Dynamic catalysis

GP 1] [R 13] So-called micro-strip electrodes (MSE) can act as electrically steerable catalysts when used to switch on and off the conversion of ammonia at moderate voltages, several hundred volts (6 vol.-% NHj, 88 vol.-% O2, balance He 0.51 ms 260-380 °C) [75]. Thereby, NO formation was observed. By emitting and accelerating electrons in the range of mA cm current density from the solid to the gas phase, radicals were formed, typically much more than the number of released electrons, e.g. 10 radicals per electron. This efficient use of energy is referred to as dynamic catalysis. The gas phase near the electrodes contains hot and cold radicals, thus providing a two-temperature system. 

Several general conclusions are drawn concerning the status of EM as a supremely versatile tool in the study of the materials chemistry of catalysts. First, it is no longer necessary to regard EM as a tool for model studies (131-133). The triumphant exploitation of the environmental cell in HRTEM marks the dawn of a new era in probing dynamic catalysis (4,87—95). Second, EM techniques, as has... 

R. Ciriminna, S. Campestrini, M. Carraro and M. Pagliaro, Dynamic Catalysis in Aerobic Oxidation by Sol-Gel Living Materials, Adv. Fund. Mater., 2005, 15, 846. 

In dynamic ETEM studies, to determine the nature of the high temperature CS defects formed due to the anion loss of catalysts at the operating temperature, the important g b criteria for analysing dislocation displacement vectors are used as outlined in chapter 2. (HRTEM lattice images under careful conditions may also be used.) They show that the defects are invisible in the = 002 reflection suggesting that b is normal to the dislocation line. Further sample tilting in the ETEM to analyse their habit plane suggests the displacement vector b = di aj2, b/1, 0) and the defects are in the (120) planes (as determined in vacuum studies by Bursill (1969) and in dynamic catalysis smdies by Gai (1981)). In simulations of CS defect contrast, surface relaxation effects and isotropic elasticity theory of dislocations (Friedel 1964) are incorporated (Gai 1981). 

This theory, as originated from the early work of Smoluchowski [20], nowadays has numerous applications in several branches of chemistry, such as colloidal chemistry, aerosol dynamics, catalysis and the physical chemistry of solutions as well as in the physics and chemistry of the condensed state [21-24]. Until recently, its branch called standard chemical kinetics [12, 15, 16] based on the law of mass action seemed to be quite a complete and universal theory. However, because of their entirely phenomenological character, theories of this kind always operate with the reaction rates K which are postulated to be time-independent parameters. 

More examples on reaction mechanisms with nonlinear steps will be discussed further in this chapter and in Chapter 8, which is devoted to dynamic catalysis. 

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