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Open AccessArticle

(Ag)Pd-Fe3O4 Nanocomposites as Novel Catalysts for Methane Partial Oxidation at Low Temperature

1
Departmento de Química Inorgánica y Química Técnica, Facultad de Ciencias, UNED, Paseo Senda del Rey, 9, 28040 Madrid, Spain
2
Instituto de Catálisis y Petroleoquímica (ICP-CSIC), C/Marie Curie, 2, Cantoblanco, 28049 Madrid, Spain
3
Departmento de Ingeniería Química, Universitat de València, C/Dr. Moliner 50, Burjassot, 46100 Valencia, Spain
*
Author to whom correspondence should be addressed.
Nanomaterials 2020, 10(5), 988; https://doi.org/10.3390/nano10050988
Received: 18 April 2020 / Revised: 14 May 2020 / Accepted: 18 May 2020 / Published: 21 May 2020
(This article belongs to the Special Issue Application of New Nanoparticle Structures as Catalysts)
Nanostructured composite materials based on noble mono-(Pd) or bi-metallic (Ag/Pd) particles supported on mixed iron oxides (II/III) with bulk magnetite structure (Fe3O4) have been developed in order to assess their potential for heterogeneous catalysis applications in methane partial oxidation. Advancing the direct transformation of methane into value-added chemicals is consensually accepted as the key to ensuring sustainable development in the forthcoming future. On the one hand, nanosized Fe3O4 particles with spherical morphology were synthesized by an aqueous-based reflux method employing different Fe (II)/Fe (III) molar ratios (2 or 4) and reflux temperatures (80, 95 or 110 °C). The solids obtained from a Fe (II)/Fe (III) nominal molar ratio of 4 showed higher specific surface areas which were also found to increase on lowering the reflux temperature. The starting 80 m2 g−1 was enhanced up to 140 m2 g−1 for the resulting optimized Fe3O4-based solid consisting of nanoparticles with a 15 nm average diameter. On the other hand, Pd or Pd-Ag were incorporated post-synthesis, by impregnation on the highest surface Fe3O4 nanostructured substrate, using 1–3 wt.% metal load range and maintaining a constant Pd:Ag ratio of 8:2 in the bimetallic sample. The prepared nanocomposite materials were investigated by different physicochemical techniques, such as X-ray diffraction, thermogravimetry (TG) in air or H2, as well as several compositions and structural aspects using field emission scanning and scanning transmission electron microscopy techniques coupled to energy-dispersive X-ray spectroscopy (EDS). Finally, the catalytic results from a preliminary reactivity study confirmed the potential of magnetite-supported (Ag)Pd catalysts for CH4 partial oxidation into formaldehyde, with low reaction rates, methane conversion starting at 200 °C, far below temperatures reported in the literature up to now; and very high selectivity to formaldehyde, above 95%, for Fe3O4 samples with 3 wt.% metal, either Pd or Pd-Ag. View Full-Text
Keywords: methane; oxidation catalysis; formaldehyde; magnetite iron oxide; Fe3O4; heterogeneous catalysis; palladium; Pd; silver; Ag; low-temperature activity; nanocomposite; Raman; TG in air; TG in hydrogen; XRD; electron microscopy; EDS methane; oxidation catalysis; formaldehyde; magnetite iron oxide; Fe3O4; heterogeneous catalysis; palladium; Pd; silver; Ag; low-temperature activity; nanocomposite; Raman; TG in air; TG in hydrogen; XRD; electron microscopy; EDS
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MDPI and ACS Style

Martínez-Navarro, B.; Sanchis, R.; Asedegbega-Nieto, E.; Solsona, B.; Ivars-Barceló, F. (Ag)Pd-Fe3O4 Nanocomposites as Novel Catalysts for Methane Partial Oxidation at Low Temperature. Nanomaterials 2020, 10, 988.

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