Grain-catalysis studies

Llorca Casanova (2000) demonstrated thatFischer-Tropsch-type (FIT ) catalytic reactions (see Fig. 5.6) occur under low pressures typical of the primitive solar nebula, converting CO and H2 into hydrocarbons. The Haber-Bosch-type (HBT) reaction converts N2 and H2 into reduced nitrogen compounds such as NH3. New 

The experiments themselves were also very simple see Fig. 5.7 (Hill Nuth 2003). As the experiment proceeds they monitored progress by using periodic 

Closed circulation maintained in system via a metal bellows pump 

Observation cell (zinc selenide windows) in IR spectrometer monitors products formed via catalysis 

Gas mix (CO+H3 or N2+H2 or CO+H2+Nj) are circulated continuously through the catalyst via a Pyrex tube inserted into the dust contained in appendix see below) 

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Since the electronic properties of solids depend on the crystal structure, the transition from the crystalline to the amorphous state is expected to result in some modification of electronic (and surface) properties. Amorphous materials have first been used in catalysis [558-560] where some evidence for higher activity has been obtained [561]. In particular, hydrogenation reactions are catalyzed by this class of materials [562]. Studies on the H recombination reaction are also available [563]. However, the evidence that the amorphous state is really the origin of enhanced catalytic activity is not completely clear [562, 564]. These materials have the peculiarity that their surface is relatively homogeneous for a solid and in particular it is free from grain boundaries [565, 566]. Therefore, they have been suggested [562] as ideal model surfaces for studying elementary catalytic reactions, since they can be prepared with controlled electronic properties and controlled dispersion. Nevertheless, many prob-... 

Table 1 of a paper by Murr (2) lists problems and/or concerns related to specific interface materials and specific components of SECS. In Table 2 of the same work, he related topical study areas and/or research problems to S/S, S/L, S/G, L/L, and L/G interfaces. It is also useful to divide interface science into specific topical areas of study and consider how these will apply to interfaces in solar materials. These study areas are thin films grain, phase, and interfacial boundaries oxidation and corrosion adhesion semiconductors surface processes, chemisorption, and catalysis abrasion and erosion photon-assisted surface reactions and photoelectrochemistry and interface characterization methods. The actual or potential solar applications, research issues and/or concerns, and needs and opportunities are presented in the proceedings of a recent Workshop (4) and summarized in a recent review (3). 

Molecules interact with the surfaces of solids in almost every environment in the universe. In addition to purely intellectual interest, we customarily justify studying these interactions on technological grounds, heterogeneous catalysis and the fabrication of microchips being the most frequently listed applications. However the field is much more broadly relevant the adsorption and desorption of atoms and molecules on the surfaces of dust grains is very important to molecule formation in the interstellar medium, reactions on the surfaces of ice crystals is important in atmospheric chemistry and reactions at surfaces determine the behaviour of medical implants in our bodies. 

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