Metal oxides humidity effects

Most of the previous work related to catalysts for chlorinated VOC abatement is focused on the development of two type of catalysts, namely those based on noble metals and on transition metal oxides. By contrast, the utility of zeolites as effective catalysts for the decomposition of chlorinated organics has not been explored in detail, when it is reported that metal loaded catalysts employed in commercial applications are susceptible to deactivation by the HCl and CI2 produced during reaction [4]. In our previous works [5,6] it was found that H-zeolites showed a high activity for chlorinated VOC destruction under dry and humid conditions, and that their activity was controlled by the presence of... 

An improvement effected by alkali metal oxide additives is also reported on HjP04-ZrSi02 [22] and zirconium phosphate [23, 24]. The addition of alkali metal ions, therefore, appears to be effective in several respects. Maintaining the alkali metal ions on the surface in humid... 

In neutral and alkaline environments, the magnesium hydroxide product can form a surface film which offers considerable protection to the pure metal or its common alloys. Electron diffraction studies of the film formed ia humid air iadicate that it is amorphous, with the oxidation rate reported to be less than 0.01 /rni/yr. If the humidity level is sufficiently high, so that condensation occurs on the surface of the sample, the amorphous film is found to contain at least some crystalline magnesium hydroxide (bmcite). The crystalline magnesium hydroxide is also protective ia deionized water at room temperature. The aeration of the water has Httie or no measurable effect on the corrosion resistance. However, as the water temperature is iacreased to 100°C, the protective capacity of the film begias to erode, particularly ia the presence of certain cathodic contaminants ia either the metal or the water (121,122). 

A good white smoke can be obtained by the formation of zinc chloride, ZnCl 2, from a reaction between zinc metal and a chlorinated organic compound (the chlorine-containing species serves as the oxidizer). Reaction products that strongly attract moisture (such as ZnCl 2) will have an enhanced smoke effect in humid atmospheres. The burning of elemental phosphoms, producing... 

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