[Ifeffit] Doubts

Shiju N. R. shiju_nr at yahoo.co.uk
Sun Apr 15 20:35:49 CDT 2007

  I am Shiju and I work as a research associate at the Chemical Engineering department of University of Cincinnati. We are working on the conversion of light alkanes using mixed oxide catalysts. We are trying to understand the structure of a Mo based mixed oxide catalyst that is highly active for this reaction using XAFS and have some data of this catalyst, collected at NSLS.
  Since I am new to XAFS, I am trying to learn it myself.  I am using Athena and Artemis. I am trying to use MoO3 as a model compound for understanding the Mo local structure in my catalyst. By following Scott Calvin's ZnO example (which is highly helpful for beginners like me), I was able to get a reasonable fit for MoO3 structure. For the next step (fitting my Mo catalyst), I would like to seek help regarding the procedure I should follow. I would like to describe my understanding to approach the fitting of my Mo catalyst and please let me know if I am right or wrong. I am going to take same MoO3 structure to form the theory and import the same paths which were used to fit model MoO3 structure. Then I will set the values of S02 and sigma2 to that obtained for MoO3 and allow E0 and delr to vary during the fitting. Please let me know if this is right approach. 
  I tried once this way, also introducing the concept suggested by Bruce Ravel to find the coordination in one of the earlier posts. I used the expression S02 = ni*amp, where i represents each path, keeping the degeneracy of each path as 1. I was able to get a fit, however, ni are fractions and their sum is much less than 6, while I am expecting an octahedral coordination of Mo in my catalyst. Is it due to any mistake in my approach? what should I do to correct it? 
  Please excuse if these questions seem silly... I am just a beginner in XAFS!

Dr. Shiju. N. R.

Research associate

Chemical and Material Engineering

University of Cincinnati


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