Redox FTIR study

Redox chemistry of Cu/ZSM-5 effect of oxygen. An FTIR study... 

Montanari, T, Matarrese, R., Artioli, N., et al. (2011). FTIR study of the surface redox states on platinum-potassium-alumina catalysts, Appl. Catal. B Environ., 105, pp. 15—23. 

On the basis of in situ FTIR studies under steady-state conditions, Topspe et al. [51] have proposed a mechanism by which ammonia is instead adsorbed on a Brpnsted acid site associated with a V +-OH site, followed by activation of the adsorbed ammonia by a nearby V +=0 group (which is reduced to a V +-OH species). Then NO reacts from the gas-phase with the activated ammonia complex leading to the formation of an intermediate, which then decomposes to nitrogen and water. Regeneration of the active sites (i.e., oxidation of the reduced V +-OH sites to V +=0 groups) occurs by gas-phase oxygen. Accordingly, the proposed catalytic cycle consists of both acid-base and redox functions. 

The quantification of the reversible metal deactivation effects induced on an Au/CZ catalyst by a series of redox pre-treatments, which consecutively changed the redox state of the support, have also been investigated using the methodology discussed above/ In this investigation, FTIR and volumetric adsorption studies of CO were combined with nanoparticle size distribution data, as determined by HAADF-STEM, and redox characterization studies of the ultimate OSC, as determined by thermo-gravimetric measurements, and XPS. 

Figure 2.28 (left) FTIR study of CO adsorption on an AU/CZ sample sulgected to a successive series of redox pre-treatments, (right) An 4f XP-spectra recorded on the Au/CZ sample subj ected to the same series of pre-treatments. Details of (a), (b) and (c) pre-treatments are given in the text. Adapted from Cies etoL with permission from John Wiley Sons. 

In addition to the FTIR study, volumetric measurements provided quantitative information about the CO chemisorbed on the metal in the series of catalysts resulting from the three redox pretreatments successively applied to the same Au/CZ sample. In accordance with the methodology developed by Lopez-Haro et these quantitative data were determined by subtraction of the second isotherms recorded for the catalyst pre-treated as indicated above, and the corresponding bare support. In this particular case, because one of the investigated Au/CZ samples had been reduced at 473 K, the second isotherm corresponding to the bare support was recorded on an oxide previously reduced at 773 K. As revealed... 

The reactivity of NO on Co +/Co + redox sites in CoAPO-18 was studied by FTIR and UV-Vis spectroscopy in a contribution of Gianotti et al. to the 12th International Zeolite Conference [787]. Dinitrosyls were found absorbing at 1903 and 1834 cm when B-sites were involved, whereas bands at 1900 and 1813 cm appeared when the dinitrosyls were stabilized on structural Co + defects (C-sites). The adsorption of NO and NO-I-O2 on Co-Y was investigated and compared with the adsorption on Co-ZSM-5 in a study by Ivanova et al. [788]. On Co-Y, they observed formation of Co +(NO)2 species with Vjs=1900 and Vs= 1819 cm >, the stability of which was similar to that formed on Co-ZSM-5 with the corresponding bands at 1894 and 1819 cm they were, however, not involved in the selective catalytic reduction. While on Co-ZSM-5 monodentate nitrates appeared, indicated by a band at 1540 cm, which easily interacted with hydrocarbons and, thus, seemed to be the key species in selective catalytic reduction (SCR), no such monodentates were detected on Co-Y. 

Gianotti E, Marchese L,Martra G, ColucciaS (1999) Reactivity of NO on Co +/Co + redox sites in CoAPO-18. FTIR and UV-Vis-NIR studies. In Treacy MMJ, Marcus BK, Bisher ME, Higgins JB (eds) Proceedings of the Twelfth International Zeolite Conference. Materials Research Society, Warrendale, vol IV, p 2775... 

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