title: Design and stabilisation of a high area iron molybdate surface for the selective oxidation of methanol to formaldehyde.
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.
authors.affiliation: University of Southampton, Southampton, SO17 1BJ, UK and UK Catalysis Hub, Research Complex at Harwell, RAL, Oxford, OX11 0FA, UK. peter.wells@rc-harwell.ac.uk.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Chapman
authors.affiliation: UK Catalysis Hub, Research Complex at Harwell, RAL, Oxford, OX11 0FA, UK. peter.wells@rc-harwell.ac.uk and Cardiff University, Cardiff, CF10 3XQ, UK.
authors.forename: Catherine
authors.initials: C
authors.lastname: Brookes
authors.affiliation: UK Catalysis Hub, Research Complex at Harwell, RAL, Oxford, OX11 0FA, UK. peter.wells@rc-harwell.ac.uk and Cardiff University, Cardiff, CF10 3XQ, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Bowker
authors.affiliation: UK Catalysis Hub, Research Complex at Harwell, RAL, Oxford, OX11 0FA, UK. peter.wells@rc-harwell.ac.uk and University College London, London, WC1H 0AJ, UK.
authors.forename: Emma K
authors.initials: EK
authors.lastname: Gibson
authors.affiliation: UK Catalysis Hub, Research Complex at Harwell, RAL, Oxford, OX11 0FA, UK. peter.wells@rc-harwell.ac.uk and University College London, London, WC1H 0AJ, UK.
authors.forename: Peter P
authors.initials: PP
authors.lastname: Wells