Search

We apply supported ionic liquid phase (SILP) catalysts to hydrogenate small 1-alkenes in a continuous fixed-bed reactor. We rationalize the origin of catalyst decomposition via IR spectroscopy and adapt the catalyst design for improved stability.

The [n]cycloparaphenylenes ([n]CPPs)-n para-linked phenylenes that form a closed-loop-have attracted substantial attention due to their unique cyclic structure and highly effective para-conjugation leading to a myriad of fascinating electronic and optoelectronic properties. However, their strained topology prevents the π-extension of CPPs to convert them either into armchair nanobelts or planarized CPP macrocycles. Here we successfully tackle this long-standing challenge and present the bottom-up synthesis and characterization of atomically precise in-plane π-extended [12]CPP on Au(111) by low-temperature scanning probe microscopy and spectroscopy combined with density functional theory. The planar π-extended CPP is a nanographene with an all-armchair edge topology. The exclusive para-conjugation at the periphery yields delocalized electronic states and the planarization maximizes the overlap of p orbitals, which both reduce the bandgap compared to conventional CPPs. Calculations predict ring currents and global aromaticity in the doubly charged system. The intriguing planar ring topology and unique electronic properties make planar π-extended CPPs promising quantum materials.

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 known to be highly prone to oxidation and in practical applications, handling of the catalyst material in air or the presence of traces of oxygen in the reactor are unavoidable. Therefore, we expect our results to be of high relevance for the application of Ga-based SCALMS catalysts. Pd–Ga alloy samples of 1.3 and 1.8 at% Pd content were exposed to molecular oxygen at different pressures between 3 × 10−7 and 1 mbar and a temperature of 550 K. We observe the formation of wetting Ga2O3 films upon exposure to molecular oxygen. The absolute thicknesses of the oxide films depend on oxygen pressure, with values ranging from ∼12 A at 10−7 to 10−5 mbar to ∼50 A at 1 mbar. The formed metal-oxide interface leads to a redistribution of Pd, which accumulates at the boundary between the wetting oxide film and the metal substrate as a response to the oxide film growth. A maximum Pd 3d intensity is observed at an oxide thickness of 5 A. For thicker films, the Pd 3d signal and the Ga 3d signal ascribed to the metallic substrate decrease in parallel, which is attributed to the oxide layer growing on top of the liquid metal alloy. From this observation, we conclude that no significant amount of Pd is bound in the newly formed oxide film. Density-functional theory (DFT) calculations support the experimental observations.

We have prepared model systems for Pd-Ga supported catalytically active liquid metal solutions (SCALMS) by physical vapor deposition of Pd and Ga in ultrahigh vacuum onto highly oriented pyrolytic graphite (HOPG) pre-modified by Ar+ bombardment. Combining AFM and IRAS with CO as a probe molecule, we investigate the growth behavior, the morphology, the surface chemistry, and the stability of Pd-Ga alloys on HOPG. Our results prove the single atom character of the active sites in Ga-rich Pd-Ga alloys. We show that upon interaction with CO, Ga is displaced from the surface and CO adsorbs in on-top position on surface Pd atoms. Experimental data on the vibrational frequencies and binding energies of CO are compared to the results of DFT calculations for CO adsorption on four different Pd-Ga models, i.e. PdGa(1 0 0), PdGa( 1 ¯ 1 ¯ 1 ¯ ), Pd-doped α-Ga(0 0 1), and Pd-doped fcc-Ga(1 0 0). The comparison suggests that widely separated Pd sites are formed in the Ga matrix.

Supported catalytically active liquid metal solutions 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 SiO2/Si(100) with low Rh content (

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. Fil: Bauer, Tanja. Universitat Erlangen-Nuremberg; Alemania Fil: Maisel, Sven. Universitat Erlangen-Nuremberg; Alemania Fil: Blaumeiser, Dominik. Universitat Erlangen-Nuremberg; Alemania Fil: Vecchietti, María Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Taccardi, Nicola. Universitat Erlangen-Nuremberg; Alemania Fil: Wasserscheid, Peter. Universitat Erlangen-Nuremberg; Alemania Fil: Bonivardi, Adrian Lionel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Görling, Andreas. Universitat Erlangen-Nuremberg; Alemania Fil: Libuda, Jörg. Universitat Erlangen-Nuremberg; Alemania

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.

For most functional oxides, structure‐selective synthesis is the key for the task‐specific production of nanomaterials. Herein, the low‐temperature synthesis in ionic liquids (ILs) is an attractive strategy to produce nanomaterials which are not accessible otherwise is described. In this study, a bench‐scale synthesis route toward Co3O4 by applying O3 on the molecular precursor Co2(CO)8 in IL medium is reported. The Co3O4 nanoparticles (NPs) are characterized by infrared (IR) spectroscopy, X‐ray diffraction (XRD), and transmission electron microscopy (TEM). This protocol yields Co3O4 with good crystallinity and narrow size distribution. In addition to conventional materials characterization, a new experimental approach is described in which the material synthesis in situ by IR reflection absorption spectroscopy (IRAS) (in situ IRAS) is followed. The in situ approach provides additional information on the growth mechanisms and kinetics and confirms that O3 treatment of Co2(CO)8 in IL exclusively yields pure Co3O4 without the formation of byproducts or intermediates.

The preparations of single (monolayer) and bulk carbides on the $\mathrm{Mo}(110)$ and $\mathrm{Mo}(100)$ single crystals are followed in situ at 1200 K using synchrotron-based high-resolution x-ray photoelectron spectroscopy of the $\mathrm{C}\phantom{\rule{0.28em}{0ex}}1s$ and core Mo $3{d}_{5/2}$ levels. By comparing the experimental results to first principles calculations using density functional theory, we suggest real-space surface structures for the carbide-modified surfaces. For a monolayer carbide on $\mathrm{Mo}(110)$, carbon dimers adsorb in the long-bridge site, most likely at a coverage of $3/8\phantom{\rule{0.16em}{0ex}}\mathrm{ML}$ carbon atoms per Mo surface atom. For the bulk carbide, we find a coverage of $\ensuremath{\sim}0.5\phantom{\rule{0.16em}{0ex}}\mathrm{ML}$ on the surface, and the calculations show that single carbon atoms are more stable than dimers on the surface. The monolayer carbide on $\mathrm{Mo}(100)$ exhibits a coverage of $\ensuremath{\sim}1\phantom{\rule{0.16em}{0ex}}\mathrm{ML}$ and agrees with previous studies, while the bulk carbide preparation probably leads to a faceting of the surface.