Showing papers by "Tanya Tsoncheva published in 2020"

Synthesis and characterization of copper-nickel ferrite catalysts for ethyl acetate oxidation

Abstract: Materials with nominal composition Cu0.5Ni0.5Fe2O4 were prepared by sol-gel auto-combustion technique using corresponding metal nitrates and citric acid as complexating agent/fuel agent. Different ratios between citric acid and metal ions were used to control the combustion reaction. For comparison, Cu0.5Ni0.5Fe2O4 ferrite was also synthesised by co-precipitation. Mossbauer spectroscopy was used for analysis of synthesised samples both at room temperature and liquid nitrogen boiling temperature. Iron distribution in tetrahedral and octahedral positions of spinel lattice was determined. Different degrees of agglomeration of the ferrite phase were estimated by super-paramagnetic behaviour of samples. In addition, methods of X-Ray Diffraction, UV-Vis, FTIR, nitrogen physisorption, TPR with hydrogen were applied for structural characterization of the materials. Some quantities of secondary phases (Cu, Cu-Ni alloy and hematite) were found out in samples prepared by auto-combustion method. The catalytic activities of the samples in ethyl acetate oxidation reaction strongly depended on the variations in the structural and texture characteristics of the samples. The sample synthesized at the highest ratio of citric acid to metal ions is characterized by the smallest ferrite crystallite size, the higher surface area and the best catalytic activity.

Mesoporous copper-ceria-titania ternary oxides as catalysts for environmental protection: Impact of Ce/Ti ratio and preparation procedure

Abstract: Hydrothermally obtained mesoporous ceria-titania mixed oxides with different composition are modified with copper using incipient wetness impregnation and “chemisorption-hydrolysis” techniques. Their catalytic properties in methanol decomposition as a source of hydrogen and total oxidation of ethyl acetate as representative volatile organic pollutant are investigated. The effect of support composition and modification method on the formation of catalytic active sites is studied. The obtained results show that the catalytic behavior is determined by the activity of finely dispersed CuO crystallites and facile electron transfer in the “conjugated” Ti Ce Cu redox centres in the interface layer. The mechanism of the formation of the interface layer and the growth of CuO crystallites during different modification procedures are discussed in details. The mesoporous Cu Ce Ti oxides demonstrate excellent catalytic activity in total oxidation of ethyl acetate. Their catalytic behavior in methanol decomposition is strongly influenced by the reductive transformations, which are provoked by the reaction medium.