静电纺丝法制备硼掺杂氧化硅纳米纤维用于低碳烷烃氧化脱氢制烯烃

乙烯和丙烯等低碳烯烃是重要的基础有机化工产品,广泛应用于化工生产的各个领域.相比于其他工艺,低碳烷烃氧化脱氢制烯烃工艺具有不受热力学平衡限制、无积炭等特点而被广泛研究.近年发现六方氮化硼(h-BN)、硼化硅(SiB6)和磷酸硼(BPO4)等非金属硼基催化剂能够高效催化烷烃氧化脱氢反应,并抑制产物烯烃的过度氧化,表现出高的催化活性和烯烃选择性.大量的研究表明,硼基催化剂活性起源于催化剂表面的"BO"物种(如B-O和B-OH等基团).氧化硼(B2O3)作为一种氧化气氛中化学性质稳定的含硼化合物,兼具丰富的"BO"位点,在反应条件下可形成多种结构以适用不同的化学环境,为制备高效的烷烃氧化脱氢催化剂提供了可能.在之前的研究中,多将B2O3浸渍在常规的TiO2,SiO2,A12O3等三维多孔载体上用于氧化脱氢反应.考虑到B2O3结构的灵活性和易于成键特性,需开发更为有效的合成策略,以提升B2O3催化剂在氧化脱氢反应中的活性和稳定性.本文采用静电纺丝技术合成了直径为100～150 nm的多孔掺硼二氧化硅纳米纤维(PBSN)用于低碳烷烃氧化脱氢反应.静电纺丝法合成的催化剂中硼物种在开放的氧化硅纤维骨架上均匀分散且稳定固载.一维纳米纤维结构不仅有利于扩散,且赋予催化剂在高重时空速(WHSV)条件下优异的烷烃氧化脱氢反应活性.在乙烷氧化脱氢反应中,当乙烷的转化率达到44.3％时,乙烯的选择性和产率分别为84％和44.2 μmol gcat-1 s-1.而在丙烷脱氢反应中,当丙烷转化率为19.2％时,总烯烃选择性及丙烯产率分别为90％和76.6 μmol gcat-1 s-1.在温度为545 ℃,丙烷WHSV高达84.6 h-1的条件下,催化剂保持长时间稳定.与其他负载型氧化硼催化剂相比,PBSN催化剂具有更高的烯烃选择性和稳定性.研究表明,在氧化硅负载B2O3催化剂催化丙烷氧化脱氢反应中,载体中Si-OH基团的存在可能会降低丙烯的选择性.瞬态分析和动力学实验表明,硼基催化剂催化烷烃氧化脱氢反应过程中O2的活化受到烷烃的影响.本文不仅为高效硼基催化剂的合成提供了新思路,也为深入理解该类催化剂上烷烃氧化脱氢反应过程提供了实验支撑.

Electrospinning synthesis of porous boron-doped silica nanofibers for oxidative dehydrogenation of light alkanes

The discovery of the high activity and selectivity of boron-based catalysts for oxidative dehydro-genation (ODH) of alkanes to olefins has attracted significant attention in the exploration of a new method for the synthesis of highly active and selective catalysts.Herein,we describe the synthesis of porous boron-doped silica nanofibers (PBSNs) 100-150 nm in diameter by electrospinning and the study of their catalytic performance.The electrospinning synthesis of the catalyst ensures the uniform dispersion and stability of the boron species on the open silica fiber framework.The one-dimensional nanofibers with open pore structures not only prevented diffusion limitation but also guaranteed high catalytic activity at high weight hourly space velocity (WHSV) in the ODH of alkanes.Compared to other supported boron oxide catalysts,PBSN catalysts showed higher olefin selectivity and stability.The presence of Si-OH groups in silica-supported boron catalysts may cause low propylene selectivity during the ODH of propane.When the ODH conversion of ethane reached 44.3％,the selectivity and productivity of ethylene were 84％ and 44.2％ gcat-1 s-1,respec-tively.In the case of propane ODH,the conversion,selectivity of olefins,and productivity of propyl-ene are 19.2％,90％,and 76.6 μmol gcat-1 S-1,respectively.No significant variations in the conversion and product selectivity occurred during 20 h of operation at a high WHSV of 84.6 h-1.Transient analysis and kinetic experiments indicated that the activation of O2 was influenced by alkanes dur-ing the ODH reaction.