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.
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.
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.
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