Study of hydroformylation of formaldehyde in the presence of rhodium catalysts byin situ IR spectroscopy and the kinetic technique

Carbonylrhodium complexes formed during hydroformylation of CH₂O from various rhodium precursors were investigated byin situ IR spectroscopy. It was found that under the conditions of the hydroformylation of CH₂O inN,N-dimethylacetamide (DMAA), RhH(CO)(PPh₃)₃, RhCl(CO)(PPh₃)₂, RhCl(PPh₃)₃, RhCl(CO)(PBu₃)₂, and [RhCl(CO)₂]₂ form complex systems that necessarily contain anionic complexes, [Rh(CO)₂L_x(DMAA)_y]^– (L = PPh₃, PBu₃,x = 1 to 2,y = 1 to 0; [Rh(CO)₄]^–). The participation of ionic structures in the hydroformylation of CH₂O, most likely, in the step of the activation of CH₂O, was proven by kinetic techniques.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1066–1069, June, 1995.     

Iron modified mesoporous carbon and silica catalysts for methanol decomposition

Iron modified silica and carbon mesoporous materials with similar textural characteristics are compared in methanol decomposition to H₂, CO and CH₄. The influence of the support on the phase composition and reductive properties of the catalysts is studied by M?ssbauer spectroscopy and TPR with hydrogen. This revised version was published online in June 2006 with corrections to the Cover Date.     

Temperature programmed reduction of silica supported nickel catalysts

Nickel oxide promoted catalysts are prepared by simple precipitation, precipitation from homogeneous solution and impregnation methods and their reduction behavior is monitored with temperature programmed reduction (TPR) technique. The effect of different parameters such as metal loading, method of preparation and heat treatment temperature are also observed on the reducibility of the catalysts. It is observed that reduction temperature increases with the increase of calcination temperature. Results indicate that the interactions between nickel oxide and silica begin with the increase of calcination temperature which leads to the formation of nickel hydrosilicates and are responsible for high temperature reduction peaks.     

Study of silica supported PtxNi1-x catalysts by ion scattering spectroscopy

As supported Pt_xNi_1–x catalysts are used for hydrogenation reactions, it seemed necessary to assess the surface composition of the reduced samples. To approach the usual reduction conditions we applied in situ reduction in a reaction chamber (1 mbar H₂ up to 500 °C) placed in ultra high vacuum recipient (UHV: 10^–9 to 2.10^–10mbar). All ion scattering spectroscopy measurements were performed in UHV. Charging of the samples was avoided by electron bombardment (5 eV). The variation of the surface composition was determined after subsequent sputtering, thermal treatment at 500 °C and during oxygen adsorption. A comparison with previous results of surface compositions of binary alloys (polycrystalline foils [1, 2] and single crystals Pt_xNi_1–x [3]) is given.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday     

Fe/Al-PILC催化C_3H_6选择性还原NO的实验研究

采用浸渍法制备了负载于铝柱撑黏土的铁基催化剂(Fe/Al-PILC),在固定床反应器上测试其催化C3H6选择性还原NO的性能。通过N2吸附-脱附、X射线衍射(XRD)、H2的程序升温还原(H2-TPR)、紫外可见光谱(Uv-vis)、吡啶吸附红外光谱(Py-FTIR)等手段对催化剂的物理化学性质进行表征。结果表明,9Fe/Al-PILC在400-550℃能够还原98%以上的NO,而且SO2和水蒸气对其催化性能的影响很小。XRD、N2吸附-脱附表征结果表明,Fe/Al-PILC催化剂中铁氧化物高度分散在载体表面,催化剂有较大的比表面积和孔容。H2-TPR结果表明,催化剂的活性主要由Fe_2O_3物相的还原性能决定。Uv-vis结果表明,催化剂的活性与铁氧低聚物种FexOy呈正相关性。Py-FTIR结果表明,催化剂表面同时存在Lewis酸和Brnsted酸,L酸性位是NO和C3H6反应的主要催化活性中心。     

Kinetic characterization of the reduction of silica supported cobalt catalysts

Abstact  The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps:

The state of the iron promoter in tungstated zirconia catalysts.

The activity and selectivity of tungstated zirconia (WZ) for the conversion of n- into isopentane are dramatically enhanced when the catalyst is modified with Pt and Fe. The state of iron in these catalysts was hitherto only poorly characterized. Therefore, in the present work we investigated the structural and electronic properties of iron in WZ catalysts containing 1 wt% Pt and 1 wt% Fe2O3, by a combination of spectroscopic techniques, namely X-ray absorption spectroscopy (XAS), in situ electron paramagnetic resonance (EPR), and M?ssbauer spectroscopy. In the oxidized catalyst, iron is present as Fe(III) and predominantly forms a surface solid solution in which the isolated Fe(III) ions are located in a distorted octahedral environment. A small amount of the total iron (around 10%) is present in the form of small iron oxide particles. Both iron species can be reduced in H2 and then easily reoxidized on exposure to air at room temperature. We infer that the promoter action of iron in these catalysts is intimately related to its redox properties and specifically affects the dehydrogenation activity of the materials.     

Superparamagnetic behavior of iron oxides supported on porous silica gels

Spinel iron oxide (Fe₃O₄-γ-Fe₂O₃) particles were supported on microbeads of silica gel by the calcination of the silica gel base adsorbing citric acid and Fe³⁺ ions. The X-ray diffraction patterns and the⁵⁷Fe Mössbauer spectra measured for the spinel iron oxide indicated that the particle size of the oxide was regulated by the mean pore diameter (4–82 nm) of the silica gel support employed. In the case of α-Fe₂O₃ particles prepared by using the same silica gel beads, it was revealed by the Mössbauer spectra and the electron micrographs that there were relatively large particles of the oxide on the surface of the beads, in addition to the particles in the silica gel micropores.     

铁铈氧化物程序升温还原过程的研究

运用原位穆斯堡尔谱、XRD测定等方法剖析了铁铈氧化物的程序升温还原过程。结果表明，金属离子间的相互作用使得氧化铁的还原温度升高，还原反应活化能提高，抗还原能力增强。     

Platinum colloid supported on graphite: X-ray photoelectron spectroscopy study

Two states of platinum, Pt⁰ and Pt^+δ, with the binding energy of the Pt(4f_7/2) line at 71.4±0.1 and 72.2±0.3 eV, are revealed by XPS in colloidal platinum deposited onto graphite. The latter state is assigned to surface Pt atoms partially oxidized due to the interaction with water and/or oxygen-terminated sulfonate group in an organic shell. The colloid deposition is found to be temperature dependent with the apparent activation energy of ∼40 kJ/mol.     

A new reagent for the visualisation of N-alkylureas on TLC plates

Summary A new reagent for the visualisation of substituted ureas on TLC plates byin situ nitrosation is described. The procedure involves spraying the plates with two different reagents, and takes about five minutes. The method was tested on four different substituted ureas. A positive identification of nitroso compounds made byin situ nitrosation is discussed.     

Ammoxidation of toluene on vanadyl polyphosphates-VO(PO3)2, 1. synthesis and characterization of the parent samples

Vanadyl polyphosphates with a P/V ratio=2 (crystalline α-VO(PO₃)₂ and β-VO(PO₃)₂ as well as amorphous VO(PO₃)₂) were synthesized, starting from usually prepared precursor VO(H₂PO₄)₂ but pursuing new methods using V₂O₅/H₃PO₄ as well as VOHPO₄·1/2 H₂O/H₃PO₄, too. The products were characterized by chemical analysis and X-ray diffractometry.In situ ESR spectroscopy was used as a tool to predict their catalytic activity in the ammoxidation reaction.     

Photocatalytic hydrogen generation from water with iron carbonyl phosphine complexes: improved water reduction catalysts and mechanistic insights

An extended study of a novel visible-light-driven water reduction system containing an iridium photosensitizer, an in situ iron(0) phosphine water reduction catalyst (WRC), and triethylamine as sacrificial reductant is described. The influences of solvent composition, ligand, ligand-to-metal ratio, and pH were studied. The use of monodentate phosphine ligands led to improved activity of the WRC. By applying a WRC generated in situ from Fe(3) (CO)(12) and tris[3,5-bis(trifluoromethyl)phenyl]phosphine (P[C(6)H(3)(CF(3))(2)](3), Fe(3)(CO)(12)/PR(3)=1:1.5), a catalyst turnover number of more than 1500 was obtained, which constitutes the highest activity reported for any Fe WRC. The maximum incident photon to hydrogen efficiency obtained was 13.4% (440 nm). It is demonstrated that the evolved H(2) flow (0.23 mmol H(2) h(-1) mg(-1) Fe(3)(CO)(12)) is sufficient to be used in polymer electrolyte membrane fuel cells, which generate electricity directly from water with visible light. Mechanistic studies by NMR spectroscopy, in situ IR spectroscopy, and DFT calculations allow for an improved understanding of the mechanism. With respect to the Fe WRC, the complex [HNEt(3)](+)[HFe(3)(CO)(11)](-) was identified as the key intermediate during the catalytic cycle, which led to light-driven hydrogen generation from water.     

Mössbauer study of the autoxidation of ethylenediaminetetraacetato-ferrate(II)

The autoxidation reaction of the Fe²⁺/ethylenediaminetetraacetic acid system has been studied in solution phase at neutral pH and in solid state using Mössbauer spectroscopy. It was found that despite the proposed reaction pathway consisting of several reaction steps under similar circumstances, no intermediate species could be seen in the Mössbauer spectra and instead of the formation of the well-known [Fe^III(EDTA)(H₂O)]^? species, the direct formation of its dimeric form was observed.     

Structure of nanocrystalline particles of metallic cobalt formed during the reduction of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> oxide

X-ray diffraction is applied to investigate metallic cobalt obtained by the reduction of nanocrystalline particles of Co₃O₄. The particles of metallic cobalt have a high concentration of stacking faults, i.e., violations of the layer packing sequence ABABAB..., which is seen in X-ray diffraction patterns as anisotropic broadening of diffraction peaks. Simulation of the diffraction patterns of α-Co with a different concentration of stacking faults is carried out.     

Selective hydrogenation of o-chloronitrobenzene (o-CNB) over supported Pt and Pd catalysts obtained by laser vaporization deposition of bulk metals

Carbon nanotubes (CNTs), γ-alumina (γ-Al₂O₃) and silica (SiO₂) supported Pt and Pd catalysts were produced by laser vaporization deposition of respective bulk metals. The catalysts were characterized by inductive coupled plasma emission spectrometer (ICP), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalytic properties of the catalysts were investigated in the liquid phase hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) under 333 K and 1.0 MPa hydrogen pressure. The results show that the catalytic properties are greatly affected by the supports. Pt/CNTs catalyst exhibits the best catalytic performance among the Pt-based catalysts, producing o-CAN with 99.6% selectivity at complete conversion. Pd/CNTs catalyst exhibits the best catalytic performance among the Pd-based catalysts, giving o-CAN with 95.2% selectivity at complete conversion. For Pt-based catalysts, geometric effect and the textures and properties of the supports play important roles on catalytic properties. On the other hand, geometric effect, electronic effect and the textures and properties of the supports simultaneously influence the catalytic properties of the Pd-based catalysts. In addition, hydrogenolysis of the C–Cl bond can be well inhibited over all catalysts prepared by laser vaporization deposition.     

In situ X-ray diffraction study of reduction processes of Fe3O4- and Fe1−xO-based ammonia-synthesis catalysts

The temperature-programmed reduction process of two types of industrial ammonia-synthesis catalysts, A110 and ZA-5, which are, respectively, based on Fe₃O₄ and Fe_1−xO precursors, were studied by in situ X-ray power diffraction (XRD). It has been found that the ZA-5 has lower reduction temperature and faster reduction rate, and its active phase α-Fe possesses a higher value of lattice microstrain than A110. The simulation based on Rietveld refinement has also shown that the shape of α-Fe grain of ZA-5 has a mixed shape of cube and sphere with more exposing (111) and (211) planes, while that of A110 looks like a concave cube with more exposing (110) planes. Based on the results obtained, a growth model of α-Fe during the reduction of Fe₃O₄- and Fe_1−xO-based ammonia-synthesis catalysts is proposed, and the origins for the activity difference has been also discussed.     

Hydrogenolysis of hexane on supported rhodium catalysts

Hexane was reacted in mixtures with excess hydrogen on 5% Rh on different supports: Al₂O₃ and SiO₂, the latter catalyst in two states: after reduction at 603 K (LT) and after a prereduction at 1253 K (HT). The main reaction was hydrogenolysis. The catalysts were characterized with the fragment composition at different temperatures and hydrogen pressures. Two surface states could be distinguished: one with more hydrogen favored single rupture, the other with less hydrogen preferred multiple fragmentation. The transition between these states could be rather abrupt, as the surface hydrogen availability changed. The tendency to produce multiple fragments increased in the order Rh/Al₂O₃< Rh/SiO₂-LT < Rh/SiO₂-HT.     

Selective catalytic oxidation of NO over iron and manganese oxides supported on mesoporous silica

The selective catalytic oxidation （SCO） of NO was studied on a catalyst consisting of iron-manganese oxide supported on mesoporous silica （MPS） with different Mn/Fe ratios. Effects of the amount of manganese and iron, oxygen, and calcination temperature on NO conversion were also investigated. It was found that the Mn-Fe/MPS catalyst with a Mn/Fe molar ratio of 1 showed the highest activity at the calcination temperature of 400 °C. The results showed that over this catalyst, NO conversion reached 70% under the condition of 280 °C and a space velocity of 5000 h-1. SO2 and H2O had no adverse impact on the reaction activity when the SCO reaction temperature was above 240 °C. In addition, the SCO activity was suppressed gradually in the presence of SO2 and H2O below 240 °C, and such an effect was reversible after heating treatment.