Ti-Doping in Silica-Supported PtZn Propane Dehydrogenation Catalysts: From Improved Stability to the Nature of the Pt-Ti Interaction

Propane dehydrogenation is an important industrial reactiontoaccess propene, the world's second most used polymer precursor.Catalysts for this transformation are required to be long living athigh temperature and robust toward harsh oxidative regeneration conditions.In this work, combining surface organometallic chemistry and thermolyticmolecular precursor approach, we prepared well-defined silica-supportedPt and alloyed PtZn materials to investigate the effect of Ti-dopingon catalytic performances. Chemisorption experiments and density functionalcalculations reveal a significant change in the electronic structureof the nanoparticles (NPs) due to the Ti-doping. Evaluation of theresulting materials PtZn/SiO2 and PtZnTi/SiO2 during long deactivation phases reveal a stabilizing effect of Tiin PtZnTi/SiO2 with a k (d) of0.015 h(-1) compared to PtZn/SiO2 witha k (d) of 0.022 h(-1) over108 h on stream. Such a stabilizing effect is also present duringa second deactivation phase after applying a regeneration protocolto the materials under O-2 and H-2 at high temperatures.A combined scanning transmission electron microscopy, in situ X-ray absorption spectroscopy, electron paramagnetic resonance,and density functional theory study reveals that this effect is relatedto a sintering prevention of the alloyed PtZn NPs in PtZnTi/SiO2 due to a strong interaction of the NPs with Ti sites. However,in contrast to classical strong metal-support interaction,we show that the coverage of the Pt NPs with TiO x species is not needed to explain the changes in adsorptionand reactivity properties. Indeed, the interaction of the Pt NPs withTi(III) sites is enough to decrease CO adsorption and toinduce a red-shift of the CO band because of electron transfer fromthe Ti-III sites to Pt-0.