Grafting of Alkali Metals on Fumed Silica for the Catalytic Dehydrogenation of Methanol to Formaldehyde

Christophe J. Baranowski,Jack Brandon,Oliver Kröcher,Ali M. Bahmanpour

doi:10.1002/cctc.202100685

Christophe J. Baranowski, Jack Brandon + Show 2 more

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https://doi.org/10.1002/cctc.202100685

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Abstract

AbstractWater free, non‐oxidative catalytic dehydrogenation of methanol to formaldehyde is an important process for the formation of anhydrous, molecular formaldehyde (FA). Sodium or sodium‐containing salts were shown to catalyze the reaction, but their reaction mechanism remains unclear. In this work, we thus investigated the performance of a series of catalysts prepared by grafting of alkali metals on amorphous silica for methanol catalytic dehydrogenation. The resulting catalysts displayed an increased activity for the catalytic dehydrogenation of methanol. Variation of the electron density of the supported alkali metal cations severely affected the FA selectivity, which followed the trend: Li>Na>K>Rb>Cs. A large gap in selectivity towards FA between ions with a high (i. e., Li, Na) and low charge density (i. e., K, Rb, Cs) was observed. Also, increased metal loading adversely affected FA selectivity and resulted in a larger production of carbon monoxide. Sodium grafted on silica yielded the best combination of moderate conversion and high selectivity.

Highlights

IntroductionWith a yearly production volume of millions of tons per year, formaldehyde (FA) is a base chemical in the industry for many materials such as resins, polymers, paints or explosives.[1]
With a yearly production volume of millions of tons per year, formaldehyde (FA) is a base chemical in the industry for many materials such as resins, polymers, paints or explosives.[1]. It is the simplest aldehyde and a highly reactive organic compound. It is commercially available as an aqueous solution containing 37 to 55 wt% FA with methanol residues from the FA synthesis process, which inhibits the formation of insoluble polymers.[2]
Considering that the basicity of the hydroxide salts increases with the alkali metal cation size, higher molar metal loadings were obtained with larger alkali metals.[35]

Summary

Introduction

With a yearly production volume of millions of tons per year, formaldehyde (FA) is a base chemical in the industry for many materials such as resins, polymers, paints or explosives.[1]. All industrial processes use a combination of nonoxidative [Eq (R1)] and oxidative methanol dehydrogenation [Eq (R2)].[3]

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