Alkali Earth Metal Molybdates as Catalysts for the Selective Oxidation of Methanol to Formaldehyde—Selectivity, Activity, and Stability

Joachim Thrane,Uffe Vie Mentzel,Max Thorhauge,Anker Degn Jensen,Martin Høj,Lars Fahl Lundegaard,Pablo Beato

doi:10.3390/catal10010082

Joachim Thrane, Uffe Vie Mentzel + Show 5 more

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https://doi.org/10.3390/catal10010082

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Abstract

Alkali earth metal molybdates (MMoO4, M = Mg, Ca, Sr, and Ba) were investigated as catalysts for the selective oxidation of methanol to formaldehyde in the search for more stable alternatives to the current industrial iron molybdate catalyst. The catalysts were prepared by either sol-gel synthesis or co-precipitation with both stoichiometric ratio (Mo:M = 1.0) and 10 mol% to 20 mol% excess Mo (Mo:M = 1.1 to 1.2). The catalysts were characterized by X-ray diffraction (XRD), nitrogen physisorption, Raman spectroscopy, temperature programmed desorption of CO2 (CO2-TPD), and inductively coupled plasma (ICP). The catalytic performance of the catalysts was measured in a lab-scale, packed bed reactor setup by continuous operation for up to 100 h on stream at 400 °C. Initial selectivities towards formaldehyde of above 97% were achieved for all samples with excess molybdenum oxide at MeOH conversions between 5% and 75%. Dimethyl ether (DME) and dimethoxymethane (DMM) were the main byproducts, but CO (0.1%–2.1%) and CO2 (0.1%–0.4%) were also detected. It was found that excess molybdenum oxide evaporated from all the catalysts under operating conditions within 10 to 100 h on stream. No molybdenum evaporation past the point of stoichiometry was detected.

Highlights

Formaldehyde is a major industrial chemical used in the production of urea, phenol, melamine, and polyacetal resins, accounting for 70% of the consumption, but with other important products as well [1]
The synthesis of formaldehyde was first reported by Butlerov in 1859, and industrial production started in Germany in 1889
Alkali earth metal molybdates have successfully been synthesized by sol-gel synthesis and co-precipitation, as confirmed by X-ray diffraction (XRD) and Raman spectroscopy

Summary

Introduction

Formaldehyde is a major industrial chemical used in the production of urea-, phenol-, melamine, and polyacetal resins, accounting for 70% of the consumption, but with other important products as well [1]. In 2017, the annual production was 50 million metric tons of formalin [2]. It is expected to grow to 60 million tons per year in the late 2020s [3], with a growth rate of 5.76%. The synthesis of formaldehyde was first reported by Butlerov in 1859, and industrial production started in Germany in 1889. There are two processes applied industrially today—the silver process, which was patented in 1910, and the Formox process using a metal oxide catalyst, which was first patented in 1921 [5]. Around two-thirds of the global capacity is based on the Formox technology [6]

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