Estos resultados hacen parte del proyecto "Desarrollo de catalizadores multifuncionales para procesos de una sola etapa, en la conversión de glucosa a ácido 2,5 furandicarboxilico (FDCA), materia prima para obtener el 2,5 furandicarboxilato de polietileno (PEF) sustituto del teraftalato de polietileno (PET) código 110965843004" que ha sido financiado por COLCIENCIAS bajo el contrato No. 047 de 2015, suscrito entre COLCIENCIAS y la Universidad Pedagógica y Tecnológica de Colombia. Gracias a este convenio, la autora ha recibido financiación por medio de contratos durante los años 2016-2017 como apoyo a su formación de estudiante de maestría.

Adsorption and surface reactions of acetone vapor were observed on the title oxides at room and higher temperatures (up to 400 °C), using in situ infrared spectroscopy. The results were correlated with results of infrared spectroscopy of adsorbed pyridine, to assess impacts of the surface acid−base properties. It was found that the availability of Lewis acid sites is essential for anchoring acetone molecules to the surface. Coexisting Lewis base sites catalyze condensation of the acetone molecules into mesityl oxide surface species, via formation and subsequent decomposition of enolate and diacetone alcohol species. When intimately coupled, the Lewis acid and base sites generate pair sites of particularly strong adsorption capacity toward condensation products thus formed. Consequently, surface active sites are blocked and adsorptive and catalytic interactions of acetone are largely suppressed.

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Pathways and generated surface species of adsorption and consequent surface reactions of acetone vapor on characterized silica, alumina, and ∼5 wt % silica-alumina were examined by in-situ infrared (IR) spectroscopy, following degassing at room (RT) and higher temperatures (100-400 °C). For reference and confirmatory purposes, adsorptives of mesityl oxide and acetic acid, and adsorbents of K-modified and pyridine-covered silica-alumina, were employed. In the absence of Lewis and Bronsted acid sites, as well as of basic sites (i.e., on silica), acetone molecules are weakly hydrogen-bonded to surface OH δ+ groups to desorb completely at 100 °C, without involvement in any further surface reactions. The availability of such acid-base sites on alumina and silica-alumina facilitates acetone chemisorption and activation for aldol condensation type surface reactions, leading to formation of surface species of mesityl oxide at RT to 200 °C and their oxidative conversion into acetate species at 300-400 °C. A more obvious availability of Bronsted acid sites on silica-alumina enhances progression of the surface reactions involved.

Pure ceria powders, CeO(2), were synthesized in heptane-microemulsified aqueous solutions of CeCl(3) or Ce(NO(3))(3) stabilized by AOT (sodium bis(2-ethylhexyl) sulfosuccinate), DDAB (di-n-didodecyldimethylammonium bromide), or DDAB + Brij 35 surfactant mixtures. Micellar DTAB (n-dodecyltrimethylammonium bromide) and vesicular DDAB systems were also used as media for generating CeO(2). Characterization of the powders by X-ray powder diffractometry, laser-Raman spectroscopy, and Fourier transform infrared spectroscopy revealed that in the presence of surfactants almost-agglomerate-free nanosized crystallites (6-13 nm) of anionic vacancy-free cubic CeO(2) were produced. In the absence of surfactants 21-nm-sized crystallites were formed, comparing with the 85-nm-sized crystallites when cubic CeO(2) was created via thermal decomposition of cerium oxalate. Surface characterization, by X-ray photoelectron spectroscopy, N(2) sorptiometry, and high-resolution electron microscopy showed AOT- or (DDAB + Brij 35)-stabilized microemulsions to assist in formation of crystallites exposing surfaces of large specific areas (up to ca. 250 m(2)/g) but of low stability to high-temperature calcination (28-13 m(2)/g at 800 degrees C). In contrast, the double-chained DDAB was found to generate cubic CeO(2) crystallites of lower initial surface areas (144 (microemulsion) to 125 (vesicles) m(2)/g)) but of higher thermal stability (55-45 m(2)/g at 800 degrees C). Hence, the latter cerias could be considered as appropriate components for total oxidation (combustion) catalysts.

Infrared spectroscopy has been used to analyse the gas-phase reaction products and the related adsorbed species obtained between room temperature and 400 "C from the dehydrogenation/dehydration reactions of propan-2-01 over a series of differently calcined catalysts of TiO,, ZrO, and HfO,. The ZrO, and HfO, results were independent of the calcination pretreatment, and the surfaces of these oxides, like that from a TiO, sample calcined at 800 "C, were dehydroxylated. Different results were obtained from a TiO, sample calcined at 300 "C which had a hydroxylated surface. The acidic sites and reactivities of the surfaces of Ti0,(300 "C) and Ti0,(800 "C) were explored by pyridine adsorption and infrared spectroscopy. Only Lewis-acid sites were detected by pyridine.On raising the reaction temperature, in all cases the dehydrogenation reaction to give acetone occurred either before or simultaneously to the onset of the dehydration reaction to give propene. Acetone production was most pronounced over ZrO, and HfO, but also occurred more with Ti0,(800 "C) than with Ti0,(300 "C). The dehydrogenation reaction was largely quenched by pre-adsorbed pyridine on both TiO, samples. The TiO, (300 "C) catalyst showed the presence of adsorbed propan-2-01 and 2-propoxide groups at room temperature. The dehydroxylated ZrO,, HfO, and Ti0,(800 "C) samples only showed appreciable amounts of 2-propoxide groups. In each case the 2-propoxide ions occurred in two different forms, presumably formed by adsorption on different types of sites.Both the acetone and propene products appeared as absorptions from 2propoxide surface species decreased in intensity, so the latter are clearly reactive species. Gas-phase acetone production was followed by the chemisorption of acetone at a higher temperature. This subsequently decomposed to give surface acetate species, and finally at 400 "C to give CO, and methane in the gas phase. Propene did not give rise to adsorbed species, or to further products in the gas phase.At the higher temperatures, above 300"C, the reaction was always selective in favour of the dehydration reaction. However, each of the dehydroxylated catalysts showed some selectivity in favour of the dehydrogenation reaction over the earliest temperature range for alcohol decomposition, between 200 and 250 "C.A discussion is given of possible mechanistic pathways for the production of surface 2-propoxide species and the two types of products, based on the infrared-supported assumption that the different adsorbed forms of 2propoxide [and possibly adsorbed propan-2-01 on Ti0,(300 "C)] are reactive intermediates.t On leave from Minia University.

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