An all-glass vibration mixed reactor for gas/solid catalyzed reactions

An all-glass vibration mixed laboratory reactor is described which operates as a continuous stirred tank reactor. The mixing and mass transfer characteristics are studied, the latter for the conversion of propan-2-ol in air on the CrO₃/SiO₂ catalyst system. The results complete data of Ref. [6].

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, . , -2- CrO₃/SiO₂. , [6].

     

Heterogeneous reactions : VII. Further studies on the heterogeneous gas/solid reactions of solid alkoxide bases with vaporized chloromethyldimethylhalosilanes

The results of the heterogeneous gas/solid reactions of chloromethyldimethylchloro (and fluoro)silane with solid lithium, sodium and potassium methoxide in the temperature range from 80–160°C are presented and discussed. Reaction with lithium methoxide serves as a clean, efficient high yield synthesis of chloromethyldimethylmethoxysilane without the complicating factors of side products or solvent to separate. The reactions of both the sodium and potassium methoxides lead to the displacement of halogen from silicon and to the displacement of the chloromethyl group. New evidence for the mechanism of the latter reaction is presented. With the potassium compound methylethyldimethoxysilane also is formed and carbene, sila-olefin addition mechanism is suggested. Surprisingly, lithium t-buthoxide did not react with the chlorosilane but did react with the fluorosilane to produce chloromethyldimethyl-t-butoxysilane in high purity and excellent yield. The reaction with potassium t-butoxide was more complicated, giving substitution for halogen and the chloromethyl group at silicon as well as t-butyl ether.     

Theory of irreversible electrode reactions coupled to ion transfer across the liquid/liquid interface

Kinetically controlled electro-oxidation of a redox probe dissolved in the organic solvent, which is interposed between an electrode surface and an aqueous solution as a thin layer, is analyzed theoretically. It is demonstrated that the electrode reaction rate constant can be measured by the variation of scan rate in linear scan voltammetry both in the absence and in the superfluity of the supporting electrolyte dissolved in the film.Dedicated to Professor Dr. Alan M. Bond on the occasion of his 60th birthday     

The contribution of microcalorimetry to the solution of problems involving a liquid/solid or a gas/solid interface,especially in physisorption

After listing a number of basic or applied problems for which it seems advantageous to determine adsorption or immersion enthalpies, this paper describes the methods currently available to determine the enthalpies of (i) immersion into a liquid, (ii) adsorption from a gas, and (iii) displacement from a liquid solution. Typical applications of each technique are reported and commented on.     

The extent of the inhomogeneous region at the gas—solid interface

A new approach to the estimation of the extent of the inhomogeneous region during the adsorption of a gas on a planar or slightly curved solid surface is developed. Relationships are derived that enable the corresponding calculations to be made for the case of dispersion interactions of gases with solids. Numerical estimations of the extent of the inhomogeneous region for graphite-helium (neon, argon, krypton, xenon, and methane) systems as a function of temperature are presented.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 431–433, March, 1995.     

Graphene oxide hydrogel at solid/liquid interface

A strong solid/liquid interfacial interaction is found between porous alumina and graphene oxide (GO) aqueous dispersion, which promotes a fast enrichment of GO on the alumina surface and results in the formation of a GO hydrogel.     

Photocatalytic reactions at the graphite/ice interface

We have studied the photodissociation of water molecules at the ice/graphite interface in the presence of submonolayer amounts of potassium. The ice films were grown at cryogenic temperatures and ultrahigh vacuum conditions. They are transparent for 240-900 nm photons, but the strong light absorption in the uppermost layers of the graphite substrate generates energetic charge carriers that may drive photoreactions at the interface. Similar schemes have been demonstrated and investigated before in the monolayer regime, without an ice layer (D. Chakarov, M. Gleeson and B. Kasemo, J. Chem. Phys., 2001, 115, 9477). Here, using ice films of tens of monolayer thickness and with different morphologies, we have investigated the confinement effects due to the ice layer, and the ice permeability for reaction products.     

Analysis of the gas states at a liquid/solid interface based on interactions at the microscopic level

The states of gas accumulated at the liquid/solid interface are analyzed on the basis of the continuum theory, in which the Hamaker constant is used to describe the long-range interaction at the microscopic scale. The Hamaker constant is always negative, whereas the "gas" spreading coefficient can be either negative or positive. Despite the complexity of gas, including that the density profile may not be uniform due to absorption on both solid and liquid surfaces, we predict three possible gas states at the liquid/solid interface, that is, complete "wetting", partial "wetting", and pseudopartial "wetting". These possible gas states correspond, respectively, to a gas pancake (or film) surrounded by a wet solid, a gas bubble with a finite contact angle, and a gas bubble(s) coexisting with a gas pancake. The typical thickness of the gas pancakes is at the nano scale within the force range of the long-range interaction, whereas the radius of the gas bubbles can be large. The state of a gas bubble(s) coexisting with a gas film is predicted theoretically for the first time. Our theoretical results can contribute to the development of a unified picture of gas nucleation at the liquid/solid interface.     

Pump-probe spectroscopy and circular dichroism of nanocrystalline benzophenone--towards absolute kinetic measurements in solid state photochemical reactions

Nanocrystals suspended in water can be used to record steady state and pump-probe absorption spectra, which should be useful for the study of excited states and reactive intermediates in the solid state.     

Alkane/Alcohol mixed monolayers at the solid/liquid interface

In this work, we present the behavior of solid monolayers of binary mixtures of alkanes and alcohols adsorbed on the surface of graphite from their liquid mixtures. We demonstrate that solid monolayers form for all the combinations investigated here. Differential scanning calorimetry (DSC) is used to identify the surface phase behavior of these mixtures, and elastic neutron incoherent scattering has been used to determine the composition of the mixed monolayers inferred by the calorimetry. The mixing behavior of the alcohol/alkane monolayer mixtures is compared quantitatively with alkane/alkane and alcohol/alcohol mixtures using a regular solution approach to model the incomplete mixing in the solid monolayer with preferential adsorption determining the surface composition. This analysis indicates the preferential adsorption of alcohols over alkanes of comparable alkyl chain length and even preferential adsorption of shorter alcohols over longer alkanes, which contrasts strongly with mixtures of alkane/alkane and alcohol/alcohol of different alkyl chain lengths where the longer homologue is always found to preferentially adsorb over the shorter. The alcohol/alkane mixtures are all found to phase separate to a significant extent in the adsorbed layer mixtures even when molecules are of a similar size. Again, this contrasts strongly with alkane/alkane and alcohol/alcohol mixtures where, although phase separation is found for molecules of significantly different size, good mixing is found for similar size species.     

Adsorption of methylmethacrylate-vinylferrocene copolymers at the solution/solid interface

A series of methylmethacrylate–vinylferrocene random copolymers was synthesized and characterized. Their adsorption from toluene and chloroform was measured onto pyrogenic silicas. The level of adsorption depended on the solvent, the surface area of the adsorbent, and the copolymer composition. Thus, an inverse adsorption-solubility relationship for toluene and chloroform was observed. However, in solvents such as tetrahydrofuran, 2-butanone, and cyclobutanone, which have strong interaction with silica, this trend was not evident. The compositional dependence of the adsorption of these copolymers in toluene and chloroform is similar. Initially, adsorption tends to increase with the vinylferrocene content in the polymer, and at equimolar copolymer compositions the adsorption reaches a maximum which is followed by a decrease in the adsorption values at high vinylferrocene contents. Gel permeation chromatography(GPC) measurements allowed us to conclude that high molecular weight polymer was preferentially adsorbed.     

Electrochemical reactions at the electrode/solution interface: Theory and applications to water electrolysis and oxygen reduction

Theoretical simulations on complex electrochemical processes have been developed on the basis of the understanding in electrochemistry, which has benefited from quantum mechanics calculations. This article reviews the recent progress on the theory and applications in electrocatalysis. Two representative reactions, namely water electrolysis and oxygen reduction, are selected to illustrate how the theoretical methods are applied to electrocatalytic reactions. The microscopic nature of these electrochemical reactions under the applied potentials is described and the understanding of the reactions is summarized. The thermodynamics and kinetics of the electrochemical reactions affected by the interplay of the electrochemical potential, the bonding strength and the local surface structure are addressed at the atomic level.     

Electrochemical reactions at the electrode/solution interface:Theory and applications to water electrolysis and oxygen reduction

Theoretical simulations on complex electrochemical processes have been developed on the basis of the understanding in electrochemistry,which has benefited from quantum mechanics calculations.This article reviews the recent progress on the theory and applications in electrocatalysis.Two representative reactions,namely water electrolysis and oxygen reduction,are selected to illustrate how the theoretical methods are applied to electrocatalytic reactions.The microscopic nature of these electrochemical reaction...     

Some methodological problems concerning nonisothermal kinetic analysis of heterogeneous solid–gas reactions

Isoconversional methods, those using only one curve α = α(T) (α is the conversion degree and T is the temperature), and invariant kinetic parameter method were applied to estimate the kinetic parameters from the following nonisothermal data: (1) simulated TG curves for a single reaction; (2) TG curves for thermal degradation of PVC; and (3) TG curves for the dehydration of CaC₂O₄·H₂O. The results obtained by applying various methods for the same system are compared and discussed. Finally, a procedure of kinetic analysis is suggested. Its application could lead to kinetic parameter values that can be used to predict either α = α(t) curves for other heating rates or α = α(T) curves for isothermal conditions. © 2001 John Wiley & Sons, Inc. Int J chem Kinet 33: 564–573, 2001     

The interaction at the solid/liquid interface of 2,4-dichlorophenoxyacetic acid with silica modified by reaction with ammonia gas

A method for the attachment of ammonia to modified silica gel has been developed. In the first step, tetraethylorthosilicate and (3-glycidoxypropyl)trimethoxysilane were co-condensed in the presence of n-dodecylamine, a neutral surfactant template, to produce a modified mesoporous silica. The epoxy group incorporated into the mesoporous silica was opened by ammonia gas thus introducing amine chelate groups covalently bound to the inorganic surface. The modified material contained 1.13+/-0.06 mmol of amine per gram of silica, exhibited a surface area of 831+/-29 m(2)g(-1) and a porous diameter of 1.95 nm. Infrared, 29Si and 13C NMR spectra were in agreement with the proposed structure of the modified mesoporous silica in the solid state. This ordered organic-inorganic hybrid presented a high capacity for the removal of the agrochemical 2,4-dichlorophenoxyacetic acid from water: the DeltaH and DeltaG values for the interaction were determined to be -110.61 and -9.37 kJ mol(-1), respectively.