🗊Презентация Heterogeneous catalysis

ҚАЗАҚСТАН РЕСПУБЛИКАСЫ БІЛІМ ЖӘНЕ ҒЫЛЫМ МИНИСТРЛІГІ ПОРТФОЛИО ПӘНІ: Физикалық химия Қ.А.Ясауи атындағы Халықаралық қазақ-түрік университеті Жаратылыстану факультеті ЖХМ-511(Ғ) тобының студенті Мәлкен.Т.А. Түркістан 2017

Plan: The basic concept of heterogeneous catalysis Adsorption theory of heterogeneous catalysis Stages of heterogeneous catalysis Concepts

heterogeneous catalysis

Describes the catalytic processes that occur at the interface of the solid phase (catalyst) and the gas phase (reactants). The central role in the process (HA) is played by physical and chemical adsorption. Adsorption Adsorption is the accumulation of molecules at the phase interface. Physical adsorption occurs under the action of van der Waals forces. Chemical adsorption (chemisorption) occurs due to the formation of chemical bonds between adsorbed molecules and the surface. Describes the catalytic processes that occur at the interface of the solid phase (catalyst) and the gas phase (reactants). The central role in the process (HA) is played by physical and chemical adsorption. Adsorption Adsorption is the accumulation of molecules at the phase interface. Physical adsorption occurs under the action of van der Waals forces. Chemical adsorption (chemisorption) occurs due to the formation of chemical bonds between adsorbed molecules and the surface.

Reactive molecules diffuse to the surface of a solid. Reactive molecules diffuse to the surface of a solid.

The reacting molecules are first adsorbed physically, then enter into chemical reactions with active surface centers (chemisorbed). Active centers are free areas of the surface where molecules of reacting substances can be adsorbed. Another part of the surface of the catalyst is occupied by adsorbed impurity molecules. The number of active sites per unit surface depends on the nature and method of preparation of the catalyst. The reacting molecules are first adsorbed physically, then enter into chemical reactions with active surface centers (chemisorbed). Active centers are free areas of the surface where molecules of reacting substances can be adsorbed. Another part of the surface of the catalyst is occupied by adsorbed impurity molecules. The number of active sites per unit surface depends on the nature and method of preparation of the catalyst.

The adsorbed atoms and molecules react chemically with the formation of products. The adsorbed atoms and molecules react chemically with the formation of products.

The molecules of the reaction products pass from the state of chemisorption to the state of physical adsorption and then desorbed from the surface. The molecules of the reaction products pass from the state of chemisorption to the state of physical adsorption and then desorbed from the surface.

The molecules of the reaction products diffuse from the surface. The molecules of the reaction products diffuse from the surface.

Concepts In heterogeneous catalysis, the reactants diffuse to the catalyst surface and adsorb onto it, via the formation of chemical bonds. After reaction, the products desorb from the surface and diffuse away. Understanding the transport phenomena and surface chemistry such as dispersion is important. If diffusion rates are not taken into account, the reaction rates for various reactions on surfaces depend solely on the rate constants and reactant concentrations. For solid heterogeneous catalysts, the surface area of the catalyst is critical since it determines the availability of catalytic sites. Surface areas can be large, for example some mesoporous silicates have areas of 1000 m2/g. The most common approach to maximizing surface area is by the use of catalyst supports, which are the materials over which the catalysts are spread.

References Gadi Rothenberg, Catalysis: Concepts and green applications, Wiley-VCH: Weinheim, ISBN 978-3-527-31824-7 Swathi, R.S. and Sebastian, K.L. Molecular mechanism of heterogeneous catalysis. Resonance Vol. 13 Issue 6 (2008) p. 548-560. Frank, B.; Blume, R.; Rinaldi, A.; Trunschke, A.; Schlögl, R. (2011). "Oxygen Insertion Catalysis by sp2 Carbon". Angew. Chem. Int. Ed. 50 (43): 10226–10230. doi:10.1002/anie.201103340. Sheehan, D.P., Nonequilibrium heterogeneous catalysis in the long mean-free-path regime, Phys. Rev. E 88 032125 (2013).