Catalysis Science of Methanol Oxidation over Iron Vanadate Catalysts: Nature of the Catalytic Active Sites

Abstract

Bulk mixed metal oxides are widely used in industry for various oxidation reactions, but there is still debate in the heterogeneous catalysis literature about the nature of their catalytic active sites. In the present study, the two-component iron vanadate mixed metal oxide system is employed to investigate the outermost surface composition and surface chemistry of the bulk FeVO4 mixed metal oxide catalyst. The bulk V2O5, α-Fe2O3, and supported 4% V2O5/α-Fe2O3 metal oxide systems were also investigated to better understand the surface composition and surface chemistry of the bulk FeVO4 catalyst. Raman spectroscopy confirmed that the bulk FeVO4 was phase pure and has no contribution from excess V2O5 and α-Fe2O3 phases. IR spectroscopy confirmed that the model supported 4% V2O5/α-Fe2O3 catalyst consists of an amorphous surface VO x monolayer on the α-Fe2O3 support. The surface chemistry of the metal oxides was chemically probed with temperature programmed CH3OH-IR spectroscopy and revealed that both intact surface CH3OH* and CH3O* species are present on the catalysts. On acidic α-Fe2O3, the surface CH3OH* and CH3O* intermediates yield CH3OH and dimethyl ether (DME), respectively. For the redox V2O5, FeVO4 and supported 4% V2O5/α-Fe2O3 catalysts: however, both surface intermediates primarily give rise to HCHO. These results confirm that the surface of bulk FeVO4 and supported 4% V2O5/α-Fe2O3 catalysts are similar and that surface VO x species are the catalytic active sites for methanol oxidation to formaldehyde over bulk FeVO4 catalysts. This conclusion is supported by HR-TEM images that reveal an amorphous VO x enriched layer of ∼1 nm at the outer surface of the bulk FeVO4 catalysts. Methanol oxidation over bulk FeVO4 was found to proceed via a Mars−van Krevelen mechanism, where the reduced surface VO x species are reoxidized by bulk lattice oxygen rather than gas phase molecular O2. This study demonstrates that the catalytic active sites for oxidation reactions over the bulk FeVO4 mixed oxide reside in the outermost surface layer and not in the bulk lattice structure.

Highly dispersed iron vanadate catalyst supported on TiO2 for the selective catalytic reduction of NOx with NH3

“…, which can be further confirmed as the surface FeVO 4 phase by comparing with the standard Raman spectra [43]. As for the 9 wt.% Fe 2 O 3 /TiO 2 and 9 wt.% V 2 O 5 /TiO 2 catalysts, on which no active phases can be de- tected by XRD either, the presence of surface Fe 2 O 3 and V 2 O 5 species were also verified, respectively, by comparing their Raman spectra with those of standard materials ( Fig.…”

“…As for the 9 wt.% Fe 2 O 3 /TiO 2 and 9 wt.% V 2 O 5 /TiO 2 catalysts, on which no active phases can be de- tected by XRD either, the presence of surface Fe 2 O 3 and V 2 O 5 species were also verified, respectively, by comparing their Raman spectra with those of standard materials ( Fig. 6F and G) [43,44]. In the following sections, the electronic property and local structure of the surface active species on the supported-type catalysts will be investigated using XAS and XPS methods.…”

Chemie mit Methan: Studieren geht über Probieren!

“…Schließlich wurde berichtet, dass die häufig verwendeten Eisen-Vanadat-Katalysatoren die Oxidation von Methanol mit dem O-H-Bindungsbruch einleiten (Reaktionsweg A in Schema 4); das katalytische Zentrum dieses Katalysators ist in dieser Studie ebenfalls charakterisiert worden. [136,137] Ich danke meinen ehemaligen und derzeitigen Mitarbeitern für ihre intellektuellen und praktischen Beiträge; ihre Namen sind in der Literatur angegeben. Die an der TU Berlin durchgeführten und hier beschriebenen Arbeiten wurden großzügig finanziert vom Fonds der Chemischen Industrie, der Deutschen Forschungsgemeinschaft, dem "Cluster …”

Synthesis of 1,3-Diols from Isobutene and HCHO via Prins Condensation-Hydrolysis Using CeO2 Catalysts: Effects of Crystal Plane and Oxygen Vacancy

“…For example, dehydration of 3-methyl-1,3-butanediol produces isoprene [3], which is mainly used as a monomer for manufacture of polyisoprene rubber and butyl rubber [4,5]. 3-methyl-1,3-butanediol can be synthesized by Prins condensation of isobutene with formaldehyde to 4,4-dimethyl-1,3-dioxane followed by its hydrolysis [6], which is a promising route because the feedstocks (isobutene [7][8][9] and formaldehyde [10,11]) can be found in bio-refineries, based on recent research and industrial progress [12][13][14]. In the synthesis route, both the Prins condensation and hydrolysis reaction require acid catalysts [3,15,16].…”