In MgO–SiO2 catalysts for the transformation of bio-ethanol into butadiene, the generation of more selective sites is achieved by the dispersion of isolated Si4+ atoms in MgO.

In this study we explore the use of Ga as a new component in MgO‐SiO2 catalysts for the Lebedev reaction (the one‐pot conversion of ethanol to butadiene). Several characterisation techniques (XRD, temperature‐programmed desorption of NH3, BET measurements, IR spectroscopy) and in situ spectroscopic studies (DRIFTS‐MS) were performed with the aim to correlate the properties of the modified materials with the catalytic results. We concluded that the wet impregnation of Ga3+ on the MgO‐SiO2 catalyst creates new Ga−O(H)−Si sites. These sites interact strongly with alcohol and not only facilitate its dehydrogenation to acetaldehyde and its transformation into the intermediate crotyl alcohol but also enhance the dehydration of the latter because of an improved acidity. However, an appropriate amount of gallium oxide is needed to avoid excessive acidity, which is conducive to an increased selectivity to ethylene.

The aerobic oxidation of trans‐1,2‐cyclohexanediol in the synthesis of adipic acid was studied. Two classes of catalysts are compared, 1) alumina‐supported Ru(OH)3, and 2) Keggin type P/Mo/V polyoxometalates. These two classes are representative examples because they are active in alcohol oxidation under quite different reaction conditions. In the former case, basic conditions are needed in order to activate the substrate, whereas with polyoxometalates, acidic conditions are used. Their catalytic behavior showed remarkable differences; in basic conditions, the reaction network was very complex, and several side reactions led to a number of by‐products, with a low selectivity to adipic acid in the end. The supported Ru(OH)3 catalyst was very efficient in 1,2‐cyclohexanediol oxidative dehydrogenation to 1,2‐cyclohexanedione, but several undesired reactions occurred starting from this key intermediate under basic conditions: rearrangement into 6‐hydroxycaprolactone and 1‐hydroxycyclopentanecarboxylic acid, and formation of the product of aldol condensation. The former compound was also an intermediate for adipic acid formation, but this reaction gave only a minor contribution to the reactant conversion. Polyoxometalates were extremely selective in 1,2‐cyclohexanediol conversion into adipic acid, but under acidic conditions the product reacted with the unconverted reactant to yield the corresponding ester.

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