Effects of Cu–Ni Bimetallic Catalyst Composition and Support on Activity, Selectivity, and Stability for Furfural Conversion to 2-Methyfuran

Supported bimetallic catalysts have been demonstrated to enhance catalytic activity, product selectivity, and catalyst stability over supported monometallic catalysts for a range of catalytic reactions. However, the surface structure and composition of bimetallic particles can differ significantly from the bulk due to variations in surface energies and interactions with adsorbates, making the design of bimetallic catalysts with targeted properties and reactivities challenging. We report here the influence of catalyst support (Al2O3 and TiO2) on the surface composition and structure of bimetallic Cu–Ni nanoparticles with varying Ni weight loading (0, 0.5, 1.5, 3, 5, and 10 wt %) at a constant Cu loading of 5 wt % and a correlation to catalytic reactivity and stability in furfural (FF) hydrodeoxygenation (HDO). Analysis via depth-profiling X-ray photoelectron spectroscopy suggested that over a range of Ni compositions in Cu–Ni/Al2O3 catalysts, Cu and Ni were distributed evenly within bimetallic particles, although Cu and Ni segregated into contiguous monometallic domains at the particle surfaces. In contrast, on Cu–Ni/TiO2 catalysts near surface alloys formed, which were enriched in Cu at the particle surfaces and exposed only dispersed Ni species. The difference in compositional structure of the Cu–Ni particles on TiO2 and Al2O3 was attributed to strong and specific interactions between Ni and TiO2. On both supports the addition of Ni to Cu catalysts resulted in enhancements in the rate of FF HDO, although Al2O3 supported bimetallic catalysts promoted hydrogenation of the furan ring, forming mostly furfural alcohol and tetrahydrofurfuryl alcohol, while TiO2 supported catalysts mostly resulted in carbonyl hydrogenolysis to form methyl furan (MF). Through optimization of support and bimetallic compositions, low-cost bimetallic catalysts were developed that demonstrated >90% MF yields in FF HDO with good stability and regenerability.