G. Mink

Hydrogenation of aniline to cyclohexylamine on NaOH-promoted or lanthana supported nickel

In the vapor phase, the selectivity of the title reaction could be increased to about 90% by promoting traditional type nickel catalysts with NaOH. The use of strongly basic lanthana as support resulted in 95–99% selectivity.

Kinetic study of the carbonyl sulphide synthesis from carbon dioxide and carbon disulphide on alumina catalysts

Abstract The kinetics of the CO 2 +CS2=2COS reaction over new and used alumina catalysts was studied at 523–623 K. The adsorption of the reaction components was measured at the temperature of the catalytic tests by volumetric and thermogravimetric methods. The number and energetics of the acidic and basic sites were investigated with a combined volumetric-microcalorimetric method using NH 3 and CO 2 as probe molecules. The equilibrium constants of the main reaction and several assumed side reactions have also been calculated. Closely zero order and first order behaviour were observed for CO 2 and CS 2 , respectively. The loss of catalytic activity upon long term loading was roughly proportional to the loss of the surface basic sites whereas the number of the acidic centers moderately increased. On all catalysts, very likely by the removal of basic OH and 0 2 -sites, carbon tetrachloride immediately caused an ultimate cession of the catalytic activity. As CS 2 also reacts with the surface OH groups, leading to H 2 S and side products, under steady state conditions the rate-determining step is considered to be the reaction of strongly adsorbed CO 2 (presumably in a bidentate or a bridging carbonate form) with physisorbed or gas-phase CS 2 . Efforts to regenerate the aged catalysts by treatments with oxygen at 573 K or by leaching with liquid phase CS 2 have failed.

Surface reactions of chlorine with /gg-alumina

The reaction of chlorine with γ-alumina was studied in the temperature range 300–1070 K by thermogravimetry and also by pulse and volumetric adsorption methods. An exclusively surface reaction was observed at 500–800 K, resulting in the consumption of chlorine and the formation of oxygen, which was detected by a gas chromatography-coupled pulse reactor. This oxygen-chlorine exchange on the surface led to a weight increase, as found in thermogravimetric experiments. As the formation of AlCl3 or AlOCl is not favoured in this temperature range for thermodynamic reasons, the observed reaction can only take place on a surface possessing excess energy. The extent of the oxygen-chlorine exchange increases with increasing temperature.

Thermogravimetric, mass spectrometric and XPS investigation on the chlorination reactions of V2O5 AND TiO2

Abstract Comparative studies on the kinetics and mechanism of the chlorination of V 2 O 5 and TiO 2 /anatase/ with CCl 4 have been performed. The chlorination of V 2 O 5 occurred to be O.5 order in CCl 4 , whereas in case of TiO 2 closely first order kinetics was observed with apparent activation energies of 77 ± 5 and 118 ± 7 kJ.mol −1 , resp. In both cases a dissociative adsorption of CCl 4 is considered to precede the reaction and the transformation of CCl 4 to CO 2 is assumed to occur via the formation of adsorbed COCl 2 intermediate. In case of V 2 O 5 , phosgene is less reactive than CCl 4 , so during the chlorination of V 2 O 5 by CCl 4 the gas phase concentration of COCl 2 might achieve a considerable level, while in the TiO 2 CCl 4 system only trace quantities of phosgene are observable. At the beginning of the reactions step by step exchange of surface O by Cl occurs, and the surface intermediates of the chlorination are V and Ti ions of lowered valence state, as it has been characterized by ESCA.

Chlorination of V2O5 by CCl4. Adsorption and steady state reaction

The adsorption of CCl4 on V2O5 as well as the steady state kinetics of the chlorination reaction in this system have been studied by volumetric and thermogravimetric methods. Though the adsorption observable below 420 K is of physical character, it can be suggested that an unmeasurable, dissociative type adsorption also occurs. The apparent activation energy of the chlorination process is 77±5 kJ mol−1, while the reaction order is 0.5 in CCl4.AbstractАдсорбция CCl4 на V2O4 и кинетика стационарной реакции изучены с помощью волюметрического и термогравиметрического методов. Ниже 420 К адсорбция носит физический характер, однако предполагается, что незначительная часть CCl4 претерпевает диссоциацию. Кажущаяся энергия активации хлорирования 77±5 кДж. моль−1, а порядок реакции составляет 0,5 по CCl4.

Chlorination of V2O5 by CCl4. The proposed reaction mechanism

Initial stage of the reaction of CCl4 with V2O5 has been studied by MS and XPS techniques. According to the proposed mechanism dissociatively chemisorbed CCl4 transforms to CO2 via adsorbed COCl2, while surface vanadium atoms involved are gaining step by step two chlorine atoms before the formation of the volatile end-product VOCl3.AbstractПервоначальная стадия реакции CCl4 с V2O5 была изучена с помощью массспектрометрии и рентгеновской фотоэлектронной спектроскопии. По предложенному механизму диссоциативно-хемосорбированный CCl4 превращается в CO2 через COCl2, поверхностные атомы ванадия постепенно принимают два хлора перед образованием летучего конечного продукта реакции VOCl3.

On the use of “pseudo-atoms” in cluster calculations for modelling molecular fragments, solids and surfaces

Abstract A procedure is developed for performing cluster calculations within the framework of the standard CNDO/2 formalism, in which some atoms of the cluster may be replaced by “pseudo-atoms” possessing only one or two hybrid orbitals directed to selected atoms of the cluster. The method is similar to those of Laszlo and Litisnkij and seems promising in calculating chemically important fragments of large (bio)organic systems, as well as in modelling the bulk of the solids and their surfaces. Correlations between the calculated quantities and some experimental results obtained by using the ESCA technique are also discussed.

The influence of submonolayer silica on the surface properties of Y-alumina

Abstract Silica was deposited onto the surface of calcined Y-alumina at 870–1140 K by the reaction with SiCl 4(g). The solid product was analysed by XPS and AAS. Comparison of the surface and bulk compositions revealed that deposited silica is located in the outermost layer. With increasing silica-content an increase of the O(1s), Si(2p) and Al(2p) binding energies occurs, indicating a continuous change of the electronic state of the surface. The Si-Auger parameter exhibits a maximum at about 3 at% Si/(Si+Al). Enhanced catalytic activity in n-hexane cracking reaction was observed for the samples with low Si-content. Correlation is established between the electronic state of Si and the catalytic activity of the samples.

TG study on the reaction of γ-Al2O3 by CCl4. Part I. Kinetic model for the chlorination process

Abstract Thermogravimetric (TG) measurements were carried out to study the chlorination of γ-alumina by gaseous CCl 4 in the temperature range 650–1123 K at 10 2 –10 4 Pa CCl 4 partial pressure. Experimental results indicate that the reaction involves two main steps: the substitution of oxygen atoms on the surface by chlorine leading to a mass gain and the volatilization of the main gaseous product, aluminium chloride, with a mass loss of the sample. These processes take place simultaneously during the course of the reaction. A kinetic model is proposed to describe these two steps providing a simple method for linearization of the initial part of the isothermal TG curves. Temperature and partial pressure dependence of the reaction rate and of the steady-state surface coverage are discussed on the basis of the proposed kinetic model. Activation energies and reaction orders are calculated for these two steps.

A kinetic study of the chlorination of MO3 by CCl4

Abstract The surface and morphological properties of molybdenum trioxide were characterized using microcalorimetric and SEM methods. The number of acidic and basic sites were measured by NH 3 and SO 2 adsorption, respectively. According to the microcalorimetric data, strong dissociative adsorption of NH 3 takes place on the surface, while there is no interaction between the MO 3 lattice and SO 2 gas. The chlorination kinetics of MO 3 with gaseous CCl 4 were studied by thermogravimetry. The values of the apparent activation energy and the formal reaction order were calculated from the temperature and partial pressure dependence of the initial rate, respectively. From the results obtained, the combined control of pore diffusion and chemical reaction, as well as the dissociative adsorption of CCl 4 , were deduced. Due to the very low porosity of the solid particles, in addition to the reaction occurring in a zone near the pore tunnels, chlorination at the external surface cannot be neglected. Thus, to describe the conversion versus time curves, a kinetic model was proposed based on the different linear rates of the interfacial chemical reaction at the external surface of the particles and that in the reaction zone controlled by pore-diffusion processes. Using this model, a fairly good correspondence between the measured and calculated kinetic curves was obtained.