Our
contribution demonstrates that rhodium, an element that has
barely been reported as an active metal for selective dehydrogenation
of alkanes becomes a very active, selective, and robust dehydrogenation
catalyst when exposed to propane in the form of single atoms at the
interface of a solid-supported, highly dynamic liquid Ga–Rh
mixture. We demonstrate that the transition to a fully liquid supported
alloy droplet at Ga/Rh ratios above 80, results in a drastic increase
in catalyst activity with high propylene selectivity. The combining
results from catalytic studies, X-ray photoelectron spectroscopy,
IR-spectroscopy under reaction conditions, microscopy, and density-functional
theory calculations, we obtained a comprehensive microscopy picture
of the working principle of the Ga–Rh supported catalytically
active liquid metal solution.
Supported catalytically
active liquid metal solutions (SCALMS)
represent a class of catalytic materials that have only recently been
developed, but have already proven to be highly active, e.g., for
dehydrogenation reactions. Previous studies attributed the catalytic
activity to isolated noble metal atoms at the surface of a liquid
and inert Ga matrix. In this study, we apply diffuse reflectance infrared
Fourier transform spectroscopy (DRIFTS) with CO as a probe molecule
to Ga/Al2O3, Pt/Al2O3,
and Ga37Pt/Al2O3 catalysts, to investigate
in detail the nature of the active Pt species. Comparison of CO adsorption
on Pt/Al2O3 and Ga37Pt/Al2O3 shows that isolated Pt atoms are, indeed, present at
the surface of the liquid SCALMS. Combining DRIFTS with online gas
chromatography (GC), we investigated the Ga/Al2O3, Pt/Al2O3, and Ga37Pt/Al2O3 systems under operando conditions during propane dehydrogenation
in CO/propane and in Ar/propane. We find that the Pt/Al2O3 sample is rapidly poisoned by CO adsorption and coke,
whereas propane dehydrogenation over Ga37Pt/Al2O3 SCALMS leads to higher conversion with no indication
of poisoning effects. We show under operando conditions that isolated
Pt atoms are present at the surface of SCALMS during the dehydrogenation
reaction. IR spectra and density-functional theory (DFT) suggest that
both the Ga matrix and the presence of coadsorbates alter the electronic
properties of the surface Pt species.
Supported catalytically active liquid metal solutions (SCALMS) have been receiving increasing attention recently. We investigated the oxidation behavior of macroscopic Rh-Ga alloy droplets and Rh-Ga model catalyst nanoparticles supported on SiO 2 /Si(100) with low Rh content (<2.5 at %) by x-ray photoelectron spectroscopy in ultra-high vacuum and under near-ambient pressure conditions using different photon energies and also using transmission electron microscopy. The experiments are accompanied by computational studies on the Ga oxide/Rh-Ga interface and Rh-Ga intermetallic compounds. For both Rh-Ga alloy droplets and Rh-Ga model catalyst nanoparticles, exposure to molecular oxygen leads to the formation of an oxide shell in which Rh is enriched. High-resolution transmission electron microscopy on the Rh-Ga nanoparticles confirms the formation of an approximately 4 nm thick gallium oxide film containing Rh. Based on ab-initio molecular dynamics and computational studies on the Ga 2 O 3 /Ga interface, it is concluded that Rh incorporation into the Ga 2 O 3 film occurs by substituting octahedrally coordinated Ga.
Indicators for H2 are crucial to ensure safety standards in a green hydrogen economy. Herein, the authors report micron‐scaled indicator supraparticles for real‐time monitoring and irreversible recording of H2 gas via a rapid eye‐readable two‐step color change. They are produced via spray‐drying SiO2 nanoparticles, AuPd nanoparticles, and indicator‐dye resazurin. The resulting gas‐accessible mesoporous supraparticle framework absorbs water from humid atmospheres to create a three‐phase‐system. In the presence of H2, the color of the supraparticle switches first irreversibly from purple to pink and further reversibly to a colorless state. In situ infrared spectroscopy measurements indicate that this color change originates from the (ir)reversible H2‐induced reduction of resazurin to resorufin and hydroresorufin. Further infrared spectroscopic measurements and molecular dynamics simulations elucidate that key to achieve this functionality is an established three‐phase‐system within the supraparticles, granting molecular mobility of resazurin. Water acts as transport medium to carry resazurin molecules towards the catalytically active AuPd nanoparticles. The advantages of the supraparticles are their small dimensions, affordable and scalable production, fast response times, straightforward bare‐eye detection, and the possibility of simultaneously monitoring H2 exposure in real‐time and ex post. Therefore, H2 indicator supraparticles are an attractive safety additive for leakage detection and localization in a H2 economy.
We have examined model systems for the recently reported Pd-Ga Supported Catalytically Active Liquid Metal Solutions (SCALMS) catalysts using near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) under oxidizing conditions. Gallium is...
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