AIR:RAFFINAGE:INGENIERIE:SURFACES+FGI:CGE:NOG:DBIThe present study is dedicated to the development of experimental procedures allowing the measurement of the individual heats of adsorption of adsorbed NH3 species on a sulfate-free TiO2 solid (P25 from Degussa). This solid has been selected because it is frequently used as support of V2O5- or/and WO3-TiO2 model catalysts for the understanding of the surface processes implicated in the selective catalytic reduction of NOx by NH3 (NH3-SCR). Two original analytical procedures denoted adsorption equilibrium infrared spectroscopy (AEIR) and temperature-programmed adsorption equilibrium (TPAE) (developed in previous works) were applied. These methods are based on (a) the experimental measurement of the change in the adsorption equilibrium coverage of the individual adsorbed species in isobar conditions and (b) the comparison of the experimental data to an adsorption model. It is shown that in the ranges of the ammonia partial pressures and reaction temperatures of the NH3-SCR process, only two adsorbed NH3 species on Lewis sites (Ti+delta) are detected on the solid dehydrated at 673 K. These species noted NH3ads.L1 and NH3ads.L2 are differentiated by their delta(s) NH3 IR bands at 300 K (1149 and 1228 cm(-1), respectively), whereas their delta(as) IR bands are at the same position (1596 cm(-1)). The AEIR and TPAE methods indicate that the heats of adsorption of the NH3ads.L1 and NH3ads-L2 species (noted E-L1(theta) and EL2(theta) accuracy +/- 5 kJ/mol) vary linearly with their respective coverages theta from E-L1(1) = 56 kJ/mol to E-L1(0) = 105 kJ/mol and from E-L2(1) = 105 kJ/mol to E-L2(0) = 160 kJ/mol. These values are compared to (a) isosteric heat of adsorption provided by the Clausius-Clapeyron method and (b) literature data using temperature-programmed desorption, microcalorimetry, and DFT calculations. Forthcoming artides show that the simplicity of the analytical procedures allows studying the impact of the presence of sulfate and VOx/WOy depositions over TiO2, on the nature and heats of adsorption of adsorbed NH3 species

The present article is dedicated to the impacts of sulfatation and/or V x O y deposition on TiO2 supports on the individual heats of adsorption of adsorbed NH3 species. The S and V loadings are similar to those of TiO2 based commercial catalysts for the selective catalytic reduction of NO x by NH3: NH3–SCR. Two original experimental procedures are used, namely, adsorption equilibrium infrared spectroscopy (AEIR) and temperature-programmed adsorption equilibrium (TPAE). They have been developed in previous works and adapted in Part 1 for the species formed by the adsorption of NH3 on a sulfate free TiO2 support (P25 from Degussa). In agreement with the literature, Raman and FTIR spectroscopies show that the impregnation of the sulfate-free and sulfated TiO2 supports by the vanadium precursor leads to well-dispersed V x O y species, which are involved in the adsorption of NH3 in the temperature T a range of 300–673 K and for adsorption P a < 0.5 kPa. Sulfate and V x O y groups favor the amount of NH4 + species without modifying their heats of adsorption as compared to the TiO2 support: they are not detected for temperatures of interest for NH3–SCR reaction. In these experimental conditions and whatever the solids, two main adsorbed NH3 species on Lewis sites (denoted NH3ads‑L1 and NH3ads‑L2) are present, characterized by two δs IR bands below 1300 cm–1 and a common δas IR band at ≈1600 cm–1. By comparison with TiO2 P25; it is shown that sulfate groups have strong impacts neither on the proportion, x 1 and x 2, of the two adsorbed species nor on their heats of adsorption (E L1(θ) and E L2(θ) with θ the coverage of the NH3ads‑L1 and NH3ads‑L2 species: x 1 = 0.65, x 2 = 0.35, E L1(1) = 56 kJ/mol, E L1(0) = 102 kJ/mol, E L2(1) = 110 kJ/mol, E L2(0) = 140 kJ/mol. The deposition of V-containing species on the sulfate-free and sulfated TiO2 surfaces leads to similar conclusions: in the experimental conditions (T a and P a) of the NH3–SCR, two adsorbed NH3 species on Lewis sites are detected with comparable proportions and heats of adsorption to those observed on the TiO2 supports.