Jean Ladrière

Phase Cooperation Between Tin and Antimony Oxides in Selective Oxidation of Isobutene To Methacrolein .1. Mechanical Mixtures of Sno2 and Alpha-sb2o4

Results are reported concerning the cooperation between SnO2 and α-Sb2O4 particles in the selective oxidation of isobutene to methacrolein. The catalysts were prepared by mechanically mixing the corresponding powders. A conspicuous catalytic synergy was observed when methacrolein production and selectivity to methacrolein formation were considered. The catalysts, both fresh and used, were characterized by XRD, 119Sn Mossbauer spectroscopy, XPS, analytical electron microscopy (AEM), and ESR in order to investigate the origin of the synergy observed. The joint use of these techniques yielded no indication that a new phase (or solid solution) formed or that mutual surface contamination during either the preparation of the mixture or the catalytic test took place. Within the sensitivity limits of the techniques used, the mechanical mixtures can be considered as composed of two pure separate phases in good contact. The origin of the observed synergy and the other experimental observations is explained in a satisfactory manner by the existence of a “remote control” mechanism, i.e., that α-Sb2O4 produces a mobile oxygen species, namely spillover oxygen, which, by flowing onto the surface of SnO2, creates on the surface of the latter new selective sites and/or regenerates those which have become deactivated. Spillover oxygen produced by α-Sb2O4 seems to control the selective catalytic sites on SnO2 by inhibiting their transformation to reduced, nonselective sites. Spillover oxygen also inhibits the formation of carbonaceous deposits.

The reactivity and stability of mixed-sulfide structures in unsupported MoS2-based hydrodesulfurization catalysts promoted by group VIII metals

Abstract Unsupported CoMo, NiMo and FeMo catalysts have been prepared by the homogeneous sulfide precipitation method and the coprecipitation method. The presence of a group VIII metal (Me) causes a decrease in the reactivity with O2 and an increase in the reducibility in H2. These effects are correlated with the increase in the catalytic activity. The stability of cobalt and iron sulfide species in CoMo and FeMo catalysts was studied by Mossbauer spectroscopy. A significant amount of MeMoS structure remains stable after strong reducing treatment. Catalysts contain also sulfur-rich group VIII metal sulfide species which appear stabilized by MoS2. The role of these species in promoting HDS activity is evaluated.

Phase cooperation between tin and antimony oxides in selective oxidation of isobutene to methacrolein III. Coprecipitated catalysts

Abstract The selectivity and yields for methacrolein in the oxidation of isobutene over pure SnO 2 and Sb 2 O 4 can be improved dramatically by impregnating the oxides with a small amount of the cation belonging to the other oxide (Sb for SnO 2 and Sn for Sb 2 O 4 ). The fresh and used samples were characterized with XRD, BET, 119 Sn Mossbauer spectroscopy, SEM, analytical electron microscopy (AEM), XPS, and ESR. For Sb 2 O 4 impregnated with Sn ions, no trace of surface contamination (monolayer or otherwise) or solid solution was detected. For SnO 2 impregnated with Sb ions, a small amount of Sb 5+ ions dissolved into SnO 2 after impregnation, but these Sb 5+ ions tend to migrate to the surface during catalytic reaction. For both systems, the impregnated ions tended to segregate, leading to the formation of a two-phase catalyst. A remote control mechanism can satisfactorily explain the results obtained. In comparison with the results obtained with SnO 2 Sb 2 O 4 mechanical mixtures reported in Part I, the impregnated catalysts have good catalytic performances, account taken of the small amount of the minor component. The difference between the catalytic properties (methacrolein yield and selectivity) of impregnated catalysts and those of mechanical mixtures can be easily explained by considering the surface areas developed and the difference in the number and quality of the contacts between the SnO 2 and Sb 2 O 4 .

Characterisation of unsupported FeMoS catalysts: Stability during reaction and effect of the sulfiding temperature

Abstract Unsupported iron, molybdenum and iron-molybdenum sulfides were prepared by the Homogeneous Sulfide Precipitation (HSP) method. They were investigated by surface area, XRD, MAS (Mossbauer Absorption Spectroscopy), electrophoretic migration, and XPS measurements; various temperature-programmed methods have also been used. Catalytic activity in the simultaneous hydrodesulfurisation of thiophene and hydrogenation of cyclohexene at 3 MPa and 573 K has been measured. It has been verified that the HSP method gives samples containing a high proportion of the Fe species giving the signal attributed to the so called “FeMoS” species, together with a noncrystalline phase possibly corresponding to FeS2 (pyrite) and some pyrrhotite (Fe1−xS). When the final reduction- sulfidation (15% H2S in H2) temperature of the HSP precipitate is increased (from 673 to 1073 K), FeS2 and the iron of FeMoS transform to troilite (FeS). Samples sulfided above 873 K no longer contain FeMoS. The FeMoS “phase” decomposes extensively during the catalytic reaction. Catalytic activity does not correlate with the quantity of FeMoS present in the samples, but seems to vary in parallel with the amount of FeS2 remaining in the working catalyst.

Nickel, iron-containing clay minerals from Niquelandia deposit, Brazil 1. Characterization

Two representative samples of Ni, Fe-containing clays from Niquelandia deposit, Colas, Brazil, have been characterized by different methods and techniques. X-ray diffraction (XRD) was used for the identification of the crystalline phases and to follow the structural modifications occurring upon thermal treatments. One of the samples (N4) is a pure smectite, while the second one (N7) is a mixture of 2:1 (smectite) and 1:1 (lizardite) phases. The thermoanalytical results [differential thermal analysis (DTA), thermogravimetric analysis (TGA)] are consistent with the XRD identification and the low nickel content of lizardite. Mossbauer spectroscopy data allow to assign most of the iron contents to two octahedral sites. From those results and the chemical analysis data, structural formulas of the smectite are proposed. Both clays are montmorillonite-type with appreciable Al for Si tetrahedral substitutions

Crystal-structure and Mossbauer Study of Trilithium Iron(iii) Trioxalate Pentahydrate

The crystal structure of the complex Li-3[Fe(C2O4)(3)]. 5H(2)O has been determined by X-ray diffraction analysis. The coordination of the iron atom is a distorted octahedron composed of the oxygen atoms of three oxalate ions. Two of the lithium ions are octrahedral and the third one is tetrahedral. Infinite chains appear along the b-axis, with alternation of Fe3+ and Li+ cations separated by oxalate anions. In agreement with this, the Mossbauer spectrum consists of an asymmetric and strongly broadened absorption pattern, indicating the presence of both paramagnetic relaxation effects and quadrupolar interaction which result from an Fe3+ interionic shortest distance of 6.559 Angstrom and from a non-cubic iron environment, respectively.

Crystal-structure and Mossbauer Study of Tetralithium Iron(iii) Trioxalate Chloride Nonahydrate

The crystal structure of the complex Li4[Fe(C2O4)3]Cl . 9H2O has been determined by X-ray diffraction analysis. It is composed of sheets perpendicular to the c-axis of the hexagonal cell. In the direction of c, short and long intervals, occupied by hydrated lithium ions, alternate between the sheets. The coordination is distorted octahedral for the iron ion, the chlorine ion and one of the lithium ions. It is nearly tetrahedral for the other lithium ions. The Mossbauer spectra are characterized by an asymmetric quadrupole doublet arising from a local distorsion of the iron octahedral coordination and the presence of a relatively fast spin-spin relaxation process.

Mossbauer Emission Studies of Co-mo/al2o3 Hydrodesulfurization Catalysts - Effects of Reduction and Sulfidation Treatments

The effect of the sulfiding temperature on the catalytic and structural properties of Co-Mo/Al2O3 catalysts is studied by taking into account the after-effects arising from 57-Co in the alumina. The catalytic activity is shown to be correlated to both MoS2 or CoMoS and Co9S8 phases.

Mossbauer Emission-spectroscopy of An Unsupported Cobalt-molybdenum Hydrodesulfurization Catalyst

A57Co doped unsupported CoMo sulfide catalyst with atomic composition ratio r=Co/(Co+Mo)=0.3 was prepared by the homogeneous sulfide precipitation method and exposed to a series of reduction-sulfidation treatments. The treated samples were analyzed by Mössbauer emission spectroscopy using very long accumulation times. Computer decomposition of the spectra revealed the presence of five different cobalt species which were identified as Co9S8, CoS1+x, and three species related to the Co−Mo−S structure. Reduction of the sample under atmospheric pressure of H2 at (and above) 573 K causes an increase of the amount of Co9S8 at the expense of all other species. These results afford a new insight into the stability of the Co−Mo−S structure and of the sulfur rich CoS1+x phase under hydrotreating conditions.

Nickel, iron-containing clay minerals from Niquelandia deposit, Brazil: 2. Behaviour under reducing conditions

The reduction behavior of two Ni, Fe-rich dioctahedral smectite clays has been investigated by temperature-programmed reduction (TPR). For both clays, the reduction process of the transition metal elements occurs in two steps. At about 400 degrees C, Fe3+ is first reduced to Fe2+. At higher temperatures, further reduction of iron and reduction of nickel are achieved. Samples reduced at 400 degrees C and 700 degrees C have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Mossbauer spectroscopy (MS), and transmission electron microscopy (TEM). After a treatment at 700 degrees C, metallic particles deposited on the silicates has been evidenced by TEM and confirmed with the other techniques