Ru-Promoted Ni/ZIF-8 Catalysts for C–C Coupling in the Upgrading of Acetone–Butanol–Ethanol Mixtures

Catalytic upgrading of acetone–butanol–ethanol (ABE) mixtures provides a route to higher-value oxygenates for chemicals and fuel precursors. Here, Ni-, Ru-, and Ni–Ru-loaded ZIF-8 catalysts were prepared and evaluated for ABE upgrading, with particular emphasis on C7 oxygenate formation and the roles of reductive activation and acid–base properties. In situ Ni K-edge X-ray absorption spectroscopy showed that Ru facilitated Ni reduction during H2 activation, while CO2-TPD indicated increased basicity upon Ni incorporation. Among the activated catalysts, bimetallic 4Ni2RuZ8_act gave the highest 2-heptanone yield, exceeding the combined yields of the corresponding monometallic catalysts and suggesting a synergistic Ni–Ru effect. A pathway involving n-butanol dehydrogenation, C–C coupling with acetone-derived species to form 3-hepten-2-one, and subsequent hydrogenation to 2-heptanone was proposed. At 240 °C for 20 h using 20 mg of catalyst, 4Ni2RuZ8_act achieved 61.8% acetone conversion and produced 432 µmol of 2-heptanone. Reuse decreased both values by approximately 20%, accompanied by partial ZIF-8 degradation and ZnO formation. These results demonstrate the potential of multifunctional Ni–Ru/ZIF-8 catalysts for ABE upgrading toward C7 oxygenates while identifying structural stability as a key challenge for further development.