Highly Stable Apatite Supported Molybdenum Oxide Catalysts for Selective Oxidation of Methanol to Formaldehyde: Structure, Activity and Stability

Joachim Thrane,Lars Fahl Lundegaard,Uffe Vie Mentzel,Lars Pilsgaard Hansen,Mikkel Juelsholt,Christopher Falholt Elvebakken,Kirsten M Ø Jensen,Anker Degn Jensen,Troels Lindahl Christiansen,Max Thorhauge,Martin Høj

doi:10.1002/cctc.202101220

Abstract

AbstractMolybdenum oxide (5 to 20 wt.%) supported on calcium or strontium hydroxyapatite were investigated as catalysts for selective oxidation of methanol to formaldehyde. These catalysts were both active and selective, with a maximum yield achieved at 95 % conversion and 96 % selectivity. The main byproducts were CO (3.2 %) and dimethyl ether (DME, 0.7 %). The catalytic performance of the catalysts was measured for up to 600 h at 350 °C. Compared to an industrial iron molybdate catalyst, the hydroxyapatite based catalysts deactivated slower. The active species were found to be a surface layer of MoOx on the hydroxyapatite support, while excess molybdenum formed crystalline (Ca/Sr)MoO4, acting as a reservoir replenishing surface MoOx lost by volatilization with methanol. The excess molybdenum in the form of (Ca/Sr)MoO4 was found to volatilize significantly slower than the excess MoO3 in iron molybdate catalysts. The combination of high activity and selectivity with low rate of Mo volatilization makes this class of catalysts interesting for industrial production of formaldehyde.

Highlights

Formaldehyde (CH2O) is an important bulk chemical, as it is the smallest aldehyde and an important C1-building block used for a variety of different products and processes.[1]
The 10 and 15 wt% MoO3/CaHAP samples were the most active of the supported catalysts on mass basis (Figure 1a and c), with the 15 wt% MoO3/CaHAP obtaining the highest selectivity towards formaldehyde, > 96 % at all temperatures, but all the catalysts showed corrected selectivities above 90 % (Figure 1b) at all temperatures
The CaHAP samples obtained a better selectivity with a lower nominal MoO3 loading than the SrHAP samples (Figure 1b), even though the surface area of the SrHAP was lower than the CaHAP, and should require less molybdenum oxide to cover the surface

Summary

Introduction

Formaldehyde (CH2O) is an important bulk chemical, as it is the smallest aldehyde and an important C1-building block used for a variety of different products and processes.[1].

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Results

Conclusion