Synthesis and characterization of nanocatalysts for ethanol oxidation

Abstract

Nowadays limited resources of fossil fuels and environmental concerns increase interest in alternative sources of energy [1]. Recently, fuel cells became very popular and interesting as a good solution for this problem. However, it should be remembered that the oxidation reaction between the catalyst and the fuel (ethanol) occurring in fuel cells is complex and generates a lot of by‐products. This whole process does not promote a better efficiency of the cell, on the contrary, it leads to poisoning of the catalyst, decreasing the efficiency of the device. Therefore the key challenge for this branch of science is primarily the development of the appropriate type of catalysts [1]. Recently promising technology seem to be ternary nanocatalysts containing platinum, rhodium, and tin oxide (IV) [2]. The motivation for our work is a better understanding of the synergistic effect between these three components in nanocatalysts, replacing the rhodium by rhenium and determining their selectivity for total oxidation of ethanol to CO 2 .In the present study we used three methods of synthesis: polyol [3], citrate [4] and microwave assisted [5]. The obtained nanoparticles were characterized by Photon Correlation Spectroscopy (PCS), Transmission Electron Microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FTIR). The HAADF STEM structural analysis showed that the nanoparticles obtained by all three methods have similar dimensions ‐ about 2 nm. In the case of the citrate and polyol methods the nanoparticles were strongly agglomerated, which was visible not only in the TEM images, but also confirmed by the results obtained by the PCS. On the other hand, nanoparticles obtained by the microwave assisted synthesis did not show such a strong agglomeration as those obtained by the two other methods. All SnO 2 samples had a crystalline structure, which was confirmed by HRSTEM images (Fig. 1). Additionally fourier transform infrared spectroscopy (FTIR) was applied to determined the structure of tin oxide obtained in the two differences synthesis (microwave and polyol assisted). It was found, that in the infrared spectrum of Sn oxide synthesized by polyol methods, a stretching modes of Sn‐O from Sn(OH) 4 was not observed. Moreover, in this samples, more stretching modes of O‐Sn‐O (Sn 4+ ) was noticed, whereas the samples synthesized by microwave methods, characterized by larger amounts of Sn‐O (Sn 2+ ) stretching modes (Fig. 2). The size of the nanoparticles varied from 2 to 12 nm, depending on the synthesis parameters. The next step is the synthesis of PtRh and PtRe nanoparticles on the obtained SnO 2 supports. Our research confirmed that the crystalline structure, particle size and shape, and surface properties are highly dependent on the chosen method of synthesis.