Infrared band spectroscopy adsorption complex

D correlation analysis is a powerful tool applicable to the examination of data obtained from infrared spectroscopy. The correlation intensities, displayed in the form of 2D maps, allow us to correlate the shift induced by CO adsorption and acidity of sites in dealuminated zeolites. Results are in accordance with previous results, obtained using only IR measurements, proving the validity of this technique. New correlations allowed the assignment of very complex groups of bands, and 2D correlation revealed itself as a great help for understanding acidity in dealuminated zeolites. 2D correlation has allowed us to validate the model obtained by NMR. 

Nitrogen dioxide, N02, is a fairly small molecule with an unpaired electron and may be expected to be a selective molecule for electron-deficient or Lewis acid sites. Nevertheless, only very little spectroscopic information on the nature of surface species formed on adsorption of N02 is available. Naccache and Ben Taarit (242) have shown by infrared spectroscopy and ESR that N02 forms Cr+N02+ and Ni+N02+ complexes on chromium and nickel zeolites. Thus, N02 behaves as an electron donor and reducing agent in these zeolites. Boehm (243) has studied the adsorption of N02 on anatase and on tj-A1203, which were pretreated at very low temperatures of only 100°-150°C. At 1380 cm-1, a band which is to be attributed to a free nitrate ion, was observed. Boehm (243) has explained the formation of the nitrate ion by the disproportionation by basic OH ions ... 

Optical spectroscopy has been applied with a good deal of success to the identification of chemisorbed species and of the nature of the surface bond. Infrared spectra have been most useful in studies of simple molecules, such as carbon monoxide adsorbed on platinum or nickel, and ultraviolet spectra for the characterisation of more complex interipediates, such as carbonium ions and ion radicals. The frequency of the adsorption band (or bands) often serves to identify the adsorbed species by comparison with spectra of known compounds. Quantitative information may then in principle be obtained by measuring the area under the adsorp-... 

The study of the dynamics of N isotope transfer under adsorption-desorption equilibrium (NO -1- O2 + He) revealed two types of NOx complexes, and their concentrations and formation rates (depending on NO and O2 concentrations) were estimated. According to in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) data, these complexes are assigned to nitrite-nitrate (1520 cm" ) and N02 species (2130 cm" ). Note that nitrite-nitrates and N02 differ clearly in the rates of their formation. Under the reaction conditions, the concentrations of both active species drop considerably. Therefore, two parallel reaction pathways were proposed that involve both active complexes. The rates of NOx complexes interaction with methane were also calculated, and the reaction with participation of N02 species was shown to proceed about 2.5 times faster than that of nitrite-nitrate. The N02 species was determined to form at the interface between CoO clusters and acid OH groups in zeolite (or at the paired Co -OH sites). This finding agrees well with in situ DRIFTS data that indicates that the N02 formation correlates with a drop in the acid OH group band intensity. 

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