Selective transformation of glycerol into 1,2-propanediol on several Pt/ZnO solids: Further insight into the role and origin of catalyst acidity

• Different Pt/ZnO solids were tested for glycerol selective transformation into 1,2-PDO.
• Supports alone were inactive in the process.
• Incorporation of the metal leads to new (mainly Lewis-type) acid sites.
• The metal intervenes in dehydration of glycerol into acetol.
• The process requires moderate acidity whereas strong acid sites lead to by-products (e.g. CC cleavage).

Microemulsion technique allowed us to synthesize different ZnO solids with similar particle sizes and textural properties. Platinum was subsequently incorporated by deposition–precipitation and impregnation methods and solids tested for glycerol selective transformation into 1,2-PDO. Incorporation of platinum led to the creation of new (mainly Lewis) acid sites. A good correlation between conversion and acidity of Pt/ZnO solids was obtained. Interestingly, despite exhibiting some acidity, supports alone were inactive in the process which evidenced the role of the metal in dehydration of glycerol into acetol. Furthermore, as the reaction proceeded some chlorine coming from the precursor (H2PtCl6) was leached which led to the disappearance of the strongest acid sites, associated to side reactions (catalytic cracking) thus resulting in an increase in selectivity to 1,2-PDO. Eventual formation of Pt–Zn alloy upon reduction of the systems at ca. 400 °C was beneficial to 1,2-PDO selectivity.

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