Effect of Palladium on Iron Fischer?Tropsch Synthesis Catalysts

Suppression by Pt of CO adsorption and dissociation and methane formation on Fe5C2(100) surfaces

To understand the chemical origin of platinum promotion effects on iron based Fischer–Tropsch synthesis catalysts, the effects of Pt on CO adsorption and dissociation as well as surface carbon hydrogenation on the Fe₅C₂(100) facet with different surface C* contents have been studied using the spin-polarized density functional theory method.

Supported Fe/MnOx catalyst with Ag doping for remarkably enhanced catalytic activity in Fischer–Tropsch synthesis

The role of Ag in the promotion of the FTS performance and the evolutions of structure and phase over the Fe/MnO_x catalyst has been clearly elucidated.

Effect of Ag and Pd promotion on CH4 selectivity in Fe(100) Fischer–Tröpsch catalysis

The current CO₂ utilization market is dominated by enhanced oil recovery and urea manufacturing; yet, the scale of demand falls well short of that deemed necessary to make a significant impact on climate change.

Hägg carbide surfaces induced Pt morphological changes: a theoretical insight

Comprehensive spin-polarized density functional theory (DFT) combined with ab initio molecular dynamic (AIMD) simulations have been performed to explore the structures, energies, and diffusion behavior of platinum on Fe₅C₂ surfaces with importance in Fischer–Tropsch (F–T) catalysis.

Iron-oxide aerogel and xerogel catalyst formulations: characterization by 57Fe Mössbauer and XAFS spectroscopies

Iron in various iron-oxide aerogel and xerogel catalyst formulations (> or =85% Fe(2)O(3); < or =10% K, Co, Cu, or Pd) developed for possible use in Fischer-Tropsch synthesis (FTS) or the water-gas-shift (WGS) reaction has been examined by (57)Fe Mössbauer spectroscopy. The seventeen samples consisted of both as-prepared and calcined aerogels and xerogels and their products after use as catalysts for FTS or the WGS reaction. Complementary XAFS spectra were obtained on the occurrence of the secondary elements in some of the same materials. A broad, slightly asymmetric, two-peak Mössbauer spectrum was obtained from the different as-prepared and calcined catalyst formulations in the majority of cases. Such spectra could only be satisfactorily fit with three quadrupole doublet components, but no systematic trends in the isomer shift and quadrupole splitting parameters and area ratios of the individual components could be discerned that reflected variations in the composition or preparation of the aerogel or xerogel materials. However, significant reductions were noted in the Mössbauer effective thickness (recoilless absorption effect per unit mass of iron) parameter, chi(eff)/g, determined at room temperature, for aerogels and xerogels compared to bulk iron oxides, reflecting the openness and lack of rigidity of the aerogel and xerogel structures. Mössbauer measurements for two aerogels over the range from 15 to 292K confirmed the greatly diminished nature of this parameter at room temperature. Major increases in the effective thickness parameter were observed when the open structure of the aerogel or xerogel collapsed during calcination resulting in the formation of iron oxides (hematite, spinel ferrite). Similar structural changes were indicated by increases in this parameter after use of iron-oxide aerogels as catalysts for FTS or the WGS reaction, during which the iron-oxide aerogel was converted to a mixture of nonstoichiometric magnetite and the Hägg carbide, chi-Fe(5)C(2), or nonstoichiometric magnetite, respectively.

High-pressure scanning tunneling microscopy: tip reactions

Scanning tunneling microscopy (STM) is an ideal tool to image conducting and semiconducting surfaces with atomic resolution. The technique provides high-resolution images in vacuum or even high-pressure environments. Since STM can be operated at elevated pressures and temperatures, images can be collected in situ under catalytic conditions. In this work, we demonstrate that artifacts can be observed when imaging in situ since reactions can occur on the tip, and care should be taken when analyzing the data obtained.

Effects of copper and palladium on the reduction of bromate by Fe(0)

Bromate reduction by Fe(0) with incorporation of copper or palladium was investigated in batch tests. The incorporation of copper led to an increase in the rate of bromate reduction, while incorporation of palladium did not show any effect on bromate reduction by Fe(0), regardless of the bimetal application techniques (either simultaneous addition of Cu(II) or Pd(IV) into the Fe-BrO3- reaction system or using copper or palladium amended iron for bromate removal). Surface analyses by X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) techniques indicated that aqueous Cu(II) was reduced and incorporated into the iron surface to form Cu2O and Cu(0). Among these two species, pure Cu(0) is not an active electron donor to the bromate reduction reaction, as shown by there being no reduction from using Cu(0) powders alone and no enhancement by Fe(0) when physically mixed with Cu(0). Although it has been proposed in the literature that the enhancement of adsorption also contributes to the enhancement of chemical reduction, this is not the case here because adsorption decreased when Cu increased. The enhanced bromate reduction rate in the presence of copper observed here is most likely the result of the newly formed active Cu(I). The presence of PdO was evidenced by XPS but yielded no enhancement in bromate reduction. Finally, the Cu2O present on the iron surface because of copper impurities in commercially available iron was found to be involved in the bromate reduction and to accelerate the reduction rate.