Potassium alumina, interaction with

This trend in the TOF values was found not to correspond with the variations in the strength of the terminal V=0 bond as measured by the respective Raman shifts (Banares, 1999 Wachs et al., 1996). Potassiumdoping of alumina-supported vanadia catalysts resulted in lower V = O frequencies, which indicated a weakened terminal V = O bond (Cortez et al., 2003). However, the propane conversion and the catalyst reducibility decreased. Therefore, it was not considered to be likely that the terminal V=0 bond is the active site for alkane ODH on supported vanadia. The same effect was observed for titania-supported vanadia. DFT calculations described a close interaction of potassium ions with both the supported vanadia and the titania support (Si-Ahmed et al., 2007 Lewandowska et al., 2008). Such an interaction leads to an elongated V=0 bond with a... 

As explained earlier, alkali metal oxides are often used as promoters for chromia-alumina, and it is of some interest to determine the manner in which the promoter interacts with the chromia. Voltz and Weller (29) studied the influence of various amounts of potassium on chromia-alumina, and concluded that potassium stabilizes the chromia against reduction to the state, although the effect was less with chromia-alumina than it was with unsupported chromia. It was postulated that the potassium combined with the supported chromia to form chromate or dichromate, and that the stabilization against reduction was due to the higher stability of potassium chromate or dichromate compared to that of the higher chromium oxides. 

Both Schlogl and Somorjai report on the interaction between oxidized iron and the promoters, mainly alumina and potassium oxide. In particular, the interaction with the structural promoter, alumina, can alter significantly the crystallography of the metallic iron surfaces formed during reduction. Since supported iron catalysts can contain much more alumina than normal for the industrial ammonia synthesis catalyst, any interaction between the iron oxide being reduced and the alumina support is much more easily observed. Some results, indicating unambiguously the effect of the interaction of iron with the alumina, will therefore be reviewed. 

The potassium ferrites form during catalyst production increase catalyst activity np to about 0.8% potash but above this level activity falls. Ammonia catalysts are said to be doubly-promoted. This is because alumina—a structural promoter—helps control and stabilize both the porosity and surface area of the reduced catalyst on the other hand, potash— an electronic promoter—increases the catalyst activity. Other promoters may have similar effects but usually interact with poisons or impurities to protect the catalyst. 

Gas chromatography columns for interplanetary exploration should be very efficient, due to the stringent demands imposed on payload. Porous-layer open tubular (PLOT) columns loaded with a styrene-divinyl benzene copolymer showed better performance than Cromosorb 103 or Porapak Q columns in the analysis of low molecular weight hydrocarbons and nitriles. Potassium chloride-deactivated alumina PLOT columns, on the other hand, were not good for the intended purpose, because low molecular weight nitriles were difficult to elute. Wall coated open tubular (WCOT) columns with a stationary chemically bonded phase of dimethyl siloxane have the mechanical resilience to endure the conditions of extraterrestrial exploration and separated efficiently C1-C4 nitriles. Permanent gases were analysed in the presence of hydrocarbons and nitriles with a PLOT capillary column. The equilibrium constant for the interaction of nitrile groups with various solutes was determined by GLC. ... 

Weller and Voltz (25), but the potassium does not stabilize the chromia against subsequent reduction. Third, the Weiss constant A of the reduced catalysts generally increases with increasing potassium content, while that of the oxidized catalysts passes through a minimum. The conclusions drawn from these data were (1) small amounts (<0.2 wt %) of potassium are not associated with the chromia, but rather with the alumina portion of the surface (2) additional potassium interacts... 

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