Promoter elements enhance the activity and selectivity of heterogeneous catalysts. Here, we show how methanol synthesis from synthesis gas over copper (Cu) nanoparticles is boosted by zinc oxide (ZnO) nanoparticles. By combining surface area titration, electron microscopy, activity measurement, density functional theory calculations, and modeling, we show that the promotion is related to Zn atoms migrating in the Cu surface. The Zn coverage is quantitatively described as a function of the methanol synthesis conditions and of the size-dependent thermodynamic activities of the Cu and ZnO nanoparticles. Moreover, experimental data reveal a strong interdependency of the methanol synthesis activity and the Zn coverage. These results demonstrate the size-dependent activities of nanoparticles as a general means to design synergetic functionality in binary nanoparticle systems.

Molybdenum loss, phase transformations and catalytic performance of an iron molybdate catalyst.

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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.

The selective oxidation of methanol to formaldehyde is a growing million-dollar industry, and has been commercial for close to a century. The Formox process, which is the largest production process today, utilizes an iron molybdate catalyst, which is highly selective, but has a short lifetime of 6 months due to volatilization of the active molybdenum oxide. Improvements of the process’s lifetime is, thus, desirable. This paper provides an overview of the efforts reported in the scientific literature to find alternative catalysts for the Formox process and critically assess these alternatives for their industrial potential. The catalysts can be grouped into three main categories: Mo containing, V containing, and those not containing Mo or V. Furthermore, selected interesting catalysts were synthesized, tested for their performance in the title reaction, and the results critically compared with previously published results. Lastly, an outlook on the progress for finding new catalytic materials is provided as well as suggestions for the future focus of Formox catalyst research.