多孔氮化硼纳米薄片非金属催化剂的构筑及其氧化脱氢性能研究

The few layered graphene and its derivatives are newly emerging green metal-free catalyst which has attracted intense interest in recent years. However, the graphene and its derivatives suffered from limited anti-oxidation ability which restrict their catalytic application from high temperature and ambient (or oxygen rich) atmosphere. The boron nitride nanosheets (BNNSs), an isoelectronic material of graphene, therefore, have been taken into the account due to its extraordinary anti-oxidation ability. The abundant surface functional groups, defects, active edge and related potential activity site of the BNNSs make it an important complementary metal-free catalyst to the graphene. In order to explore the catalytic properties of the individual BNNSs, it is essential to integrate the two-dimensional BNNSs components into three-dimensional porous architectures, which can also avoid the restacking of the BNNSs and the loss of the isolated BNNSs with flow. In this proposal, the porous BNNSs will be synthesized by solid state reaction with the assistant of gas, oxides or metal template. The surface chemistry (functional groups, defects and doped hetero-atom) of the porous BNNSs will be adjusted using different synthetic routes, synthesis procedure and post-treatment. Then the porous BNNSs were selected as a metal-free catalyst for the gas phase oxidative dehydrogenation of benzyl alcohol and ethylbenzene. Comparing the catalytic properties of those porous BNNSs, we will study the correlation between the surface chemistry and catalytic performance. The reaction mechanism will also be revealed by the in-situ analysis such as FT-IR, Raman as well as theoretical stimulation. The implementation of this proposal will provide not only alternative routes for the gram-scale synthesis of porous BNNSs, but also experimental data and theoretical foundation for the metal-free oxidative dehydrogenation over BNNSs catalyst.

石墨烯及其衍生物是近年非金属催化领域的前沿和热点之一，但是石墨烯容易氧化，限制了它在空气等相对富氧环境下气相催化氧化方面的应用。其等电子体氮化硼纳米薄片(BNNSs，白石墨烯)有更好的抗氧化性能，也有丰富的酸碱性官能团、缺陷与活性边缘，是石墨烯非金属催化剂的重要补充。本项目通过固相反应技术，在气泡、氧化物、金属等模板的作用下，获取由二维BNNSs形成的三维多孔结构，避免催化应用中片层团聚和游离片层流失的问题。通过制备路线、合成工艺以及后处理调节BNNSs的表面化学性质(表面基团、缺陷与掺杂)，并研究BNNSs非金属催化苯甲醇、乙苯的氧化脱氢性能。探讨催化性能和表面化学性质间的关联，结合原位分析以及理论计算手段，推测其活性位，研究其催化反应机理。项目的开展在丰富多孔BNNSs材料制备技术的同时，也为新型BNNSs非金属催化剂的开发和应用提供实验数据和理论依据。

本项目通过固相反应中的气泡模板以及固体颗粒模板获取了多孔BNNSs催化剂，在系统地对其形貌、比表面积等参数调变的基础上，重点研究了BN表面物种和模型催化反应性能间的关联。针对氧化脱氢反应中，表面积碳往往是活性位点的情况，在对BN-C的碳含量、形貌以及比表面积调制的基础上，系统考察了CO2气氛下BCN的乙苯氧化脱氢行为，发现比活性和表面碳含量/物种无直接关联。CO2可将氮化硼边缘活化成B-O位点，乙苯则通过>B-O-C键吸附活化。在系统调变多孔氮化硼表面物种的基础上，发现>B-O物种也抑制了负载型铁催化剂的尺寸，使其还原温度升高100 °C的同时造成费托合成FTY急剧降低。但和>B-O不同，表面>N-H呈碱性，起供电子作用，也能够锚定Fe催化剂，有较好的稳定性和更好的甲烷选择性。以薄层BCN包覆纳米铁催化剂表面，发现Fe-BN界面有FTS活性的增强，包覆层稳定催化剂使之连续运行1000小时而无失活。在这些基础上，我们将工作拓展到多孔洞B、N双杂石墨烯体系，孔结构由气泡产生，而面内孔则由富氮物种和MgO反应产生，发现非金属氧还原的活性物种遵循BC3 > 石墨化氮 > 吡啶氮的规律，DFT计算表明B、N元素分离有协同增强作用，这和我们报道的氮杂体系中吡啶氮 > 石墨化氮的规律有所不同。