纳米碳材料的选择性修饰及高效催化烷烃脱氢的研究

Conversion of light alkanes to their corresponding olefins has been a highly interesting topic in the field of catalysis. In the exploration of new catalysts with high efficiency at low energy consumption, nanocarbon materials have shown their unique advantages; they are expected to replace traditional metal/metal oxide catalysts. However, nanocarbon materials at the present stage still suffer from poor efficiency and the lacked control of the complex surface functional groups, particularly oxygen groups, thereby limit their practical implementation. This project proposes a "solid-solid" functionalization method, aiming to selectively modify the surface of nanocarbon materials with metal nitrates in order to create reactive oxygen species and defects on the surface of nanocarbon materials. This strategy is rationalized by the interaction between nanocarbon and metal nitrates under pyrolysis condition, which has been reported to exhibit a strong interaction that surface carbon species could be severely etched. This method will be developed into a novel green technology for nanocarbon modification. In addition, metal oxide/nanocarbon composite catalysts with high catalytic activity and selectivity for the dehydrogenation of alkanes to olefins are the expected outcome of this project. Finally, the effect of the specific modification on the morphology, structure and surface properties of nanocarbon will be investigated by means of advanced in situ characterization techniques (e.g., HRTEM, IR) and in situ reaction methods (e.g., GC-MS). Any possible synergistic effect between metal oxide and nanocarbon on the dehydrogenation reaction are to be thoroughly investigated, which would provide an experimental and theoretical basis for further development of nanocarbon materials for broader applications.

利用烷烃制备相应的烯烃一直以来都是催化领域的研究热点。在探索高效、低能耗的新型催化剂上，纳米碳材料（碳纳米管、石墨烯等）表现出了其独特的优势，有望取代传统的金属/金属氧化物催化剂。然而，纳米碳材料在实际使用中还存在着表面活性含氧官能团修饰较为复杂、效率较低等缺点，限制了其进一步的应用。本项目拟提出一种“固-固”官能化法，利用金属硝酸盐修饰纳米碳材料的表面，通过硝酸盐在高温分解过程中与纳米碳材料表面发生相互作用，在纳米碳材料表面选择性产生活性氧官能团和缺陷位，进而发展一种新型高效的纳米碳修饰新技术。最后结合原位表征技术（如原位透射电镜、原位红外等）及原位反应实验（如气质联用等），深入解析修饰过程对纳米碳形貌、结构、表面性质的影响，以及金属氧化物-纳米碳协同作用提高烷烃脱氢反应活性和寿命的影响机制，为进一步推动纳米碳材料的应用提供实验和理论基础。

纳米碳材料具有较大的比表面积、丰富的含氧官能团、易于修饰的表面和高的化学稳定性，并且来源丰富、可再生，有望替代传统的金属及金属氧化物催化剂直接用于烷烃催化转化等反应中。纳米碳非金属催化已成为国际材料与催化领域最活跃的研究方向之一。纳米碳材料在催化领域的应用很大程度上取决于其表面物理化学性质，如含氧官能团的种类与数目、缺陷和表面酸碱性等，这也是目前该领域研究的难点和挑战。本项目从纳米碳材料的绿色可控改性出发，借用硝酸盐固固修饰的思想减少改性过程中的酸碱污染，在纳米碳材料表面选择性地生成单一特定的活性官能团，从而提高纳米碳材料催化烷烃转化的活性。同时深入研究了硝酸盐改性纳米碳材料的调控机制，以及活化烷烃的作用本质。经过近3年的系统性研究工作，我们圆满完成了项目研究计划和目标，主要取得如下研究进展：1. 掌握了金属硝酸盐固固法可控改性纳米碳材料的方法，制备了氧化镁-碳纳米管、氧化镁-石墨烯、氧化铈-碳纳米管复合催化剂；2. 通过电镜、X射线衍射、X射线光电子能谱、物理吸附等表征分析阐明了固固法改性对纳米碳材料形貌和结构的影响；3. 将改性后的系列催化剂用于丁烷氧化脱氢和乙苯直接脱氢反应，显著提高了反应活性；4. 利用动力学分析和表征技术阐明了改性催化剂对烷烃脱氢活性的调控机制和作用本质。. 项目共发表论文6篇，申请中国发明专利2项，毕业博士研究生1名，硕士研究生1名。项目研究工作的科学意义在于掌握了固固法可控修饰纳米碳材料的方法，加深了对非金属纳米碳催化材料活性来源的认识，掌握了纳米碳催化剂表面基团和缺陷对其催化活性的影响规律，为高活性纳米碳催化剂的可控制备和新型催化剂的开发提供参考。