Nitrogen-doped hollow carbon materials are regarded as a highly promising catalyst support, owing to their structural advantages such as low density, high specific surface area, efficient mass transfer performance, and abundant nitrogen species, which collectively contribute to effectively stabilizing and dispersing metal active sites. In this work, for the first time, a nitrogen-doped hollow carbon spheres (NHCS) was synthesized by coating SiO₂ nanospheres with a porphyrin-based organic frameworks (POFs) via a solvothermal method, followed by high-temperature pyrolysis and alkaline etching treatment. The influence of pyrolysis temperature on the physical and chemical properties of the material was systematically investigated. Results indicate that NHCS800, pyrolyzed at 800 ℃, exhibited optimal structural stability and the most abundant surface defect sites. The Co/NHCS800 catalyst was prepared by uniformly dispersing cobalt nanoparticles on the support surface via a simple impregnation-reduction method. Characterization results revealed that the average size of the cobalt nanoparticles in the catalyst was approximately 2.5 nm, which was significantly smaller than that of cobalt particles formed in the absence of the support. For the catalytic dehydrogenation of ammonia borane (AB) via methanolysis, the Co/NHCS800 catalyst was ultrasonically dispersed in a single-neck round-bottom flask containing 5 mL of methanol. The flask was fixed in a constant-temperature water bath maintained at 25 ℃. Once the temperature stabilized, 1.0 mmol of AB was rapidly added under vigorous stirring. The time required to generate every 5 mL of hydrogen gas was recorded until gas evolution ceased. The Co/NHCS800 catalyst demonstrated a remarkably high turnover frequency (TOF) value of 57.9 min⁻¹ for the methanolysis of ammonia borane. The catalysts were comprehensively characterized throughout the synthesis process using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and nitrogen adsorption-desorption measurements to monitor their morphological and structural evolution. The interaction between the metal and support was further investigated by X-ray photoelectron spectroscopy (XPS). The analysis indicates that the superior catalytic activity can be attributed to the large specific surface area of the support and the presence of ultrafine metal nanoparticles, as well as the strong electron transfer effect between nitrogen species and metal atoms.

Key words: hollow carbon sphere, Co nanoparticles, ammonia borane, methanolysis, hydrogen production