Design and stabilisation of a high area iron molybdate surface for the selective oxidation of methanol to formaldehyde

Chapman, S., Brookes, C., Bowker, M., Gibson, E. K. and Wells, P. P. (2016) Design and stabilisation of a high area iron molybdate surface for the selective oxidation of methanol to formaldehyde. Faraday Discussions, 188, pp. 115-129. (doi: 10.1039/C5FD00153F) (PMID:27067956)

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The performance of Mo-enriched, bulk ferric molybdate, employed commercially for the industrially important reaction of the selective oxidation of methanol to formaldehyde, is limited by a low surface area, typically 5–8 m2 g−1. Recent advances in the understanding of the iron molybdate catalyst have focused on the study of MoOx@Fe2O3 (MoOx shell, Fe2O3 core) systems, where only a few overlayers of Mo are present on the surface. This method of preparing MoOx@Fe2O3 catalysts was shown to support an iron molybdate surface of higher surface area than the industrially-favoured bulk phase. In this research, a MoOx@Fe2O3 catalyst of even higher surface area was stabilised by modifying a haematite support containing 5 wt% Al dopant. The addition of Al was an important factor for stabilising the haematite surface area and resulted in an iron molybdate surface area of ∼35 m2 g−1, around a 5 fold increase on the bulk catalyst. XPS confirmed Mo surface-enrichment, whilst Mo XANES resolved an amorphous MoOx surface monolayer supported on a sublayer of Fe2(MoO4)3 that became increasingly extensive with initial Mo surface loading. The high surface area MoOx@Fe2O3 catalyst proved amenable to bulk characterisation techniques; contributions from Fe2(MoO4)3 were detectable by Raman, XAFS, ATR-IR and XRD spectroscopies. The temperature-programmed pulsed flow reaction of methanol showed that this novel, high surface area catalyst (3ML-HSA) outperformed the undoped analogue (3ML-ISA), and a peak yield of 94% formaldehyde was obtained at ∼40 °C below that for the bulk Fe2(MoO4)3 phase. This work demonstrates how core–shell, multi-component oxides offer new routes for improving catalytic performance and understanding catalytic activity.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Gibson, Dr Emma
Authors: Chapman, S., Brookes, C., Bowker, M., Gibson, E. K., and Wells, P. P.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Faraday Discussions
Publisher:Royal Society of Chemistry
ISSN (Online):1364-5498
Published Online:08 December 2015
Copyright Holders:Copyright © 2016 The Authors
First Published:First published in Faraday Discussions 188:115-129
Publisher Policy:Reproduced under a Creative Commons License

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