Yu.P. Tulenin

On the role of heterogeneous and homogeneous processes in oxidative dehydrogenation of C3-C4 alkanes

Abstract The effects of reactor arrangement, catalyst particle size and void volume on the oxidative dehydrogenation (ODH) of propane and iso -butane are studied. In an empty quartz reactor, a high conversion of alkane (up to 36% with a 40% ODH selectivity) can be achieved. Packing of the reactor with different solids (quartz, γ-Al 2 O 3 , complex V-containing oxide catalysts) leads to a drastic change in reaction parameters, which is strongly dependent on the chemical nature of solids and their particle size. The analysis of observed phenomena indicates that: (a) the termination of gas-phase chain reaction takes place on the surface of any solid material; (b) certain solids behave as active generators of free radicals, thus initiating the new reaction pathway which develops both in the gas-phase and on the solid surface.

Effect of redox treatment on methane oxidation over binary catalyst

Publisher Summary This chapter discusses the oxidative transformations of methane with a catalyst system that combines an oxide and a metal component. The presence of both components gave rise to complex oscillation phenomena. The influence of pretreatment and reaction conditions over a wide range of parameters on the oscillatory process was studied. The possible role of mass transfer and the balance of heat in the reactor were analyzed and a model for the role of the components in the binary catalyst system is suggested. A chromel–alumel thermocouple (diameter 0.3 mm, sheathed in a quartz cover or bare) was placed co-axially into the reactor filled with oxide catalyst, making it possible to detect temperature oscillations, accompanying concentration oscillations. This thermocouple in bare form also acts as the metal component in the oxide-metal binary system. The surface area of the thermocouple filament is ∼ 7.5x10 -5 m -2 . The effect of the state of the surface on the kinetic behavior was studied, using various feeder, including the methane-oxygen mixture alternating with inert (He), oxidizing (O 2 ), and reducing (H 2 ) gases. If the oxide component is removed from the reactor, no conversion of reactants is observed, indicating a very low activity of the metal filament in methane oxidation. No reaction occurs also when ethane is added to the methane–oxygen mixture. Oxidation of methane in the presence of such a binary oxide-metal catalyst proceeds in an oscillatory regime and both temperature and concentration oscillations take place. Oscillations arise at the temperature at which the rate of reaction over the oxide component becomes noticeable (∼500 °C).

Effect of pressure on the process of methane oxidative dimerization Part 1. The mechanism of heterogeneous inhibition. of the gas phase reactions

Abstract The possibility is shown of volume process heterogeneous inhibition by magnesium oxide of oxidative methane transformation under gas pressure. A scheme is suggested of the gas phase reaction inhibition mechanism based on the double role of MgO surface which is simultaneously a source and adsorbent of active species.

Redox properties and catalytic performance of complex oxides in oxidative coupling of methane

Abstract The redox properties of model Mn-containing mixed oxide are studied. It is shown that water evolution can determine the rate of oxide reduction. The kinetic model of the redox process taking into account surface interactions and diffusion of oxygen, hydrogen and hydroxy ions in the oxide lattice can describe successfully the experimental data. The influence of slow water evolution on catalytic performance of the oxides in oxidative coupling of methane is discussed.

Effect of pressure on the process of methane oxidative dimerization. Part 2. The catalyzed reaction in conditions of suppression of the gas phase reaction

Abstract It is shown that in methane oxidative dimerization over 1% La 2 O 3 /MgO catalyst at 1123 K in conditions of gas phase process suppression the increase of pressure from 0.1 to 0.8 MPa gives rise to an increase of methane conversion which is accompanied by a more than triple increase of ethylene/ethane ratio. The selectivity of the reaction products formation does not directly depend on pressure being influenced only by the degree of methane conversion.