Aqueous-Phase Methane Oxidation over Fe-MFI Zeolites; Promotion through Isomorphous Framework Substitution

Abstract

Fe- and Cu-containing zeolites have recently been shown to be efficient catalysts for the one-step selective transformation of methane into methanol in an aqueous medium at only 50 °C, using H2O2 as green oxidant. Previously, we have observed that Fe species alone are capable of catalyzing this highly selective transformation. However, further catalytic testing and spectroscopic investigations demonstrate that although these extra-framework Fe species are the active component of the catalyst, significant promotion is observed upon the incorporation of other trivalent cations, e.g., Al3+ or Ga3+, into the MFI-framework. While these additional framework species do not constitute active catalytic centers, promotion is observed upon their incorporation as they (1) facilitate the extraction of Fe from the zeolite framework and hence increase the formation of the active Fe species and (2) provide an associated negatively charged framework, which is capable of stabilizing and maintaining the dispersion of the cationic extra-framework Fe species responsible for catalytic activity. By understanding these phenomena and subsequently controlling the overall composition of the catalyst (Fe and Al), we have subsequently been able to prepare a catalyst of equal intrinsic activity (i.e., TOF) but five-times higher productivity (i.e., space-time-yield) compared with the best catalysts reported for this reaction to date.

Identification of Active and Spectator Sn Sites in Sn‐β Following Solid‐State Stannation, and Consequences for Lewis Acid Catalysis

“…Preliminary characterization of the synthesized catalysts was performed with pXRD (Figure ) and UV/Vis spectroscopy (Figure S2). Analysis of the ligand‐to‐metal charge transfer bands of metal‐containing zeolites with diffuse reflectance UV/Vis spectroscopy (DRUV/Vis) provides a great deal of insight of the metal site speciation . The UV/Vis spectra obtained for the synthesized samples (containing between 2 and 10 wt % Sn) all exhibit a sharp maximum at approximately 219 nm, indicative of isolated, tetrahedral Sn IV species that are isomorphously substituted into the zeolite framework.…”

Selective Oxidation of Methane to Methanol Using Supported AuPd Catalysts Prepared by Stabilizer-Free Sol-Immobilization

“…These catalysts were synthesized by wet impregnation from chloride precursors onto the support, typically producing a broad range of particle sizes. The catalysts were comprised of alloyed AuPd nanoparticles, with particle sizes ranging from [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] nm and Au-rich nanoparticles 100-200 nm in size. 19 The presence of sub-nm AuPd particles and clusters of Pd were also identified, reflecting the poor control of metal dispersion and speciation provided by wet impregnation.…”

Von Sonnenlicht zu Brennstoffen: aktuelle Fortschritte der C1‐Solarchemie

“…[61] Beispielsweise ist die POM zu Methanol, das direkt in Brennstoffen verwendet werden kann, sehr erstrebenswert. B. an Zeolith verankertes Fe [69][70][71] und Cu. [66][67][68] Auch Heterogenkatalysatoren kçnnen Methan zu Methanol umwandeln, z.…”

“…[66][67][68] Auch Heterogenkatalysatoren kçnnen Methan zu Methanol umwandeln, z. B. an Zeolith verankertes Fe [69][70][71] und Cu. [72,73] Bei diesem Verfahren sind hohe Reaktionstemperaturen (400-800 K) und -drücke (20-70 bar) erforderlich, um vernünftige Methan-Umwandlungsgeschwindigkeiten zu erzielen.…”