Coordinatively unsaturated single-atom Cu catalysts with enhanced catalytic activity for furfural upgrading

The regulation of coordination number of metal single-atom (SA) sites is important and effective to tailor their catalytic performances. Herein, we report a novel defect-induced strategy for the fabrication of Cu SAs with unsaturated coordination configurations (Cu1C2). During the synthesis, polyvinyl pyrrolidone is employed to stabilize atomic Cu nodes and generate pores in adjacent areas. Systematical characterizations indicate the atomic distribution of Cu on C2 sites at the edge of pores in carbon support. The unsaturated coordination configurations and edge effect of the Cu1C2 moieties endow it with asymmetric geometry and shortened Cu-C bond length, leading to polarized charge distributions and up-shifted total density of states towards the Fermi level, which could facilitate O2 activation and lower oxidative coupling barriers. Impressively, Cu1C2@C exhibits superior catalytic performances in the oxidative coupling of furfural with isopropanol into 4-(2-furyl)-buten-2one (a typical C8 biofuel intermediate), outperforming the Cu1C4@C counterpart.