Pt speciation on ZSM-5 by IR of probes co-adsorption and chemometric analysis

The platinum speciation, nanoparticle size and reactivity of fresh and aged Pt/ZSM-5 catalysts prepared from colloids impregnation have been determined by in situ and operando Fourier Transform Infrared spectroscopy. From CO chemisorption, it has been shown that an oxidative ageing treatment at 1073 K leads to the formation and stabilization of particular Pt species. CO chemisorption done over the same sample previously saturated by d3-acetonitrile indicates that these atoms exhibit Lewis acidity and are in exchange position of the zeolite framework. The evolution of this electron deficient Pt species during a CO oxidation TPSR has been studied by chemometric analysis of the obtained operando spectra. Such unsaturated Pt centres are capable to adsorb up to two carbonyls. After thermal desorption at 475 K, they are found irreversibly transformed into metallic surface atoms.

Air ageing treatment performed at high temperature on Pt nanoparticles supported on acidic ZSM-5 zeolite leads to a metal re-dispersion. Part of the Pt is found grafted into the zeolite channels in the cationic exchange position. Such metal sites are capable to adsorb up to 2 CO probe molecules at room temperature. The transformation is reversible upon CO oxidation reaction at 500 K.Figure optionsDownload as PowerPoint slideResearch highlights
► Co-adsorption of d3-acetonitrile-d3 and CO allows the characterization of Pt atoms in cationic positions.
► The evolution of the Pt speciation during CO oxidation TPSR is fully depicted by chemometric analysis.
► Air ageing treatment at high temperature leads to partial metal re-dispersion.