How the Cobalt Position in the Keggin Anion Impacts the Activity of Tungstate Catalysts in the Furfural Acetalization with Alkyl Alcohols

Keggin heteropolyacids (HPAs) comprise a class of versatile catalysts, which have properties that can be easily adjusted through modification in their structure, such as the protons exchange, the removal or one or more MO unity (i. e., W or Mo) followed by doping with transition metals, or even less frequently, the substitution of heteroatom (i. e., P or Si). In this work, these effects were assessed by modifying the structure of silicotungstic acid (i. e., H4SiW12O40) with Co2+ cations. A series of Cobalt-polyoxometalates (i. e., Co2SiW12O40, K6CoW12O40, K8SiW11O39, K6SiCoW11O39, K8CoW11CoO39) were synthesized and catalytically evaluated in furfural acetalization with alkyl alcohols. Spectroscopy analyses (i. e., UV-Vis, FT-IR, EDS), powder X-ray diffraction patterns, scan electronic microscopy images, surface area, porosity, and thermal analyses provided the main physicochemical properties of the synthesized salts. Acidity properties were assessed by potentiometric titration and adsorbed Py-FT-IR spectroscopy. The impact of temperature, nature, and catalyst loading, and type of alcohol were investigated. The K6CoW12O40 salt was the most active and selective catalyst. We paid special attention to correlating the catalyst activity with its composition and properties.

Automated summary

Keggin heteropolyacids (HPAs) are versatile catalysts with adjustable properties through structural modification. This study evaluated the effects of structure modification on the catalytic performance by synthesizing a series of cobalt-polyoxometalates and found that K6CoW12O40 salt exhibited the highest activity and selectivity.