Search

Efficient neutralization of the exhaust gases from the automobile engines as well as development of the active and stable catalytic systems for pollution control remain actual challenge since the internal combustion engine was discovered. The present work was focused on the study of metal–metal and metal-support interactions taking place in the palladium- and rhodium-containing samples supported on delta-alumina. Catalytic performance of the catalyst was studied in three-way catalysis under both the stoichiometric and reductive conditions. Thermal stability was examined using a prompt thermal aging procedure. The samples were characterized by means of luminescence and UV–vis spectroscopies, since due to low metal loading the most of other characterization techniques was not applicable. All the samples were found to undergo deactivation during the aging procedure. However, in the case of the alloyed samples, the deactivation process is diminished due to a noticeable metal–metal interaction. The strength of this interaction increases along with decrease of palladium loading and reaches its maximum for PdRh32(alloy) system, which shows the best stability at 1000 °C. For the bimetallic system with Pd:Rh ratio of 4:1, an effect of reactivation was observed at 800 °C. After the aging at 800 °C, the sample has showed the improved catalytic activity. Then, being heated up to 1000 °C, the active metal particles were shown to undergo rapid agglomeration. [ABSTRACT FROM AUTHOR]

In the present work, ceria-supported Au–Pt catalyst with metal ratio 3:2 was prepared using a "single-source precursor" concept. The double complex salt [AuEn2]2[Pt(NO2)4]3·6H2O was used as such precursor. CeO2 of unique morphology with developed surface area (120 m2/g) obtained by urea precipitation technique was used as a support. According to XRD data, size of the alloyed Au–Pt particles was estimated to be less than 3 nm. It was shown that bimetallic Au–Pt system intensifies release of oxygen from the CeO2 lattice. The 0.5%Au2Pt3/CeO2 catalyst was comparatively studied in low temperature CO oxidation (simplified model reaction mixture) and under prompt thermal aging conditions (complex reaction mixture) with regard to monometallic reference samples 0.2%Au/CeO2 and 0.3%Pt/CeO2. The catalytic performance of the samples was found to be significantly dependent on the reaction and pre-treatment conditions. In the case of the bimetallic catalyst, reversible redistribution and enrichment of the nanoparticle surface with Pt or Au were shown to be the key factor defining the activity. [ABSTRACT FROM AUTHOR]

A series of three-way catalysts containing palladium and rhodium were prepared by an incipient wetness impregnation of support with aqueous solution of [Pd(NH3)4](NO3)2 and Na3[Rh(NO2)6] compounds. Both pure and La-doped aluminum oxides were used as a support. The catalysts showed very close activity under stoichiometric and reductive conditions, but were different in terms of thermal stability being tested in a prompt thermal aging regime. UV-Vis and luminescence spectroscopies were found to be informative for diagnostics of rhodium and palladium concentration and state, thus giving the possibility to follow the changes taking place with active components (migration, agglomeration, bulk diffusion). [ABSTRACT FROM AUTHOR]

A series of supported Pd/ZrO2 catalysts with Pd loading from 0.2 to 2 wt % was synthesized. The ZrO2 material prepared by a similar technique was used as a reference sample. The samples have been characterized by means of transmission electron microscopy (TEM), Xray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), testing reaction of ethane hydrogenolysis (HGE), N2 adsorption, and electron paramagnetic resonance (EPR) spectroscopy. 1,3,5-trinitrobenzene was used as a probe molecule for the EPR spin probe method. The catalytic performance of samples was tested in the model reaction of CO oxidation. It was shown that the concentration of donor sites of support measured by EPR spin probe correlates with catalytic behavior during light-off tests. Low concentration of donor sites on a support's surface was found to be caused by the presence of the specific surface defects that are related to existence of coordinately unsaturated structures. [ABSTRACT FROM AUTHOR]