Maria Wojciechowska

MgF2 as a non-conventional catalyst support

Abstract This review reports progress in the study of the surface structure of MgF 2 and its use as a support of catalytically active phases. Magnesium fluoride was applied first as a support in catalysis for systems containing individual oxides of transition metals (Mo, V, W, Cu, Cr) and then two different oxide phases (Cu-Cr, Cu-Mn), a metal phase (Ru, Pd) or heteropolyacids. Its use as a support enabled determination of the structure and surface properties of these catalysts. The MgF 2 -supported catalysts are characterized by high activity and selectivity in such processes as: hydrodechlorination of chlorofluorocarbons (CFCs), hydrodesulfurization of organic compounds and purification of fuel combustion products from nitrogen oxides. Magnesium fluoride has been also used in MgF 2 -doped chromium or aluminum fluoride catalysts for Cl/F exchange on hydrochlorocarbons.

Structure and catalytic activity of double oxide system: Cu–Cr–O supported on MgF2

Abstract Two series of chromium–copper catalysts were prepared: co-impregnated and consecutively impregnated. On the basis of XPS, IR, EPR, X-ray investigations, and catalytic tests, a conclusion was drawn, that on the surface of each sample, an interaction between copper and chromium ions occurred, leading to an electron transfer from chromium to copper. As a result, Cr 6+ and Cu 1+ centres were formed. These sites were responsible for the catalytic activity of studied samples. The order of active phase deposition determined the properties of consecutively impregnated catalysts. The best performance was found for consecutively impregnated copper–chromium catalysts, which showed the highest influence of copper–chromium interaction on the properties of such systems. The surface structures of particular catalysts were proposed.

MgF2 as a non‐conventional catalytic support. Surface and structure characterization

The paper presents results of studies on the structure of MgF2 support, performed using various experimental methods such as XRD, IR, temperature‐programmed techniques and low‐temperature nitrogen adsorption. MgF2 is characterized by an XRD spectrum with over 40 patterns, which enabled us to follow the changes in crystallite size and internal tension caused by the thermal treatment. TPE‐H2O and TG allowed an estimation of the surface OH groups concentration as ∼3–4 nm-2.

New supported ruthenium catalyst for hydrodesulfurization reaction

Abstract The effect of the kind of ruthenium precursor {Ru 3 (CO) 12 or RuCl 3 · n H 2 O} and the activation conditions on the performance of Ru/MgF 2 preparations in thiophene hydrodesulfurization has been studied. The highest activity, higher than that of the commercially available system CoMo/Al 2 O 3 , was revealed by the Ru/MgF 2 catalyst sulfided in the 50% H 2 S/He atmosphere. According to the results of TPR study, this preparation was characterized by exceptionally high content of RuS 2 , which seems to be responsible for its high activity. As follows from the product distribution of thiophene HDS, the activation in the H 2 S/He atmosphere mainly leads to the formation of saturated products (butane), while the activation in the atmosphere of H 2 S/H 2 , to the formation of unsaturated products (butene-1, cis - and trans -butene-2).

New Promising Iridium Catalyst for Toluene Hydrogenation

The use of an iridium active phase and magnesium fluoride as a support allowed us to obtain new catalysts of high activities in the hydrogenation of toluene. The Ir/MgF2 catalyst was four times more active than the iridium system supported on commercial Al2O3. The nature of iridium precursors [H2IrCl6 or Ir4(CO)12] and catalyst pretreatment conditions (reduction or oxidation/reduction) appeared to have a clear effect on the activity of Ir/MgF2 catalysts. For the catalysts obtained from iridium carbonyl, the highest activity was obtained after direct reduction of the catalysts, whereas for the catalysts obtained from hexachloroiridium acid, the highest activity was obtained after reduction of the preliminary oxidized catalysts.

High‐Selectivity Hydrogenation of Chloronitrobenzene to Chloroaniline Over Magnesium Fluoride‐Supported Bimetallic Ruthenium‐Copper Catalysts

Hydrogenation of halonitrobenzenes is the way to produce halogenated anilines that are important reagents for the manufacture of a wide variety of drugs, pesticides, pigments, and dyes. However, the production of halogenated anilines is accompanied by a complication, their easy hydrodehalogenation, which results in the formation of undesirable by-products. This issue generates serious technological problems and increases production costs associated with the separation and purification of the final product. Therefore, much effort is directed to working out a system of possibly the lowest or even zero hydrodehalogention activity, which would produce chloroanilines with a 100 % yield. One of the solutions proposed involves the use of untypical supports such SnO2, [2] g-Fe2O3, [3] g-ZrP, and MgF2. [5] Many promising results achieved by us in the case of the Ru/MgF2 [5] catalyst have prompted attempts at improving selectivity by admixing ruthenium with copper. Copper, as a group Ib element, preferentially occupies edges, corners, and other low coordination metal sites on the catalyst surface, thus changing the catalyst structure. As hydrogenolysis of the carbon-halogen bond is a structure-sensitive reaction, it is very likely that such a change can result in the increase of selectivity of chloronitrobenzene reduction to chloroaniline. Our study was inspired by papers published by Sinfelt et al. in 1970s, who have shown that the addition of copper to group VIII metal decreases hydrogenolysis activity markedly, but its effect on other reactions such as hydrogenation is much smaller. Although bimetallic Ru Cu catalysts have been known for many years, their use in the hydrogenation of chloronitrobenzene has, to our knowledge, not been reported before. A support of the active phase was magnesium fluoride, which is a mesoporous material of the surface area of 50 m g . Synthesis of the porous MgF2 is very easy and cheap, with Mg(CO3)2 and 40 % aqueous solution of hydrofluoric acid as substrates. Monometallic ruthenium and copper catalysts were produced by the traditional and simple method of the support impregnation with aqueous solutions of ruthenium(III) chloride and copper(II) nitrate, respectively, whereas the bimetallic catalysts were prepared by co-impregnation. After the evaporation of water, the catalysts were dried and reduced in an H2 atmosphere. Parameters characterizing the catalysts are given in Table 1. The data presented in Table 1 will be discussed later in relation to the catalytic data. Hydrogenation of ortho-chloronitrobenzene (o-CNB) to ortho-chloroaniline (o-CAN) was performed in a liquid-phase at

Surface chemistry of porous magnesium fluoride

Abstract Porous preparations of magnesium fluoride were obtained from magnesium sulphate and magnesium carbonate and their surface properties have been studied. It has been shown that pure magnesium fluoride has a weak surface acidity of the Lewis type and no protonic sites stronger than H R ⩽0.82. Base properties of MgF 2 surfaces are more pronounced than acid ones, but the base strength is low. Surfaces of MgF 2 also bear oxidizing and reducing centres capable of forming ion radicals with adsorbed perylene and tetracyanoethylene. The low catalytic activity of magnesium fluoride for acid catalysed reactions suggests the application of MgF 2 as a catalyst support rather than as a catalyst.

Influence of activation and the HDS reaction on the structure of magnesium fluoride-supported Ru catalysts derived from ruthenium chloride hydrate

The effect of activation conditions and the hydrodesulfurization (HDS) process on the structure of Ru/MgF2 prepared from RuCl3⋅nH2O precursor catalysts was studied. During the first 6-7 h of the HDS process significant differences in activities were detected between samples pretreated in 50% H2S/H2 and in 50% H2S/He. During this transient time, the Ru/MgF2 catalyst pretreated in 50% H2S/H2 increased in activity while the activity of that pretreated in H2S/He decreased. XRD, TPR and quantitative analysis of sulfur content revealed that directly after activation in H2S/He crystalline ruthenium sulfide is the main component of the surface, whereas after activation in H2S/H2 both RuS2 and metallic Ru are present on the surface. These differences decrease during the thiophene HDS process. Despite the different pretreatment conditions, the composition of the surface tends to “equilibrate”, which results in similar activity after prolonged reaction time.

INTERACTION OF MAGNESIUM FLUORIDE WITH COPPER(II) AND VANADIUM(V) OXIDES

Abstract Copper(II) oxide and vanadium(V) oxide deposited on MgF 2 were studied by IR and EPR methods. The results obtained indicated that on the surface of MO x /MgF 2 systems (M = Cu, V) the surface cations are coordinated by oxygen ions as well as the fluoride anions of the support lattice. It is supposed that the incorporation of fluoride ions from the surface of MgF 2 into the structure of the latter two complexes is hindered.

The effect of catalyst preparation on the performance of magnesium fluoride supported ruthenium

The effect of different ruthenium precursors on the structure and catalytic properties of the Ru/MgF2 system was studied with such methods as IR, XPS, EPR and catalytic test reactions. The adsorption of probe molecules (CO and O2) revealed a greater ability to transfer an electron from ruthenium in the case of samples obtained from Ru3(CO)12 than in the case of samples obtained from RuCl3. Besides, metallic crystallites of different size were obtained depending on the precursor used. Namely, the average cluster size was 1.5 times smaller for carbonyl samples in comparison with chloride ones. Both series of preparations were active in redox or acid-base reactions. The activities of the carbonyl samples were higher than those of the chloride catalysts, particularly in reactions that require the presence of acid centers.