Metal phase and structural characterization of iron and palladium catalysts by Moessbauer effect spectroscopy, transmission electron microscopy/energy dispersive X-ray spectroscopy and solid-state nuclear magnetic resonance.

摘要

The catalytic behavior of supported metal particles can be markedly influenced by their structure and phase composition. In this investigation, Mossbauer effect spectroscopy (MES), solid-state nuclear magnetic resonance (NMR) and transmission electron microscopy/energy dispersive x-ray spectroscopy (TEM/EDS) were used to characterize the structure and metal phases within Fe, Fe-Mn and Pd particles.;In the first part of this study, the sintering behavior and phase composition of Fe particles derived from metal carbonyl clusters (MCCs) were determined on differently pretreated carbon black supports. It is proposed that small Fe carbide/oxide particles formed during the initial MCC decomposition process were stabilized by active sites on the carbon surface. The same carbide/oxide phase was formed when mixed-metal Fe-Mn MCCs were decomposed on carbon black. MES showed that the Fe-Mn clusters decomposed via Fe-only clusters at temperatures below 473 K. The Fe and Mn remained in contact with each other after reduction at 673 K, although no bulk Fe;TEM studies of large Fe-Mn particles supported on graphite showed the effects of reduction and oxidation pretreatments on the particle morphology. While the particles were solid following an initial reduction, they assumed a hollow spherical geometry following oxidation at 523 K. The results are consistent with a model where diffusion of Fe ions through an Mn oxide layer takes place during oxidation.;Finally, the phases of deuterium in Pd/SiO