炭材料空位、氮掺杂和受限空间协同催化氧化SO2机理研究

Compared to the industrial production of sulfuric acid at a temperature as high as 400℃，the SO2 of flue gases can be straightforward catalytically oxidized to form sulfuric acid by porous carbon-based catalyst in the presence of O2 and H2O. No clear mechanism has been proposed yet for the unique process. In our recent explorations, isolated SO2 and H2SO3 molecules were found to be oxidized with rather low barriers. On the basis of these tasks, aimed to uncover the key scientific problems on the catalytic desulfurization processes in pores of carbon materials and the promotion effects of N-doping, the first-principles and molecular dynamic methods will be used combined to investigate the adsorption, diffusion, reaction and sulfuric acid desorption in the confined pore spaces systematically. The effects of carbon vacancies on the wall will be investigated as well. A synergetic mechanism for the catalytic oxidation of SO2 between vacancies and confined space will be proposed subsequently. Computational simulation and experimental methods will be used combined to investigate the adsorption and reaction in the pores of carbon materials due to the N-doping pattern and content. The experimental methods include chemical vapor deposition and in situ infrared spectroscopy. The promotion mechanism by N-doping will be clarified, which provide theoretical guidance for the N-doping fabrication of carbon catalyst.

多孔炭基催化剂能在100℃以下直接利用烟气中的H2O、O2和SO2生成硫酸，与工业制硫酸高达400℃的反应温度形成对比，这一奇特现象至今没有得到明确的机理性解释。申请者在前期探索中发现，单个SO2和H2SO3分子极易被炭材料表面活性氧物种氧化，本申请拟在此基础上，针对炭材料中孔隙结构内的催化脱硫反应和氮掺杂促进脱硫性能现象中的关键科学问题，采用分子动力学和第一性原理相结合的计算模拟方法，系统研究孔道受限空间与孔内碳原子空位对H2O/O2/SO2混合体系的吸附、扩散、氧化和产物硫酸脱附的影响规律，据此阐明空位与炭材料受限空间协同催化氧化SO2机理。运用计算模拟与化学气相沉积和原位红外实验相结合的研究方法，研究氮掺杂类型和含量对反应物吸附和反应特性的影响规律，明确氮掺杂促进催化脱硫的原理，为脱硫炭材料的氮掺杂改性提供理论指导。

炭基催化法烟气技术能够50～100C温度范围内实现低浓度SO2深度脱除，并以硫酸形式回收硫资源。由于反应温度低，脱硫效率高，大多数情况下，含SO2烟气不需要升温，脱硫后也不需要再热以避开露点。因此，在大气质量持续改善的压力下，应用前景广阔。但由于对炭材料脱硫机理认识不足，不能有效设计和优化催化剂，导致成本难以降低，限制了炭基催化发烟气脱硫技术的推广应用。本项目采用计算模拟研究方法，研究了炭材料孔道结构和非金属元素掺杂对脱硫活性的影响，发现无水条件下，吡啶氮-石墨氮共掺杂石墨烯结构能垒为0.50eV，相邻六元炭环上双石墨氮掺杂石墨烯结构综合反应能垒为0.60 eV，都远低于氧分子在完美石墨烯表面解离能垒1.78eV。对于碳纳米管而言，其曲率对O2解离，SO2氧化活性有重要影响。曲率越大，SO2被环氧基氧化越容易，但O2分子解离越困难。目前发现双石墨氮掺杂的（6，6）碳纳米管外表面综合反应能累为0.62 eV。现有结构表明碳材料孔道结构和氮掺杂都能够较好的促进O2分子的吸附活化，提高碳材料催化氧化SO2的效果。但是仍然无法解释在低至50摄氏度的温度，为何碳材料还具有较高的催化脱硫性能。尚未发表的结果表明，氮掺杂结构提高表面碱性，能够促进SO2水化形成亚硫酸，从而在合适孔道内被O2分子不经解离直接氧化，有可能是实际条件下的反应过程。