Selective upgrading of ethanol with methanol in water for the production of improved biofuel—isobutanol

Sustainable production of liquid transportation fuels and chemicals remains essential both commercially and scientifically. Isobutanol has gained great attention as an improved “drop-in” biofuel and important commodity chemical with broad applications. Ethanol could be upgraded with methanol in water for the production of isobutanol through cross condensation. High isobutanol selectivity is obtained (>90%) due to precise control on the reactivity of methanol and ethanol feedstock over Ir catalysts immobilized on N functionalized carbon materials. Only under a narrow range of preparation conditions could the catalysts distinguish the reactivity of methanol and ethanol nicely. The experimental results evidenced that the properties of Ir, especially the particle size and oxidation state, were particularly important for the desired activity. Control experiments also indicated that the effect of Ir catalysts on the intermediate aldol C–C formation step, rather than the dehydrogenation step, was critical in determining the product selectivity. Furthermore, the Ir catalysts could tolerate some typical biogenic impurities, which enables catalytic upgrading of bio-ethanol broth after centrifugation and decolourization. All these results indicate the promising application of the developed Ir catalysts in producing biofuels as well as useful chemicals from ethanol upgrading.