Catalyst Precursors For Oxidation Research Articles

Promoter effect of Co on the catalytic activity of Re/γ-Al2O3 catalysts for the HDS and HDN of gas oil

Abstract This work reports the effect of Co content and catalysts preparation on the surface structure of two catalyst series prepared by either co-impregnation or sequential impregnation and their catalytic activity for the simultaneous hydrodesulphurisation (HDS) and hydrodenitrogenation (HDN) of gas oil. Structural characteristics and degree of dispersion of the Co and Re phases in the oxidic catalyst precursors were obtained by X-ray diffraction, energy-dispersive X-ray analysis, UV–vis diffuse reflectance spectroscopy (DRS) and electrophoretic migration (EM), and in the sulphided catalysts by X-ray photoelectron spectroscopy (XPS). The UV–vis diffuse reflectance spectra demonstrated that Co in its oxidic state was in tetrahedral coordination (as surface CoAl 2 O 4 ) and in octahedral coordination (as surface Co 3 O 4 ), with a relative Co 3 O 4 /CoAl 2 O 4 proportion increasing with Co content, and that Re was present mainly as distorted isolated ReO 4 − monomeric species on the alumina surface and in small amounts probably as associated ReO 4 − type Re 2 O 7 in high Co-content catalysts. Consistently, XPS results of sulphided catalysts revealed that in both series the major part (>67%) of the Co remained in oxided state, while the Re phase was fully sulphided. The dispersion of sulphided Re decreased gradually with Co loading for the co-impregnated catalysts, due to the strong Co/alumina interaction, and drastically with Co incorporation for sequentially impregnation catalysts due to a partial dissolution and re-distribution of Re during Co impregnation. Catalytic activity results revealed synergetic effects in HDS and HDN between Co and Re in both series, with an optimum at an atomic ratio of about 0.40 Co/Re. The magnitude of the synergy was greater for HDS than for HDN, especially at low reaction temperature, and slightly higher for the coimpregnated catalysts reflecting the better Re dispersion. The observed CoRe synergy was thought to be related to the formation of a mixed Co-Re-S phase and to hydrogen spillover from separate Co sulphide to Re sulphide, participating to a different extent depending on the reaction temperature.

Self‐Assembled Two‐Dimensional Water‐Soluble Dipicolinate Cu/Na Coordination Polymer: Structural Features and Catalytic Activity for the Mild Peroxidative Oxidation of Cycloalkanes in Acid‐Free Medium

AbstractThe new water‐soluble 2D Cu/Na coordination polymer [Cu(μ‐dipic)2{Na2(μ‐H2O)4}]n·2nH2O (1) has been synthesized by self‐assembly in aqueous medium from copper(II) nitrate, dipicolinic acid (H2dipic) and sodium hydroxide in the presence of triethanolamine. It has been characterized by IR spectroscopy, FAB+‐MS, elemental and single‐crystal X‐ray diffraction analyses, the latter featuring a layered 2D metal–organic structure that is extended to a 3D supramolecular assembly by extensive hydrogen bonding between adjacent layers and involving crystallization water molecules. Compound 1 has been shown to act as a catalyst precursor for the peroxidative oxidation of cyclohexane and cyclopentane to the corresponding cyclic ketones and alcohols by aqueous H2O2 in MeCN solution and in the absence of acid additives.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Influence of reduction temperature and metal loading on the performance of molybdenum phosphide catalysts for dibenzothiophene hydrodesulfurization

Two series of alumina-supported molybdenum phosphide (MoP) catalysts with low and high metal loadings were prepared by temperature-programmed reduction of the oxidic catalyst precursors in hydrogen to different temperatures (823, 923, 1023 and 1123 K, respectively). Effects of reduction temperature and metal loading on the surface distribution and the type of species formed were studied by TPR, SBET, XRD, HRTEM, 31P NMR, 27Al NMR and in the reaction of dibenzothiophene (DBT) hydrodesulfurization (HDS) performed in a flow reactor at 553 K and total hydrogen pressure of 3.4 MPa. HRTEM and 31P NMR confirmed formation of MoP phase on all catalysts. The 9.9 wt% Mo catalyst activated at lowest reduction temperature (823 K) was found to be most active among the catalysts studied. The presence of a low amount of Mo0 species on the surface of this catalyst does not appear to be a drawback for the catalytic activity. The increase in both metal loading (from 9.9 to 15 wt% Mo and from 3.2 to 4.8 wt% P) and reduction temperature (from 823 to 1123 K) was found to be detrimental for HDS activity due to sintering of active phase, and also to decrease in specific area and formation of phosphate species.

Synthesis, Characterization, Luminescence, and Electrochemistry of the Tetranuclear Gold(I) Amidinate Clusters, Precursors to CO Oxidation Catalysts: Au4[(ArNC(H)NAr)]4, Au4[(PhNC(Ph)NPh)]4 and Au4[PhNC(CH3)NPh)4

AbstractA summary of the chemistry of the tetranuclear Au(I) amidinate complexes is presented. Tetranuclear Au(I) amidinate clusters are produced by the reaction of the sodium salt of a amidine ligand with the gold precursor Au(THT)Cl in a (1:1) stoichiometry. The structures of the tetranuclear Au4[ArNC(H)NAr]4, Ar = C6H4‐4‐OMe, C6H3‐3,5‐Cl, C6H4‐4‐Me, C6H4‐3‐CF3, C6F5, C10H7 and the tetranuclear Au4[(PhNC(Ph)NPh]4 and Au4[PhNC(CH3)NPh]4 have been characterized by X‐ray crystallography. The average Au···Au distance between adjacent Au(I) atoms is ˜3.0 Å, typical of compounds having an aurophilic interaction. The four gold atoms are located at the corner of a rhomboid with the amidinate ligands bridged above and below the near plane of the four Au(I) atoms. The angles at Au···Au···Au in the cyclic units are between 70° and 116°. The tetranuclear gold(I) amidinate clusters each show different luminescence behavior. The tetranuclear clusters Au4[(ArNC(H)NAr]4, Ar = C6H4‐4‐OMe, Ar = C6H4‐3‐CF3, Ar = C6H4‐4‐Me and Ar = C6H4‐3,5‐Cl are the first tetranuclear gold(I) cluster species from group 11 elements that show fluorescence at room temperature. The tetranuclear naphthyl derivative Ar = C10H7 is luminescent only at 77 K. The pentafluorophenyl derivative Ar = C6F5 does not show any photoluminescence in the solid state nor in the solution. The lifetimes of the naphthyl and trifluoromethylphenyl complexes are in the millisecond range indicating phosphorescent processes. Electrochemical and chemical oxidation studies of the tetranuclear Au(I) amidinate clusters are presented. The tetranuclear complexes Au4[ArNC(H)NAr]4, Ar = C6H4‐4‐OMe, Ar = C6H4‐4‐Me, and Ar = C6H3‐3,5‐Cl, show three reversible waves at 0.75, 0.95, 1.09 V vs. Ag/AgCl at a scan rate of 500 mV/s in 0.1 M Bu4NPF6/CH2Cl2 at a Pt working electrode in CH2Cl2. Three reversible waves at 0.87, 1.19, 1.42 V vs. Ag/AgCl at a scan rate of 100 mV/s are also observed for the tetranuclear complex Au4[PhNC(Ph)NPh]4 in CH2Cl2. The pentafluorophenyl amidinate derivative, Au4[ArNC(H)NAr]4, Ar = C6F5 shows no oxidation wave below 1.8 V. Recently it has been shown that Au4[ArNC(H)NAr]4 is a very effective catalyst precursor for room temperature CO oxidation.

Effect of silicates on the structure of Ni-containing catalysts obtained from hydrotalcite-type precursors

New nickel hydrotalcite-like compounds with silicates as interlayer anions used as catalyst precursors in the catalytic partial oxidation of methane were prepared by the coprecipitation method. The properties of these materials were compared with those of compounds obtained from carbonate-containing materials. The precursors and calcined samples were characterized by powder X-ray diffraction, FT-IR and Vis/UV/NIR spectroscopies, thermal analyses (DTA and TG), temperature programmed reduction (TPR) and N 2 adsorption/desorption at −196 °C. The results show that the incorporation of silicates in the lamellar compounds modifies the structural and textural properties of the precursors. After calcination, silicates – which are non-volatile anions – contribute to the final structure of the catalysts, which form a new forsterite-like phase, increasing their specific surface area but not altering the reducibility of the nickel species.

TOF‐SIMS characterization of an aluminovanadate oxide catalyst

AbstractTime‐of‐flight Secondary Ion Mass Spectrometry (TOF‐SIMS) has been employed to characterize the surface physical and chemical state of aluminovanadate oxide catalyst precursors (‘VAlO’) precipitated at different pH values in the range of 5.5…10. The reference oxide V2O5 has also been studied for comparison purposes. It is shown that the analysis of molecular ion emission yields valuable information on the surface elemental and phase composition. Increasing pH values while precipitating from aqueous precursor solutions are found to result in a monotonic variation of the surface composition, in a progressive hydroxylation of aluminium and vanadium and in an increasing dispersion of vanadium oxide species. SIMS data evaluated on the basis of Plog's valence model of molecular ion emission reveal reduced V4+ states, the fraction of which is dependent on the pH value. The SIMS results are supported by XPS data. The enhancement of the catalytic activity in oxidative propane dehydrogenation over VAlO prepared at high precipitation pH is in good correlation with the measured surface characteristics. Copyright © 2007 John Wiley & Sons, Ltd.

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.

Characterization of nanostructured binary molybdenum oxide catalyst precursors for propene oxidation

High-resolution transmission electron microscopy characterization of molybdenum oxide catalyst precursors is carried out for a better understanding of the mechanisms leading to the active catalytic material. The precipitated material consists of both large-unit cell crystals and randomly orientated clusters on a 3-5 nm scale. The crystalline clusters are embedded in non-crystalline material, preventing the formation of large well-defined inactive orthorhombic MoO(3) crystals during activation of the catalyst material.

The effect of processing conditions on carbon nanostructures formed on an iron-based catalyst

The carbon nanostructures formed during chemical vapour deposition (CVD) of ethene and hydrogen over an iron(III) oxide catalyst precursor have been investigated. Graphitic nanofibres and carbon nanotubes were both observed during synthesis, with the structures observed depending on the temperature and gas mix (C 2H 4 and H 2) used. Mixtures ranging from 100% to 5% ethene in hydrogen were investigated at different temperatures. During the synthesis, the iron(III) oxide was transformed into iron carbide (Fe 3C). The samples were characterised using transmission electron microscopy and X-ray diffraction. Filamentous nanostructures were observed with high hydrogen content (⩾80%) in the gas stream, whereas no filamentous structures were observed with ⩽20% H 2. The temperature of synthesis was varied between 500 and 800 °C, with higher temperatures giving higher carbon deposition rates, but also affected the nanostructures observed. However, it was found that increasing the temperature during CVD did not change the type of carbon deposited but did increase the deposition rate, providing a route to increase growth yields for a desired type of carbon nanostructure.

新規シルセスキオキサンの合成と触媒機能

Preparation of novel oligosilsesquioxanes-based materials and metal-containing ones as homogeneous and heterogeneous catalysts of excellent activity are reviewed. The authors examined the activity of a V-containing silsesquioxane as a homogeneous catalyst for the photo-oxidation of simple alkanes. For the epoxidation of alkenes catalyzed by Ti-silsesquioxanes, the presence of alkenylsilyl substituents around the Ti center shows significant promotional effects. By utilizing silsesquioxanes bearing appropriate functional groups, novel caged molecules with organic-inorganic hybrid structures were prepared as well as soluble cooligomers, starburst-type polymers, and a dendrimer containing metallasilsesquioxanes. Furthermore, the authors found that these metal-containing silsesquioxanes can be good precursors of oxide catalysts with high BET surface areas and uniformly-controlled pores. Remarkably, the catalysts containing V and Al species were found to show excellent activity for photo-assisted aerobic oxidation of methane into methanal and the cracking of cumene, respectively.

Heterobimetallic Complexes as Catalyst Precursors for the Oppenauer-Type Oxidation of Alcohols

A heterobimetallic Ru(II)-Rh(I) complex has been identified as a potent catalyst precursor for the Oppenauer-type oxidation of alcohols. With 0.1–0.5 mol% of this complex and K2CO3 as the co-catalyst, it is possible to oxidize secondary and primary alcohols at ambient temperature using acetone as the solvent and oxidation agent.

A Heterobimetallic Rhodium(I)—Ruthenium(II) Catalyst for the Oppenauer‐Type Oxidation of Primary and Secondary Alcohols under Mild Conditions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Heterobimetallic Rhodium(I)−Ruthenium(II) Catalyst for the Oppenauer-Type Oxidation of Primary and Secondary Alcohols under Mild Conditions

A heterobimetallic complex, in which a RuCl2(acetone) (PPh3)(2) fragment is connected via three chloro bridges to a (eta(4)-C4Ph4CO)RhCl fragment, has been identified as a potent catalyst precursor for the Oppenauer-type oxidation of alcohols. With 0.1-0.5 mol % of this complex and K2CO3 as the cocatalyst, it is possible to oxidize secondary and primary alcohols at room temperature using acetone as the solvent and oxidation agent.

Preparation and Characterization of Lamellar Vanadyl Alkylphosphates as Catalyst Precursors for the Selective Oxidation of Butane

Abstract Vanadyl alkylphosphates consisting of V4+ and P5+ were synthesized by the reaction of a solid mixture of V2O5 and V4O9 (2:3 in mol) with P2O5 in primary aliphatic (from C1 to C8), secondary aliphatic (C3 and C4), and alicyclic (C5) alcohols, and were characterized by means of elemental analysis, thermogravimetric analysis, X-ray diffraction, IR spectroscopy, and magnetic susceptibility. The chemical formulae of the products were determined to be VO(RO)x(HO)1−xPO3·(ROH)y (x = 0.5–0.7, y = 0.3–0.5 for primary aliphatic alcohols; x = 0.1–0.2, y = 0.4–0.9 for secondary aliphatic and alicyclic alcohols; and R = organic group). X-ray diffraction revealed that the compounds had a lamellar structure, where the organic groups existed as double layers with a tilt of about 56° against the basal plane. Magnetism and IR spectroscopy demonstrated that the construction of the basal planes in the vanadyl alkylphosphates was similar to that of VOHPO4·0.5H2O, which consists of V4+ dimers linked with PO4, except for vanadyl sec-butylphosphate, consisting of isolated V4+ monomers. Calcination of vanadyl methylphosphate and vanadyl cyclopentylphosphate brought about crystallites of (VO)2P2O7. These (VO)2P2O7 exhibited high selectivities to maleic anhydride (65–68%) for the selective oxidation of butane under a high concentration of butane (5.0%).

Preparation of catalyst precursors for selective oxidation of n-butane by exfoliation–reduction of VOPO 4·2H 2O in primary alcohol

A new method through intercalation and exfoliation of VOPO 4·2H 2O crystallites in primary alcohol (1-propanol or 1-butanol), followed by reduction with the alcohol, have been investigated for the preparation of catalyst precursor. Lamellar compounds, consisting of V 4+, P 5+ and alkyl group with thin film-like morphology, were formed and was characterized by means of XRD, IR, TG/DTA, and elemental analysis. The chemical formula of the precursor obtained by exfoliation–reduction in 1-butanol was shown to be VO{( n-C 4H 9) 0.16H 0.84}PO 4·0.8H 2O. On the other hand, a direct reduction of VOPO 4·2H 2O in the alcohol gave a mixed phase shown by (VOHPO 4·0.5H 2O) 0.3(VO{( n-C 4H 9) 0.3H 0.7}PO 4·3H 2O) 0.7 comprising plate-like microcrystallites. These precursors transformed to (VO) 2P 2O 7 phase during an activation process at 703 K in the presence of a mixture of n-butane 1.5% and O 2 17% in He balance. The obtained (VO) 2P 2O 7 through the exfoliation–reduction was well crystallized and consisted of thin flaky crystallites. It was found that (VO) 2P 2O 7 thus prepared through the exfoliation–reduction was highly active and selective for oxidation of n-butane.

Catalytic oxidation of THF with homo and hetero metallic Mo/Ru complexes and molecular oxygen

The novel complex Ind(CO) 3Mo–Ru(CO) 2Cp ( 1) (Ind=η 5-indenyl,Cp=η 5-cyclopentadienyl), as well as other hetero and homo metallic complexes of molybdenum and ruthenium are catalyst precursors in the aerobic oxidation of THF under ambient conditions. Selectivities towards γ-butyrolactone of up to 70% are obtained. For the first time in this transformation, propylformate is isolated besides the lactone.

Effects of ball milling on the doped vanadium phosphorus oxide catalysts

Vanadium phosphorus oxide (VPO) catalyst precursors were prepared in organic phase by using isobutanol as the reducing agent. They were doped by combined components—Zn+Zr+Mo, Zr+Zn and Zr+Mo—through impregnation. In order to increase the catalyst surface areas, the catalyst precursors were ball milled in different solvents for a certain period of time. X-ray diffraction (XRD), X-ray fluorescence spectrometer (XFS), DTA/TGA, X-ray photoelectron spectrometer (XPS) and BET were used to examine the bulk and surface properties of the final catalysts and their precursors. Catalytic performances were measured in the selective oxidation of n-butane into maleic anhydride (MA). The results revealed that ball milling could improve the performances of these VPO catalysts, without destroying the active physico-chemical structure and without exerting great influence on the surface characteristics of the catalysts. Interaction between the combined moderators was also preliminarily discussed. The Mo component was found to have some kind of stabilizing effect on the catalyst surface of this system.

Structure and Site Evolution of Iron Oxide Catalyst Precursors during the Fischer−Tropsch Synthesis

The contacting of Fe oxide precursors with synthesis gas (H2/CO mixtures) leads to structural and chemical changes and to the formation of the active sites required for the Fischer−Tropsch synthesis (FTS). The local structure and oxidation state of the starting Fe2O3 precursors promoted by Cu and/or K were probed using in situ X-ray absorption spectroscopy during these processes. The activation of these precursors occurs via reduction to Fe3O4 followed by carburization to form FeCx. FTS reaction rates increased markedly during the initial stages of carburization, suggesting that the conversion of near-surface layers of Fe3O4 to FeCx is sufficient for the formation of the required active sites. Thus, bulk structural probes, and any ex situ techniques without concurrent measurements of the products evolved during activation and FTS, can lead to misleading structure−function relations. The initial rate of carburization and the extent of carburization and the FTS rate at steady-state were higher for Fe2O3 precursors containing either Cu or K. These effects were stronger when both promoters were present. K and Cu provide CO and H2 activation sites, which lead to the nucleation of multiple carbide regions on Fe oxide surfaces. The larger number of nucleation sites leads to higher initial carburization rates and to smaller FeCx crystallites. These smaller crystallites, in turn, provide higher active surface areas, shorter bulk diffusion distances, more complete carburization of Fe2O3 precursors, and higher steady-state FTS rates. These effects of K and Cu on the number of available FeCx sites were confirmed by titrating surface sites using CO after FTS reactions. It appears that K and Cu act predominantly as structural promoters, which increase the surface area of the active FeCx phases. Chemical promotion of catalytic rates by these additives appears not to be required to explain the observed FTS rate enhancements in the presence of K or Cu. These structural promotion effects of Cu and K account for the apparent but non-causal correlation between bulk FeCx contents and FTS rates at steady-state, even though the carburization of only near-surface regions in bulk Fe3O4 is sufficient to achieve steady-state FTS turnover rates.

Preparation and characterization of new Mg–Al–Fe oxide catalyst precursors for dehydrogenation of ethylbenzene in the presence of carbon dioxide

New catalysts based on hydrotalcite-like precursors (Mg–Fe and Mg–Al–Fe) were synthesized. The structure of catalyst precursors was confirmed by XRD, FT–IR and TG. Appearance of separate brucite phase was observed for Mg–Fe precursors with excess of Mg, while for Mg–Al–Fe precursors, increase in Al content led to a formation of MgAl2(OH)8 and mixed Al–Fe hydroxides apart from hydrotalcite phase. During calcination, the hydrotalcite like precursors spread their surface area and transform into mixed oxide. The mixed oxides were applied in ethylbenzene (EB) dehydrogenation with CO2. The activity losses with time-on-stream were completely restored by oxygen pulses.

Synthesis of Novel Layered Vanadyl Alkylphosphates as Catalyst Precursors for Selective Oxidation of n-Butane.

Synthesis of Novel Layered Vanadyl Alkylphosphates as Catalyst Precursors for Selective Oxidation of n-Butane.