Synthesis And H₂S Removal Properties Of Nitrogen-Rich Mesoporous Carbons

Due to the unique and controlled pore structure and surface chemistry, mesoporous carbon materials have been widely used in the fields of catalysis, gas separation, electrochemistry, and so on. In this thesis, a series of mesoporous carbon with controllable nitrogen doping (NMCs) was prepared and used for the metal-free catalysts for low-temperature H2S oxidation. The major findings of this work are summarized as follows:(1) Mesoporous carbons with high level nitrogen doping were developed for the first time as metal-free catalysts for low-temperature H2S oxidation to elemental sulfur. The effects of nitrogen content and chemical state of nitrogen functionalities on the catalytic performance were studied. The catalytic performance was found to be strongly depended on the nitrogen content. While the mesoporous carbons were doped only with a mediate amount of nitrogen (e.g.4.3wt.%), the materials showed no specialty in the catalytic oxidation of H2S. However, while the nitrogen doping reached a certain high level (e.g.8.5wt.%), the nitrogen-rich mesoporous carbons exhibited inconceivable catalytic activity and selectivity toward H2S oxidation at low temperature. This result indicated that there is a critical value in nitrogen content or carbon surface basicity, which when exceeded results in an unprecedented metal-free catalytic activity for H2S oxidation. Further study suggested that the prindilic nitrogen atoms were responsible for the catalytic activity in the H2S oxidation.(2) The catalytic performance was also depended on the mesoporous structure of the NMCs. The product sulfur was found to be homogenously deposited on the surface of carbon framework. Thus, the sulfur capacity was increased linearly with the mesopore volume increasing, due to larger sulfur storehouse for the NMCs with higher pore volume. Meanwhile, the NMCs with relatively small pore size showed higher catalytic activity.(3) Owing to the metal-free characteristic, the NMC can be easily regenerated by CS2scrubbing and the product sulfur can be recovered. During five regeneration tests, there is a slight decrease in catalytic activity of the NMC. We further compared the structure and chemical nature of the fresh NMC with the regenerated NMC after five cycling tests. No obvious differences were found between the fresh and regenerated NMCs. To our knowledge, this is the first example of regenerated carbon catalyst for H2S removal integrated with the sulfur recovery. (4) Compared to the state-of-the-art H2S desulfurizer (impregnated activated carbons), the as-prepared metal-free NMCs showed higher catalytic activity, higher selectivity, regenerated ability, and higher oxidation stability. All these results suggest that such metal-free carbons could indeed overcome the limitations of the conventional H2S catalysts and provide suitable, sustainable, and cheap solutions for the technological development in H2S removal.