Unprecedented selectivity behavior in the direct dehydrogenation of n-butane to n-butenes with similar active Pt nanoparticle size: unveiling structural and electronic characteristics of supported monometallic catalysts.

Abstract

In this work, supported Pt monometallic catalysts were prepared using oxide and carbon supports by conventional impregnation methods. Similar Pt metallic nanoparticle sizes (mean sizes about 1.8-2 nm) have been obtained using different Pt precursor loadings (0.3 to 5 wt%). For comparison, catalysts with larger nanoparticle sizes were prepared using the liquid phase reduction method. Characterization results indicate different electronic and structural characteristics for the Pt nanoparticles, comparing nanoparticles with similar and different sizes, implying that both the Pt loading and the preparation method affect the formation of different metallic phases. We used the direct dehydrogenation of n-butane to n-butenes reaction as a test reaction to study the catalytic behavior of the Pt nanoparticles obtained at different Pt atomic concentrations. Surprisingly, Pt catalysts with the lowest metallic loading show the highest selectivities to olefins. Besides, Pt catalysts supported on carbon materials showed higher selectivity to butenes than those supported on oxide materials, this was attributed to a higher electron density in the Pt active sites. Likewise, at low Pt loadings, the CNP-supported Pt nanoparticles could be confined at the defect in the nanotube structure as crystalline agglomerates of atoms with few layers or monolayers with very few surface adatom or stepped adatom nanostructures or simply as a group of atoms, thus creating active Pt sites that favor the dehydrogenation reaction over secondary reactions.