I. Pasquon

The nature of the active component in a Fe2O3MoO3 catalyst: II. Study of the variations occurring during high temperature treatment☆

Abstract In this paper the variation of both chemical and catalytic activity of Fe 2 O 3 MoO 3 catalyst occurring as a result of high-temperature treatment is investigated. Three variations with temperature are observed. The first occurs at about 350 °C and is characterized by the start of bulk diffusion, increase of the electrical conductance, and formation of high amounts of CO in methanol oxidation. The second occurs at about 450–500 °C and is characterized by the complete oxidation of Fe 2+ to Fe 3+ and by the decrease of the isomerization power of 1-butene of the catalyst. The third variation occurs at about 600 °C and is characterized by a final decrease of surface area, by a strong decrease of catalytic activity and a variation of the IR spectra in the region of MoO stretching frequency.

Higher Alcohol Synthesis over Alkali Metal-Promoted High-Temperature Methanol Catalysts

Abstract Unpromoted and potassium- and caesium-promoted ZnCrO and MnCrO catalysts have been characterized and tested in the direct synthesis of methanol and hig

Oxidation of butenes to maleic anhydride on MnMoO4 based catalyst

The oxidation of n-butene-1 was carried out in a stirred tank reactor and in a pulse reactor using MnMoO4 as a catalyst. This catalyst exhibits a fairly good selectivity to maleic anhydride. MnMoO4 shows a polyfunctional nature; it is possible to distinguish the properties of isomerization, dehydrogenation, oxidation with oxygen insertion, and complete oxidation by varying parameters such as temperature, oxygen concentration and contact time. The compositions of the products in the oxidation of n-butene-1 carried out in a pulse reactor are completely different in the presence and in the absence of oxygen, respectively. In the absence of oxygen, MnMoO4 is a very selective catalyst in the dehydrogenation of n-butene-1 to butadiene. In the presence of oxygen, CO and CO2 are the main products together with small amounts of maleic anhydride. The selectivity of MnMoO4 to butadiene formation has been attributed to the presence of MoO bonds which are responsible for dehydrogenation reactions. A monocenter oxidation mechanism, accounting for the formation of CO, CO2, and maleic anhydride, has been proposed in which the gaseous oxygen is considered to be adsorbed on the same center of the hydrocarbon.

An investigation of the thermodynamic constraints in higher alcohol synthesis over Cs-Promoted ZnCr-oxide catalyst

Abstract A thermodynamic analysis of the oxygenate products of the higher alcohol synthesis (HAS) over an alkali promoted high-temperature methanol synthesis catalyst is performed for a wide range of operating conditions. By comparing actual fugacity ratios with equilibrium constants it is found that a number of reactions approach chemical equilibrium under typical synthesis conditions, namely: (a) formation of methanol; (b) water-gas shift reaction; (c) formation of methyl formate and possibly of higher methyl esters; (d) hydrogenation of aldehydes to primary alcohols; (e) hydrogenation of ketones to secondary alcohols; (f) ketonization reactions. The prevailing thermodynamic constraints determine the relative amounts of primary and secondary alcohols, aldehydes, ketones, esters, and acids. They also explain the experimental effects of temperature, pressure, and feed composition on the same products, as well as some of the differences in product composition observed between the HAS over modified high-temperature and low-temperature methanol catalysts. The observed departures from equilibrium provide insight into the reaction network and information on the mechanism of the synthesis. It is also found that the reactions under thermodynamic control are related to some of the major catalytic functions of ZnCr-oxide systems identified by an independent temperature-programmed surface reaction investigation.

Nature of the active component in a Fe2O3MoO3 catalyst: I. Study on the catalyst reduction and oxidation

The reduction of a catalyst based on Fe2O3MoO3 with N2H2 and N2NH3 as reducing mixtures has been studied by a thermogravimetric method. At the same time the products formed have been analyzed by IR and X-ray powder-diffraction techniques. The initial catalyst contains ferric molybdate, which is the first that is reduced (to ferrous molybdate), and molybdic anhydride, which is reduced to MoO2. Thermal treatments of the catalyst at a temperature higher than 600 °C in air flow can lead to irreversible phenomena, such as sintering. Oxidations, following a reduction, must be carried out at T > 450 °C to ensure a total reoxidation of ferrous molybdate, and with an oxidizing mixture containing a low percentage of O2 (e.g., 5%) in nitrogen, to avoid catalyst decomposition due to local overheating. The reoxidation rate is higher than the rate of reduction. The behavior of ferric molybdate during reduction suggests that the combined iron oxide of the catalyst plays a determining role in the oxidation processes of organic molecules carried out in the presence of catalysts based on Fe2O3MoO3.

A mathematical model for the catalytic hydrogenolysis of carbohydrates

Abstract A new technology aimed at obtaining ethylene and propylene glycols from renewable raw materials via catalytic hydrogenolysis of carbohydrates is being developed inside the Ferruzzi Group. Experimental runs in batch and continuous flow microscale reactors have been carried out to investigate the reaction network, the role of the catalytic agents and the influence of the operating conditions over a wide experimental range. Results obtained have been used to develop a mechanistic kinetic model suitable to account for the observed reagent conversions and product selectivities. The mathematical model has been also validated by further runs at the pilot scale.

Synthesis of alcohols from carbon oxides and hydrogen. V. Catalyticbehaviour of pure Cr, Zn, Mn oxides towards CO/H2

Abstract Pure oxides of Mn, Zn and Cr have been prepared and characterized. Their catalytic behaviour in the direct synthesis of higher alcohols from CO and H2 has been studied in terms of the elementary reactions: formation of methanol, chain growth to higher alcohols, direct water-gas shift reaction, methanation, formation of heavier hydrocarbons. The results provide useful references when analyzing catalysts with more complex formulations.

Liquid phase epoxidation of cyclohexene by tert-butyl hydroperoxide on a Mo-based catalyst

Abstract A kinetic and spectroscopic study has been carried out on the epoxidation of cyclohexene by tert-butyl-hydroperoxide in the presence of MoO2(oxine)2. This catalyst gives quantitative yields of cyclohexene oxide at 80 °C, and is quite stable in t-BuO2H itself. The kinetic investigation of the reaction leads to the following rate law rate = k[t-BuO2H] [cyclohexene] [MoO2(oxine)2]. On the basis of a spectroscopic study, the presence of a catalyst—hydroperoxide reversible complex as the active species in the epoxidation is advanced. The spectroscopic study also indicates that the formation of this active species comes from the opening of a Mo—chelate bond. An oxidative degradation product of the catalyst, which was less soluble and less active than MoO2(oxine)2 and had been obtained by prolonged heating, was isolated and tested as an epoxidation catalyst. The presence of molybdenum—peroxy groups in this compound is indicated by permanganate titration and its infrared spectrum. The influence of the nature of the ligand on activity and selectivity were also investigated. Very strong ligands lead to inactive catalysts, while very labile ligands lead to catalysts with low selectivity.

Adsorption of propylene and acrolein on a BiMoSi oxide catalyst

After vacuum treatment of BiMoSi oxides (in the range 20–430 °C), IR spectroscopy reveals that MoO3 is present on the surface. MoO3 may be present in the starting pressed sample, but may also form from decomposition at high temperature of one of the two bismuth molybdates that constitute the mixed oxides. The presence of C3H6 in the gas phase influences the MoO bond of the MoO3 at the surface. Acrolein adsorption occurs already at room temperature and causes the disappearance of the 990 cm−1 band assigned to the vibration of the MoO bond. Desorption at 225 °C partially restores this band. The infrared spectra of the sample after acrolein adsorption also reveal the presence of firmly adsorbed and weakly adsorbed species. Bands assigned to CO stretching vibrations and CH2 saturated stretching and bending vibrations are seen, but not bands assigned to vibrations of the structure [RCOO]−.

Study of the interaction between CoMoO4 and 341-1341-1341-1-Al2O3 by Raman spectroscopy

Raman spectroscopy has been used to study the solid state reaction of MoO3 and CoMoO4 with γ-Al2O3 and the compounds formed upon the adsorption of Co(II) an Mo (VI) on γ-Al2O3. Results show that γ-Al2O3 endows CoMoO4 and MoO3 with a high reactivity, giving Raman-inactive compounds.AbstractСпектроскопия комбинационного рассеивания была использованиа для изучения твердофазной реакции MoO3 и CoMoO4 с γ-Al2O3 и соединениями, образующимися за счет адсорбции Co(II) и Mo(VI) на γ-Al2O6. Результаты указывают на то, что γ-Al2O3 придает высокую реактивность CoMoO4 и MoO3, давая при этом Раман-неактивные соединения.