ORAL

SESSION: AdvancedMaterialsTueAM-R7	Marquis International Symposium on New and Advanced Materials and Technologies for Energy, Environment and Sustainable Development(3rd Intl Symp. on New and Advanced Materials and Technologies for Energy, Environment and Sustainable Development)
Tue Oct, 24 2017	Room: Condesa IB
Session Chairs: Yoshitaka Matsukawa; Lasse Rosendahl; Session Monitor: TBA

11:30: [AdvancedMaterialsTueAM02] Keynote
FTIR Spectroscopy for Characterization of Surface Properties of Disperse Materials
Alexey Tsyganenko¹ ; ¹St.Petersburg State University, St. Petersburg, Russian Federation;
Paper Id: 252 [Abstract]

Surfaces and interfaces are everywhere: in the ground, seawater, atmosphere, space, and even in the living organisms. Vibrational spectroscopy is the most powerful non-destructive method for surface characterization. Spectra of surface functional groups and adsorbed test molecules provide information on the nature of active sites, their strength and concentration. Variable temperature spectroscopy data enable us to study thermodynamics of surface processes and measure the energy or entropy of adsorption. At low-temperatures it is possible to see the spectra of CO, NO, H2 N2 or other simple molecules that do not adsorb at room temperature. Using low-temperature adsorption of weak CH proton-donating molecules such as CHF3, we can characterize the basicity of surface electron-donating sites. Carrying out simultaneous measurements of spectra, pressure and temperatures one can obtain spectrokinetic data and get information about the height of activation barriers of surface reactions. To trap the unstable intermediates of catalytic processes we can follow spectra evolution with temperature and observe the chain of reactant transformations. In particular, the method can be applied to the studies of photocatalytic reactions, modeling the reactions at the surface of atmospheric aerosol particles. The structure of intermediates can be clarified using isotopic substitution, then the detailed mechanism of catalytic processes could be established. Some adsorption products cannot be stabilized at low temperatures, but arise at the surface as a result of thermal excitation. So, CO forms with the cations in zeolites two kinds of complexes. Besides the usual C-bonded structure the energetically less favorable O-bonded species arise and exist in thermodynamic equilibrium with usual form. Such linkage isomerism was established for some other adsorbed species, such as cyanide ion CN- produced by HCN dissociation. FTIR spectra are sensitive to lateral interactions between the adsorbed species, which shift the bands of test molecules or complicate their contours. Co-adsorption of acidic and basic molecules leads to mutual enhancement of adsorption. Acidity of surface sites can be increased by adsorbed acidic molecules, this is consistent with superacidity of oxides doped with SO42-. By means of isotopic dilution this static interaction can be distinguished from the dynamic one. The latter, called also as resonance dipole-dipole (RDD) interaction, accounts for the vibrational energy exchange in the adsorbed layer. Its spectral manifestation provide additional information on the geometry of surfaces. Quantitative spectral analysis of surface sites is not possible without the knowledge of absorption coefficients of test molecules. Quantum chemical calculations and electrostatic approach predict the correlation between the frequency shifts on adsorption and the absorption coefficients, in a fair agreement with the experimental data.

SESSION: AdvancedMaterialsWedAM-R7	Marquis International Symposium on New and Advanced Materials and Technologies for Energy, Environment and Sustainable Development(3rd Intl Symp. on New and Advanced Materials and Technologies for Energy, Environment and Sustainable Development)
Wed Oct, 25 2017	Room: Condesa IB
Session Chairs: Amr Henni; William Proud; Session Monitor: TBA

15:30: [AdvancedMaterialsWedAM07]
FTIR Spectroscopy of Strongly Absorbing Molecules Adsorbed on Highly Scattering Disperse Materials
Alexey Tsyganenko¹ ; Roman Novikov² ; Oleg Pestsov³ ; ¹St.Petersburg State University, St. Petersburg, Russian Federation; ²St.Petersburg State University, St.Petersbur, Russian Federation; ³St.Petersburg State University, St.Petersburg, Russian Federation;
Paper Id: 379 [Abstract]

Most disperse solids are highly scattering objects. Here we analyze the difficulties in spectral studies of such materials, and suggest ways on how to work with them. To see the spectra of adsorbed species, the background spectrum of the sample before adsorption has to be subtracted. However, for very intense bands of gases adsorbed on strongly scattering media, the scattering coefficient changes near the absorption bands, following the variations of refraction index. The problem is illustrated by the spectrum of CO2 adsorbed on a thin layer of NaX zeolite. In order to reduce the effect of scattering it is possible to register the spectrum of "diffuse transmittance" when only the light deviated due to scattering reaches the detector. Combining the usual spectrum with such one, it is possible to reconstruct the pure absorption spectrum. Another way to lower the effect of scattering is to immerse the sample in a liquid, such as liquid oxygen. Spectrum of NaX with adsorbed CO2 submerged in O2 displays a complex structure of the band, more visible after subtraction of the initial spectrum. The structure is not seen at lower coverages, nor in the region of admixed 13CO2 molecules. From this we have concluded that it is not the presence of different sites, but the resonance dipole-dipole interaction between the adsorbed molecules. This effect was shown to determine the band shape of adsorbed SF6, so that the spectra of interacting molecules provide information about the geometry of adsorbed layer. Due to low frequencies the effect of scattering here is negligible, but weak distortions of band contours can be caused by the reflection that also depends on the refraction index. The presented results show that FTIR spectroscopy still remains a promising method for the studies of surface properties of dispersed solid materials.