PHYSICO-CHEMICAL PROPERTIES OF COMPOSITES ON THE BASE OF CERIA OBTAINED BY A CITRIC ACID METHOD

Abstract

Composites with the formula nMOx–СеО2, where n is the mole part of copper or manganese oxide have been synthesized via citric acid aided route. Physico-chemical properties of materials obtained are investigated by XRD, low temperature desorption of nitrogen and by temperature-programmed reduction (TPR). It is defined that the composites with the n < 0.25 (for Cu) and < 0.75 (Mn) are the solid solutions obtained by the replacement of cerium ions in the structure of fluorite (СеО2) by copper or manganese ions. The existence of the separate phases of oxides such as CuO and Mn3O4 has been identified in the XRD patterns of composites with formula 0.25CuО–СеО2 and 0.75MnOx–СеО2. The parameters of cell and the particles size for all samples are calculated; decreasing these values occurs due to the solid solutions formation. Specific area of composites obtained is much bigger than specific area of individual oxides; the biggest values are determined for the samples containing the biggest part of copper or manganese oxide. According to TPR profiles of composites themaximal intensity of low temperature peak has the composite 0.25CuО–СеО2 that means the biggest part of the solid solution; so this material is the most active in CO and ethanol combustion. This fact can be explained by appearance of additional oxygen vacancies when ions Ce4+ are replacement by ions with the less oxidation state. The quantities of hydrogen used for reduction of samples with the copper oxide and samples with the manganese oxide with n < 0.5 are much bigger than the theoretical values; in this case the reduction of the part of ceria in the solid solution is happened. The composite 0.25MnOx–CeO2 is the most active in the ethanol combustion; full conversion to CO2 is finished at 205°С. The high activity of individual oxide MnOx and the composite 0.75MnOx–СеО2 in the reaction of toluene oxidation explains by the biggest part of Mn3+ ions in their structure among the all oxides investigated.