Monometallic 50 wt % Cu/Al2O3 catalyst and bimetallic catalysts containing 25 wt % Co/25 wt % Cu, 25 wt % Co/25 wt % Fe, and 25 wt % Cu/25 wt % Fe, supported on Al2O3, were prepared by impregnation and coimpregnation methods. For bimetallic catalysts, metal oxides were in the form of spinel oxides, which exhibited a strong metal–support interaction. The decomposition of methane over these catalysts led to the formation of pure hydrogen and carbon nanotubes on their surfaces. The activation energy, total carbon yield, and amount of hydrogen formed, by using the prepared catalysts, were in agreement with the metal dispersion and acid–base site ratio on the surface of the catalysts. Cu−Fe/Al2O3 catalyst exhibited a stable hydrogen formation rate of 58 mmol min−1 g−1 at a temperature of 650 °C. All catalysts exhibited deactivation after 500 min, which occurred due to the formation of carbon on the surface of the catalysts. The carbon material deposited predominantly assumed the form of multiwalled carbon nanotubes, as evidenced by high-resolution TEM and Raman spectroscopy. Thermogravimetric analysis finally confirmed that Cu−Fe/Al2O3 exhibited a higher yield of multiwalled carbon nanotubes.
COBISS.SI-ID: 6028314
The effect of the FePO4 material phase transformation in the direct selective oxidation of methane to methanol was studied using various oxidants, i.e. O2, H2O and N2O. The phases of the heterogeneous catalyst applied, before and after the reactions, were characterized by M¨ossbauer spectroscopy. The main reaction products were methanol, carbon monoxide and carbon dioxide, whereas formaldehyde was produced in rather minute amounts. The Mössbauer spectra showed the change of the initial catalyst material, FePO4 (tridymite-like phase (tdm)), to the reduced metal form, iron(II) pyrophosphate, Fe2P2O7, and thereafter, the material phase change was governed by the oxidation with individual oxidizing species.Mössbauer spectroscopy measurements applied along with X-ray diffraction (XRD) studies on fresh, reduced and spent catalytic materials demonstrated a transformation of the catalyst to a mixture of phases which depended on operating process conditions. Generally, activity was low and should be a subject of further material optimization and engineering, while the selectivity towards methanol at low temperatures applied was adequate. The proceeding redox mechanism should thus play a key role in catalytic material design, while the advantage of iron-based heterogeneous catalysts primarily lies in them being comparably inexpensive and comprising non-critical raw materials only.
COBISS.SI-ID: 5967386
Department of Catalysis and Chemical Reaction Engineering (CatReactEng) is evaluating biomass as a possible complementary feedstock for the gasoline, diesel and kerosene production by its gasification in fluidised-bed reactor, subsequent Fischer–Tropsch (FT) synthesis, and by co-feeding the products in hydrocracker. Alternatively, biopolymers such as (hemi)cellulose and lignin can be utilised in existing or modified units or converted to value-added chemicals. Furthermore, within the Horizon 2020 project (ADREM), CatReactEng is involved in methane activation by the oxidative or non-oxidative CH4 coupling into liquid fuels using renewable energy sources (e.g. by plasma). An attempt of catalysis and the energy integration in the periods of surplus electricity (H2 production) by the direct methanol synthesis from CO2 (captured from flue gases) is also being investigated by the CatReactEng within MEFCO2 project (Horizon 2020). Several other fossil and renewable feedstock conversions are being investigated.
COBISS.SI-ID: 6061082