Mixed oxide

About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.

Catalytic performance of Co and Ni doped Fe-based catalysts for the hydrogenation of CO2 to CO via reverse water-gas shift reaction

Abstract: Utilization of CO2 by converting it into CO via reverse water-gas shift (rWGS) reaction is of particular interest due to the direct use of CO as feedstock in many significant industrial processes. Here, Co and Ni doped Fe-based catalysts, supported over γ-Al2O3 were prepared by a wet-impregnation method and evaluated for hydrogenation of CO2 to CO at temperatures range of 450–650 °C and atmospheric pressure. The catalytic activity in rWGS reaction mainly depends on the oxide phase of the iron. It was found that introduction of Co- or Ni- in iron oxide catalyst significantly enhanced the activity as compared to the undoped Fe/Al2O3 catalyst. However, among the doped catalysts, Co-Fe/Al2O3 showed highest CO yield (48%) and stable time-on-stream performance for 40 h at 3:1 H2/CO2 feed ratio and space velocity of 1000 mL/gcat.min at 650 °C and atmospheric pressure. The better performance of Co-Fe/Al2O3 catalyst was due to the improved reducibility of iron-oxide after doping of Co- and formation of mixed oxide, which is non-selective for methane formation under the rWGS reaction conditions. The detailed characterization results on surface area, size, morphology, reducibility and thermal stability of the prepared Fe-based catalysts obtained by BET, particle size analysis, SEM, XRD, TPR, and TGA techniques were used to understand the role of dopant in enhancement of the observed catalytic activity.

Electrical behaviour of powdered tin–antimony mixed oxide catalysts

Abstract: A series of tin + antimony mixed oxide powders, calcined at 773 K, has been studied by electrical conductivity. A continuity in the electrical behaviour is found between semiconducting SnO2 and insulating Sb2O4. Pure stannic oxide is an n-type semiconductor and its free electrons come from the first ionization of anionic vacancies whose concentration is ≈ 1018 cm–3 at 608 K under 2.13 × 104 Pa O2. The enthalpy of formation of these vacancies and the ionization energy of their 2nd electrons have been estimated. As the Sb content increases, antimony dissolves into the SnO2 structure in the 5+ state, which increases the conductivity, σ, up to a maximum corresponding to 6.1 Sb atom %. Around this value formation of the Sb2O4 phase begins. The increased conductivity of mixed oxides with high Sb content (>20 atom %), compared with that of Sb2O4, which is an insulator, is attributed to a doping effect by Sn4+ cations in Sb3+ lattice positions of Sb2O4. Comparison of how both σ and catalytic properties vary with Sb content shows that electron transfer between catalyst and adsorbed species is not the rate limiting step in propene oxidation and that the solid solution of Sb5+ in SnO2 cannot constitute the active phase for acrolein formation.

Synthesis, characterization and ethanol partial oxidation studies of V2O5 catalysts supported on TiO2–SiO2 and TiO2–ZrO2 sol–gel mixed oxides

Abstract: Sol–gel derived titania based mixed oxides TiO2–SiO2 and TiO2–ZrO2 were used as supports for preparing a series of catalysts with vanadia contents varying between 1–25 wt.%. The supports and the catalysts were characterized by employing 51 V and 1 H solid-state MAS NMR, diffuse reflectance FT-IR, and BET surface area measurements. The partial oxidation activities of the catalysts were tested using ethanol oxidation as the model reaction. 51 V solid-state NMR studies of the calcined catalysts showed the peaks corresponding to the presence of polymeric tetrahedral vanadia species at low vanadia loadings and 51 V chemical shifts corresponding to amorphous V2O5 like phases were observed in the catalysts with high V2O5 contents. After outgassing the catalysts, a broadening of the peaks was observed indicating a change in the coordination environment around vanadium. DRIFTS studies of the catalysts indicated the vibrations corresponding to VO bonds of V2O5 agglomerates, in the catalysts with high vanadia loadings. Acetaldehyde was obtained as the major product with traces of ethylene, ether, acetic acid, ethyl acetate, and COx during the ethanol partial oxidation activity studies of mixed oxide supported vanadia catalysts.