VOx/Fe2O3 Shell\u2013Core Catalysts for the Selective Oxidation of Methanol to Formaldehyde

Pip Hellier,Peter P Wells,Diego Gianolio,Michael Bowker

doi:10.1007/s11244-017-0873-2

Abstract

Efficient oxidation catalysts are important in many current industrial processes, including the selective oxidation of methanol to formaldehyde. Vanadium-containing catalysts have been shown to be effective selective oxidation catalysts for certain reactions, and research continues to examine their applicability to other reactions of interest. Several VOx/Fe2O3 shell–core catalysts with varying VOx coverage have been produced to investigate the stability of VOx monolayers and their selectivity for methanol oxidation. Catalyst formation proceeds via a clear progression of distinct surface species produced during catalyst calcination. At 300 °C the selective VOx overlayer has formed; by 500 °C a sandwich layer of FeVO4 arises between the VOx shell and the Fe2O3 core, inhibiting iron cation participation in the catalysis and enhancing catalyst selectivity. The resulting catalysts, comprising a shell–subshell–core system of VOx/FeVO4/Fe2O3, possess good catalytic activity and selectivity to formaldehyde.

Highlights

The production of formaldehyde is an important industrial process, with millions of tonnes produced globally each year [1]
The surfaces and structural changes occurring on VOx/Fe2O3 catalysts in relation to calcination temperature and ML coverage will be probed by X-ray Absorption Spectroscopy (XAS) and complementary characterisation techniques, including Raman, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD)
When analysed in concert with XRD and XPS, TPD measurement of 3 ML VOx/Fe2O3 suggests that segregation is achieved in the catalyst: formaldehyde is observed without concomitant C O2 production (Fig. 1)

Summary

Introduction

The production of formaldehyde (in the form of formalin) is an important industrial process, with millions of tonnes produced globally each year [1]. Our initial studies have focussed on methanol oxidation in order to gauge the catalytic properties with respect to formaldehyde production of V Ox in shell–core catalysts and demonstrate clear segregation of the catalyst into VOx shell and Fe2O3 core components. This shell–core approach has previously been studied in MoO3/Fe2O3 catalysts for methanol oxidation, where it was seen that high selectivity to formaldehyde can be maintained at high methanol conversions [16,17,18,19,20]. The surfaces and structural changes occurring on VOx/Fe2O3 catalysts in relation to calcination temperature and ML coverage will be probed by XAS and complementary characterisation techniques, including Raman, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD)

Results and Discussion

Conclusions

Catalytic Testing

Characterisation