Modelling of the deposition of molybdenum on silicon from molybdenum hexafluoride and hydrogen

The deposition of molybdenum on silicon from MoF6 and H2 is studied using a microbalance setup. The deposition rate is time dependent, which is explained by the significant contribution of the reduction of MoF6 by Si. A model taking into account both deposition routes and in particular diffusion of Si through the growing layer allows to describe the observations quantitatively. The relative importance of two routes was assessed and the kinetics of the reduction by H2 could be distinguished from the overall growth kinetics. A partial reaction order of 1.4 in hydrogen was found for the reduction of MoF6 by H2. The order in MoF6 is negative

CFD based optimization of anionic polymerization in micro flow

Abstract onl

Design of adiabatic fixed-bed reactors for the partial oxidation of methane to synthesis gas. Application to production of methanol and hydrogen-for-fuel-cells.

Adiabatic fixed-bed reactors for the catalytic partial oxidn. (CPO) of methane to synthesis gas were designed at conditions suitable for the prodn. of methanol and hydrogen-for-fuel-cells. A steady-state, one-dimensional heterogeneous reactor model was applied in the simulations. Intra-particle concn. gradients were taken into account explicitly, by solving the continuity equations in the catalyst pellet at each position along the fixed-bed reactor coordinate. The reactor designs are based on supported Ni catalysts, which catalyze the indirect formation of synthesis gas via total oxidn. followed by steam reforming and water-gas shift. In both cases water was added as a reactant. Atm., air-based fixed-bed CPO reactors for fuel-cell applications are feasible due to low catalyst temps. At high-pressure methanol conditions, however, catalyst deactivation will be important as a result of the calcd. high catalyst temps. The influence of the steam-reforming rate was investigated sep. by performing simulations with the kinetic reforming models proposed by Numaguchi and Kikuchi (Chem. Eng. Sci. 43 (1988) 2295) and Xu and Froment (AIChE J. 35 (1989) 88). The influence of the oxidn. kinetics was studied as well. Application of different reforming models leads to significantly different max. catalyst temps. Also, the possible occurrence of gas-phase reactions was investigated: homogeneous reactions will be important at conditions suitable for methanol prodn

Micro structured reactors for synthesis/decomposition of hazardous chemicals. Challenging prospects for micro structured reaction architectures (4)

A review. This paper completes a series of four publications dealing with the different aspects of the applications of micro reactor technol. This article focuses on the application of micro structured reactors in the processes for synthesis/decompn. of hazardous chems., such as unsym. dimethylhydrazine (UDMH), a component of high-energy propellant for liq. fuel rockets. Several examples including highly exothermic reactions with a highly toxic component of high-energy propellant, unsym. dimethylhydrazine, are reviewed. [on SciFinder (R)

Analysis of the isothermal forced flow chemical vapour infiltration process. Part I: Theoretical aspects

In this paper the densification of a cylindrical pore due to a first order heterogeneous deposition reaction on the wall is described. The basic understanding of these mechanisms can aid in the prediction of the infiltration time and composite porosity after densification. The results of the modelling are compared with experimental results which are reported in an additional paper, i.e. Part 2 of this study. The main characteristic parameter that determines the infiltration behaviour is the gas velocity

The oxidative coupling of methane over MgO-based catalysts : a steady-state isotope transient kinetic analysis

To study the heterogeneous steps of the oxidative coupling of methane to ethane and ethene over MgO, Li/MgO and Sn/Li/MgO, oxygen and carbon dioxide isotope step experiments were carried out in the absence of reaction, and oxygen and methane isotope step experiments were carried out in a tubular reactor at 1023 K, atmospheric pressure, an inlet molar ratio of CH4/O2 equal to 4, a methane conversion of 24%, and an oxygen conversion of 85%. The steady-state axial total concentration profiles of the reactants, intermediates, and products have a significant influence on the shapes of the transient isotope responses under these conditions. Oxygen interacts strongly with all catalysts used by dissociative reversible adsorption, except for lined-out Li/MgO. Both surface and bulk lattice oxygen participate in the reaction. The promotion with lithium and even more with tin increases the mobility of oxygen in the bulk of the catalyst and the amount of exchangeable oxygen per unit BET surface area. Carbon in methane can either react to C2 products, without any significant interaction with the catalyst, or show a weak reversible interaction with the catalyst, which does not lead to C2 products. In the absence of reaction, carbon dioxide interacts with the catalyst only in the presence of lithium. Under reaction conditions, the experiments can be described satisfactorily by postulating a methoxy species as the only carbon-containing intermediate on the catalyst leading to carbon dioxide