Promotion of Pd nanoparticles by Fe and formation of a Pd3Fe intermetallic alloy for propane dehydrogenation

Silica supported Pd (similar to 2 nm), Pd3Fe (similar to 2 nm) and Pd3Fe_large (similar to 12 nm) catalysts were synthesized and tested for propane dehydrogenation at 510 degrees C. At the 10% conversion, Pd and Pd3Fe catalysts exhibited propylene selectivity of 45% and 94%, respectively. Moreover, the latter showed a turnover rate (TOR) of 0.2 s(-1), which is five times higher than that of the Pd catalyst (0.04 s(-1)). Pd K edge XAS, XRD, and CO adsorbed IR were used to characterize the geometric structure of the catalysts. By combined comparison of XRD and XAS spectra of Pd3Fe and Pd3Fe_large catalysts, we successfully identified the crystalline phase in the 2 nm Pd3Fe catalyst. The CO adsorbed IR suggests that the formation of Pd3Fe breaks the ensemble of Pd, which is responsible for the increase of selectivity. The Pd L edge XAS was used to characterize the electronic structure of the catalysts. The Pd3Fe catalyst exhibits an increase of the edge energy compared with the Pd catalyst, which indicates the change of d-band structure in the bimetallic catalyst. The change in the electronic structure is likely the reason for the increase in TOR.