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Abstract: The N2O decomposition over Fe-ferrierite, Fe-beta, and Fe-ZSM-5 has been recently studied [K. Jisa, J. Novakova, M. Schwarze, A. Vondrova, S. Sklenak, Z. Sobalik, J. Catal. 262 (2009) 27] and a superior activity of Fe-ferrierite with respect to Fe-beta and Fe-ZSM-5 has been shown. In this study, we investigated (1) plausible active sites for the N2O decomposition over Fe-ferrierite and (2) the origin of the distinct reactivity of Fe-ferrierite, Fe-ZSM-5 and Fe-beta employing a combined theoretical (periodic DFT) and experimental (UV–vis–NIR spectroscopy, IR spectroscopy, 29Si MAS NMR spectroscopy and catalytic batch experiments) approach. We evidenced that two Fe(II) cations accommodated in two adjacent six-membered rings in the eight-membered ring channel (β sites) of Fe-ferrierite (the calculated Fe–Fe distance is 7.4Å) form the active site responsible for the superior activity of this catalyst in the N2O decomposition in the absence of NO. Similar structures can be formed in Fe-beta. However, the probability of their formation is very low. For Fe-ZSM-5, the geometrical arrangement of the cationic positions is far from that in Fe-ferrierite and it is not suitable for the N2O decomposition. Therefore, the predicted order of the activity of the Fe(II) exchanged zeolites agrees with our experimental findings and it is: Fe-ferrierite≫Fe-beta>Fe-ZSM-5. We further showed that the accommodation of divalent cations in rings forming cationic sites can lead to significant rearrangements of the local structures of the zeolite framework, and therefore, the precise structure of sites binding a divalent cation cannot be derived from results of X-ray diffraction experiments, but can be inferred from theoretical calculations. [Copyright &y& Elsevier]

Abstract: Quantitative surface enhanced resonance Raman scattering (SERRS) requires effective adsorption of the analyte onto the metal surface. A range of dyes incorporating the benzotriazole group has been specifically designed to achieve this and they have proved successful labels for obtaining very sensitive analysis. However, if the spectra were more fully understood, the differences between the Raman spectrum in solution and on the surface could provide unique structural information on the nature of the surface layer. Using density functional theory (DFT) calculations the Raman and Infra-red (IR) spectra of the dye 3,5-dimethoxy-4-(6′-azobenzotriazolyl)-phenylamine (ABT-DMOPA) were assigned. A good correlation was found between the computed and experimental frequencies. Two competing isomers were compared and gave a largest error in fit for any clearly assigned band in the Raman spectrum of 41cm−1 and an overall fit error of ∼15cm−1. For the IR spectrum the largest error was 24cm−1 with an overall fit error of ∼8cm−1. Comparison of resonance Raman, SERS and SERRS spectra of the dye showed intensity changes which suggest the formation of a complex with silver on the surface. In the 1600–1630cm−1 region, one vibration is reduced in intensity whilst one is greatly enhanced as surface attachment occurs, giving a good marker for surface attachment. [Copyright &y& Elsevier]