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The influence of nanostructures and interaction of Sn and Ir in oxygen evolution catalysts in a polymer electrolyte membrane electrolyzer were investigated. For this aim, two synthesis methods, namely, the one-step solution combustion method and the precipitation–deposition method with sodium borohydride reduction, were evaluated to prepare distinct nanostructures. Sn addition to Ir-based oxygen evolution reaction catalysts has been reported to yield materials with higher activity; however, in our case, this was observed only for Sn/Ir catalysts prepared by the precipitation–deposition method. The nanolayer of Sn/SnO2deposited over metallic Ir particles was identified to enhance the interfacial contacts, resulting in synergistic interactions. By deconvolution of the polarization curves into constituting contributions, the performance improvement was attributed to the higher exchange current density of the Sn/Ir powder as a consequence of a higher number of surface reaction sites created by the Sn–Ir interactions.

The direct synthesis of methanol via the hydrogenation of CO2, if performed efficiently and selectively, is potentially a powerful technology for CO2mitigation. Here, we develop an active and selective Cu–Zn/SiO2catalyst for the hydrogenation of CO2by introducing copper and zinc onto dehydroxylated silica via surface organometallic chemistry and atomic layer deposition, respectively. At 230 °C and 25 bar, the optimized catalyst shows an intrinsic methanol formation rate of 4.3 g h–1gCu–1and selectivity to methanol of 83%, with a space-time yield of 0.073 g h–1gcat–1at a contact time of 0.06 s g mL–1. X-ray absorption spectroscopy at the Cu and Zn K-edges and X-ray photoelectron spectroscopy studies reveal that the CuZn alloy displays reactive metal support interactions; that is, it is stable under H2atmosphere and unstable under conditions of CO2hydrogenation, indicating that the dealloyed structure contains the sites promoting methanol synthesis. While solid-state nuclear magnetic resonance studies identify methoxy species as the main stable surface adsorbate, transient operando diffuse reflectance infrared Fourier transform spectroscopy indicates that μ-HCOO*(ZnOx) species that form on the Cu–Zn/SiO2catalyst are hydrogenated to methanol faster than the μ-HCOO*(Cu) species that are found in the Zn-free Cu/SiO2catalyst, supporting the role of Zn in providing a higher activity in the Cu–Zn system.

The oxidative coupling of methane (OCM) was investigated using a catalyst with a core@shell structure or a physical mixture comprised of MgO and SiC or Fe3O4, which was thermally activated viatwo different heating methods, namely, conventional resistive heating and microwave heating. The use of microwave radiation together with the catalyst structure was essential to achieve high reaction efficiency. The C2selectivity and yield were correlated with the presence of temperature gradients in the catalytic bed under microwave radiation. These thermal gradients and their distribution were experimentally evaluated using operandothermal visualization. Hotspots and thermal gradients were beneficial to achieve a higher CH4conversion; however, it was found that a uniform reactor temperature was crucial to attain a high C2yield in OCM and the core@shell structure is beneficial. The hypothesis that an enhanced OCM performance can be achieved by keeping the catalyst material hot and the gas cold, using microwave to prevent uncontrolled gas-phase reactions was supported by a kinetic study and experimentally demonstrated.

Integrated CO2capture and conversion processes bring the promise of drastic abatement of CO2emission together with its valorisation to chemical building blocks such as CH4and CO. Isothermal CO2capture and reduction (CCR) on a K-promoted Cu/Al2O3was recognised as an effective catalytic strategy for removing CO2from diluted stream and converting it to syngas (H2+ CO) employing green H2as reducing agent. The dual functionality of the catalyst is the key of this dynamic process, in which the alkaline metal introduces the capture functionality and copper ensures the selective conversion of the captured CO2to CO. However, the highly dynamic state of the catalyst at reaction conditions represents a barrier for the identification of the catalytic mechanism of CCR, which is vital for rational process improvement and design. In this work, we conducted a mechanistic investigation of CCR by means of spatiotemporal operandomethodologies, gaining insights into dynamic variation of temperature, gas concentration and reactive surface species in the CCR reactor. The results show the unique potassium state exothermically captures CO2as surface carbonates which can be reduced to CO rapidly under H2atmosphere. When the surface carbonates are transformed to formates the reaction path is altered and the reduction to CO becomes slower. By designing controlled catalytic experiments, we further demonstrate the active involvement of CO in the capture mechanism and the effectiveness of CO2capture in presence of an oxidised surface, extending the perspectives and suitability of CCR to treat actual complex effluent streams.

The reaction pathway of high-pressure CO2hydrogenation over a Cu/ZnO/Al2O3catalyst is investigated through the gradients of reactants/products concentration and catalyst temperature within the catalytic reactor. This study reveals that methanol is formed through direct CO2hydrogenation at low temperature, while above 260 °C methanol formation is mediated viaCO which is formed by reverse water–gas shift reaction.

TiO2is an active material for photocatalytic CO2reduction. Its performance is improved by the addition of a metal or metal oxide as a cocatalyst. The enhanced electron-trapping capability is widely attributed to the function of these cocatalysts, but their precise roles are not fully understood. Here, we report how Pt and Co cocatalysts boost the formation of H2and CH4during photocatalytic CO2reduction. More specifically, we used in situ diffuse reflectance infrared Fourier transform spectroscopy and multivariate spectral analysis to identify (in)active surface intermediates. Surface formates were identified as reactive intermediates common to all TiO2-based catalysts. The catalytic activity and product selectivity are determined by the unique function of the cocatalyst, which distinctly interacts with the TiO2surface to produce and decompose formates to H2or CH4. The evolution of the surface species also clarifies the transient nature of photocatalytic activities and how the TiO2surface and cocatalysts are deactivated under photocatalytic conditions.

Methyl formate synthesis by hydrogenation of carbon dioxide in the presence of methanol offers a promising path to valorize carbon dioxide. In this work, silica-supported silver nanoparticles are shown to be a significantly more active catalyst for the continuous methyl formate synthesis than the known gold and copper counterparts, and the origin of the unique reactivity of Ag is clarified. Transient in situ and operando vibrational spectroscopy and DFT calculations shed light on the reactive intermediates and reaction mechanisms: a key feature is the rapid formation of surface chemical species in equilibrium with adsorbed carbon dioxide. Such species is assigned to carbonic acid interacting with water/hydroxyls on silica and promoting the esterification of formic acid with adsorbed methanol at the perimeter sites of Ag on SiO2to yield methyl formate. This study highlights the importance of employing combined methodologies to verify the location and nature of active sites and to uncover fundamental catalytic reaction steps taking place at metal–support interfaces.

Efficient mass transfer and light utilization are essential for high photocatalytic production rates. Here, we present a hierarchical three-dimensional (3D)-printed aerogel photocatalyst that unites both aspects by taking inspiration from the light scattering in clouds during photochemical processes and from mass transfer in plants during photosynthesis. We combine the geometric freedom of additive manufacturing with computational fluid dynamics and Monte Carlo simulations to guide the implementation of a self-supported aerogel in a continuous gas flow reactor. Here, 3D microstructuring reduced the pressure drop of a monolithic aerogel by 5 orders of magnitude without compromising the gas permeation and the light-harvesting efficiency of the intrinsic nanoporous material. We match the macroscopic thickness with the ultraviolet (UV) light penetration depth and show that the 3D aerogel of 1.1 mm thickness improves photocatalytic hydrogen production rates relative to the nanoparticle powder by a factor of five from 1.3 to 6.6 μmol g–1h–1for TiO2and from 30.0 to 141.8 μmol g–1h–1for Au/TiO2, respectively. Ultimately, our approach can be applied for other nanomaterials to boost the overall performance of a variety of photochemical processes and reactor designs.

Promotion of semiconductor metal oxides by specific chemical elements is a widespread approach to enhance photocatalytic water splitting activity. An extraordinary boosting of activity has been recently reported by Zn (dopant) and Rh–Cr (co-catalyst) promotion to Ga-oxide-based photocatalysts. Herein, we report the general applicability of the effectiveness of the promotion strategy used for Ga oxides to Ta and Ti oxides in water splitting under UV irradiation using a slurry reactor. Photophysical characterization (photoluminescence and its decay) was used to clarify the specific roles of Zn and Rh–Cr and their synergetic catalytic action. Our experiments indicate that Zn acts as a booster of charge separation lifetime. Zn promotion alone, however, does not trigger a great boost in catalytic activity in the absence of Rh–Cr. It is only when Rh–Cr is added that the charge separation boost is fully exploited and driven within the catalyst towards overall water splitting. Effective wavelength ranges of the excitation UV light source were also investigated in detail, leading to questioning the dominant semiconductor bandgap model for this class of catalysts.

Integrated CO2capture and conversion (ICCC) using dual-function materials (DFMs) is one of the key technologies for addressing critical global environmental and energy issues. DFMs generally consist of alkali or alkaline earth metals for CO2capture and transition metal catalysts for CO2conversion. In this study, we studied the ICCC to CO using transition-metal-free DFMs to demonstrate their potential to directly produce syngas from atmospheric-level CO2. Among the DFMs prepared herein, Na/Al2O3exhibited excellent performance and achieved a CO2conversion exceeding 90% and CO selectivity exceeding 95% at a reaction temperature of 450–500 °C. Na/Al2O3maintained its capture and conversion capacity throughout a 50-cycle stability test without significant deactivation. Furthermore, in the scale-up experiments using Na/Al2O3DFM, a syngas-like mixture an H2/CO molar ratio of 3.3 (48.1 vol% H2and 14.5 vol% CO) was directly obtained from 400 ppm CO2. These results suggest that ICCC using the transition-metal-free Na/Al2O3DFM may be practicable provided the CO2capture capacity of the DFM is further improved while maintaining the aforementioned advantages.

Water isotope exchange in the presence of CO on two undoped tin dioxides has been studied using modulation excitation diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and resistance measurements at 300 °C. Our results reveal that the material synthesized from tin tetrachloride (SnO2Cl) manifests higher affinity to chemisorbed water than that made from tin hydroxide acetate (SnO2Ac). The latter was shown to exhibit a strong correlation between the evolution of surface OH groups (bridging type, involved in hydrogen bonding) and electric resistance upon increasing concentration of CO. Water desorption kinetics, being independent of CO concentration for both materials, was found to be slower for SnO2Cl by ca. 30% with respect to SnO2Ac. High affinity to water as well as low sensor signals to CO in humid air reported for SnO2Cl were proposed to originate from traces of Cl ions (about 0.15 wt % for SnO2Cl and 0.03 wt % for SnO2Ac) and not microstructure, which has been confirmed to be similar for both materials. Two types of water adsorption and two CO sensing mechanisms are proposed for SnO2Cl and SnO2Ac on the basis of the results.

Numerous hyper-cross-linked polymers (HCPs) have been developed as CO2adsorbents and photocatalysts. Yet, little is known of the CO2and H2O adsorption mechanisms on amorphous porous polymers. Gaining a better understanding of these mechanisms and determining the adsorption sites are key to the rational design of improved adsorbents and photocatalysts. Herein, we present a unique approach that combines density functional theory (DFT), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and multivariate spectral analysis to investigate CO2and H2O adsorption sites on a triazine–biphenyl HCP. We found that CO2and H2O adsorb on the same HCP sites albeit with different adsorption strengths. The primary amines of the triazines were identified as favoring strong CO2binding interactions. Given the potential use of HCPs for CO2photoreduction, we also investigated CO2and H2O adsorption under transient light irradiation. Under irradiation, we observed partial CO2and H2O desorption and a redistribution of interactions between the H2O and CO2molecules that remain adsorbed at HCP adsorption sites.

CO2hydrogenation over K and Ba promoted Cu/Al2O3catalyst was systematically investigated to study the promoter effects in a wide range of pressure conditions. The catalysts prepared by the impregnation method were characterized by XRD, physisorption, N2O-pulse chemisorption, H2-TPR, and CO2-TPD techniques. The catalytic performance was evaluated using a fixed-bed microreactor for a pressure and temperature range of 0.40–36 MPa and 443–553 K. The influence of promoters on the formation of surface species present during the reaction was examined by in situDRIFTS. As expected from thermodynamics, high pressure and low temperature are the favourable conditions to achieve high selectivity to methanol over the Cu/Al2O3catalyst. Improved reaction performance towards methanol synthesis and reverse water-gas shift (RWGS) reaction was observed for the Ba and K promoted Cu/Al2O3catalysts, respectively. Notably, with the Ba promotion the selectivity to methanol was enhanced to 62.2% compared to 46.6% of the unpromoted Cu/Al2O3catalyst at 10 MPa and 473 K at the expense of a lowered CO2conversion. In contrast, the K promoted catalyst exhibited high selectivity to CO (95.8%) under the same reaction conditions. Formation of dimethyl ether, significant over the unpromoted Cu/Al2O3catalyst at 0.4–10 MPa, was strongly suppressed at 36 MPa. Ba and K promoters effectively suppressed the formation of dimethyl ether under all examined pressure conditions by weakening the acidity of the alumina support. The strong promotional effects of K was explained by the predominant coverage of both Cu and alumina surface sites, creating specific active sites stabilizing surface intermediate species and preferring the RWGS pathway. On the contrary, the Ba promoter covers the alumina surface exclusively and renders Cu accessible and more easily reducible, promoting methanol synthesis. The effects of promoters on the catalytic performance were found to be valid at low and at elevated pressures.

The structure of [Fe(Htrz)2(trz)]BF4(1, Htrz =1,2,4-4-H-triazole, trz = 1,2,4-triazolate) at the low-spin (LS) and high-spin (HS) states and structural transitions between the two states were investigated by in situ high-resolution synchrotron X-ray powder diffraction (XRPD) combined with Raman spectroscopy using a modulation-enhanced technique. The crystal structures of the LS and HS states were determined. A 1D chain structure of 1at both LS and HS states was proven, and the lattice expansion upon LS−HS transition was mainly caused by the elongation of the chain. The differences in the behavior of the spin transition observed by XRPD and Raman spectroscopy were explained by the local sensitivity of the two different techniques and also by the spatial propagation of spin crossover phase transition within the crystallite and the body of the grain. Moreover, we demonstrated that the two-dimensional correlation analyses facilitate (i) understanding the data obtained by combined techniques, (ii) clarifying correlation between the signals gained by the different probes, and (iii) extracting information on temporal evolution of transformation processes.

The adsorption of (rac)-BINAP on palladium nanoparticles as well as on a Pd film has been investigated with the aim to unravel the adsorption geometry of BINAP applied for the chiral modification of Pd metal surfaces in catalysis. The Pd nanoparticles with a narrow size distribution were characterized by attenuated total reflection (ATR)-IR spectroscopy. The adsorption geometry of BINAP was determined from the analysis of the experimental IR spectra and their comparison with the spectrum calculated by DFT using a model where BINAP is adsorbed on the (111) surface of a Pd cluster. The studies revealed that BINAP adsorbs with its C2symmetry axis perpendicular to the Pd surface, and due to the steric hindrance by the phenyl rings connected to the two P atoms, the main interaction with the surface occurs via the two aromatic rings that are oriented parallel to the surface and not directly via the two P atoms. The remaining two phenyl rings are orientated in a tilted position toward the surface. To examine the generality of the proposed adsorption geometry, we also studied the adsorption of (rac)-BINAP from an organic liquid phase on a Pd model film by in situ ATR-IR spectroscopy combined with modulation excitation spectroscopy (MES). Two methods for enhancing the transient sorption of BINAP were applied: (a) temperature increase, and (b) introduction of coadsorbates which could compete with BINAP for adsorption sites on the Pd surface. The latter method proved to be powerful for adsorption studies at moderate temperature when the substrate strongly interacts with the surface and signals from surface adsorbates are very weak.

Vibrational characteristics of Ba(NO3)2, one of the key components in an important automotive catalytic technology, NOxstorage and reduction (NSR), were investigated by ab initio molecular dynamics. In particular, the fundamental, overtone, and combination bands of surface and bulk Ba(NO3)2were calculated and compared with experimental infrared (IR) spectra measured by internal and diffuse reflection sampling configurations. Using the densities of characteristic internal vibrational modes, the origins of the experimental IR bands in the regions of fundamental as well as overtone and combination vibrations were clarified. Furthermore, the molecular dynamics based vibrational analysis showed that the bands in the overtone and combination band region (1600−3000 cm−1), typically neglected in NSR studies, contain chemically rich information and can assist in the firm identification of surface nitrates and their adsorption configurations.

In dye-sensitized solar cells, three structurally similar dyes are commonly employed to sensitize anatase nanocrystals, namely, the cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) dye (N3) and its twice deprotonated (N719) and completely deprotonated (N712) forms. Using density functional theory, several possible binding geometries of these dyes are identified on the anatase(101) surface. Computed relative energies show that protonation of the surface can strongly influence the relative stabilities of these configurations and could induce a conformational transition from double bidentate-bridged binding to mixed bidentate/monodentate binding. Attenuated total reflection (ATR)-IR experiments and computed vibrational spectra provide additional support for a protonation-dependent equilibrium between two different configurations. Furthermore, self-assembly in chains of hydrogen-bonded dye molecules seems structurally favorable on the anatase(101) surface; for enantiopure dyes, a packing density of 0.744/nm2could be achieved.

Polarization-modulation infrared reflection−absorption spectroscopy (PM-IRRAS), facilitating simultaneous selective detection of liquid phase and surface bound species, was applied to study the liquid-phase oxidation of benzyl alcohol to benzaldehyde on a Pd film. Experiments under aerobic and anaerobic conditions revealed significantly higher activity under anaerobic conditions and higher selectivity under aerobic conditions. Under anaerobic conditions toluene was the major side product. CO2and benzoic acid, not yet detected by in situ IR during this reaction, were observed as degradation and side products in the liquid phase. Enhanced formation of CO2and benzoic acid was observed under aerobic conditions where no surface signals could be detected. In contrast, under anaerobic conditions CO formed by decarbonylation of benzaldehyde was observed on the Pd (111) surface, delayed with respect to the formation profile of benzaldehyde in the liquid phase. Both CO and oxygen were found to poison the surface for alcohol oxidation. The poisoning by oxygen was more effectual than that by CO, which was attributed to the low surface area of the Pd film as well as the non-site-selective nature of the alcohol oxidation. No benzoate species were present on the Pd surface. This confirmed the hypothesis that benzoate species only adsorb on the basic support sites and not on Pd.

{Cu(bpy)(H2O)2(BF4)2(bpy)} (Cu‐MOF; MOF=metal–organic framework; bpy=4,4′‐bipyridine), with a 3D‐interpenetrated structure and saturated Cu coordination sites in the framework, possesses unexpectedly high activity in the ring‐opening reaction of epoxides with MeOH, although the reaction rate drops remarkably with more bulky alcohols. This (apparent) size selection and the single Cu2+sites in an identical environment of the crystalline matrix resemble zeolites. The real nature of active sites was investigated by attenuated total reflection infrared (ATR‐IR), Raman, EPR, and UV/Vis spectroscopies. Cu‐MOF has highly dynamic structural properties that respond to MeOH; its framework dimensions change from 3D to 2D by restructuring to a symmetric coordination of four bpy units to Cu. This interaction is accompanied by the partial dissolution of Cu‐MOF as multi‐Cu clusters, in which Cu2+ions are connected with bpy ligands. Although both molecular and surface catalysis contribute to the high rate of alcoholysis, the soluble oligomeric species (Cumbpyn) are far more active. Finally, addition of diethyl ether to the reaction mixture induces the reconstruction of dissolved and solid Cu‐MOF to the original framework structure, thereby allowing excellent recyclability of Cu‐MOF as an apparent heterogeneous catalyst. In contrast, the original Cu‐MOF structure is maintained upon contact with larger alcohols, such as iPrOH and tBuOH, thus leading to poor activity in epoxide ring opening.

Support effects in NOxstorage-reduction (NSR) have been investigated by means of space- and time-resolved in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) using Pt−Ba catalysts supported on six different metal oxides (MOx= Al2O3, TiO2, SiO2, CeO2, ZrO2, and Ce0.5Zr0.5O2) and hydrogen as reductant. The NSR performance was significantly influenced by the type of oxide supports. The NOxstorage capacity followed the order CeO2> Ce0.5Zr0.5O2> Al2O3> ZrO2> TiO2> SiO2, which is in agreement with the basicity of the oxides. In contrast, the rate of NOxreduction showed the reverse order. The study shows that storage and reduction of NOxand spillover processes are influenced by the type of support. As a result of this, the support material also affects the concentration gradients along the catalyst bed which in turn has an effect on the NSR performance. Strong basicity is beneficial for efficient NOxstorage during lean periods but decreases the rate of NOxreduction during rich periods by stabilizing surface and bulk nitrates. The high oxygen-storage ability of CeO2and Ce0.5Zr0.5O2further decreases the rate of NOxreduction due to the consumption of reductant with the stored oxygen to form water. In practice, there seems to be a trade-off between efficient NOxstorage and NOxreduction rate determined by the nature of the support material. In this respect the most widely used catalyst based on γ-alumina as support seems to be a good compromise for achieving efficient storage and fast reduction of NOx. However, CeO2and Ce0.5Zr0.5O2have a potential to serve as suitable support materials for efficient NSR catalysts if they are modified to enhance the reduction rate.

Vibrational characteristics of bulk Ba species relevant in NOxstorage and reduction, namely, BaO, BaO2, Ba(NO3)2, and BaCO3, have been investigated by first-principle calculations and compared with experimental Far-IR, Mid-IR, and Raman spectra. IR and Raman intensities were calculated and compared to experimental data reported in literature. The study provides an unambiguous and firm assignment of experimentally observed bands for these important barium compounds and a detailed description of the corresponding vibrational modes.

Was, wo, wann: Eine Kombination von oberflächen‐ (diffuse reflectance infrared Fourier transform spectroscopy, DRIFTS) und volumenempfindlicher Detektion (Raman‐Spektroskopie), angewendet an unterschiedlichen Katalysatorbett‐Positionen, eignet sich hervorragend dafür, das Verständnis komplexer dynamischer Oberflächen‐ und Volumenprozesse zu vertiefen, wie sie in der heterogenen Katalyse häufig auftreten.

What, where, when: A combination of both surface‐sensitive (diffuse reflectance infrared Fourier transform spectroscopy, DRIFTS) and bulk‐sensitive (Raman spectroscopy) detection at different catalyst‐bed positions is shown to be a powerful tool to facilitate deeper understanding of complex dynamic surface and bulk processes, which occur widely in heterogeneous catalysis.

Complete reaction pathways relevant to CO2hydrogenation by using a homogeneous ruthenium dihydride catalyst ([Ru(dmpe)2H2], dmpe=Me2PCH2CH2PMe2) have been investigated by ab initio metadynamics. This approach has allowed reaction intermediates to be identified and free‐energy profiles to be calculated, which provide new insights into the experimentally observed reaction pathway. Our simulations indicate that CO2insertion, which leads to the formation of formate complexes, proceeds by a concerted insertion mechanism. It is a rapid and direct process with a relatively low activation barrier, which is in agreement with experimental observations. Subsequent H2insertion into the formateRu complex, which leads to the formation of formic acid, instead occurs via an intermediate [Ru(η2‐H2)] complex in which the molecular hydrogen coordinates to the ruthenium center and interacts weakly with the formate group. This step has been identified as the rate‐limiting step. The reaction completes by hydrogen transfer from the [Ru(η2‐H2)] complex to the formate oxygen atom, which forms a dihydrogen‐bonded RuH⋅⋅⋅HO(CHO) complex. The activation energy for the H2insertion step is lower for the transisomer than for the cisisomer. A simple measure of the catalytic activity was proposed based on the structure of the transition state of the identified rate‐limiting step. From this measure, the relationship between catalysts with different ligands and their experimental catalytic activities can be explained.

Reaction pathways during CO2hydrogenation catalyzed by the Ru dihydride complex [Ru(dmpe)2H2] (dmpe=Me2PCH2CH2PMe2) have been studied by DFT calculations and by IR and NMR spectroscopy up to 120 bar in toluene at 300 K. CO2and formic acid readily inserted into or reacted with the complex to form formates. Two formate complexes, cis‐[Ru(dmpe)2(OCHO)2] and trans‐[Ru(dmpe)2H(OCHO)], were formed at low CO2pressure (<5 bar). The latter occurred exclusively when formic acid reacted with the complex. A RuH⋅⋅⋅HOCHO dihydrogen‐bonded complex of the transform was identified at H2partial pressure higher than about 50 bar. The transform of the complex is suggested to play a pivotal role in the reaction pathway. Potential‐energy profiles along possible reaction paths have been investigated by static DFT calculations, and lower activation‐energy profiles via the transroute were confirmed. The H2insertion has been identified as the rate‐limiting step of the overall reaction. The high energy of the transition state for H2insertion is attributed to the elongated RuO bond. The H2insertion and the subsequent formation of formic acid proceed via Ru(η2‐H2)‐like complexes, in which apparently formate ion and Ru+or Ru(η2‐H2)+interact. The bond properties of involved Ru complexes were characterized by natural bond orbital analysis, and the highly ionic characters of various complexes and transition states are shown. The stability of the formate ion near the Ru center likely plays a decisive role for catalytic activity. Removal of formic acid from the dihydrogen‐bonded complex (RuH⋅⋅⋅HOCHO) seems to be crucial for catalytic efficiency, since formic acid can easily react with the complex to regenerate the original formate complex. Important aspects for the design of highly active catalytic systems are discussed.

The direct conversion of CO2to CH3OH represents an appealing strategy for the mitigation of anthropogenic CO2emissions. Here, we report that small, narrowly distributed alloyed PdGa nanoparticles, prepared via surface organometallic chemistry from silica-supported GaIIIisolated sites, selectively catalyze the hydrogenation of CO2to CH3OH. At 230 °C and 25 bar, high activity (22.3 molMeOHmolPd–1h–1) and selectivity for CH3OH/DME (81%) are observed, while the corresponding silica-supported Pd nanoparticles show low activity and selectivity. X-ray absorption spectroscopy (XAS), IR, NMR, and scanning transmission electron microscopy–energy-dispersive X-ray provide evidence for alloying in the as-synthesized material. In situ XAS reveals that there is a dynamic dealloying/realloying process, through Ga redox, while operando diffuse reflectance infrared Fourier transform spectroscopy demonstrates that, while both methoxy and formate species are observed in reaction conditions, the relative concentrations are inversely proportional, as the chemical potential of the gas phase is modulated. High CH3OH selectivities, across a broad range of conversions, are observed, showing that CO formation is suppressed for this catalyst, in contrast to reported Pd catalysts.

The comparison between experimental and calculated VCD spectra allowed the unequivocal assignment of the absolute configuration of heptahelicene C30H18as P.

In situattenuated total reflection infrared spectroscopy studies during the enantioselective hydrogenation of ethyl pyruvate in “supercritical” ethane over a chirally modified PtAl2O3catalyst show the preferential adsorption of ethyl pyruvate as cis-conformer and indicate a hydrogen bond interaction of this species with the co-adsorbed modifier cinchonidine.

In situ attenuated total reflection infrared spectroscopy studies during the enantioselective hydrogenation of ethyl pyruvate in “supercritical” ethane over a chirally modified Pt/Al₂O₃ catalyst show the preferential adsorption of ethyl pyruvate as cis-conformer and indicate a hydrogen bond interaction of this species with the co-adsorbed modifier cinchonidine.