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

Design and stabilisation of a high area iron molybdate surface for the selective oxidation of methanol to formaldehyde
Design and stabilisation of a high area iron molybdate surface for the selective oxidation of methanol to formaldehyde
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 m(2) 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 m(2) 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.
0301-7249
115-129
Chapman, Stephanie
02fa6ac4-c0e7-4cd3-8ffb-bf1c88cbfd45
Brookes, Catherine
fcbf76ed-9e86-4aea-b8f5-174607bae342
Bowker, Michael
c9ab10a5-d144-4533-bf6d-2fa16b669565
Gibson, Emma K.
738c74e4-ab68-42fe-bda8-9d4a43669b31
Wells, Peter
bc4fdc2d-a490-41bf-86cc-400edecf2266
Chapman, Stephanie
02fa6ac4-c0e7-4cd3-8ffb-bf1c88cbfd45
Brookes, Catherine
fcbf76ed-9e86-4aea-b8f5-174607bae342
Bowker, Michael
c9ab10a5-d144-4533-bf6d-2fa16b669565
Gibson, Emma K.
738c74e4-ab68-42fe-bda8-9d4a43669b31
Wells, Peter
bc4fdc2d-a490-41bf-86cc-400edecf2266

Chapman, Stephanie, Brookes, Catherine, Bowker, Michael, Gibson, Emma K. and Wells, Peter (2016) Design and stabilisation of a high area iron molybdate surface for the selective oxidation of methanol to formaldehyde. Faraday Discussions, 188, 115-129. (doi:10.1039/c5fd00153f). (PMID:27067956)

Record type: Article

Abstract

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 m(2) 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 m(2) 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.

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Accepted/In Press date: 8 December 2015
e-pub ahead of print date: 8 December 2015
Published date: 1 July 2016
Organisations: Organic Chemistry: SCF

Identifiers

Local EPrints ID: 400537
URI: https://eprints.soton.ac.uk/id/eprint/400537
ISSN: 0301-7249
PURE UUID: 1d66b748-e8b4-4249-9dc8-a0f2ab54634c
ORCID for Peter Wells: ORCID iD orcid.org/0000-0002-0859-9172

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Date deposited: 19 Sep 2016 10:31
Last modified: 15 Aug 2019 00:43

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