Honeycomb structure, transition from

Catalysts that promote the combustion of CO and hydrocarbons are, in general, the transition-metal oxides and the noble metals. These materials are supported on a structure ( FIGURE 1425) that allows the best possible contact between the flowing exhaust gas and the catalyst surface. A honeycomb structure made from alumina (AI2O3) and impregnated with the catalyst is employed. Such catalysts operate by first adsorbing oxygen gas present in the exhaust gas. This adsorption... 

In a monodisperse foam the deformation of spherical bubbles and formation of films at the places of their contact starts when the gas content in the system reaches - 50% (vol.) for simple cubic bubble packing or 74% for close (face-centred) cubic or hexagonal packing (foam expansion ratio - 4). In a polydisperse foam the transition to polyhedral structure starts at expansion ratio n - 10-20, according to [ 10] but, as reported in [51], this can occur at n < 4, the latter being more probable. The structure which corresponds to the transition of bubbles from spherical to polyhedral shape is called occasionally honeycomb structure. 

Fig. 23 A Chemical structure of a DBA derivative with alkoxy chains and cartoon demonstrating the transition from a porous honeycomb structure to a dense packing upon elongation of the alkyl chains. B Guest-induced transition from a dense network to a honeycomb network. The graph shows the honeycomb coverage as a fimction of the guest (g) to host h) ratio. STM images (96nmx96nm) recorded at the 1,2,4-trichlorobenzene-graphite interface for different guest to host (g/h) ratios. (Reproduced with permission from [66])...

The coordination chemistry of oxalate (ox, C2042-) compounds provides a series of very interesting compounds from the stereochemical and magnetic points of view [197]. Most frequently the compounds form honeycomb layers in the presence of transition metal ions, in which the stereochemistry of the metal ion coordination sphere alternates between A and A. However, a three-dimensional homochiral structure is also possible. On the other hand, the negative charge of the oxalates necessitates the incorporation of cations between them, which provides the opportunity to introduce chirality and additional functionality in materials. The compound formed between homochiral manganese II oxalate and iron II tris bipyridinc (bpy) with formula [Mn oxls]2 " [Fcn(bpy)3]2+ crystallises in the space group fJ4 32. 

The concentration of 0.30 M CUSO4 (in 0.50 M H2SO4) is the transitional concentration between lower and higher concentrations of Cu(ll) ions. The mixture of holes forming the honeycomb-like structure and dish-like holes was obtained by electrodeposition from this solution at an overpotential of 1,000 mV (Fig. 4.6) [19]. 

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