非金属硼化物催化低碳烷烃氧化脱氢制烯烃的科学基础

Catalytic conversion of light alkanes to light alkenes is an important process towards efficient of light alkanes currently being burned or vented. Oxidative dehydrogenation (ODH), benefiting from free of thermodynamic limits, offers a promising technology to produce light alkenes from alkanes and accordingly can promote the convertion efficiency and reduce the energy consumption. However, there are substantial challenges to design and synthesize the high-efficient catalyst which can promote the efficient activation of alkanes and selective conversion to alkenes, and shut off the deep oxidation of more reactive alkenes under the severe conditions of alkane activation. This project aims to develop nonmetallic boride catalysts and study their catalytic behaviors in ODH of light alkanes to alkenes. The contents include three aspects: synthesis of novel porous boride catalysts with rich defective sites, understanding of ODH mechanism on boride catalysts, and exploration of procotols for fabrication of boride catalysts for industrial scale. In order to understand the origin of the catalytic activity of borides in ODH and the factors determining their performance, in-situ characteristic means, kinetic measurements and theoretical calculations will be carried out to characterize the active center of catalysts in ODH of propane, to explore the activating pathway and reconstructing mechanism of alkane molecule on the catalyst surface, to identify the effect of chemical composition and crystal structure on the catalytic performances, and to identify the correlation of catalytic performance with catalyst structure, with which the catalytic nature of nonmetallic borides will be revealed. These studies will establish a new catalytic technology of alkane dehydrogenation based on borides, and provides scientific basis for the efficient utilization of abundant resources of light alkanes and boron ores.

低碳烷烃高效转化制低碳烯烃是实现烷烃资源高值化利用的重要途径。烷烃氧化脱氢制烯烃工艺不受热力学平衡限制，有利于提高反应效率，降低能耗。但目前最好的钒系催化剂，由于深度氧化，烯烃选择性仍有待提高，且有大量CO2生成。非金属氮化硼能够有效活化低碳烷烃，抑制烯烃产物深度氧化。本项目拟开展耐高温、耐氧化非金属硼化物催化低碳烷烃氧化脱氢制烯烃研究。发展纳米多孔硼化物催化剂可控制备方法，考察其烷烃氧化脱氢性能，阐明硼化物中元素组成、晶体结构等对催化脱氢性能的影响机制，获得构效关联规律，结合原位表征和理论计算，从能量、几何和电子结构等方面探索烷烃分子的有氧活化路径和重构机理，认知催化剂活性中心，构建合理的烷烃氧化脱氢反应图像，揭示非金属硼化物的催化活性本质。从实际应用角度，探索适合于工业应用的硼基催化剂成型方法，形成基于非金属硼化物的烷烃脱氢催化新体系，为烷烃资源和硼矿资源的高效利用奠定科学基础。

低碳烷烃高效转化制低碳烯烃是实现烷烃资源高值化利用的重要途径。本项目开展了耐高温、耐氧化非金属硼化物催化低碳烷烃氧化脱氢制烯烃研究。通过制备活性的六方氮化硼、碳化硼、硅化硼和磷化硼催化剂，明晰了无氧硼体系催化低碳烷烃氧化脱氢反应活性位与反应机理，发现催化活性与骨架第二元素电负性呈负相关，阐明了六方相和斜方六面体相含硼催化剂比立方相催化剂具有更高的反应活性，提出烷烃选择性脱氢和稳定的B–OR中间物种是抑制烯烃深度氧化主要原因。通过制备高分散氧化硼体系、负载低聚BxOy物种的催化剂、多孔磷酸硼催化剂，揭示了链状和环状硼氧物种是活性位，解析了表面反应通道和气相反应通道协同的复杂反应网络；发现了含硼化合物催化剂硼化学环境对催化性能的影响，表面硼羟基分布与催化剂本征催化活性呈正相关，三配位硼氧物种反应活性高于四配位硼氧物种和磷氧物种，为硼基催化材料的设计合成指明了方向。基于对硼基催化体系催化本质的认识，优化了粉体催化剂效率因子，构筑了蜂窝状、纤维状和涂层整体式氮化硼催化剂，建立硼基催化剂成型方法，强化反应传质、传热，并基于硼基催化烷烃ODH反应的“表面-气相”独特特征，调节硼胚胎分子筛催化剂后体积，提高丙烯选择性，实现高反应通量下的高烯烃选择性及收率。研究获得的对氮化硼反应活性的认知也促使我们重新审视传统的将氮化硼作为惰性载体的观点，创制了高分散的氮化硼负载Fe、Cu、Ni等金属氧化物的催化剂，并用于低碳醇等脱氢转化及环氧丙烷与CO2环加成、CO甲烷化反应，发现BN可通过与金属氧化物的强相互作用将其锚定在载体上，抑制其在反应中烧结，并调控其氧化还原性能，实现反应物的高效转化和产物的高选择性生成。本项目研究成果构建了合理的烷烃氧化脱氢反应图像，揭示了非金属硼化物的催化活性本质，发展了适合于工业应用的硼基催化剂成型方法，形成基于非金属硼化物的烷烃脱氢催化新体系，奠定烷烃资源和硼矿资源的高效利用的科学基础。