Thermo- and photospillover of hydrogen atoms in multicomponent systems

Thermo- and photospillover of hydrogen atoms in multicomponent systems 

A majority of publications available at the moment on the spillover effect, i.e., the effect in which active particles in heterogeneous systems flow from an activator (donor) to carrier (acceptor), is devoted to hydrogen. Among the systems considered are mainly metal-oxide ones, where this interesting effect has been observed for the first time [35]. 

The effect has attracted considerable interest, when the mechanism of heterogeneous thermo- and photoprocesses on the so-called deposited metal catalysts was studied. The catalysts usually consist of two components an inert carrier (AI2O3, Si02, etc.) and an activator. The role of an activator is usually played by metals (Pt, Pd, Ni, etc.) dispersed on the surface of a carrier. 

Note that this method enables one to observe variation of electric conductivity of a sample due to adsorption of hydrogen atoms appearing as a result of the spillover effect, no more. In a S3rstem based on this effect it is rather difficult to estimate the flux intensity of active particles between the two phases (an activator and a carrier). The intensity value obtained from such an experiment is always somewhat lower due to the interference of two opposite processes in such a sample, namely, birth of active particles on an activator and their recombination. When using such a complicated system as a semiconductor sensor of molecular hydrogen (in the case under consideration), one should properly choose both the carrier and the activator, and take care of optimal coverage of the carrier surface with metal globules and effect of their size [36]. 

In order to develop more informative and direct method of studying the spillover effect of active particles, the authors of [37] suggested to use the sensor method of detecting migrating particles based on separation of sensor and emitter (donor) of active particles. The latter consists of small metal globules, or clusters (with a diameter of about 20-30 A) of Pt, Pd, Ni, etc. (activator) deposited on quartz or sapphire (AI2O3) plate in the form of a strip less than 1 cm wide. The sensor for detection of hydrogen atoms consisted of a zinc oxide strip (with a width of about 0.1 cm and thickness wlOO nm) deposited on the same plate at a distance of 0.03 or 0.6 cm (two versions) from the inner boundaries of activator strips [38]. 

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