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Table 3 Evaluation of EXAFS refinement of dehydrated VxOy/SBA-15.

From: Structural characterization of vanadium oxide catalysts supported on nanostructured silica SBA-15 using X-ray absorption spectroscopy

Type R [Å] σ22]   Procedure #1   Procedure #2  
  N Z ± z F Z ± z F
R(V-O) 4(2) 1.81 0.11 0.7 1.78 0.005 0
σ2(V-O) 4 0.0066 0.0047 0.7 0.0075 0.0004 0
R(V-O) -(2) 1.75 0.04 0.4 - -  
R(V-O) 1 2.89 0.01 0.5 2.90 0.011 0
σ2(V-O) 1 0.0014 0.0017 0.9 0.0017 0.0018 0.7
R(V-V) 1 3.29 0.017 0 3.29 0.016 0
σ2(V-V) 2 0.0135 0.0203 0.7 0.0135 0.00035 0.3
R(V-V) 1 3.61 0.019 0 3.62 0.024 0
R(V-Si) 1 2.54 0.01 0 2.54 0.011 0
σ2(V-Si) 1 0.0115 0.0011 0.3 0.0121 0.0011 0
E0 - -0.9 -0.3 0.8 - - -
  1. V K edge XAFS parameters (Z for distances R and disorder parameter σ2) obtained from two different procedures of fitting a model structure (i.e. "ordered V2O7 dimers" on SiO2 support) to the experimental XAFS FT(χ(k)*k3) of dehydrated VxOy/SBA-15 (10.8 wt %) (details of fit given in Table 2) together with confidence limits (± z, referring to 95% of fit residual) and significance parameters F (details given in text). Fit residual 3.1 for Procedure #1 and 3.6 for Procedure #2.