Abstract
This work presents the physicochemical characterization and activity of zirconia-supported silver catalysts for the oxidation of pollutants present in diesel engine exhaust (propane, propene, naphthalene and soot). A series of silver-supported catalysts AgxZ (x = 1, 5 and 10 wt.%, Z = zirconia) were prepared, which were studied by various characterization techniques. The results show that silver is mainly found under the form of small metal nanoparticles (<10 nm) dispersed over the support. The metallic phase coexists with the AgOx oxidic phases. Silver is introduced onto the zirconia, generating Ag–ZrO2 catalysts with high activity for the oxidation of propene and naphthalene. These catalysts also show some activity for soot combustion. Silver species can contribute with zirconia in the catalytic redox cycle, through a synergistic effect, providing sites that facilitate the migration and availability of oxygen, which is favored by the presence of structural defects. This is a novel application of the AgOx–Ag/ZrO2 system in the combustion reaction of propene and naphthalene. The results are highly promising, given that the T50 values found for both model molecules are quite low.
Highlights
Mobile emission sources generate a large amount of pollutants, which are emitted into the atmosphere and cause serious environmental problems, both historically and in human health
The prepared catalysts were examined by using various analytical techniques (SEM-EDS, X-ray diffraction (XRD), DRS, transmission electron microscopy (TEM), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS))
It was observed that part of the silver was in a metallic state, in the form of nano-sized particles, and evidence was found for the existence of oxidic species at low concentration
Summary
Mobile emission sources generate a large amount of pollutants, which are emitted into the atmosphere and cause serious environmental problems, both historically and in human health. Serve et al studied Ag catalysts supported on yttria-stabilized zirconia (YSZ) for soot oxidation They proposed that Ag favors the activation of the dissociatively adsorbed oxygen, and the lattice integration of gaseous oxygen. They have shown that the formation of Ox − species can be promoted with the presence of Ag to obtain higher NO and soot oxidation activities Another desirable characteristic is that the support possesses certain levels of acidity to favor the adsorption of the hydrocarbon. The focus will be on the formation of supported Ag nanoparticles, and in the study of this catalytic system in oxidation reactions of pollutants generated in emission sources The activity of these catalysts is analyzed in the oxidation reactions of model molecules of different hydrocarbons at very low concentrations: propane, propene, and naphthalene. X-ray photoelectron spectroscopy (XPS) was employed to obtain information about the species at the surface level
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