Experimental. Solids, characterizations and pretreatmentsIn the present study, the sulfate free and sulfated TiO 2 solids are P25 from Degussa (55 m 2 /g) and DT51 (80 m 2 /g) from Millenium Inorganic Chemical respectively which have been (a) used as supports of NH 3 -SCR catalysts and (b) characterized considering their a = 18 torr) on TiO 2 -P25 and Al 2 O 3 have been ascribed by Kakeuchi et al. 15 to d-H and Hbond IR bands respectively of polymeric H 2 O chains. It must be noted that the positions of the d-H IR bands, 36-37 are in the same wavenumber range than the OH groups of the metal oxides and the ν 1 and ν 3 IR bands of isolated H 2 O species, 11-17 leading to difficulties in the interpretation of the IR spectra of adsorbed H 2 O species.

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The present study is a part of an experimental microkinetic approach of the selective reduction of NO x to N2 with NH3 in excess of O2 on V2O5/WO3/TiO2 catalysts (NH3-selective catalytic reduction (NH3-SCR) reaction). Water is always present either in the reactive gas mixtures representative of industrial processes or produced by the reaction. This suggests that H2O may modify the coverage of the pivotal adsorbed NH3 intermediate of the reaction by either a competitive adsorption or reactions (i.e., formation of NH4 +). In the temperature range of interest for NH3-SCR (T ≥ ≈423 K), Fourier transform infrared spectroscopy and volumetric measurement using a mass spectrometer are used to study the impacts of the NH3-H2O coadsorption on the coverages of adsorbed NH3 (molecular adsorption) and H2O (molecular and dissociative adsorption) species on two sulfated solids: a 0.7% V2O5/9% WO3/TiO2 NH3-SCR catalyst and its TiO2 support. Regardless of the solid, it is shown that at the NH3-H2O coadsorption equilibrium, (a) NH3 dominates the adsorption on the Lewis sites (i.e., the introduction of NH3 at the H2O adsorption equilibrium displaces H2Oads‑L species at the benefit of NH3ads‑L species) and (b) the introduction of H2O at the NH3 adsorption equilibrium increases significantly the amount of adsorbed NH4 + species. This is ascribed to the H2O dissociation, which is operant on a small number of sites forming new Brønsted sites without a strong impact on the amount of Lewis sites. The surface composition of the solids has a limited impact on the coverages during the NH3-H2O coadsorption except on the fact that the NH4 + species is more stable on the NH3-SCR catalyst. In Part 6 of the present study (10.1021/acs.jpcc.8b05847), it is shown that the present experimental data are consistent with the mathematical formalism of a competitive Temkin model (named Temkin-C) developed without major approximations. The experimental procedure (present study) and the mathematical Temkin-C formalism (Part 6) can be applied for all solids having a significant IR transmission, thus offering a method to study the surface acidity during realistic experimental conditions (in the presence of H2O), which is of interest for different catalytic processes such as NH3-SCR and alcohol dehydration.

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The adsorption of x% CO/He (x = 1 and 2) on a reduced 10 wt % Co/Al2O3 catalyst at an adsorption temperature of 560 K > T a > 420 K leads to the formation of a linear CO species on Co° sites (denoted LCo° species) with an infrared (IR) band at ≈2030 cm–1 at full coverage. This adsorption is associated with the formation of carbon that is implicated in the reconstruction of the surface of the cobalt particles, leading to the progressive transformation of the LCo° species into a new linear CO species on Co°C sites of the reconstructed surface with an IR band at ≈2060 cm–1. An experimental microkinetic approach of the reconstruction process via the LCo° → LCo°C transformation reveals the impact of different kinetic parameters such as the reaction temperature, the CO partial pressure, and the presence of hydrogen. During the reconstruction the coverages of the LCo° and LCo°C species remain very high (>0.95) due to their high heats of adsorption determined by the Adsorption Equilibrium Infra Red spectroscopy method. It is shown that the rate of the reconstruction process is controlled by that of the disappearance of the LCo° species via its dissociation into adsorbed elemental carbon and oxygen species according to a pseudo first kinetic order elementary step involving a small amount of free cobalt sites (≈4 × 1012 sites/cm2 of cobalt particles). The impact of the reaction temperature on the LCo° → LCo°C transformation indicates that (a) the activation energy of the LCo° dissociation which controls the reconstruction process is ≈125 kJ/mol and (b) the formation of elemental carbon via the disproportionation of the LCo° species seems unlikely. These two conclusions are consistent with literature data on density functional theory (DFT) calculations. For adsorption temperature >560 K, the formation of superficial graphitic like species overlaps the reconstruction process. In the presence of hydrogen, the reconstruction is observed for H2/CO ratios <3 but not for higher values (i.e., H2/CO = 10).

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The present article is dedicated to the adsorption of CO on reduced 2% Pd/Al 2 O 3 and 2% Pd-x% Sn/Al 2 O 3 (weight %, x = 2 or 5 wt %) in the 300−713 K temperature range to study the geometric and electronic effects of Sn on the palladium adsorption sites. Using Fourier transform infrared (FTIR) spectroscopy, it is shown that the insertion of Sn leads to (a) the total disappearance of the Pd sites forming bridged CO species (denoted as "B"), which are the dominant species on Pd 0 particles and (b) a significant increase in the Pd sites forming linear CO species (denoted as "L"). This is ascribed to a geometric effect of Sn that dilutes the superficial palladium sites. The measurement of the individual heats of adsorption of the different adsorbed CO species by using two original temperature-programmed adsorption equilibrium methods (denoted AEIR and TPAE) allows the estimation of the electronic effect of Sn on the Pd sites. On 2% Pd/ Al 2 O 3 , in parallel to the formation of two strongly adsorbed B CO species, two linear L1 Pd 0 and L2 Pd 0 CO species are formed, which exhibit different heats of adsorption. For the dominant L1 Pd 0 CO species, the heat of adsorption decreases linearly, from 92 kJ/mol to 54 kJ/mol, as its coverage increases at coverage 0 and 1, respectively, while that of the L2 Pd 0 species is >165 kJ/mol at coverage 1. On the two Pd−Sn containing particles, two linear CO species are formed denoted L1 2Pd−xSn and L2 2Pd−xSn with x = 2 or 5. The L1 2Pd−xSn species dominates the CO adsorption on the two solids. It is shown that its heat of adsorption (which is slightly dependent on x) linearly varies with its coverage: ∼90 kJ/mol and ∼50 kJ/mol at low and high coverage, respectively. The comparison with the heat of adsorption of L1 Pd 0 indicates that the electronic effect of tin is very modest, compared to its geometric effect. This conclusion is consistent with literature data dedicated to DFT calculation. Moreover, (a) XRD and TEM/ EDX analysis suggest that bimetallic particles such as Pd 3 Sn and Pd 2 Sn are present and (b) the impact of tin on the H 2 chemisorption on Pd 0 sites are presented.