Search

Glucose-to-fructose isomerization is the key process in the reaction sequence that can lead to the total conversion of biomass into valuable fine chemicals. However, it is challenging to find an efficient, cost-effective- and waste-minimized process to produce High Fructose Corn Syrup (HFCS) without using non-green approaches. To this end, hydrotalcite (MgAl-layered double hydroxides (MgAl-LDH)) catalyzed glucose isomerization in ethanol seemed to be one of the most promising processes in the last decade. In contrast to the well-studied reaction carried out in aqueous solutions, when ethanolic solutions are used, many potentially important properties of the LDHs cannot be studied in terms of how they affect their own catalytic abilities. Neither the effect of the basic site distribution, nor the morphological aspects and the role of surface hydration have been elucidated so far. In this study, the systematic alteration of the textural and structural parameters of hydrotalcites and hydrocalumites (Ca2Al-LDH) revealed clear structure–activity-selectivity relationships. These indicate that the rate-determining factor is the hydrophilicity and the LDH surface factors affecting it, which determine the catalytic performance of the LDH catalyst more than any other factor. This is evidenced by the fact that the catalytic efficiency of hydrotalcites can be improved by reducing their basicity. When isomerizations catalyzed by the easily recyclable LDH with suitable surface features are carried out, a truly similar catalytic performance (71% glucose conversion, 83% fructose selectivity, 59% fructose yield) can be achieved as was previously described, but at a significantly lower reaction temperature (120 °C → 80 °C). [ABSTRACT FROM AUTHOR]

Carbon spheres were applied as templates to synthesize titanium dioxide hollow spheres. The templates were purified with either ethanol or acetone, and the effects of this treatment on the properties of the resulting titania were investigated. The photocatalytic activity of the catalysts was measured via the decomposition of phenol model pollutant under visible light irradiation. It was found that the solvent used for the purification of the carbon spheres had a surprisingly large impact on the crystal phase composition, morphology, and photocatalytic activity. Using ethanol resulted in a predominantly rutile phase titanium dioxide with regular morphology and higher photocatalytic activity (r0,phenol = 3.9 × 10−9 M∙s−1) than that containing mainly anatase phase prepared using acetone (r0,phenol = 1.2 × 10−9 M∙s−1), surpassing the photocatalytic activity of all investigated references. Based on infrared spectroscopy measurements, it was found that the carbon sphere templates had different surface properties that could result in the appearance of carbonate species in the titania lattice. The presence or absence of these species was found to be the determining factor in the development of the titania's properties. [ABSTRACT FROM AUTHOR]

In this work, the effect of the nature of oxide support on the reaction mechanism of the partial oxidation of ethanol on Rh catalyst was studied by diffuse reflectance infrared (DRIFTS) and X-ray photoelectron spectroscopy (XPS). The conversion of ethanol and the product distribution were analysed by gas chromatography. The highest ethanol conversion was measured on Rh/CeO 2 catalyst. The results showed that the nature of the oxide support affected the reaction mechanism. On supported Rh catalysts ethanol adsorption gives rise to ethoxide species, which can be decomposed to CO 2 , CO and CH 4 and dehydrogenated, forming acetaldehyde. The latter species are oxidized to acetate or dehydrogenated to acetyl species on Rh/Al 2 O 3 and on Rh/CeO 2 . On Rh/TiO 2 the acetaldehyde can also be oxidized in a parallel process to HCOOH/HCOO (a) which forms CO 2 and water. Furthermore, the acetate species previously formed can be decomposed to CH 4 , CO and/or oxidized to CO 2 via carbonate species at higher temperature depending on the oxide support. On silica support acetaldehyde was the dominant intermediate and it desorbed or directly decomposed with or without oxygen to CO 2 and methane. The partial oxidation of ethanol proceeds on partially oxidized Rh sites on Rh/Al 2 O 3 , Rh/TiO 2 and on Rh/CeO 2 . In spite of the presence of O 2 , ceria is not fully oxidized during the partial oxidation of ethanol. [ABSTRACT FROM AUTHOR]