Comparison lateral thinking

A comparison of XRD patterns a and a or f and f in Fig. 1 raises the question as to what has become of the active component, the quantity of which is about 10% by weight in a catalyst. First of all, the active components no longer exist in the crystalline state. It is also unlikely that they have become an amorphous mass. Later on we shall provide further evidence to verify that the active component in each case has not formed stoichiometric compound with the support nor has dissolved in the support to form solid solution. It is then reasonable to think that the active component has dispersed as a monolayer on the surface of the support. In view of the high surface area of the supports and the heavy metals in the active components of these catalysts, a monolayer may still amount to a considerable percentage, usually more than 10% by weight, of an active... 

Only two examples of standard copolymers with 14C- abelled propylene have been reported (29, 72). In one study (72) they had to be used because of the low C3 concentration range (0—10% by moles) covered by calibration. (We shall deal with this subject later, since we think that this is an inappropriate choice of analytical band.) The other paper (29) dealing with 14C-labelled C3 contains the remarkable conclusion that comparison of two sets of copolymers prepared with 14C-ethylene and l4C-propylene, respectively, ruled out any possibility of anomalous isotope effects on the polymerization. 

Athough the above criteria look sensible and consistent with each other, we don t claim that they allow to reach the actual surface area of the sample (which, furthermore is never realty accessible by the BET method in the case of microporous materials, as developed later on in this paper). We simply think that these criteria, easy to apply and to introduce in the automatic processing of data (especially in the software of modem adsorption equipment) can make easier and safer the comparison between BET results obtained in different places. We have been using them systematically, for years, and never found any problem in their application [7,8]. Furthermore, the two checks of consistency hereafter were systematically applied and we never saw them failing ... 

---