Hans-Günther Lintz

Oszillationen der reaktionsgeschwindigkeit bei der reaktion von NO MIT CO an platin im Knudsengebiet

The reduction of NO by CO on a polycrystalline platinum ribbon is studied in a open system at pressures less than 5 × 10−4Torr (6.7 × 10−2Pa). In the temperature range 440 < T/K < 520 one can initiate sustained oscillations of the reaction rate in an oxidizing atmosphere (1 < pNO/pCO < 4). At constant feed of gas to the reactor this can be obtained by a temperature jump, at constant temperature of the catalyst these oscillations may be created by the variation of the partial pressure of one of the reactants. As the oscillations arise isothermally under Knudsen conditions they cannot be due to the coupling of transport phenomena and reactions at the catalyst surface. The interaction between adsorbed gases and the surface structure must play the determinant roll.

Die kinetik der reaktion zwischen no und co an polykristallinem platin bei niedrigen drucken: I. Messmethode und experimenteller Befund

The reaction between NO and CO on a polycrystalline platinum ribbon under stationary conditions is followed by mass-spectrometry using isotopically labelled 13CO. At temperatures from 300 to 1100 K the ratio of the partial pressure of reactants varies between 0.1 < PNOPCO < 10, the value of total pressure in the reactor being 1.75 × 10−4 or 4.2 × 10−3 Torr. The main reaction to N2 and CO2 is accompanied by the parallel reaction to N2O and CO2 which attains under certain conditions up to 50% of the total reaction. The pronounced temperature dependence of the reaction rate leads to maximum values between 500 and 650 K, the corresponding values of the reaction probabilities are as high as 0.3.

DIe kinetik der reaktion zwischen NO und CO an polykristallinem platin bei niedrigen drucken: II. Deutung und aufstellung einer elementarreaktionensequenz

Abstract The experimental results of the reaction between NO and CO on polycrystalline platinum are described using a sequence of elementary steps which include molecular adsorption and desorption of the reactants, dissociation of adsorbed NO to N 2 and atomic oxygen and finally reaction of this oxygen with CO forming CO 2 . The model takes into account two different kinds of surface sites. Calculations based on slightly modified literature values of model-param- eters show good agreement with the experimental results.

Alternative Reaction Engineering Concepts in Partial Oxidations on Oxidic Catalysts

The production of organic oxygenates by partial oxidation on oxidic catalysts is of considerable industrial importance. Excellent selectivities and yields are often obtained in multitubular reactors due to high performance catalysts. However, there are several processes, e.g., the production of maleic anhydride and phthalic anhydride, where the product yield could be enhanced and improvements are desirable. Various reaction engineering concepts are proposed for that purpose, from reactor structuring to electrochemical promotion. In this article, the actual state of these efforts, which are often at the very beginning, is reviewed.

The oxidation of solvents in air on oxidic catalysts: formation of intermediates and reaction network

The oxidation of typical solvents present in air has been investigated over oxidic catalysts. The results show that the formation of partially oxidized intermediates generally takes place. In the case of the post-combustion of isopropanol, acetone and butyl acetate the kinetics of the production of such intermediates can be quantified by the use of simple reaction networks and appropriate rate equations. In this way, pitfalls in the dimensioning of reactors with integrated regenerative heat exchange may be avoided.

The low temperature limit of the application of solid electrolyte potentiometry in heterogeneous catalysis

Solid Electrolyte Potentiometry is an electrochemical method to characterise the state of solid catalysts under working conditions. Its application is temperature limited due to polarization effects at the catalyst electrode. A new operational definition of this temperature limit is proposed which is based on the measurements of exchange current densities.

The oxidation of carbon monoxide on polycrystalline rhodium under Knudsen conditions. I: Reaction with oxygen

The reaction between oxygen and carbon monoxide on a polycrystalline rhodium ribbon under stationary conditions is followed by mass spectrometry. At temperatures from 300–1100 K the ratio of the partial pressures of reactants varies between 0.1 < pO2/pCO < 100. The value of the total pressure in the reactor varies between 10−5 and 10−4 Torr. The reaction on rhodium shows similar features as in the case of platinum. The results are consistent with a simple elementary reaction sequence but quantitative agreement by model calculations was not obtained.

The oxidation of carbon monoxide on polycrystalline rhodium under knudsen conditions: II. Reaction with nitrogen monoxide

Abstract The reaction between carbon monoxide and nitrogen monoxide on a polycrystalline rhodium ribbon under stationary conditions is followed by mass spectrometry. In the temperature range 300 to 1100 K the ratio of the partial pressures of the reactants varies between 0.1

Die Kinetik der Reaktion zwischen Distickstoffoxid und Kohlenmonoxid an polykristallinem Rhodium bei niedrigen Drucken

The reaction between nitrous oxide and carbon monoxide on a polycrystalline rhodium ribbon under stationary conditions is followed by mass-spectrometry using isotopically labelled 13CO. At temperatures from 300—HOOK the ratio of the partial pressures of reactants varies between 0.01 < Pu o/pco < 100> me value of the total pressure in the reactor between 10~5 and 10~4Torr. The measured reaction rate is of the same order of magnitude as in the case of the reaction between CO and NO under identical conditions. At temperatures above 800 the results can be interpreted by means of a simple elementary reaction sequence.

The oxidation of carbon monoxide on polycrystalline rhodium under knudsen conditions: III. Simultaneous reaction with oxygen and nitrogen monoxide

Abstract The CO oxidation using mixtures of oxygen and nitrogen monoxide has been studied under stationary conditions. The measured selectivities could not always be foreseen from the results obtained in the binary systems CO/O2 and CO/NO. At high temperatures the amount of NO reduced is directly proportional to its fraction in the oxidizing gas. At low temperatures, NO may be reduced with high selectivity even in the presence of high oxygen concentration.