Optimization of Co-N-C catalyst with enhanced accessible active sites for HCHO oxidation through high-temperature pyrolysis

Two-dimensional materials have garnered significant attention in the field of catalysis due to their high electron transfer efficiency. In this study, a quasi-two-dimensional carbon–nitrogen doped cobalt-based catalyst (Co-N-C (F)) was synthesized for the investigation of formaldehyde (HCHO) oxidation at room temperature. The electronic coordination structure of the catalyst was modified by varying the calcination temperature, resulting in the formation of Co-N 4 sites that enhance the degradation of the intermediate formate. Additionally, the quasi-2D structure formed during high-temperature pyrolysis retains characteristics of the ZIF 3D material, with a high specific surface area and a porous aggregation structure, which further enhances the exposure of active centers and diffusion of the feed gas. Characterization results showed that the number of Co-N 4 sites on the catalysts increases with the rise in pyrolysis temperature, with the Co-N-C (F)-1000 catalyst exhibiting the highest concentration of Co-N 4 sites. Activity test results indicated that the Co-N-C (F)-1000 catalyst achieved a 100 % HCHO removal rate at 25 °C, with WHSV 200,000 mL/(g·h). In contrast, the activity of the Co-N-C (F)-1100 catalyst decreased, which could be attributed to the aggregation of Co particles at excessively high temperatures. The HCHO oxidation mechanism of the Co-N-C (F) catalysts was investigated using in situ diffuse reflectance infrared spectroscopy ( in situ DRIFTS), and the reaction was found to follow the sequence HCHO → HCOO − → CO 2  + H 2 O, with formate degradation as a rate-limiting step.