Showing papers by "Martin Schmal published in 2021"

The LaCo1−xVxO3 Catalyst for CO Oxidation in Rich H2 Stream

Abstract: The LaCo1−xVxO3 catalysts for CO oxidation in H2 rich stream were studied. These perovskite-type oxides with variable amounts of vanadium (x = 0, 0.05 and 0.1) were synthesized by modified citrate method. It was found that the modification in LaCoO3 perovskite after vanadium addition affected directly the structure and morphology leading to decrease in the crystallite size and increase in BET surface area. XPS results confirmed quantitatively the higher presence of V4+ species at the surface of the modified perovskite. The existence of Co2+ was reported to facilitate the interplay between Co2+/Co3+ and V5+/V4+ redox couples, which can enhance the lattice oxygen mobility and create interfacial active sites of CoOx/V2O5. Tests during 20 h on stream at 250 °C showed excellent stability, high resistance to coke deposition and no sintering. Perovskite modified by addition of vanadium LaCo1−xVxO3 for preferential CO oxidation in H2-rich stream.

Synthesis of few-layered graphene sheets as support of cobalt nanoparticles and its influence on CO hydrogenation

Abstract: We prepared few-layered reduced graphene oxide (rGO) as support in CO hydrogenation reaction. We investigated the graphene structure, mostly its electron donation effects to the cobalt particles, exploring the CO dissociation and the reaction results. Some modifications in the graphene synthesis method allowed the obtaining of a few-layered structure. No crystalline areas were detected. The prepared reduced graphene oxide was decorated with cobalt nanoparticles using the precipitation-deposition method (15% wt) in an alcoholic media. The catalyst was characterized before and after reaction by several techniques. XPS results revealed a higher concentration of Co2+ species at the surface and electrostatic interaction with the support. Diffuse Reflectance Infrared Fourier Transform Spectroscopy analysis (DRIFTS) suggested formate species formation on the catalyst surface and the absence of bridge-bonded adsorbed CO. The electronic interaction between cobalt nanoparticles and graphene affected carbon monoxide dissociation, preventing the electron backdonation from the active metal NPs to CO molecules.

Tri-Reforming of Methane over NdM0.25Ni0.75O3 (M = Cr, Fe) Catalysts and the Effect of CO2 Composition

Abstract: The NdM0.25Ni0.75O3 (M = Cr, Fe) named NCN and NFN catalysts precursors were synthesized and characterized. The CO2 utilization in the feed was studied in the methane tri-reforming to produce syngas at 850 °C. The catalysts presented orthorhombic structure and the elements (Nd, Cr or Fe, Ni and O) on the surface showed homogeneous dispersion. XPS indicates different states of nickel, iron and chromium, respectively, Ni2+, Fe3+ and Fe2+ and Cr3+ (or Cr4+) and Cr6+ species. The Tri-Reforming of Methane (TRM) was performed for conditions 1CH4:0.5CO2:0.5O2 (A) and 1CH4:1CO2:0.25O2 (B), both with 0.25 H2O diluted in He. The conversions of methane were 74% for the NCN and 65% for the NFN catalysts. Both catalysts showed ratios (H2/CO) of 1.5 and 2 for conditions A and B, respectively, at 850 °C.

Ruthenium Catalyst Supported on Multi-Walled Carbon Nanotubes for CO Oxidation

Abstract: This work proposes the synthesis of the 5%wt Ru on MWCNT catalyst and the influence of feed rate and testing variables for low-temperature oxidation affecting the CO2 yield. Morphology and incorporation of the nanoparticles in carbon nanotubes were investigated by specific surface area (BET method); thermogravimetric analyses (TGA); X-ray diffraction; Raman spectroscopy, transmission electron microscopy (TEM) and XPS. The conversions of CO and O2 were mostly 100% in groups C1 and C2 (temperature between 200 and 500°C with low WHSV). In order to assess the effect of mass on catalytic activity, condition C3 was tested at even lower temperatures. In the tested catalyst, high activity (100% CO and O2 conversion) was observed, keeping it active under reaction conditions, suggesting oxi-reduction of the RuO2 at surface without affecting the MWCNT but Lewis acid influencing the CO2 yield.

Structural and morphological characterization of the perovskite LaFe 0.2 Cr 0.8-x Co x O 3 ( x = 0.0, 0.2, 0.4, 0.6, 0.8) for selective oxidation of CO

Abstract: Five compositions of the system LaFe0.2Cr0.8-XCoXO3 (x = 0.0, 0.2, 0.4, 0.6, 0.8) were synthesized by using a combustion technique to investigate the structural and morphological properties of doped LaCrO3 perovskite oxides. The optimal physicochemical conditions for the synthesis of the materials from citrate precursors at low temperature were studied through gravimetric and differential thermal analysis (TGA-DTA). X-ray diffraction (XRD) and electron microscopy (SEM-TEM) characterization of the calcined oxides confirmed the formation of a single perovskite-type structure in all the materials. The incorporation of cobalt into the structure was associated with an evolution from a rhombohedral R3-c to an orthorhombic Pnma 62 structure, with nanometric particle sizes and relevant surface properties. The results obtained from Raman and X-ray photoelectron spectroscopy (XPS) evidenced that the chemical composition and the electronic state of the cations were in accordance with the proposed system and the employed synthesis method. The conversion of CO and O2 was between 83.5 and 100% for all oxides, depending on the cobalt content, and the positive effect of temperature on the conversion and the selectivity for the formation of CO2. Stability tests confirmed a stable conversion of CO and O2, with high initial values around 96% ± 0.97, which stabilized at 83.5% ± 0.87 for the less reactive materials.