Transforming carbon dioxide into valuable chemicals and fuels, is a promising tool for environmental and industrial purposes. Here, we present catalysts comprising of cobalt (oxide) nanoparticles stabilized on various support oxides for hydrocarbon production from carbon dioxide. We demonstrate that the activity and selectivity can be tuned by selection of the support oxide and cobalt oxidation state. Modulated excitation (ME) diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveals that cobalt oxide catalysts follows the hydrogen-assisted pathway, whereas metallic cobalt catalysts mainly follows the direct dissociation pathway. Contrary to the commonly considered metallic active phase of cobalt-based catalysts, cobalt oxide on titania support is the most active catalyst in this study and produces 11% C2+ hydrocarbons. The C2+ selectivity increases to 39% (yielding 104 mmol h−1 gcat−1 C2+ hydrocarbons) upon co-feeding CO and CO2 at a ratio of 1:2 at 250 °C and 20 bar, thus outperforming the majority of typical cobalt-based catalysts.
in the early stage fragmentation of
two structurally analogous silica-supported hafnocene- and zirconocene-based
catalysts were observed during gas-phase ethylene polymerization at
low pressures. A combination of focused ion beam-scanning electron
microscopy (FIB-SEM) and nanoscale infrared photoinduced force microscopy
(IR PiFM) revealed notable differences in the distribution of the
support, polymer, and composite phases between the two catalyst materials.
By means of time-resolved probe molecule infrared spectroscopy, correlations
between this divergence in morphology and the kinetic behavior of
the catalysts’ active sites were established. The rate of polymer
formation, a property that is inherently related to a catalyst’s
kinetics and the applied reaction conditions, ultimately governs mass
transfer and thus the degree of homogeneity achieved during support
fragmentation. In the absence of strong mass transfer limitations,
a layer-by-layer mechanism dominates at the level of the individual
catalyst support domains under the given experimental conditions.
We present in-situ experiments to study the possible formation of cobalt carbides during Fischer-Tropsch synthesis (FTS) in a Co/TiO2 catalyst at relevant conditions of pressure and temperature.The experiments were performed using a combination of X-ray Raman scattering (XRS) spectroscopy and X-ray diffraction (XRD). Two different experiments were performed: (1) a Fischer-Tropsch Synthesis (FTS) reaction of a ~ 14 wt.% Co/TiO2 catalyst at 523 K and 5 bar under H2-lean conditions (i.e., a H2:CO ratio of 0.5) and ( 2) carburization of pure cobalt (as reference experiment). In both experiments, the Co L3-edge XRS spectra reveal a change in the oxidation state of the cobalt nanoparticles, which we assign to the formation of cobalt carbide (Co2C). The C K-edge XRS spectra were used to quantify the formation of different carbon species in both experiments.
Molybdenum phosphide (MoP) catalysts have recently attracted attention due to their robust methanol synthesis activity from CO/CO2. Synthesis strategies are used to steer MoP selectivity toward higher alcohols by investigating the promotion effects of alkali (K) and CO‐dissociating (Co, Ni) and non‐CO‐dissociating (Pd) metals. A systematic study with transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and X‐ray absorption spectroscopy (XAS) showed that critical parameters governing the activity of MoP catalysts are P/Mo ratio and K loading, both facilitating MoP formation. The kinetic studies of mesoporous silica‐supported MoP catalysts show a twofold role of K, which also acts as an electronic promoter by increasing the total alcohol selectivity and chain length. Palladium (Pd) increases CO conversion, but decreases alcohol chain length. The use of mesoporous carbon (MC) support has the most significant effect on catalyst performance and yields a KMoP/MC catalyst that ranks among the state‐of‐the‐art in terms of selectivity to higher alcohols.
The degradation of plastic waste in aquatic environments, leading to plastic particles at the micro‐ and nanoscale is of growing concern. However, conventional analytical techniques either lack sufficient spatial resolution or the necessary spectroscopic means to investigate individual plastic nanoparticles. Both are however necessary to understand how macro‐ and micro‐sized plastic particles break down into nanometer‐sized particles. Here we show that a hybrid analytical technique, combining the spatial resolution of atomic force microscopy (AFM) with the chemical information from infrared (IR) spectroscopy, meets these requirements. We studied nanometer‐sized particles of polystyrene (PS), a plastic that is extensively used worldwide. We demonstrate that we can detect and quantify these so‐called nanoplastics down to 20 nm in size and discuss their physicochemical properties. We show that in saline aqueous environments, in the absence of light, oxidative degradation and chain scission are the main mechanisms to form and degrade PS micro‐ and nanoplastics.
The Cr/SiO2 Phillips catalyst has taken a central role in ethylene polymerization since its invention in 1953. The uniqueness of this catalyst is related to its ability to produce broad molecular weight distribution (MWD) PE materials as well as that no co‐catalysts are required to attain activity. Nonetheless, co‐catalysts in the form of metal‐alkyls can be added for scavenging poisons, enhancing catalyst activity, reducing the induction period, and tailoring polymer characteristics. The activation mechanism and related polymerization mechanism remain elusive, despite extensive industrial and academic research. Here, we show that by varying the type and amount of metal‐alkyl co‐catalyst, we can tailor polymer properties around a single Cr/SiO2 Phillips catalyst formulation. Furthermore, we show that these different polymer properties exist in the early stages of polymerization. We have used conventional polymer characterization techniques, such as size exclusion chromatography (SEC) and 13C NMR, for studying the metal‐alkyl co‐catalyst effect on short‐chain branching (SCB), long‐chain branching (LCB) and molecular weight distribution (MWD) at the bulk scale. In addition, scanning transmission X‐ray microscopy (STXM) was used as a synchrotron technique to study the PE formation in the early stages: allowing us to investigate the produced type of early‐stage PE within one particle cross‐section with high energy resolution and nanometer scale spatial resolution.
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