No abstract

Ceria (CeO2) supports are unique in their ability to trap ionic platinum (Pt), providing exceptional stability for isolated single atoms of Pt. The reactivity and stability of single‐atom Pt species was explored for the industrially important light alkane dehydrogenation reaction. The single‐atom Pt/CeO2 catalysts are stable during propane dehydrogenation, but are not selective for propylene. DFT calculations show strong adsorption of the olefin produced, leading to further unwanted reactions. In contrast, when tin (Sn) is added to CeO2, the single‐atom Pt catalyst undergoes an activation phase where it transforms into Pt–Sn clusters under reaction conditions. Formation of small Pt–Sn clusters allows the catalyst to achieve high selectivity towards propylene because of facile desorption of the product. The CeO2‐supported Pt–Sn clusters are very stable, even during extended reaction at 680 °C. Coke formation is almost completely suppressed by adding water vapor to the feed. Furthermore, upon oxidation the Pt–Sn clusters readily revert to the atomically dispersed species on CeO2, making Pt–Sn/CeO2 a fully regenerable catalyst.

The nature and evolution of the hydrocarbon pool (HP) species during the Methanol-to-Olefins (MTO) process for three small-pore zeolite catalysts, with a different framework consisting of large cages interconnected by small eight-ring windows (CHA, DDR, and LEV) was studied at reaction temperatures between 350 and 450 °C using a combination of operando UV–vis spectroscopy and online gas chromatography. It was found that small differences in cage size, shape, and pore structure of the zeolite frameworks result in the generation of different hydrocarbon pool species. More specifically, it was found that the large cage of CHA results in the formation of a wide variety of hydrocarbon pool species, mostly alkylated benzenes and naphthalenes. In the DDR cage, 1-methylnaphthalene is preferentially formed, while the small LEV cage generally contains fewer hydrocarbon pool species. The nature and evolution of these hydrocarbon pool species was linked with the stage of the reaction using a multivariate analysis of the operando UV–vis spectra. In the 3-D pore network of CHA, the reaction temperature has only a minor effect on the performance of the MTO catalyst. However, for the 2-D pore networks of DDR and LEV, an increase in the applied reaction temperature resulted in a dramatic increase in catalytic activity. For all zeolites in this study, the role of the hydrocarbon species changes with reaction temperature. This effect is most clear in DDR, in which diamantane and 1-methylnaphthalene are deactivating species at a reaction temperature of 350 °C, whereas at higher temperatures diamantane formation is not observed and 1-methylnaphthalene is an active species. This results in a different amount and nature of coke species in the deactivated catalyst, depending on zeolite framework and reaction temperature.

Bandshape luminescence thermometry during in situ temperature measurements has been reported by preparing three catalytically relevant systems, which show temperature-dependent luminescence. One of these systems was further investigated as a showcase for application. Microcrystalline NaYF4 doped with Er3+ and Yb3+ was mixed with a commercial zeolite H-ZSM-5 to investigate the Methanol-to-Hydrocarbons (MTH) reaction, while monitoring the reaction products with online gas chromatography. Due to the exothermic nature of the MTH reaction, a front of increased temperature migrating down the fixed reactor bed was visualized, showing the potential for various applications of luminescence thermometry for in situ measurements in catalytic systems.

Ceria (CeO 2 )s upports are unique in their ability to trap ionic platinum (Pt), providing exceptional stability for isolated single atoms of Pt. The reactivity and stability of single-atom Pt species was explored for the industrially important light alkane dehydrogenation reaction. The singleatom Pt/CeO 2 catalysts are stable during propane dehydrogenation, but are not selective for propylene.D FT calculations show strong adsorption of the olefin produced, leading to further unwanted reactions.Incontrast, when tin (Sn) is added to CeO 2 ,t he single-atom Pt catalyst undergoes an activation phase where it transforms into Pt-Sn clusters under reaction conditions.F ormation of small Pt-Sn clusters allows the catalyst to achieve high selectivity towards propylene because of facile desorption of the product. The CeO 2 -supported Pt-Sn clusters are very stable,e ven during extended reaction at 680 8 8C. Coke formation is almost completely suppressed by adding water vapor to the feed. Furthermore,u pon oxidation the Pt-Sn clusters readily revert to the atomically dispersed species on CeO 2 ,m aking Pt-Sn/CeO 2 af ully regenerable catalyst.

In this work, during the methanol-to-olefins (MTO) reaction, the formation of hydrocarbon pool species as well as the accumulation of coke and coke precursor molecules were monitored with operando UV-vis spectroscopy.

In small-pore zeolite catalysts, where the size of the pores is limited by eight-ring windows, aromatic hydrocarbon pool molecules that are formed inside the zeolite during the Methanol-to-Olefins (MTO) process cannot exit the pores and are retained inside the catalyst. Hydrocarbon species whose size is comparable to the size of the zeolite cage can cause the zeolite lattice to expand during the MTO process. In this work, the formation of retained hydrocarbon pool species during MTO at a reaction temperature of 400 °C was followed using operando UV–vis spectroscopy. During the same experiment, using operando X-ray Diffraction (XRD), the expansion of the zeolite framework was assessed, and the activity of the catalyst was measured using online gas chromatography (GC). Three different small-pore zeolite frameworks, i.e., CHA, DDR, and LEV, were compared. It was shown using operando XRD that the formation of retained aromatic species causes the zeolite lattice of all three frameworks to expand. Because of the differences in the zeolite framework dimensions, the nature of the retained hydrocarbons as measured by operando UV–vis spectroscopy is different for each of the three zeolite frameworks. Consequently, the magnitude and direction of the zeolite lattice expansion as measured by operando XRD also depends on the specific combination of the hydrocarbon species and the zeolite framework. The catalyst with the CHA framework, i.e., H-SSZ-13, showed the biggest expansion: 0.9% in the direction along the c-axis of the zeolite lattice. For all three zeolite frameworks, based on the combination of operando XRD and operando UV–vis spectroscopy, the hydrocarbon species that are likely to cause the expansion of the zeolite cages are presented; methylated naphthalene and pyrene in CHA, 1-methylnaphthalene and phenalene in DDR, and methylated benzene and naphthalene in LEV. Filling of the zeolite cages and, as a consequence, the zeolite lattice expansion causes the deactivation of these small-pore zeolite catalysts during the MTO process.

The effect of physicochemical properties on catalyst deactivation, overall olefin selectivity and ethylene/propylene ratio during the methanol-to-olefins (MTO) reaction is presented for two zeolites with the DDR topology, Sigma-1 and ZSM-58.