Hi Juan, Another suggestion in the mean time (until you can do a temperature series) is to fit multiple coordination shells--there are some excellent papers by Anatoly that do that with systems very much like yours. The reasoning is that for very small samples, the coordination number of shells at higher Reff will be suppressed MORE than the nearest neighbor coordination number, with the ratio determined by the size and shape of the catalyst particles. This helps some in separating coordination number effects from other effects which have been mentioned (e.g. correlation with sigma2, sample homogeneity, etc.). If the suppression in S02 is due to one of the latter factors, I'd expect it to affect all coordination shells pretty much equally, but if it's due to small crystallite size, it should be highly influenced by including more shells in your fit. Combining this with, e.g., a temperature series might well provide you even more confidence that you understand what's going on. --Scott Calvin Sarah Lawrence College