钌基催化剂配位环境对聚乙烯氢解性能影响研究

doi:10.11949/0438-1157.20240634

摘要/Abstract

摘要：

聚乙烯氢解可以产生多种碳氢化合物，产品分布非常宽，产物选择性调控具有一定挑战性。通过调控钌负载量制备了不同钌粒径的Ru/CeO₂催化剂，利用TEM、in situ DRIFTS和模型计算等多种技术，发现聚乙烯催化氢解的产物分布与钌金属配位环境密切相关。表征和模型计算表明，不同尺寸的钌纳米颗粒具有不同的几何结构和配位环境。钌平均粒径为0.85 nm时，低配位的边/角位点占主导，其C₂~C₄₀选择性达到92%。钌平均粒径达到2.75 nm时，高配位的平台位点占主导，C₂~C₄₀选择性仅为8%，甲烷选择性高达92%。结合截断六角双锥模型和CO-DRIFTS实验，推断Ru/CeO₂催化剂上产物的选择性可能与聚乙烯氢解中间体与钌纳米颗粒表面的相互作用有关，提出了Ru/CeO₂催化剂上聚乙烯氢解两种反应路径与配位环境的关系。

关键词: 废塑料降解, 催化剂, 加氢, 碳氢化合物, 钌纳米颗粒

Abstract:

Polyethylene hydrogenolysis can yield a diverse range of alkanes and exhibit a broad product distribution, thus selective regulation of products is a formidable challenge. A series of Ru/CeO₂ catalysts with different Ru particle sizes were prepared by regulating Ru loading. It was observed that the product distribution of polyethylene hydrogenolysis closely correlated with the coordination environments of metal Ru as determined by multiple techniques including TEM, in situ DRIFTS and model calculations. Characterizations and model calculations revealed that Ru nanoparticles with different particle sizes exhibited different metal dispersion, geometric structures and coordination environments. The C₂-C₄₀ alkanes selectivity of 92% was achieved using Ru particle sizes with mean diameter of 0.85 nm where the edge/corner sites with low-coordination are dominant. The C₂-C₄₀ alkanes selectivity of 8% and the methane selectivity of 92% was obtained using the Ru particle sizes with mean diameter of 2.75 nm where the terrace sites with highly coordinated platform sites are dominate. Combined with truncated hexagonal bipyramid model and CO-DRIFTS experiment, the selectivity of products over Ru/CeO₂ catalysts was correlated with the interaction between intermediates of polyethylene hydrogenolysis and the surface of Ru nanoparticles. Furthermore, the relation between reaction pathways in polyethylene hydrogenolysis and coordination environments of metal Ru was proposed.

Key words: degradation of waste plastic, catalyst, hydrogenation, hydrocarbons, ruthenium nanoparticles

中图分类号:

TQ426

颜诗宇, 高姣姣, 杨太顺, 谢尚志, 杨艳娟, 徐晶. 钌基催化剂配位环境对聚乙烯氢解性能影响研究[J]. 化工学报, DOI: 10.11949/0438-1157.20240634.

Shiyu YAN, Jiaojiao GAO, Taishun YANG, Shangzhi XIE, Yanjuan YANG, Jing XU. Effect of coordination environment of ruthenium-based catalysts on their performance for polyethylene hydrogenolysis[J]. CIESC Journal, DOI: 10.11949/0438-1157.20240634.

图/表 13

图1 不同钌负载量的Ru/CeO2催化剂的性能评价注:(反应条件:1g PE, 50 mg Ru/CeO2, 3.5 MPa H2, 500 r/min, 4 h)

Fig.1 Performance evaluation of Ru/CeO2 catalysts with different Ru loadings(Reaction condition: 1g PE, 50 mg Ru/CeO2, 3.5 MPa H2, 500 r/min, 4 h)

表1 纯CeO2载体的性能评价

Table 1 Performance evaluation of CeO2 support

催化剂	产率=选择性×转化率			转化率
催化剂	CH₄	C₂-C₆	C₇-C₄₀	转化率
CeO₂	0.1%	0.2%	1.1%	1.4%

图2 相同钌投入量的Ru/CeO2催化剂的性能评价注:(反应条件:1 g PE, Ru/CeO2 (1 mg-Ru), 3.5 MPa H2, 500 rpm, 4 h)

Fig.2 Performance evaluation of Ru/CeO2 catalysts with the same Ru amount(Reaction condition: 1 g PE, Ru/CeO2 (1 mg-Ru), 3.5 MPa H2, 500 rpm, 4 h)

表2 催化剂结构参数表

Table 2 Physicochemical properties of the catalysts

催化剂	钌含量^① /%	比表面积^② /(m²/g)	孔容^{③ /}(cm³/g)	平均孔径^④ /nm	钌平均粒径^⑤ /nm	钌金属分散度^⑥ /%
CeO₂	-	16.4	0.045	6.66	-	-
0.5% Ru/CeO₂	0.38	17.9	0.051	7.25	0.85	100
2% Ru/CeO₂	1.83	18.8	0.049	7.12	1.55	85
9% Ru/CeO₂	8.58	13.0	0.028	8.41	2.75	48

图3 CeO2和还原后的Ru/CeO2催化剂的氮气脱附曲线(a)和孔径分布(b)

Fig.3 Nitrogen desorption curves (a) and pore size distribution (b) of CeO2 and Ru/CeO2 catalysts after reduction

图4 CeO2和还原后的Ru/CeO2催化剂的XRD谱图

Fig.4 XRD patterns of CeO2 and Ru/CeO2 catalysts after reduction

图5 CeO2和Ru/CeO2催化剂的H2-TPR图

Fig.5 H2-TPR profiles of CeO2 and Ru/CeO2 catalysts

图6 Ru/CeO2催化剂的TEM图像（所有样品均为还原后催化剂）

Fig.6 TEM images of Ru/CeO2 catalysts (All samples are reduced catalysts)

图7 钌纳米颗粒的几何结构理论模型示意图和三种切面的各位点的原子配位数

Fig.7 Geometric structure model and the atomic coordination number of Ru nanoparticle

图8 不同类型的活性位点的比例和数量

Fig.8 the fraction and number of different types of active site

图9 Ru/CeO2催化剂的CO-DRIFT图谱

Fig.9 CO-DRIFT spectra of Ru/CeO2 catalysts

图10 产物选择性与氢气压力的关系

Fig.10 The relationship between product selectivity and H2 pressure

图11 Ru/CeO2催化PE氢解的两种可能反应机制（参考Nakagawa等[45]）

Fig.11 Two possible mechanisms with which hydrogenolysis on the surface of Ru/CeO2 could proceed (based on the works of Nakagawa et al.[45])

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