Sub-nano supported Pt cluster catalysts deactivate quickly due to a combination of coking and sintering, when used in high temperature and hydrocarbon-rich reactions such as alkane dehydrogenation. We used an ALD-like deposition process to selectively dope small, size-selected Ptn/alumina model catalysts with controlled amounts of Ge. For example, Pt4/alumina was converted to Pt4Ge/alumina, and found to be substantially more stable in repeated runs to 750 K, with substantially less carbon deposition. XPS and ion scattering are used to probe changes in electronic environment and morphology during the Ge treatment and in subsequent reactions. Combining the conclusions drawn from experiments and from density functional theory (DFT), Ge modification of the small Pt clusters was found to suppress coking by altering the electronic and adsorbate binding properties for a model alkene (ethylene), quenching unpaired spins, resulting in π-bonding of ethylene dominating, and suppressing the di-σ bonding that occurs in pure Pt clusters. For Pt4Ge/alumina, the isomer population present at 700 K is predicted to include only ~2% supporting strong di-sigma binding, which tends to lead to further dehydrogenation and carbon deposition. Most interestingly, the small amount of ethylene dehydrogenation observed on Pt4Ge clusters has little effect on the availability of ethylene binding sites. The PtGe clusters were also thermally stable during and post multiple TPD experiments, thus indicating a high potential in sintering prevention.

Excellent performance of Pt4Ge/alumina model catalysts in preventing carbon deposition and sintering in dehydrogenation of alkanes

ACS Spring Meeting 2021

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