Benzyltoluene (H0-BT) is a promising liquid organic hydrogen carrier (LOHC) molecule. Catalytic hydrogenation of H0-BT to perhydro benzyltoluene (H12-BT) and dehydrogenation back to H0-BT to release the chemically bound hydrogen constitute a suitable and technically relevant hydrogen storage cycle. Herein, we report the development of a bimetallic Pt-Re/Al2O3 catalyst for the dehydrogenation of H12-BT under moderate conditions to enable heat integration of the endothermal dehydrogenation reaction with low temperature waste heat streams. The reducibility of the catalyst is compared to a monometallic Pt/Al2O3 reference system using temperature-programmed reduction (TPR) and in situ reduction during X-ray absorption spectroscopy (XAS) to gain insight on the mode of interaction between Pt and Re. TPR and XAS propose full reduction of Pt, while rhenium oxide is only partially reduced at 400 degrees C. Analysis by means of extended X-ray absorption fine structure suggests a lower coordination number and thus smaller entities of Pt for bimetallic catalysts with increasing Re loading. Further, an electronic modification of Pt is observed, which mostly stems from residual Cl-species from the Pt-precursor, but may also indicate direct interaction with Re. Structural promotion of Pt by Re provided a strong stabilization of smaller clusters and nanoparticles leading to a high Pt dispersion even during catalyst activation in H2 at high temperatures of 700 degrees C. When compared to the monometallic reference, particularly the initial hydrogen release is accelerated when using Pt-Re/Al2O3 catalysts. Mechanistically, the bimetallic catalysts outperformed the monometallic reference catalyst due to an efficient initial dehydrogenation of H12-BT and a short lifetime of the partially dehydrogenated intermediate (H6-BT) yielding H0-BT as the desired product of the consecutive reaction. The catalytic performance and XAS studies suggest an optimized structural composition of the active Pt phase, potentially via an ensemble effect, which allows for efficient H2 release from H12-BT. H2 release from the liquid organic hydrogen carrier perhydro benzyltoluene (H12-BT) was accelerated using bimetallic Pt-Re/Al2O3 catalysts. An optimum Pt : Re ratio was identified and catalysts characterisation provided insight on Pt-Re interaction.

The benzyltoluene (BT)-based liquid organic hydrogen carrier (LOHC) system currently considered for largescale applications represents a mixture of regioisomers. To characterize this complex system, a comprehensive experimental database for various thermophysical properties of synthesized BT isomers and their mixtures without and with the presence of hydrogen (H2) close to vapor-liquid equilibrium is established using optical and conventional techniques at process-relevant temperatures and pressures up to 573 K and 6 MPa. The surface tension varies by less than 4% among the dehydrogenated (H0-BT) or hydrogenated (H12-BT) isomers. The density and viscosity of mixtures of H0-BT or H12-BT isomers can be described by simple mixing rules with average absolute relative deviations of 0.022% and 0.38%. With increasing H2 pressure, the viscosity remains nearly constant, while the interfacial tension decreases by up to 5%. The thermal and mutual diffusivity of H12ortho-BT containing dissolved H2 at 6 MPa decrease and increase with increasing temperature.

The water gas shift reaction (WGSR) is catalyzed by supported ionic liquid phase (SILP) systems containing homogeneous Ru complexes dissolved in ionic liquids (ILs). These systems work at very low temperatures, that is, between 120 and 160 °C, as compared to >200 °C in the conventional process. To improve the performance of this ultra-low-temperature catalysis, we investigated the influence of various additives on the catalytic activity of these SILP systems. In particular, the application of methylene blue (MB) as an additive doubled the activity. Infrared spectroscopy measurements combined with density functional theory (DFT) calculations excluded a coordinative interaction of MB with the Ru complex. In contrast, state-of-the-art theoretical calculations elucidated the catalytic effect of the additives by non-covalent interactions. In particular, the additives can significantly lower the barrier of the rate-determining step of the reaction mechanism via formation of hydrogen bonds. The theoretical predictions, thereby, showed excellent agreement with the increase of experimental activity upon variation of the hydrogen bonding moieties in the additives investigated.

Defined surface functionalities can control the properties of a material. The layer-by-layer method is an experimentally simple yet very versatile method to coat a surface with nanoscale precision. The method is widely used to either control the chemical properties of the surface via the introduction of functional moieties bound to the polymer or create nanoscale surface topographies if one polymeric species is replaced by a colloidal dispersion. Such roughness can enhance the stability of a liquid film on top of the surface by capillary adhesion. Here, we investigate whether a similar effect allows an increased retention of liquid films within a porous surface and thus potentially increases the stability of ionic liquid films infused within a porous matrix in the supported ionic liquid-phase catalysis. The complex geometry of the porous material, long diffusion pathways, and small sizes of necks connecting individual pores all contribute to difficulties to reliably coat the required porous materials. We optimize the coating process to ensure uniform surface functionalization via two steps. Diffusion limitations are overcome by force-wetting the pores, which transports the functional species convectively into the materials. Electrostatic repulsion, which can limit pore accessibility, is mitigated by the addition of electrolytes to screen charges. We introduce nanoscale topography in microscale porous SiC monoliths to enhance the retention of an ionic liquid film. We use γ-Al2O3 to coat monoliths and test the retention of 1-butyl-2,3-dimethylimidazolium chloride under exposure to a continuous gas stream, a setup commonly used in the water-gas shift reaction. Our study showcases that a hierarchical topography can improve the stability of impregnated ionic liquid films, with a potential advantage of improved supported ionic liquid-phase catalysis.

Supported ionic liquid-phase (SILP) catalyzed water–gas shift reaction with in situ product removal is presented. A facilitated transport membrane coated onto the smooth outside of the SiC monolith allowed preferential removal of CO2 compared to H2.

Homogeneous catalysts, usually being active in liquid environment,offer several benefits for highly selective processes. However, the oftentedious product separation and catalyst recycling, requiring energy and chemical input, renders such processes energy inefficient. Here,

A monolithic γ-Al 2 O 3 support is developed to scale up the WGS process using the supported ionic liquid-phase concept in a structured reactor. The support-ionic liquid-catalyst system maximizes loading and mechanical resistance while achieving high activity and selectivity.

CuGax alloy nanoparticles supported on SiO2 can be obtained by surface organometallic chemistry. This catalyst is active and selective for the hydrogenation of CO2 to CH3OH, related to the formation of an optimal interface between Cu and GaIIIOx.

In situDRIFT spectroscopy and DFT identify Cu carbonyl shuttles that enhance the performance of Ru-based SILP water–gas shift catalysts.

Selective hydrogenation of CO2 into methanol is a key sustainable technology. Here, we show that Cu/Al2O3 prepared via Surface Organometallic Chemistry, displays particularly high activity towards CO2 hydrogenation compared to Cu/SiO2, yielding CH3OH, dimethyl ether (DME) as well as CO. Then, by combining advanced operando spectroscopy and DFT calculation, we show that CH3OH formation involves formate intermediates and that the increase of rate originates from the metal-oxide interface. Al2O3 also promotes the subsequent conversion of CH3OH to DME, evidencing bifunctional catalysis, but also increases the rate of CO formation. The latter takes place i) directly by activation of CO2 at the metal-oxide interface, and ii) indirectly via the conversion of formate surface species and CH3OH to methyl formate that is further decomposed into CH3OH and CO. This study showcases how Al2O3, a Lewis acidic and non-reducible support, can promote CO2 hydrogenation by enabling multiple competitive reaction pathways on the oxide and metal-oxide interface.

Selective hydrogenation of CO2 into methanol is a key sustainable technology, where Cu/Al2O3 prepared by surface organometallic chemistry displays high activity towards CO2 hydrogenation compared to Cu/SiO2, yielding CH3OH, dimethyl ether (DME), and CO. CH3OH formation rate increases due to the metal-oxide interface and involves formate intermediates according to advanced spectroscopy and DFT calculations. Al2O3 promotes the subsequent conversion of CH3OH to DME, showing bifunctional catalysis, but also increases the rate of CO formation. The latter takes place 1) directly by activation of CO2 at the metal-oxide interface, and 2) indirectly by the conversion of formate surface species and CH3OH to methyl formate, which is further decomposed into CH3OH and CO. This study shows how Al2O3, a Lewis acidic and non-reducible support, can promote CO2 hydrogenation by enabling multiple competitive reaction pathways on the oxide and metal-oxide interface.

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

In times of depleting fossil fuel reserves, optimizing industrial catalytic reactions has become increasingly important. One possibility for optimization is the use of homogenous catalysts, which are advantageous over heterogeneous catalysts because of mild reaction conditions as well as higher selectivity and activity. A new emerging technology, supported ionic liquid phase (SILP), was developed to permanently immobilize homogeneous catalyst complexes for continuous processes. However, these SILP catalysts are unable to form freestanding supports by themselves. This study presents a new method to introduce the SILP system into a support made from multi-walled carbon nanotubes (MWCNT). In a first step, SILP catalysts were prepared for hydroformylation as well as low-temperature water-gas shift (WGS) reactions. These catalysts were integrated into freestanding microtubes formed from MWCNTs, with silica (for hydroformylation) or alumina particles (for WGS) incorporated. In hydroformylation, the activity increased significantly by around 400% when the pure MWCNT material was used as SILP support. An opposite trend was observed for WGS, where pure alumina particles exhibited the highest activity. A significant advantage of the MWCNT composite materials is the possibility to coat them with separation layers, which allows their application in membrane reactors for more efficient processes.

The catalytic properties of zeolites are intimately linked to the distribution and relative positions of Al atoms and defects in the pore network. However, characterizing this distribution is challenging, in particular when different local Al arrangements are considered. In this contribution we use a combination of first principles calculations and experimental measurements to develop a model for the Al-distribution in protonated SSZ-13. We furthermore apply this model to understand trends in OH-IR, 27Al-NMR and 29Si-NMR spectra. We use a Boltzmann distribution to predict the proton position for a given local Al configuration and show that for each configuration several H positions are occupied. Therefore a multi-peak spectrum in OH-IR vibrational spectroscopy is observed for all Al configurations, which is in line with experimentally measured spectra for zeolites at different Si/Al ratios. From NMR spectroscopy we find that the proton position leads to significant shifts in 27Al-NMR and 29Si-NMR spectra due to the modification of the local strain, which is lost when a uniform background charge is introduced. These findings are supported by experimental measurements. Finally we discuss the shortcomings of the presented model in terms of unit cell size and the impact of adjacent unit cells.

Cu/ZrO2/SiO2 are efficient catalysts for the selective hydrogenation of CO2 to CH3OH. In order to understand the role of ZrO2 in these mixed-oxides based catalysts, in situ X-ray absorption spectroscopy has been carried out on the Cu and Zr K-edge. Under reaction conditions, Cu remains metallic, while Zr is present in three types of coordination environment associated with 1) bulk ZrO2, 2) coordinatively saturated and 3) unsaturated Zr(IV) surface sites. The amount of coordinatively unsaturated Zr surface sites can be quantified by linear combination fit of reference X-Ray absorption near edge structure (XANES) spectra and its amount correlates with CH3OH formation rates, thus indicating the importance of Zr(IV) Lewis acid surface sites in driving the selectivity toward CH3OH. This finding is consistent with the proposed mechanism, where CO2 is hydrogenated at the interface between the Cu nanoparticles that split H2 and Zr(IV) surface sites that stabilizes reaction intermediates.

Small and narrowly distributed Cu nanoparticles, supported on SiO2 decorated with isolated TiIV sites, prepared through surface organometallic chemistry, showed significantly improved CO2 hydrogenation activity and CH3 OH selectivity compared to the corresponding Cu nanoparticles supported on SiO2 . These isolated Lewis acid TiIV sites, evidenced by UV/Vis spectroscopy, are proposed to stabilize surface intermediates at the interface between Cu nanoparticles and the support.

The Cu-exchanged zeolite SSZ-13 is a highly active material in the selective catalytic reduction of nitrogen oxides and the conversion of methane to methanol. In this material, a distribution of active sites is present and its characterization is a long standing challenge. In this contribution, we combine molecular dynamics simulations and high-level first principles calculations to obtain accurate phase diagrams, photoabsorption, and photoluminescence spectra of Cu-I sites in SSZ-13 and compare them to specifically designed experimental measurements. We start our analysis by using molecular dynamics and random phase approximation calculations to calculate phase diagrams for Cu anchored in extra-framework and silanol defect sites. Subsequently, we combine molecular dynamics and a time dependent hybrid Hartree-Fock like linear response scheme to calculate photoabsorption and photoluminescence spectra. We determine that at low temperatures Cu-I is coordinated to multiple H2O molecules. At elevated temperatures and low pressures, all H2O molecules desorb and Cu-I migrates to defect sites, as long as defects are present in the material. Theoretically predicted and experimentally measured optical spectra are in excellent agreement. Additionally, we discuss the impact of defects on the observed luminescence spectra. We expect that the methods developed here will be used to better understand the distribution of Cu sites in the zeolite SSZ-13 under various conditions. Further, this work sheds light on a potential role of defects in the coordination of Cu-I in deNO(x)-SCR in aged catalysts and helps with understanding luminescence spectra of transition-metal sites in zeolites.

Ru-based SILP systems efficiently catalyze the low-temperature water-gas shift reaction (WGSR).

Copper nanoparticles supported on zirconia (Cu/ZrO2) or related supported oxides (Cu/ZrO2/SiO2) show promising activity and selectivity for the hydrogenation of CO2 to CH3OH. However, the role of the support remains controversial because most spectroscopic techniques provide information dominated by the bulk, making interpretation and formulation of structure-activity relationships challenging. In order to understand the role of the support and in particular of the Zr surface species at a molecular level, a surface organometallic chemistry approach has been used to tailor a silica support containing isolated Zr(IV) surface sites, on which copper nanoparticles (similar to 3 nm) are generated. These supported Cu nanoparticles exhibit increased CH3OH activity and selectivity compared to those supported on SiO2, reaching catalytic performances comparable to those of the corresponding Cu/ZrO2. Ex situ and in situ X-ray absorption spectroscopy reveals that the Zr sites on silica remain isolated and in their +4 oxidation state, while ex situ solid-state nuclear magnetic resonance spectroscopy and catalytic performances show that similar mechanisms are involved with the single-site support and ZrO2. These observations imply that Zr(IV) surface sites at the periphery of Cu particles are responsible for promoting CH3OH formation on Cu-Zr-based catalysts and provide a guideline to develop selective CH3OH synthesis catalysts.

In this work we present an alternate method for the conversion of tetrahydropyran-2-methanol (THP2M), a cellulose-derived renewable building block, to 1,6-hexanediol (1,6-HDO).