High-conversion data, site density

Determining Site Density from High-Conversion Data... 

In Section II,B,8 we discussed the question of determining site densities using high-conversion data. We developed a method applicable in the inter-conversion of three isomers when there is a common surface complex for the three possible reactions. We have tested this method using the conversion of 1-butene to cis- and rrans-2-butene over silica-alumina, a system that, according to Hightower and Hall, proceeds through a common surface complex (111). Their conclusion has been confirmed experimentally (112) and by semiempirical quantum-chemical calculations (113). 

It is of interest to compare in absolute values, the HDS activity and SV of two catalysts. (Data for calculation are taken from Ref. 65) For the 2 wt% Mo EV was 3—4 x 10 functioning site mg , the converted thiophene 3,5 X 10 mol/pulse. These values were 4 x 10 f site mg and 4,37 x 10 mol/pulse respectively for the Co(4 wt%) Mo (8wt%) catalyst, i.e., the ratio of V values was 11.76, and that of the thiophene conversions -12, 5. This seems to indicate the reliability of the applied method. It is seen from the data that the maximal density of sites with the higher H2 S release rate within the 0.3-0.4 Co/(Co- - Mo) ratio is typical for the CoMoS phase. At higher Co content, the CogSs phase formation hinders the formation of vacancies with the high sulfur release rate required for this. 

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