The paper by A. Muiioz-Pbz and M. F. to be a warning in favor of a more rigorous interpretation of XANES spectra by carefully considering the detailed origin of the spectral features in the framework of multiple scattering theory. The authors conclude that, in general, results simply obtained without this analysis could be misleading, and we can of course only agree with this statement.We point out, however, that ab initio simulations on model compounds and the interpretation of experimental XANES spectra arising from Ti atoms absorbing in complex sites (eventually surrounded by adsorbates) are two different things. The complexity of the systems investigated in ref 2 is such that, unlike other authors and as stated clearly as the general philosophy of the paper, we have decided to stay on the more safe and cautious ground of the semiquantitative analysis of the data by considering only intensity and full width at halfmaximum of pre-edge peaks and without pretending to extract more information than actually possible. The correctness of ' And INFN this approach is also recognized by the authors of ref 1 in the last sentence of the first paragraph.With regard to the details of the contribution,' the spectra 1-4 reported in Figure 1A of ref 1 represent the simulation of the rutile XANES spectra performed on clusters of TiiOj of increasing size. This figure clearly shows the importance of long-range effects in the obtained XANES line shape, including the pre-edge features. This data, while interesting on its own account, does not subvert at all the fact that the intense and sharp pre-peak in the Ti XANES spectra is the fingerprint of Ti in tetrahedral symmetry and that a progressive erosion and simultaneous enlargement of the peak indicates (although only in a semiquantitative way) clearly a local change of coordination number and symmetry at the Ti centers. This fact is demonstrated by numerous papers on model compounds quoted in ref 2. Moreover, the high quality of the Ti-silicalite samples investigated in ref 2 (where the Ti/Si ratio is on the order of should guarantee the total incorporation of Ti atoms in the framework, preventing the presence of extraframework clusterized Ti species, as already documented in several by means of numerous and independent characterization techniques like XRD, UV-vis, EPR, IR, Raman, E M S , and XANES. Consequently, Ti atoms being isolated framework species, their second shell environment is formed by Si atoms only. TiiOj clusters are thus unlikely to be present in our samples (with the exception of the trivial TilO4).Finally, we point out that in our previous paper2 the main conclusions about coordination numbers and symmetry, both in the presence and in the absence of adsorbed molecules, were reached only after a detailed comparison with the extended part of the spectrum and with other spectroscopic techniques (IR, Raman, UV-vis, and EXAFS2s3). References and Notes(1) Muhoz-Piez, A.; Ruiz-L6pez, M. F.

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In a previous contribution (J. Phys. Chem. 1994, 98, 4125) we reported EXAFS data collected at ADONE on a high quality Ti-silicalite (TS-1) sample (Ti ) 1.47 wt %) dehydrated in a carefully controlled atmosphere at 400 K. The importance of that paper was to definitively clarify that Titanium atoms occupy silicon substitutional framework positions. However, due to the large incertitude associated with the estimated first shell Ti-coordination number (N ) 4.4 ( 0.6), it was not possible to clarify if only perfect "closed" Ti(OSi) 4 sites are present or if a considerable fraction of defective "open" Ti(OSi) 3 (OH) sites must also be considered (in an ideal EXAFS measurement N is expected to be five if only open sites are present, due to the insertion of a fifth oxygen of the silanol formed in the adjacent Si center when the Ti-O-Si bridge is broken). We report more recent EXAFS data collected at LURE DCI on a high quality TS-1 (Ti ) 2.03 wt %) sample: the higher photon flux of that facility and the higher Ti content of the sample has allowed us to remarkably increase the signal/noise ratio with a consequent reduction of the errors associated with the fitted parameters. The quality of the fit, performed on a wider ∆k range, has also been strongly improved. Our new measurements indicate that a first shell coordination number higher than four (4.44 ( 0.25). This suggests that, even for samples dehydrated in a carefully controlled atmosphere at 400 K, a considerable fraction of sites exhibits the substitution of a bridged oxygen with two OH groups. Being the value of the error bars associated to the EXAFS analysis of fundamental importance for the solidity of our conclusions, both statistical and systematic errors associated with our measurement and data analysis have been deeply discussed. EXAFS results are also qualitatively confirmed by a parallel photoluminescence study, where the presence, in both emission and excitation spectra, of two distinct bands clearly indicates that we are dealing with two family of Ti sites characterized by slightly different environments. For both techniques, the comparison with measurements performed on the Ti(OSi(CH 3 ) 3 ) 4 model compound, where Ti has both the first and the second coordination shells identical to those of Ti (perfect sites) in TS-1, strongly validates our conclusions.

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