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The present study is dedicated to the characterization (identification, heats of adsorption and coverages) of the adsorbed species formed by the adsorption and coadsorption of NH and H 2 O on two SiO 2 solids. The Adsorption Equilibrium InfraRed spectroscopy (AEIR) which allowed (a) to show that NH 3 and H 2 O are mostly adsorbed on free SiOH groups via H-bonds and (b) to determine their individual heats of adsorption: 53 kJ/mol and 49 kJ/mol whatever their coverages (Langmuir adsorption model) for NH 3ads and H 2 O ads , respectively. These values consistent with microcalorimetry literature data explain that their coverages are decreased upon NH 3-H 2 O co-adsorption considering a competitive Langmuir model. However, the Temperature Programmed Adsorption Equilibrium (TPAE) procedure achieved from MS data indicated that a minor amount of other NH 3 species (not detected using FTIR) are more strongly adsorbed and that hydrolysis of SiOSi siloxane by H 2 O could occur in parallel. NH 3-H 2 O coadsorption leads to formation of NH 4 + species which involves H 2 O adsorbed species. Both NH 3 and H 2 O are not adsorbed above 450 K which means that the SiO 2 contribution to the characterization of the acidity of metal oxides catalysts supported on SiO 2 using NH 3 as probe molecule in the presence of H 2 O is negligible above this temperature.

Two different TiO 2 /SiO 2 compounds containing TiO 2 nanodomains dispersed over SiO 2 were investigated applying the AEIR method at the adsorption equilibrium of NH 3 and H 2 O from 300 to 723 K, particularly for the measurement of the individual heats of adsorption of the different species on Lewis acidic sites (LAS) and Brønsted acidic sites (BAS) as evaluation of the strength of the sites. It revealed two types of NH 3 adsorption sites: the first ones could correspond either to NH 3 species H-bonded to free OH groups or to coordinated weak LAS (named L1). The second ones (L2) were attributed to strongest LAS similar to those present at the surface of TiO 2 nanocrystallites. They also correspond to the stronger adsorption sites of H 2 O. Two types of Brønsted acid sites (BAS) were additionally evidenced by the AEIR method and proposed to be specifically located on the Si−O−Ti bridging bonds at the TiO 2 /SiO 2 interface. The heats of adsorption of the different adsorbed species provided by the AEIR method were consistent with literature data on average values of the heats of adsorption of NH 3 and H 2 O from microcalorimetry measurements. The surface acidity of the two compounds in the presence of H 2 O was determined using NH 3 −H 2 O coadsorption. At T ≥ 473 K, the NH 3 species on the L2 sites were not significantly displaced from the surface whatever the partial pressure of H 2 O studied in agreement with the Temkin competitive model using the individual heats of adsorption of the NH 3 and H 2 O species. This model also revealed the presence of a small amount of H 2 O species adsorbed on L2 sites allowing H 2 O dissociation or/and hydrolysis of SiOTi or TiOTi bridges, leading to the formation of a much higher amount of BAS. Therefore, this original work combining the AEIR method and the Temkin competitive model provided new insights for understanding water effects on acidic oxide catalysts.

H 4 SiW 12 O 40 heteropolyanions, WO 3 , TiO 2 and SnO 2 were supported over SiO 2 at high loading by wet impregnation or grafting methods and evaluated in the dehydration of isobutanol to butenes. Their structural and textural properties were determined by different techniques such as XRD, TEM, IR, XPS and N 2 liquid physisorption respectively. Most of the prepared compounds contained amorphous oxide clusters of few nanometers lying over SiO 2 and were mesoporous. Their acidic properties (nature, density and strength) were investigated by pyridine and CO adsorption followed by FTIR. H 4 SiW 12 O 40 /SiO 2 contained strong Brønsted acid sites while mostly moderate Lewis acid sites were present on TiO 2 /SiO 2 and SnO 2 /SiO 2. WO 3 /SiO 2 had a mixed character with both moderate Brønsted and Lewis sites. The catalytic activity was related to the Brønsted acidity and the best selectivity to butenes close to 100% were obtained for the catalysts containing moderate and weak sites (WO 3 /SiO 2 and TiO 2 /SiO 2). Except for SnO 2 /SiO 2 catalysts, which were unstable and unselective to dehydration products, a significant selectivity to linear butenes (ca 30%) was obtained. This isomerisation activity was mainly related to equilibrium between carbocations formed after E 1 elimination of water. Its slight increase for H 4 SiW 12 O 40 /SiO 2 (and to a lesser extent WO 3 /SiO 2) was attributed to strong Brønsted acid sites able to convert isobutene to linear butenes.

The impact of polypropylene and high-density polyethylene backbone binders on the structure of organic matrix, feedstock, and ceramic parts is investigated in terms of morphology in this paper. The miscibility of wax with polyethylene and polypropylene is investigated in the molten state via a rheological study, revealing wax full miscibility with high-density polyethylene and restricted miscibility with polypropylene. Mercury porosimetry measurements realized after wax extraction allow the characterization of wax dispersion in both neat organic blends and zirconia filled feedstocks. Miscibility differences in the molten state highly impact wax dispersion in backbone polymers after cooling: wax is preferentially located in polyethylene phase, while it is easily segregated from polypropylene phase, leading to the creation of large cracks during solvent debinding. The use of a polyethylene/polypropylene ratio higher than 70/30 hinders wax segregation and favors its homogeneous dispersion in organic binder. As zirconia is added to organic blends containing polyethylene, polypropylene, and wax, the pore size distribution created by wax extraction is shifted towards smaller pores. Above zirconia percolation at 40 vol%, the pore size distribution becomes sharp attesting of wax homogeneous dispersion. As the PP content in the organic binder decreases from 100% to 0%, the pore size distribution is reduced of 30%, leading to higher densification ability. In order to ensure a maximal densification of the final ceramic, polyethylene/polypropylene ratios with a minimum content of 70% of high-density polyethylene should be employed.

A noninvasive and low cost colorimetric test is proposed to detect microorganisms in complex media via volatile metabolites released by enzymatic activity. The sensor is based on a hydrid organic-inorganic nanoporous xerogel. This transparent and colorless silica matrix traps and concentrates targeted volatile metabolites which are then detected by absorbance measurements. Ortho-nitrophenol was chosen as a volatile metabolite. At a first stage, the trapping efficiencies of various functionalized xerogels were compared in order to optimize the detection of ortho-nitrophenol. As a second step, we used xerogels with the best composition to detect E. coli cells in blood samples.