Speaker
Description
The implementation of single atom catalysts (SACs) critically depends on the stability of single atoms towards sintering. We have recently shown that the catalyst pre-treatment with oxygen plasma improves stability and reactivity of Pt/CeO2 SACs in CO oxidation.1 Here we focused on employing “cold” plasma to SACs for reactions under the reducing (H2 containing) atmosphere. In this work, we investigated the reaction of propane dehydrogenation to propene (PDH) over Pt/Al2O3 SACs, in particular to examine, whether the plasma pre-treatment can improve stability of SACs and maintain high Pt dispersion under reductive conditions or show any other beneficial effect on the catalytic performance. We found that the catalyst, pre-treated with the hydrogen plasma before the conventional calcination/reduction steps, showed considerably increased propane conversion without loss of selectivity, whereas argon plasma caused no such effect. The structural and chemical evolution of the catalysts studied by STEM, XAS, XPS, and DRIFTS showed that the H2 plasma: (i) partially reduces singly dispersed Pt2+ species and thus promotes Pt clustering; (ii) decreases the amount of Cl remaining after use of the hexachloroplatinic acid precursor; and (iii) enhances hydroxylation of the alumina support. Upon subsequent oxidation/reduction at elevated temperatures, the Pt single atoms sinter into nanoparticles of almost the same size (~ 1.5 nm) and surface structure, irrespective of the plasma pre-treatment. We propose that the promotional effect of the H2 plasma lies in specific modification of the alumina surface that in turn alters the metal/support interaction and formation of a more active Pt/Al2O3 interface during the oxidation/reduction steps.
