氮化碳负载钯催化剂的制备及对SBS选择性催化加氢性能的研究

Study on preparation of Pd catalyst supported on carbon nitride for the selective hydrogenation of SBS

苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)选择性催化加氢是保留链段中苯环不被加氢而C C双键选择性加氢,从而得到具有更优异性能的高附加值氢化产物SEBS。为了消除反应物大分子孔内扩散限制问题,采用胶体SiO_(2)亚微米球为模板,通过氰胺热缩合成功合成了三维有序超大孔氮化碳(3DOM g-C_(3)N_(4)),以其为载体采用化学还原负载法得到了具有超大孔结构的Pd/3DOM g-C_(3)N_(4)催化剂,并将其用于SBS的选择性催化加氢反应。结果表明,Pd/3DOM g-C_(3)N_(4)催化剂具有超大孔-大孔-介孔多级孔三维贯穿结构且Pd颗粒尺寸小、分散均匀,该催化剂在较为温和的反应条件下,即表现出极为优异的加氢活性和选择性。根据红外表征计算得到其对SBS的1,2-C C和1,4-C C总加氢度达到98%,而对苯环没有加氢,选择性为100%。其优异的催化性能主要归功于载体独特的超大孔-大孔-介孔多级孔三维贯穿结构可以有效消除大分子在孔隙中的扩散限制,从而提高了对活性位点的可接近性;Pd和载体氮化碳中的吡啶N之间存在强相互作用,有利于Pd的锚定,进而获得颗粒尺寸小且分散度和稳定性高的Pd纳米颗粒。

The selective catalytic hydrogenation of styrene-butadiene-styrene block copolymer(SBS)is to selectively hydrogenate the unsaturated C C in polybutadiene segment while maintaining the phenyl group in polystyrene segment intact so as to yield high-valued hydrogenated products SEBS with greatly improved performance.In order to eliminate the diffusion limitation,herein,three-dimensional ordered super-macroporous carbon nitride(3DOM g-C_(3)N_(4))was successfully synthesized via thermal condensation of cyanamide with colloidal SiO_(2)sub-microspheres as the template.Afterwards,the Pd/3DOM g-C_(3)N_(4)catalyst was obtained by chemical reduction method and applied for selective catalytic hydrogenation of SBS.The results showed that the Pd/3DOM g-C_(3)N_(4)catalyst possessed a three-dimensional penetrating structure of super-macroporous-macroporous-mesoporous multistage pore with the small-sized and well-dispersed Pd nanoparticles over it.Such catalyst exhibited excellent hydrogenation activity and selectivity under mild reaction conditions.According to the Fourier transform infrared(FTIR)characterization,the total hydrogenation degree of 1,2-C C and 1,4-C C to SBS was 98%,while the benzene ring was not hydrogenated thus the selectivity to C C was 100%.The excellent catalytic performance is mainly attributed to the unique three-dimensional penetrating structure of super-macroporous-macroporous mesoporous multistage pore of the support,which can effectively eliminate the macromolecules diffusion limitation in pores,thereby greatly improving the accessibility to the active sites.The strong interaction between Pd and pyridinic N in the g-C_(3)N_(4)support is beneficial to anchoring Pd^(2+)during impregnation process,and then obtains Pd nanoparticles with small particle size and high dispersion and stability.