Heterogeneous Cu-Fe oxide catalysts for preferential CO oxidation (PROX) in H2-rich process streams.

The influence of Fe loading in Cu-Fe phases and its effect on carbon monoxide (CO) oxidation in H2-rich reactant streams were investigated with the catalyst material phases characterized by Field Emission Scanning Electron Microscopy (FESEM), X-ray diffraction (XRD) studies and Mössbauer Spectroscopy (MS). There was no change in the oxidation state of the Fe ions with copper or iron loading. The catalytic activity was examined in the feed consisting of H2, H2O and CO2 for the preferential CO oxidation (PROX) process. These catalysts showed an optimized performance in converting CO in WGS streams in the temperature range of 80-200 °C. In addition to the formation of the CuFe2O4 phase, the Fe and Cu were found to be incorporated into a Cu-Fe supersaturated solid solution which improved CO oxidation activity, with carbon dioxide and water produced selectively with high catalytic activity in depleted hydrogen streams. Relatively high conversion of CO was obtained with high Fe metal loading. In addition to their catalytic efficiency, the employed heterogeneous catalysts are inexpensive to produce and do not contain any critical raw materials such as platinum group metals.

The effect of oxidant species on direct, non-syngas conversion of methane to methanol over an FePO4 catalyst material.

The effect of the phase transformation of a FePO4 catalyst material from the tridymite-like (tdm) FePO4 to the α-domain (α-Fe3(P2O7)2) during the direct selective oxidation of methane to methanol was studied using oxidant species O2, H2O and N2O. The main reaction products were CH3OH, carbon dioxide and carbon monoxide, whereas formaldehyde was produced in rather minute amounts. Results showed that the single-step non-syngas activation of CH4 to oxygenate(s) on a solid FePO4 phase-specific catalyst was influenced by the nature of the oxidizer used for the CH4 turnover. Fresh and activated FePO4 powder samples and their modified physicochemical surface and bulk properties, which affected the conversion and selectivity in the partial oxidation (POX) mechanism of CH4, were investigated. Temperature-programmed re-oxidation (TPRO) profiles indicated that the type of moieties utilised in the procedures, determined the re-oxidizing pathway of the reduced multiphase FePO4 system. Mössbauer spectroscopy measurements along with X-ray diffraction (XRD) examination of neat, hydrogenated and spent catalytic compounds, demonstrated a variation of the phosphate into a mixture of crystallites, which depended on operating process conditions (for example time-on-stream). The Mössbauer spectra revealed the change of the initial ferric orthophosphate, FePO4 (tdm), to the divalent metal form, iron(ii) pyrophosphate (Fe2P2O7); thereafter, reactivity was governed by the interaction (strength) with individual oxidizing agents. The Fe3+ ↔ Fe2+ chemical redox cycle can play a key mechanistic role in tailored multistep design, while the advantage of iron-based heterogeneous catalysis primarily lies in being inexpensive and comprising non-critical raw resources. When compared to the other catalysts reported in the literature, the FePO4-tdm phase catalysts showed in this work exhibited a high activity towards methanol i.e., 12.3 × 10-3 µmolMeOH gcat h-1 using N2O as an oxidant. This catalyst also showed a high activity with O2 as an oxidant (5.3 × 10-3 µmolMeOH gcat h-1). Further investigations will include continuous reactor unit engineering optimisation.

Shape manipulation of ion irradiated Ag nanoparticles embedded in lithium niobate.

Spherical silver nanoparticles were prepared by means of ion beam synthesis in lithium niobate. The embedded nanoparticles were then irradiated with energetic (84)Kr and (197)Au ions, resulting in different electronic energy losses between 8.1 and 27.5 keV nm(-1) in the top layer of the samples. Due to the high electronic energy losses of the irradiating ions, molten ion tracks are formed inside the lithium niobate in which the elongated Ag nanoparticles are formed. This process is strongly dependent on the initial particle size and leads to a broad aspect ratio distribution. Extinction spectra of the samples feature the extinction maximum with shoulders on either side. While the maximum is caused by numerous remaining spherical nanoparticles, the shoulders can be attributed to elongated particles. The latter could be verified by COMSOL simulations. The extinction spectra are thus a superposition of the spectra of all individual particles.