsenic by precipitation is proposed.     

Nickel Amine Complexes as Structure-Directing Agents for Aluminophosphate Molecular Sieves: A New Route to Supported Nickel Catalysts

Open framework aluminophosphates (AlPOs) with the framework types CHA, AFI, AEI, SAS and SAV have been prepared using nickel complexes of linear and macrocyclic polyamines as structure-directing agents: The [Ni(diethylenetriamine)₂]²⁺ complex has been used to prepare aluminophosphate-fluoride versions of the CHA and AFI topologies as well as substituted metalloaluminophosphates (MAPOs) and silicoaluminophosphates (SAPOs) with the CHA topology; the nickel complex of the macrocycle 1,4,7,10-tetraazacyclododecane (cyclen) acts as a structure-directing agent for MAPO-18 (AEI topology), and the nickel complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam) and 1,4,8,11-tetramethylcyclam direct the formation of STA-6 (SAS topology) or STA-7 (SAV topology) depending on the inorganic composition and the type of amine added as a cobase to control the synthesis pH. Magnesioaluminophosphate-5 (AFI topology) containing complexed nickel has been prepared using a novel mixed azamacrocycle-quinuclidinium cation as a structure-directing agent. Nickel complex-containing AlPOs and SAPOs with the CHA framework topology have been calcined and used as catalysts for the conversion of butane over the temperature range 375 – 575°C with a WHSV of 1.8 h^-1. The inclusion of nickel increases the rate of conversion and also changes the composition of the products from the full C1–C4 range to pure methane. This behavior is attributed to the reduction of Ni(II) to finely dispersed supported nickel particles.     

Polymer and Silica Supported Tridentate Schiff Base Vanadium Catalysts for the Asymmetric Oxidation of Ethyl Mandelate – Activity,Stability and Recyclability

Homogeneous tridentate Schiff base vanadium catalysts derived from salicylaldehydes and tert‐leucinol or tert‐leucine are known to be excellent catalysts for the asymmetric oxidation of α‐hydroxy esters including ethyl mandelate. Herein, new analogous supported, semi‐soluble and insoluble catalysts are synthesized and their activities relative to the homogeneous catalyst are reported. The new catalysts are characterized by ¹H and ¹³C NMR spectroscopy, mass spectrometry (EI, ESI, FAB), X‐ray crystallography, elemental analysis, gel permeation chromatography (GPC), Fourier transform infrared (FT‐IR) spectroscopy, and nitrogen physisorption. The effects of support material, synthesis procedure, and reaction solvent are examined to probe the utility of these catalysts. Linear poly(styrene) supported catalysts are partially soluble under the reaction conditions, and it is shown that the soluble species contribute significantly to the catalytic reactivity. Insoluble catalysts based on the same vanadyl complexes supported on cross‐linked poly(styrene) resin or mesoporous silica allow for catalyst recovery and recycle, showing equivalent selectivities over multiple reaction cycles. The mesoporous silica supported catalyst exhibits greater selectivity than the analogous homogeneous and polymer supported catalysts. Rigorous recycle studies show a loss of activity in each recycle, which is attributed to the decomposition of some portion of the vanadyl complexes in each cycle.     

负载型臭氧氧化催化剂研究进展

多相催化臭氧化技术是一种高效的污水净化技术。其中负载型臭氧氧化催化剂因其催化效果好、易分离、重复率用率高等优点而成为研究热点之一。依据不同的载体类型,将负载型臭氧氧化催化剂进行归纳分类,并综述了不同载体的催化剂在催化臭氧氧化水处理中的最新应用。     

Molecular Dispersion of Metal Complexes within Zeolitic Solids: An Alternative Way to Prepare Supported MOx Catalysts

Molecular Designed Dispersion (MDD) of metal complexes on a highly porous support is a novel synthesis method to prepare high quality heterogeneous catalysts. The process basically consists of two steps: (1) the anchoring of the complex onto the support in a controlled way and (2) the mild oxidation of the grafted complex towards catalytically active metal-oxide surface structures.This article presents two typical case studies: (1) the incorporation of cationic Cu-complexes in a H-ZSM-5 zeolite from the liquid phase and (2) the gas phase modification of pure silica MCM-48, using the VO(acac)₂ complex. In both cases, superior catalysts are obtained. Detailed chemical, physical and catalytical analyses of these catalysts are discussed in the text. Comparison is made with analogous catalysts, prepared by conventional methods.     

无机物负载型钯催化剂的研究进展

钯催化剂是重要的金属催化剂,近年来,负载型钯催化剂作为一类新型催化剂广受关注。介绍了以硅胶、MCM-41分子筛、活性炭和金属氧化物等无机物为载体的负载型钯催化剂的特征及应用,并展望了其在不对称反应中的开发应用前景。     

年产20 kt硝酸钾生产装置概况

介绍年产20kt农用硝酸钾生产装置及其运转装置。该装置是采用硝酸铵与氯化钾复分解循环法工艺技术，经生产实践证明，装置具有生产产品质量，原料利用率高，生产成本低，无污染等优点。它的建成与投产成功，为我国今后更大规模的硝酸钾装置的设计生产打下了良好的基础。