No abstract

The Mo/SnO 2 catalyst was prepared by the impregnation method and characterized by thermal analysis, X-ray diffractometry, diffuse reflectance infrared (DRIFT) spectroscopy as well as N 2 adsorption/desorption (BET method) techniques. The results permit to infer that the highly dispersed Mo ions strongly affect SnO 2 crystallization forming only MoO 3 and SnO 2 phases. Moreover, the thermal behavior of Mo/SnO 2 showed the dissolution of MoO 3 in SnO 2 crystals at temperatures above 750°C. Nevertheless, reduced MoO 3 /SnO 2 presented marked activity and selectivity towards CH 4 decomposition at 700°C so as to forming a formaldehyde intermediate but rather favored the formation of CO 2 .

The thermal evolution process of a SnO2 thin film from SnCl2*2H2O precursor dissolved in ethanol was followed by\ud thermogravimetry combined with mass spectrometry (TG-MS), diffuse reflectance Fourier transform infrared spectroscopy\ud (DRIFT) and infrared emission spectrometry (IRES). The precursor salt solution was deposited on a titanium metal sheet. After evaporation of the solvent, the gel-like film was heated in a thermobalance in an oxidative environment to 600 °C. Mass\ud spectrometric ion intensity curves showed the liberation of chlorinated species, alcoholic fragments and CO2 as combustion\ud product and from the decomposition of surface carbonyls, carboxylates and carbonates. The presence of O–H, C–H and C–O\ud bands in the infrared spectra was confirmed and their assignment was made by the deconvolution of the recorded curves as a function of the firing temperature

CO adsorption at low temperature has been used to probe Lewis acid sites created upon dehydroxylation of γ-Al 2 O 3 and reduction of Mo/Al 2 O 3 catalysts, using Fourier Transform Infrared spectroscopy (FTIR). Carbon-monoxide adsorption on γ-Al 2 O 3 and Mo/Al 2 O 3 catalysts dehydroxylated and reduced at different temperatures was studied at 78 K by IR spectroscopy. However, our results indicate that there is an approximately linear correlation between the increase either of dehydroxylation or the extent of reduction of the catalysts and the increasing absorbance of CO due to CO adsorption on Lewis acid sites created upon dehydroxylation of γ-Al 2 O 3 and reduction of Mo/Al 2 O 3 .

In order to explore the influence of CeO 2 doped Mo/Al 2 O 3 catalyst on the structure and surface characteristics (surface area and porosity), an investigation was undertaken by using N 2 adsorption (BET method), thermal analysis (TG and DTA), XRD and in-situ diffuse reflectance infrared (DRIFT) techniques. In this work, the Mo/Al 2 O 3 and Ce-Mo/Al 2 O 3 samples were prepared with 20% Mo loading. The characterization results suggest that the Mo species were highly dispersed on alumina support and the addition of Ce exhibited reasonably lower specific surface area (29.6 m 2 /g). The results showed that the Ce-Mo/Al 2 O 3 material prepared by co-precipitation and calcined at 873 K revealed interactions between ceria and molybdena which were evidenced by DTA, XRD and DRIFT. The results showed diminishing particles size of the two ions and formation of MoO -Ce linkages (875 cm-1), respectively. This proposed interaction is further emphasized by the absence of Ce-O vibration modes at 480 and 740 cm-1 and the appearance of coupled O=Mo=O species (995 and 1035 cm-1) which could affect the catalytic activity of the catalyst that will be discussed in a subsequent publication.