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Abstract
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), X-ray 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.
Highlights
The role of the atomically dispersed forms of the supported precious metals (PM) in the course of catalytic reactions is intensively discussed in literature [1,2,3,4,5,6,7]
It should be noted that stabilization of a major part of the supported metal in the form of the isolated atoms or ions is caused by the existence of coordinatively unsaturated structures on an oxide surface, and can be only observed at a very low concentration of introduced PM
Similar results have been recently reported for the series of Pd/γ-Al2 O3 catalysts active in the CO oxidation containing very low concentration of the supported metal [7]
Summary
The role of the atomically dispersed forms of the supported precious metals (PM) in the course of catalytic reactions is intensively discussed in literature [1,2,3,4,5,6,7]. The transfer from nanosized particles to the atoms or ions stabilized on a carrier’s surface could lead to a radical change in their coordination environment that, in turn, might have a strong effect on catalytic activity. It should be noted that stabilization of a major part of the supported metal in the form of the isolated atoms or ions is caused by the existence of coordinatively unsaturated structures on an oxide surface, and can be only observed at a very low concentration of introduced PM. In the case of Pt/γ-Al2 O3 catalyst, the role of such centers could be played by the unsaturated penta-coordinated Al3+ species, which are believed to anchor the atoms of supported metal, preventing them from possible agglomeration at elevated temperatures [5,6].
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