to the metal nanoparticles, single-atom catalysts (SAC) display superior catalytic activity and selectivity in various metalcatalyzed process by virtue of their atomic dispersion, the highest atomic efficiency, and unsaturated coordination. [1,2] In this fast-developing field, several strategies have been provided for preparing metal single-atom materials, including impregnation strategy, coordination site construction strategy, spatial confinement strategy, defect design strategy, transforming metal nanoparticles into SAC, chemical etching, electrochemical method, etc. Accordingly, various supported metal single atom catalysts, including the most published Pt, Al, Fe, Pd, Co, and Ni, Cu, Au Rh, Ag, etc., have been demonstrated to exhibit good catalytic performance. [2][3][4][5][6] Because of their high surface free energy, single atoms are usually loaded on substrates with high surface area and abundant anchoring sites to prevent aggregation during synthetic and catalytic process. Typical supports include zeolite, [7] COFs/MOFs, [8] defect-rich oxides, sulfides, [9,10] nitrides, [11,12] carbon materials [13,14] and polymers. [15] When a single atom is well dispersed on the substrate, the metal-support interaction and coordination environment will change accordingly. In this regard, the support has a significant impact on tailoring the catalytic activity, selectivity and stability of a single atom.The polymers containing N, P, and S species were usually applicative to synthesize SAC via the strong coordination interaction. The reported methods usually require a pyrolysis process to produce heteroatom-doped carbon substrate that provides the coordination environment of anchoring metal atom. Chen et al. reported that single atom Fe catalysts with different coordination sites were fabricated by the pyrolysis of Fe-polyphthalocyanine at temperatures from 500-700 °C. [16] Perez-Ramirez and co-workers designed single gold atoms on nitrogen-doped carbon from polyaniline pyrolysis at 800 °C for molecular recognition in alkyne semi-hydrogenation and the single-atom Au/NC-T catalysts show selective structure sensitivity for different groups. [17] Because polymer materials need to be calcined at high temperatures, the processing properties of carbon materials become extremely poor, and it is difficult to further prepare catalysts for film formation or other shapes, which is conducive to industrial production. Based on this, Metal single atom catalysts (SAC) have been successfully used in heterogeneous catalysis but developing a scalable and economic support for SAC is still a great challenge. Here, cyclized polyacrylonitrile (CPAN) is proposed as a promising support for single atom metal catalysts. CPAN can be easily prepared from cheap industrial product polyacrylonitrile (PAN), which has excellent processability. A series of SAC on CPAN (M/CPAN, M = Ag, Cu, Ru) are designed and the catalytic activities of the as synthesized M/CPAN are investigated by the model reduction reaction of p-nitrophenol (4-NP). M/CPAN presents ex...