Fabrication of complex model oxide catalysts: Mo oxide supported on Fe3O4(111)

Chanut Bamroongwongdee,Philip R Davies,Dyfan Edwards,Michael Bowker,Robert J Davies,Albert F Carley

doi:10.1039/c2fd20134h

Chanut Bamroongwongdee, Philip R Davies + Show 4 more

Open Access

https://doi.org/10.1039/c2fd20134h

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Journal: Faraday discussions	Publication Date: Dec 18, 2012
Citations: 10	License type: cc-by

Affiliation: Cardiff University

Abstract

Industrial catalysts for the oxidation of methanol to formaldehyde consist of iron molybdate [Fe2(MoO4)3]. Using a variety of techniques we have previously shown that the surface of these catalysts is segregated in MoO3, and in order to understand the relationship between surface structure and reactivity for these systems we have begun a surface science study of this system using model, single crystal oxides. Model catalysts of molybdenum oxide nanoparticles and films on an Fe3O4(111) single crystal were fabricated by the hot-filament metal oxide deposition technique (HFMOD), where molybdenum oxides were produced using a molybdenum filament heated in an oxygen atmosphere. Low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and scanning tunnelling microscopy (STM) have been used to investigate molybdenum oxide nanoparticles and films deposited on Fe3O4(111). The molybdenum oxide film forms in the highest oxidation state, +6, and is remarkably stable to thermal treatment, remaining on the surface to at least 973 K. However, above approximately 573 K cation mixing begins to occur, forming an iron molybdate structure, but the process is strongly Mo coverage dependent.

Highlights

Formaldehyde, one of the most important industrial chemicals, is produced from methanol using either silver or iron molybdate catalysts
scanning tunnelling microscopy (STM) images of the clean Fe3O4(111) surface at relatively low magnification (Fig. 2a) show terraces tens of nm in width separated by steps of $0.5 nm height (Fig. 2e), consistent with the expected height of the repeat unit for Fe3O4 in the [111] direction.[16,17]
Our conditions and STM images are similar to those reported by Lennie et al.,[21] who refer to the hexagonal surface structure as ‘‘Termination A’’ and assign it to a layer of oxygen capping an octahedral iron layer

Summary

Introduction

Formaldehyde, one of the most important industrial chemicals, is produced from methanol using either silver or iron molybdate catalysts. We present here results detailing the deposition of molybdenum oxide films on a bulk iron oxide single crystal surface for use as a model catalyst in the investigation of iron molybdate catalysis, with the aim of identifying the nature of, and formation of the active phase and, of the active site for selective methanol oxidation.

Results

Conclusion