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

doi:10.11949/0438-1157.20221307

Abstract

Abstract:

The selective catalytic hydrogenation of styrene-butadiene-styrene block copolymer (SBS) is to selectively hydrogenate the unsaturated CC 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-C₃N₄) was successfully synthesized via thermal condensation of cyanamide with colloidal SiO₂sub-microspheres as the template. Afterwards, the Pd/3DOM g-C₃N₄ catalyst was obtained by chemical reduction method and applied for selective catalytic hydrogenation of SBS. The results showed that the Pd/3DOM g-C₃N₄ 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-CC and 1,4-CC to SBS was 98%, while the benzene ring was not hydrogenated thus the selectivity to CC 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-C₃N₄support is beneficial to anchoring Pd²⁺ during impregnation process, and then obtains Pd nanoparticles with small particle size and high dispersion and stability.

Key words: g-C₃N₄, super-macroporous support, supported Pd catalyst, SBS, hydrogenation

摘要：

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CC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SiO₂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-C₃N₄），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-C₃N₄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-C₃N₄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-CC和1,4-CC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。

关键词: g-C₃N₄, 超大孔载体, 负载型 Pd基催化剂, SBS, 加氢

CLC Number:

TQ 032.4

Mengxin LIANG, Yan GUO, Shidong WANG, Hongwei ZHANG, Pei YUAN, Xiaojun BAO. Study on preparation of Pd catalyst supported on carbon nitride for the selective hydrogenation of SBS[J]. CIESC Journal, 2023, 74(2): 766-775.

梁梦欣, 郭艳, 王世栋, 张宏伟, 袁珮, 鲍晓军. 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[J]. 化工学报, 2023, 74(2): 766-775.

Figures/Tables 11

Fig.1 Schematic illustration of the synthetic strategy for Pd/3DOM g-C3N4 catalyst

Fig.2 The structural formula of SBS

Fig.3 The morphology of SiO2, 3DOM g-C3N4 and Pd/3DOM g-C3N4 and the Pd particle size distribution of Pd/3DOM g-C3N4

Fig.4 Texture images of 3DOM g-C3N4 support and Pd/3DOM g-C3N4 catalyst

Table 1 Physiochemical parameters of 3DOM g-C3N4 support and Pd/3DOM g-C3N4 catalyst

Samples	BET surface area/(m²/g)	Pore volume/(cm³/g)	Pore size/nm
3DOM g-C₃N₄	21	0.03	3.7/30
Pd/3DOM g-C₃N₄	24	0.05	3.9/32

Fig.5 XPS spectra of 3DOM g-C3N4 and Pd/3DOM g-C3N4 catalyst

Table 2 XPS data for 3DOM g-C3N4 and Pd/3DOM g-C3N4 catalyst

Samples	N/%	C/%	O/%	Pd/%	Binding energy/eV			Graphitic N/%	Pyrrolic N/%	Pyridinic N/%
Samples	N/%	C/%	O/%	Pd/%	Graphitic N	Pyrrolic N	Pyridinic N	Graphitic N/%	Pyrrolic N/%	Pyridinic N/%
3DOM g-C₃N₄	48.45	46.36	5.19	—	400.80	399.71	398.26	7.19	17.95	74.85
Pd/3DOM g-C₃N₄	48.20	44.23	7.02	0.54	400.85	399.70	398.47	8.13	19.39	72.84

Fig.6 Morphology of g-C3N4 and Pd/g-C3N4 and pore structure of g-C3N4

Fig.7 The FTIR spectra of SBS and SEBS produced by Pd/3DOM g-C3N4 and Pd/g-C3N4

Fig.8 The 1H NMR spectra of SBS and SEBS produced by Pd/3DOM g-C3N4

Fig.9 TG curve, thermal condensation process of the cyanamide precursor and schematic illustration of the carbon nitride-supported Pd catalyst

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