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.

Liquid organic hydrogen carriers represent an interesting alternative for hydrogen storage and transport. We demonstrate a method to simultaneously increase the activity of LOHC dehydrogenation catalysts and reduce side product formation.

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, AuPd 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 AuPd 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.

In order to move from a carbon-based energy system to a more sustainable one, focus is put on liquid organic hydrogen carrier (LOHC) systems for CO 2 -free hydrogen storage and release. In this study sulfur as a dopant for the Pt/TiO 2 catalyst was identified to be a selective poison resulting in high performing catalysts in the dehydrogenation experiments with the LOHC system perhydro dibenzyltoluene/dibenzyltoluene (H18-DBT/H0-DBT). The Pt/TiO 2 and S−Pt/TiO 2 catalysts were compared to the current benchmarks Pt/γ-Al 2 O 3 and S−Pt/γ-Al 2 O 3 . S−Pt/TiO 2 was found to achieve a high degree of dehydrogenation of 98% which is competitive to the benchmark S−Pt/γ-Al 2 O 3 . In addition, analyses of the side products resulted in a higher selectivity toward dibenzyltoluene for S−Pt/TiO 2 than for the γ-Al 2 O 3 supported catalysts. Characterization with infrared spectroscopy (IR), transmission electron microscopy (TEM), and diffuse reflectance infrared Fourier transform spectroscopy with CO as adsorbing molecule (CO−DRIFTS) suggest the presence of strongly chemisorbed sulfur species as well as SMSI effects of the Pt/TiO 2 catalysts. Based on kinetic studies, a batch and plug flow reactor for the dehydrogenation reaction were simulated for both titania supported catalysts. According to the calculations, the sulfur doped catalyst displays higher conversions in both batch and plug flow operation as compared to the unmodified system Pt/TiO 2 .

Solid catalysts with ionic liquid layers (SCILLs) show improved performance as compared to ionic liquid (IL)-free catalysts. To realize the beneficial IL-induced modification, the IL layer should be stable under reaction conditions but also permeable for gaseous reactants entering through the IL phase. Herein, we applied (polarization modulation-) infrared reflection absorption spectroscopy ((PM-)­IRAS) to investigate the CO permeability of model SCILL systems. We investigated three different IL model systems prepared by physical vapor deposition (PVD) in ultrahigh vacuum (UHV) on atomically clean Pt(111), namely, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)­imide ([C4C1Pyr]­[NTf2]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)­imide ([C2C1Im]­[NTf2]), and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([C4C1Pyr]­[OTf]). The adsorption geometries of the anions depend on the surface structure, IL coverage, and precoverage of CO. At room temperature, IL multilayers of randomly oriented species grow on top of strongly adsorbed wetting layers. Upon heating, a partial wetting transition induces the coexistence of an IL wetting monolayer film with three-dimensional droplets. Gas-phase CO does not permeate through IL multilayers, while it penetrates the IL wetting monolayer leading to mixed IL/CO films. The partial dewetting transition and the permeability differ drastically with the temperature and IL. Consequently, the morphology of the IL films could be a factor that determines the catalytic behavior of SCILLs to a significant extent.

Control of metal–support interactions is one of the major challenges in heterogeneous catalysis. In this study, we explored the effect of Eu doping on the metal–support interactions in Au/Ce1–x Eu x O2 catalysts applied in the oxidation of CO. We probe the catalysts with CO under realistic conditions by near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). NAP-XPS allows in situ investigation of the surface reducibility of the ceria support and charging of the Au nanoparticles. Both parameters are crucial, as they are responsible for the efficiency of Au/ceria catalysts in the CO oxidation. We found that doping of the ceria support with Eu decreases the reducibility of Ce4+ in the Au/Ce1–x Eu x O2 system and the population of Auδ+ sites. We identified the available CO adsorption sites on Au/ceria (Auδ−, Au0, and Auδ+) in the typical temperature window of the CO oxidation reaction by in situ DRIFTS. We found that the difference in the catalytic activity of Au/CeO2 and Au/Ce0.80Eu0.20O2 does not origin from an electronic effect of the Eu dopant or different adsorption sites but from the size of the Au nanoparticles. The most active Au nanoparticles are very small, reactive Au nanoparticles, which are exclusively present on the undoped ceria support.

We have prepared model systems for Pt–Ga supported catalytically active liquid metal solutions (SCALMS) by physical vapor deposition of Pt and Ga onto highly oriented pyrolytic graphite (HOPG). Prior to metal deposition, the HOPG support was modified by Ar+ bombardment. In this work, we focus on the stability of the Pt–Ga deposits toward agglomeration, which is a critical challenge in application. Specifically, we study the behavior of the model catalysts in ultrahigh vacuum (UHV) and under near ambient pressure (NAP) conditions at different temperatures. We use CO as a probe molecule to examine changes in the surface composition of the Pt–Ga deposits by in situ infrared reflection absorption spectroscopy (IRAS). In specific, we combine IRAS and ex situ atomic force microscopy (AFM) to study changes induced by annealing. We find that sintering effects are strongly dependent on the thickness of the deposited Pt–Ga layers. Our data suggest that particle ripening leads to a separation of the system into disperse Pt-rich and large Ga-rich particles. In the NAP regime, we performed simultaneous measurements with polarization modulation IRAS (PM-IRAS) and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). The alloying of Pt and Ga is accompanied by a shift of Pt 4f and Ga 3d photoelectron lines to higher binding energies. Although partial oxidation of Ga is observed upon CO exposure at pressures in the millibar regime, PM-IRAS shows adsorbed CO at a frequency typical for Pt ensembles in a Ga matrix.

Addition of CuCl to supported ionic liquid phase (SILP) catalysts enhances the activity in the low temperature water–gas shift (WGS) reaction.