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

DOI: 10.1039/C5FD00153F DOI Help

Authors: Stephanie Chapman (University of Southampton) , Catherine Brookes (University of Cardiff) , Michael Bowker (University of Cardiff) , Emma Gibson (University College London) , Peter Wells (University College London)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Faraday Discussions

State: Published (Approved)
Published: December 2015
Diamond Proposal Number(s): 10306

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 m2g-1. Recent advances in the understanding of the iron molybdate catalyst has focussed 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 haematite surface area and resulted in an iron molybdate surface area of ~ 35 m2g-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 the MoOx@Fe2O3 catalyst proved amenable to bulk characterisation techniques; contributions from Fe2(MoO4)3 were detectable by Raman, XAFS, ATR-IR and XRD. Temperature-programmed pulsed flow reaction of methanol showed 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 the bulk Fe2(MoO4)3 phase. This work demonstrates how core-shell, multi-component oxides offer new routes to improving catalytic performance and understanding catalytic activity.

Subject Areas: Chemistry

Instruments: B18-Core EXAFS

Added On: 22/12/2015 13:04


Discipline Tags:

Physical Chemistry Catalysis Chemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS)