Quantification and qualification by in-situ FTIR of species formed on supported-cobalt catalysts during the Fischer-Tropsch reaction

Facet sensitivity of iron carbides in Fischer-Tropsch synthesis

Fischer-Tropsch synthesis (FTS) is a structure-sensitive reaction of which performance is strongly related to the active phase, particle size, and exposed facets. Compared with the full-pledged investigation on the active phase and particle size, the facet effect has been limited to theoretical studies or single-crystal surfaces, lacking experimental reports of practical catalysts, especially for Fe-based catalysts. Herein, we demonstrate the facet sensitivity of iron carbides in FTS. As the prerequisite, {202} and {112} facets of χ-Fe5C2 are fabricated as the outer shell through the conformal reconstruction of Fe3O4 nanocubes and octahedra, as the inner cores, respectively. During FTS, the activity and stability are highly sensitive to the exposed facet of iron carbides, whereas the facet sensitivity is not prominent for the chain growth. According to mechanistic studies, {202} χ-Fe5C2 surfaces follow hydrogen-assisted CO dissociation which lowers the activation energy compared with the direct CO dissociation over {112} surfaces, affording the high FTS activity.

Effects of Different Reductive Agents on Zn-Promoted Iron Oxide Phases in the CO2–Fischer–Tropsch to Linear α-Olefins

The pretreatment atmosphere has a significant impact on the performance of iron-based catalysts in carbon dioxide (CO2) hydrogenation. In this study, we investigated the effects of carbon monoxide (CO), syngas (H2/CO), and hydrogen (H2) on the performance of iron-based catalysts during the pretreatment process. To evaluate the structural changes in catalysts after activation and reaction, we analyzed their morphology and particle size, the surface and bulk phase composition, carbon deposition, the desorption of linear α-olefins and reaction intermediates using transmission electron microscope (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Mössbauer spectroscopy (MES), temperature-programmed desorption (TPD), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). Raman and XPS showed that the H2 pretreatment catalyst caused the absence of iron carbides due to the lack of carbon source, and the CO and syngas pretreatment catalysts promoted the formation of carbon deposits and iron carbides. While the bulk phase of the CO and syngas pretreatment catalyst mainly consists of iron carbide (FeCx), XRD and MES revealed that the bulk phase of the H2 pretreatment catalyst primarily consisted of metallic iron (Fe) and iron oxide (FeOx). The composition of the phase is closely associated with its performance at the initial stage of the reaction. The formation of olefins and C5+ products is more encouraged by CO pretreatment catalysts than by H2 and syngas pretreatment catalysts, according to in situ DRIFTS evidence. Ethylene (C2H4)/propylene (C3H6)-TPD indicates that the CO pretreatment catalyst is more favorable for the desorption of olefins which improves the olefins selectivity. Based on the analysis of the TEM images, H2 pretreatment stimulated particle agglomeration and sintering. In conclusion, the results show that the CO-pretreatment catalyst has higher activity due to the inclusion of more FeOX and Fe3C. In particular, the presence of Fe3C was found to be more favorable for the formation of olefins and C5+ hydrocarbons. Furthermore, carbon deposition was relatively mild and more conducive to maintaining the balance of FeOx/FeCx on the catalyst surface.

Palygorskite-Based Organic-Inorganic Hybrid Nanocomposite for Enhanced Antibacterial Activities

A synergistic antibacterial strategy is effective in enhancing the antibacterial efficacy of a single antibacterial material. Plant essential oils (PEOs) are safe antibacterial agents. However, some of their characteristics such as intense aroma, volatility, and poor thermal stability limit their antibacterial activity and applications. In this paper, five kinds of PEOs were incorporated onto ZnO/palygorskite (ZnO/PAL) nanoparticles by a simple adsorption process to form organic-inorganic nanocomposites (PEOs/ZnO/PAL) with excellent antibacterial properties. TEM and SEM analyses demonstrated that ZnO nanoparticles uniformly anchored onto the surface of rod-like PAL, and that the structure of ZnO/PAL maintained after the incorporation of ZnO nanoparticles and PEOs. It was found that carvacrol/ZnO/palygorskite (CAR/ZnO/PAL) exhibited higher antibacterial activities than other PEOs/ZnO/PAL nanocomposites, with minimum inhibitory concentration (MIC) values of 0.5 mg/mL and 1.5 mg/mL against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively. Moreover, the antibacterial efficiency of CAR/ZnO/PAL nanocomposites was superior to that of ZnO/PAL and pure CAR, demonstrating the synergistic effect that occurs in the combined system. PAL serving as a carrier for the combination of organic PEOs and ZnO nanoparticles is an effective strategy for enhanced, clay-based, organic-inorganic hybrid antibacterial nanocomposites.