Adsorption Properties of Iron and Iron−Manganese Catalysts Investigated by in-situ Diffuse Reflectance FTIR Spectroscopy

Abstract

The adsorption properties of the precipitated Fe and FeMn catalysts were studied by in-situ diffuse reflectance FTIR using CO, NO and CO + H 2 (syngas) as probe molecules. CO and NO adsorption on the oxidized Fe sample reveals the presence of Fe(III) and Fe(II) on the surfaces. On the H 2 -reduced Fe sample, the adsorbed probes mainly dissociate because of the high reactivity of the formed fine Fe(0) particles. Upon reduction in syngas, significant amount of carbonaceous and hydrocarbon fragment species is deposited on the surfaces which prevents from the access of the probe molecules to the metallic iron species. But, the spectra recorded from the thermal desorption of the adsorbed syngas displays three desorption bands with their frequencies nearly coinciding with those of the C-O vibrations in Fe 3 (CO) 12 iron carbonyl, claiming that the size of the formed Fe(0) particles is indeed very small. With addition of manganese to the sample, the Fe(II) species dominates on the surface. After reduction either in H 2 or in syngas, the Fe(II) and Fe(0) sites are indicated by NO adsorption. CO and syngas adsorption gives rise to a large number of distinct bands corresponding to linear and bridged adsorption species. The bands of CO adsorbed on the deep hollow sites of Fe(0) implies that the size of the Fe(0) particles formed on the reduced FeMn sample is larger than that on the reduced Fe one. The adsorption features of the Fe(0) particles formed on the FeMn samples reduced either in syngas or in H 2 (without formation of iron carbides) are quite similar, suggesting that the adsorption properties of the reduced FeMn samples are not determined by the formed iron carbides, but rather by surface Fe(0) particles of different sizes.

Combinatorial Computational Chemistry Approach for Materials Design:Applications in deNOx Catalysis, Fischer-Tropsch Synthesis, Lanthanoid Complex, and Lithium Ion Secondary Battery

“…Comparing six calculated results for Fe-based catalysts, stronger E ads gives longer R C-O , indicating higher catalytic activity for CO activation. Jiang et al experimentally observed that CO conversion does not decrease on the Fe/Mn catalysts in the presence of H 2 S in syngas flow for a long time [52]. However, when we compared both Fe-based and Co-based catalysts, we found that E ads value alone does not explain the activation of CO molecule over catalyst.…”

Investigation of solid phase upon γ-irradiation of ferrihydrite-ethanol suspension

“…Alternatively, this band can be assigned to CO bands of an iron carbonyl complex. The very weak IR band observed at 1769 cm À 1 may arise from CO adsorbed on ferrihydrite (Jiang et al, 2000). The bands at 2362 and 2338 cm À 1 in sample FH-3 are due to CO 2 from air.…”

Rapidly Quenched Skeletal Fe-Based Catalysts for Fischer−Tropsch Synthesis

“…The changes in peak positions are consistent with the consensus that K and Mn can influence the interaction of CO on Fe as electronic promoters. [28][29][30][31] Moreover, Figure 3 implies that Mn and K tend to occupy the more open Fe(111) surface on R-Fe crystallites, which weakens the high-temperature desorption peak.…”