CeO2-Nb2O5 mixed oxide catalysts: Preparation, characterization and catalytic activity in fructose dehydration reaction

Abstract

In this work, ceria-niobia mixed oxides have been prepared by coprecipitation. The structural, textural, and surface properties of these materials have been fully characterized using appropriate techniques (low-temperature adsorption-desorption of nitrogen, thermogravimetric analysis, X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and temperature-programmed reduction/oxidation (TPR/O)). The acid-base properties were estimated by the adsorption of appropriate probe molecules - NH3 or SO2 were used to estimate the population, strength and strength distribution of acid or basic sites, by means of adsorption microcalorimetry. The nature of acidic sites was determined through the adsorption/desorption of pyridine, studied by infrared spectroscopy. New phases between the oxides were not formed, while there is evidence of interaction between them, as revealed by XRD and Raman spectroscopy. All investigated mixed oxide samples are amphoteric and possess red-ox centers on their surface. Both red-ox and acid-base properties are dependent on the ratio of ceria to niobia in the samples. Both Lewis and Brnsted acid sites are present on the surface of the mixed oxides. In order to check catalytic abilities of these materials, reaction of fructose dehydration has been performed. All the investigated materials are catalytically active in fructose dehydration; conversion of fructose and selectivity to 5-hydroxymethylfurfural (5-HMF) improved with increasing content of niobia in the samples.