G. R. Kosmambetova

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.

Synthesis of Nanosized ZnO/MgO Solid and Its Catalytic Activity for CO Oxidation

Abstract ZnO/MgO solid samples containing ZnO nanoparticles of controllable size were prepared using colloidal technique. The catalytic performance of the ZnO/MgO samples for CO oxidation was measured. The reaction rate of CO oxidation on the ZnO nanoparticles with variable average radius (2.01−2.29 nm) shows nonmonotonic dependence caused by the quantum-confinement effect.

Structural Organization of Nanophase Catalysts for Preferential CO Oxidation

The structural organization of the main types of catalysts for the purification of hydrogen-containing mixtures from CO impurities by preferential oxidation (PROX), such as deposited systems based on noble metals including dispersed gold and its alloys and multicomponent oxide systems, is examined. It is shown how the structure of the active center, the nature of the support, the nature of interaction between the components of the catalyst, and their dispersity affect the activity and selectivity of PROX catalysts. Special attention is paid to structural organization of copper–cerium oxide systems deposited on zirconium dioxide and the effect of its structural and textural characteristics on the formation of the active centers in the preferential oxidation of CO.

Effect of ultrasonic treatment of the mechanically mixed nanosized CuO–MgO solids on their catalytic properties in the CO oxidation

ABSTRACT The ultrasonic and the combined ultrasonic/mechanochemical treatments were used for the 1% СuO–MgO catalyst preparation by a simple mechanical mixing of the CuO nanopowder with MgO. Results of the XRD and TEM studies show that the ultrasonic treatment significantly increases the CuO nanoparticle size. The CO oxidation study reveals that the impact of the force treatments caused by the ultrasonic and the combined ultrasonic/mechanochemical activation leads to the catalyst deactivation due to the CuO nanoparticles agglomeration.

Effect of the Size of Chromium(III) Oxide Crystallites Obtained by Thermolysis of a Carboxylate Complex on Their Catalytic Properties in the Oxidation of CO

It was established that the activity of catalysts prepared by mechanical mixing of aluminum oxide and the products from thermal decomposition of a carboxylate complex of chromium at 300-700 °C depends non-monotonically on the size of chromium oxide crystallites in the range of 10-50 nm. It was shown that the highest activity is achieved on catalysts in which the size of the chromium oxide crystallites is 23 nm.

Nanosize Effect in Heterogeneous Catalytic Processes Over Copper, Iron, and Zirconium Oxides

A summary is given of the results of studies of the catalytic properties of nanophase systems derived from copper, iron, and zirconium oxides in the ethanol steam reforming, the oxidation of carbon monoxide, the preferential oxidation of CO in the presence of excess hydrogen, the oxidation of benzyl alcohol, and the cracking of triglycerides. A relationship was found between the catalytic activity of copper, iron, and zirconium oxides and the size of their nanoparticles. The reasons for the nanophase effect in these processes were elucidated for a number of systems.

EFFECT OF THE CARBON SUPPORT ON THE CATALYTIC ACTIVITY OF PLATINUM NANOPARTICLES IN THE WATER GAS SHIFT REACTION

Platinum nanoparticles supported on carbon nanotubes display higher activity in the water gas shift reaction with close to 100% conversion of CO at 400–450 °C than for platinum supported on SKT activated carbon. A TEM study showed that this effect may be attributed to stabilization of the platinum nanoparticles on the surface of the carbon nanotubes, which prevents their agglomeration during the reaction.