Design and stabilisation of a high area iron molybdate surface for the selective oxidation of methanol to formaldehyde. (12th April 2016)

• Record Type: Journal Article
• Authors: Chapman, Stephanie; Brookes, Catherine; Bowker, Michael; Gibson, Emma K.; Wells, Peter P.
• Is Part Of: Faraday discussions. Volume 188(2016)
• Page Start: 115
• Page End: 129
• Publication Date: 2016-04-12
• Subjects: Chemistry -- Periodicals; Metallurgy -- Periodicals; Electrochemistry -- Periodicals; 540
• DOI: 10.1039/c5fd00153f
• Languages: English
• ISSNs: 1359-6640

Abstract

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 MoO x @Fe2 O3 (MoO x shell, Fe2 O3 core) systems, where only a few overlayers of Mo are present on the surface. This method of preparing MoO x @Fe2 O3 catalysts was shown to support an iron molybdate surface of higher surface area than the industrially-favoured bulk phase. In this research, a MoO x @Fe2 O3 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 MoO x surface monolayer supported on a sublayer of Fe2 (MoO4 )3 that became increasingly extensive with initial Mo surface loading. The high surface area MoO x @Fe2 O3 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.