Heat and mass transfer at ignition of solid condensed substance with relatively low calorific power by a local energy source

Macroscopic laws of heat and mass transfer at gas-phase ignition of solid condensed substance with relatively low calorific power by a typical local energy source, namely, a small hot metal particle shaped as a parallelepiped, are investigated. The proposed model takes into account a group of interrelated processes of heat and mass transfer with thermal decomposition and chemical reaction in the interaction of solid and a source with limited energy content. The influence of the heat content of a local energy source on the characteristics of the process is analyzed.     

Geometric and electronic approaches to size effects in heterogeneous catalysis

The influence of electronic and geometric factors is considered in the context of the manifestation of size effects in heterogeneous catalytic oxidation and hydrogenation reactions. Both of the factors are interdependent; however, the electronic factor predominates with regard to small metal and metal oxide particles (smaller than 10 nm), for which the energies of electron transitions in an activated complex are size-dependent. Only the geometry of active component nanoparticles exerts the main effect on the catalytic properties of coarser particles. In this case, the geometric factor depends on the accessibility of the active surface to reactants. The probability of the occurrence of complex active centers including several surface atoms increases as the active component particles of a catalyst become larger. The efficiency of the approach proposed to study the activating effect of nanophase catalysts is demonstrated using the oxidation and hydrogenation reactions of carbon oxides and the hydrogenation of acetonitrile and acetone as examples.     

Characteristics of heat and mass transfer at ignition of a thin film of condensed liquid substance by hot particles of different configuration

Characteristics of a complex of heat-mass transfer processes with phase transitions and chemical reaction are numerically investigated at ignition of a thin film of typical liquid condensed substance by single hot metal particles shaped as a hemisphere, disc, and parallelepiped. The influence of a source configuration with a limited energy content on the ignition delay time of liquid is estimated. The ranges of heat source parameters at which the influence of the source configuration on the ignition delay time is minimal are determined.     

Kinetic modeling for the conversion of synthesis gas to dimethyl ether on a mixed Cu-ZnO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst with γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

A model is proposed for the kinetics of the direct conversion of synthesis gas to dimethyl ether (DME) on a bifunctional catalyst in a flow reactor. Calculations for the yield of methanol and DME were carried out using literature data for the kinetics of methanol synthesis and methanol dehydration.     

Secondary reactions of ethylene and propylene in the Fischer-Tropsch synthesis on cobalt-aluminum and cobalt-chromium catalysts

The only secondary reaction of olefins in the Fischer-Tropsch synthesis on Co/SiO₂·Al(III) and Co/SiO₂·Cr(III) with 2.7·10⁻⁶ and 4.0·10⁻⁶ g-ion/m² cation concentration in the support matrix, respectively, is dimerization of ethylene to give a four-carbon intermediate, which participates in the growth of C-C bond chains according to the classical FT synthesis mechanism. When the chromium concentration is increased by a factor of 1.7, secondary ethylene reactions occurring on the acid sites of the catalyst are also observed. When the aluminum concentration is increased by a factor of 3.4, we observe the oligomerization of ethylene and propylene. The secondary reactions of ethylene mainly result in linear hydrocarbons, while oligomerization involving propylene gives a significant amount of branched hydrocarbons. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 115–120, March–April, 2008.