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Faraday Discuss. 2016 Jul 4;188:115-29. doi: 10.1039/c5fd00153f.

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

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University of Southampton, Southampton, SO17 1BJ, UK and UK Catalysis Hub, Research Complex at Harwell, RAL, Oxford, OX11 0FA, UK.
UK Catalysis Hub, Research Complex at Harwell, RAL, Oxford, OX11 0FA, UK. and Cardiff University, Cardiff, CF10 3XQ, UK.
UK Catalysis Hub, Research Complex at Harwell, RAL, Oxford, OX11 0FA, UK. and University College London, London, WC1H 0AJ, UK.


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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