Selective etherification of hydroxymethylfurfural to biofuel additives over Cs containing silicotungstic acid catalysts

• Cs exchanged STA catalysts are active for selective etherification of HMF.
• Catalysts activity depends on the number of Cs ions in STA.
• New acidic sites generated with the exchange of STA protons with Cs ions.
• Selectivity of HMF etherification also depends on reaction parameters.

A series of Cs exchanged silicotungstic acid (STA) catalysts were prepared and their physico-chemical properties were derived from FT-Infrared, X-ray diffraction, Laser Raman, temperature programmed desorption of ammonia and BET surface area. The characterization results revealed that the Keggin structure of STA remained intact even after Cs ions replaced its protons. The catalysts activity was evaluated for the selective etherification of 5-hydroxymethylfurfural (HMF) with ethanol for the synthesis of 5-ethoxymethylfurfural (EMF). The partial exchange of Cs ions with protons of STA resulted an increase in acidity and the catalysts with two Cs ions in STA showed highest acidity. The activity was explained based on the acidity, surface and structural properties of the catalysts. A detailed study was made on the effect of various reaction parameters such as influence of reaction temperature, reaction time, Cs content on STA to unveil the optimize reaction conditions. The catalyst was recovered easily from the reaction mixture and reused at least four times with constant activity.

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