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2 3 4
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Continued:
Finally, below (Graph 1) we can see the time–sliced values (across 2-minute intervals) for the enthalpies of adsorption on first exposure of each of the clays to 5% ammonia, plotted against time into the interaction. This plot of the data clearly shows that the adsorption processes proceed in a non–linear way. This observation allows us to conclude that there is a distribution of energy on the surface sites of both clays and that the accessibility of the higher energy sites is restricted until some of the more accessible lower energy sites have been occupied by ammonia. This highlights the discovery that two catalysts, which are nominally the same material but which were prepared in different laboratories, display markedly different performances.
Graph 1
 Click to see full size
The radically different behavior of the two K10 materials, which were supplied as having the same nominal characteristics, can be seen in the tabulated data in Table 1 shown previously.
The point here is that the two materials not only display different capacities for 5% ammonia in nitrogen and significantly different molar enthalpies of adsorption, but they also display different kinetics (as in rates) of adsorption. This demonstrates the value of the flow–through approach since all these quantities have been measured with one experiment on each sample.
The differences in surface chemical activity between materials that are nominally the 'same' can be very significant in large–scale production processes. The fact that the flow microcalorimeter can quantify these differences in one (automated) experiment can not only be applied to materials from different suppliers, but in the words of a Dow research technologist: "[The FMC] can even differentiate between the clay lots from one raw material supplier". From "Microcalorimetry Reveals Key Surface Chemistries" in R & D Magazine, December 1993, H. Goldner.
See the FMC Literature References.
The model of Flow Microcalorimeter used for these studies was an FMC–4110
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