Molecular Transition Metal Oxide Electrocatalysts for the Reversible Carbon Dioxide-Carbon Monoxide Transformation.

Carbon monoxide dehydrogenase (CODH) enzymes are active for the reversible CO oxidation-CO2 reduction reaction and are of interest in the context of CO2 abatement and carbon-neutral solar fuels. Bioinspired by the active-site composition of the CODHs, polyoxometalates triply substituted with first-row transition metals were modularly synthesized. The polyanions, in short, {SiM3 W9 } and {SiM'2 M''W9 }, M, M', M''=CuII , NiII , FeIII are shown to be electrocatalysts for reversible CO oxidation-CO2 reduction. A catalytic Tafel plot showed that {SiCu3 W9 } was the most reactive for CO2 reduction, and electrolysis reactions yielded significant amounts of CO with 98 % faradaic efficiency. In contrast, Fe-Ni compounds such as {SiFeNi2 W9 } preferably catalyzed the oxidation of CO to CO2 similar to what is observed for the [NiFe]-CODH enzyme. Compositional control of the heterometal complexes, now and in the future, leads to control of reactivity and selectivity for CO2 electrocatalytic reduction.

In†Situ Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy of Nickel-Catalyzed Hydrogenation Reactions.

Synthesis methods to prepare lower transition metal catalysts and specifically Ni for Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy (SHINERS) are explored. Impregnation, colloidal deposition, and spark ablation have been investigated as suitable synthesis routes to prepare SHINERS-active Ni/Au@SiO2 catalyst/Shell-Isolated Nanoparticles (SHINs). Ni precursors are confirmed to be notoriously difficult to reduce and the temperatures required are generally harsh enough to destroy SHINs, rendering SHINERS experiments on Ni infeasible using this approach. For colloidally synthesized Ni nanoparticles deposited on Au@SiO2 SHINs, stabilizing ligands first need to be removed before application is possible in catalysis. The required procedure results in transformation of the metallic Ni core to a fully oxidized metal nanoparticle, again too challenging to reduce at temperatures still compatible with SHINs. Finally, by use of spark ablation we were able to prepare metallic Ni catalysts directly on Au@SiO2 SHINs deposited on a Si wafer. These Ni/Au@SiO2 catalyst/SHINs were subsequently successfully probed with several molecules (i. e. CO and acetylene) of interest for heterogeneous catalysis, and we show that they could be used to study the in situ hydrogenation of acetylene. We observe the interaction of acetylene with the Ni surface. This study further illustrates the true potential of SHINERS by opening the door to studying industrially relevant reactions under in situ or operando reaction conditions.

Capturing the Genesis of an Active Fischer-Tropsch Synthesis Catalyst with Operando X-ray Nanospectroscopy.

A state-of-the-art operando spectroscopic technique is applied to Co/TiO2 catalysts, which account for nearly half of the world's transportation fuels produced by Fischer-Tropsch catalysis. This allows determination of, at a spatial resolution of approximately 50 nm, the interdependence of formed hydrocarbon species in the inorganic catalyst. Observed trends show intra- and interparticular heterogeneities previously believed not to occur in particles under 200 µm. These heterogeneities are strongly dependent on changes in H2 /CO ratio, but also on changes thereby induced on the Co and Ti valence states. We have captured the genesis of an active FTS particle over its propagation to steady-state operation, in which microgradients lead to the gradual saturation of the Co/TiO2 catalyst surface with long chain hydrocarbons (i.e., organic film formation).

Oxytocinergic modulation of speech production-a double-blind placebo-controlled fMRI study.

Many socio-affective behaviors, such as speech, are modulated by oxytocin. While oxytocin modulates speech perception, it is not known whether it also affects speech production. Here, we investigated effects of oxytocin administration and interactions with the functional rs53576 oxytocin receptor (OXTR) polymorphism on produced speech and its underlying brain activity. During functional magnetic resonance imaging, 52 healthy male participants read sentences out loud with either neutral or happy intonation, a covert reading condition served as a common baseline. Participants were studied once under the influence of intranasal oxytocin and in another session under placebo. Oxytocin administration increased the second formant of produced vowels. This acoustic feature has previously been associated with speech valence; however, the acoustic differences were not perceptually distinguishable in our experimental setting. When preparing to speak, oxytocin enhanced brain activity in sensorimotor cortices and regions of both dorsal and right ventral speech processing streams, as well as subcortical and cortical limbic and executive control regions. In some of these regions, the rs53576 OXTR polymorphism modulated oxytocin administration-related brain activity. Oxytocin also gated cortical-basal ganglia circuits involved in the generation of happy prosody. Our findings suggest that several neural processes underlying speech production are modulated by oxytocin, including control of not only affective intonation but also sensorimotor aspects during emotionally neutral speech.

Restructuring of titanium oxide overlayers over nickel nanoparticles during catalysis.

Reducible supports can affect the performance of metal catalysts by the formation of suboxide overlayers upon reduction, a process referred to as the strong metal-support interaction (SMSI). A combination of operando electron microscopy and vibrational spectroscopy revealed that thin TiOx overlayers formed on nickel/titanium dioxide catalysts during 400°C reduction were completely removed under carbon dioxide hydrogenation conditions. Conversely, after 600°C reduction, exposure to carbon dioxide hydrogenation reaction conditions led to only partial reexposure of nickel, forming interfacial sites in contact with TiOx and favoring carbon-carbon coupling by providing a carbon species reservoir. Our findings challenge the conventional understanding of SMSIs and call for more-detailed operando investigations of nanocatalysts at the single-particle level to revisit static models of structure-activity relationships.

The concept of active site in heterogeneous catalysis.

Catalysis is at the core of chemistry and has been essential to make all the goods surrounding us, including fuels, coatings, plastics and other functional materials. In the near future, catalysis will also be an essential tool in making the shift from a fossil-fuel-based to a more renewable and circular society. To make this reality, we have to better understand the fundamental concept of the active site in catalysis. Here, we discuss the physical meaning - and deduce the validity and, therefore, usefulness - of some common approaches in heterogeneous catalysis, such as linking catalyst activity to a 'turnover frequency' and explaining catalytic performance in terms of 'structure sensitivity' or 'structure insensitivity'. Catalytic concepts from the fields of enzymatic and homogeneous catalysis are compared, ultimately realizing that the struggle that one encounters in defining the active site in most solid catalysts is likely the one we must overcome to reach our end goal: tailoring the precise functioning of the active sites with respect to many different parameters to satisfy our ever-growing needs. This article ends with an outlook of what may become feasible within the not-too-distant future with modern experimental and theoretical tools at hand.

On the Cobalt Carbide Formation in a Co/TiO2 Fischer-Tropsch Synthesis Catalyst as Studied by High-Pressure, Long-Term Operando X-ray Absorption and Diffraction.

Operando X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) were performed on a Co/TiO2 Fischer-Tropsch synthesis (FTS) catalyst at 16 bar for (at least) 48 h time-on-stream in both a synchrotron facility and a laboratory-based X-ray diffractometer. Cobalt carbide formation was observed earlier during FTS with operando XAS than with XRD. This apparent discrepancy is due to the higher sensitivity of XAS to a short-range order. Interestingly, in both cases, the product formation does not noticeably change when cobalt carbide formation is detected. This suggests that cobalt carbide formation is not a major deactivation mechanism, as is often suggested for FTS. Moreover, no cobalt oxide formation was detected by XAS or XRD. In other words, one of the classical proposals invoked to explain Co/TiO2 catalyst deactivation could not be supported by our operando X-ray characterization data obtained at close to industrially relevant reaction conditions. Furthermore, a bimodal cobalt particle distribution was observed by high-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray analysis, while product formation remained relatively stable. The bimodal distribution is most probably due to the mobility and migration of the cobalt nanoparticles during FTS conditions.

Dynamic restructuring of supported metal nanoparticles and its implications for structure insensitive catalysis.

Some fundamental concepts of catalysis are not fully explained but are of paramount importance for the development of improved catalysts. An example is the concept of structure insensitive reactions, where surface-normalized activity does not change with catalyst metal particle size. Here we explore this concept and its relation to surface reconstruction on a set of silica-supported Ni metal nanoparticles (mean particle sizes 1-6 nm) by spectroscopically discerning a structure sensitive (CO2 hydrogenation) from a structure insensitive (ethene hydrogenation) reaction. Using state-of-the-art techniques, inter alia in-situ STEM, and quick-X-ray absorption spectroscopy with sub-second time resolution, we have observed particle-size-dependent effects like restructuring which increases with increasing particle size, and faster restructuring for larger particle sizes during ethene hydrogenation while for CO2 no such restructuring effects were observed. Furthermore, a degree of restructuring is irreversible, and we also show that the rate of carbon diffusion on, and into nanoparticles increases with particle size. We finally show that these particle size-dependent effects induced by ethene hydrogenation, can make a structure sensitive reaction (CO2 hydrogenation), structure insensitive. We thus postulate that structure insensitive reactions are actually apparently structure insensitive, which changes our fundamental understanding of the empirical observation of structure insensitivity.

Understanding carbon dioxide activation and carbon-carbon coupling over nickel.

Carbon dioxide is a desired feedstock for platform molecules, such as carbon monoxide or higher hydrocarbons, from which we will be able to make many different useful, value-added chemicals. Its catalytic hydrogenation over abundant metals requires the amalgamation of theoretical knowledge with materials design. Here we leverage a theoretical understanding of structure sensitivity, along with a library of different supports, to tune the selectivity of methanation in the Power-to-Gas concept over nickel. For example, we show that carbon dioxide hydrogenation over nickel can and does form propane, and that activity and selectivity can be tuned by supporting different nickel particle sizes on various oxides. This theoretical and experimental toolbox is not only useful for the highly selective production of methane, but also provides new insights for carbon dioxide activation and subsequent carbon-carbon coupling towards value-added products thereby reducing the deleterious effects of this environmentally harmful molecule.

Effect of Feedstock and Catalyst Impurities on the Methanol-to-Olefin Reaction over H-SAPO-34.

Operando UV/Vis spectroscopy with on-line mass spectrometry was used to study the effect of different types of impurities on the hydrocarbon pool species and the activity of H-SAPO-34 as a methanol-to-olefins (MTO) catalyst. Successive reaction cycles with different purity feedstocks were studied, with an intermittent regeneration step. The combined study of two distinct impurity types (i.e., feed and internal impurities) leads to new insights into MTO catalyst activation and deactivation mechanisms. In the presence of low amounts of feed impurities, the induction and active periods of the process are prolonged. Feed impurities are thus beneficial in the formation of the initial hydrocarbon pool, but also aid in the unwanted formation of deactivating coke species by a separate, competing mechanism favoring coke species over olefins. Further, feedstock impurities strongly influence the location of coke deposits, and thus influence the deactivation mechanism, whereas a study of the organic impurities retained after calcination reveals that these species are less relevant for catalyst activity and function as "seeds" for coke formation only.

Transition from in-hospital ventilation to home ventilation: process description and quality indicators.

The current demographic development of our society results in an increasing number of elderly patients with chronic diseases being treated in the intensive care unit. A possible long-term consequence of such a treatment is that patients remain dependent on certain invasive organ support systems, such as long-term ventilator dependency. The main goal of this project is to define the transition process between in-hospital and out of hospital (ambulatory) ventilator support. A further goal is to identify evidence-based quality indicators to help define and describe this process. This project describes an ideal sequence of processes (process chain), based on the current evidence from the literature. Besides the process chain, key data and quality indicators were described in detail. Due to the limited project timeline, these indicators were not extensively tested in the clinical environment. The results of this project may serve as a solid basis for proof of feasibility and proof of concept investigations, optimize the transition process of ventilator-dependent patients from a clinical to an ambulatory setting, as well as reduce the rate of emergency re-admissions.