质谱学报2026，Vol.47Issue(5)：707-718,12.DOI:10.7538/zpxb.2026.0002
基于质谱对Pt/ZSM-5低温催化裂解高密度聚乙烯制液态产物及其反应机理的研究
Study of Catalytic Performance and Reaction Mechanism of Low-Temperature Catalytic Cracking of Hight-Density Polyethylene to Liquid Products Over Pt/ZSM-5 Based on Mass Spectrometry
摘要
Abstract
The global plastic waste crisis is worsening,and effective chemical upcycling technologies are urgently needed.Upgrading waste polyolefins into valuable liquid fuels under mild conditions is a promising route for plastic recycling.However,the complex reaction networks involved make it difficult to understand the underlying mechanisms and optimize catalysts.Here,offline gas chromatography-mass spectrometry(GC-MS)was combined with synchrotron radiation photoionization mass spectrometry(SR-PIMS)to investigate the catalytic cracking of high-density polyethylene(HDPE)over Pt/ZSM-5 at 280℃.Pt/ZSM-5 catalysts with different loadings were prepared by impregnation and characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD),N2 physisorption,and ammonia temperature-programmed desorption(NH3-TPD).TEM results showed the uniform dispersion of~4.7 nm Pt nanoparticles at a loading of 0.5 wt%,whereas higher loading(1.5 wt%)led to agglomeration and partial pore blockage.This observation correlated with a volcano-shaped trend between Pt loading and catalytic performance.NH3-TPD confirmed that Pt did not significantly alter the acid site distribution of ZSM-5,indicating that the observed catalytic effects are metal-specific.Offline GC-MS analysis of the liquid products enabled precise quantification of product distributions,identifying 0.5%Pt/ZSM-5 as the optimal catalyst.Compared with HZSM-5,Pt increased the selectivity of liquid products by about 50%and the aromatic yield by 33%.SR-PIMS,with its tunable photon energy,provided deeper mechanistic insights.Under low-pressure conditions(266 Pa)using 9.2 eV photons,reactive C4-C9 alkyl radicals were captured in situ for the first time during HDPE catalytic cracking.A direct comparison between HZSM-5 and 0.5%Pt/ZSM-5 revealed that Pt significantly reduced radical concentrations,offering direct evidence for radical quenching by Pt sites.Under near-ambient-pressure conditions(5×104 Pa)with 11 eV photons,real-time monitoring of product evolution during temperature-programmed reactions elucidated the temperature-dependent interplay between cracking,hydrogenolysis,and aromatization.Pt modification notably enhanced medium-chain olefins(C5-C8)and aromatics at higher temperatures(>300℃),while light alkanes showed distinct evolution patterns that reflected shifts in the dominant reaction mechanisms.Furthermore,the detection of H2 at 15.5 eV confirmed Pt's low-temperature dehydrogenation activity at 280℃.Based on this complementary mass spectrometric evidence,a reaction mechanism involving three primary Pt-mediated pathways was proposed:1)hydrogenolysis of C-C bonds to enhance alkane production;2)dehydrogenation to lower the energy barrier for aromatization;3)radical quenching,in which reactive intermediates are converted to stable products via surface alkyl species.The synergy between Pt metal sites and ZSM-5 acid sites thus enables selective liquid hydrocarbon production under mild conditions.While this work establishes a complete mass spectrometric evidence chain for metal-acid bifunctional catalysis in polyolefin upgrading,several aspects warrant further investigation.The exact nature of Pt-radical interactions and the dynamics of hydrogen transfer between metal and acid sites remain to be elucidated,potentially through advanced spectroscopic techniques and theoretical calculations.Moreover,extending this methodology to real-world plastic waste containing additives and contaminants would help assess its practical applicability.The demonstrated capability of SR-PIMS for capturing reactive intermediates opens new avenues for mechanistic studies in polymer catalysis.关键词
高密度聚乙烯(HDPE)/同步辐射光电离质谱(SR-PIMS)/催化裂解/中间体/原位Key words
high-density polyethylene(HDPE)/synchrotron radiation photoionization mass spectrometry(SR-PIMS)/catalytic cracking/intermediates/in situ分类
化学化工引用本文复制引用
李想,雷晨杰,曹钢,刘成园,潘洋..基于质谱对Pt/ZSM-5低温催化裂解高密度聚乙烯制液态产物及其反应机理的研究[J].质谱学报,2026,47(5):707-718,12.基金项目
国家自然科学基金面上项目(1257350) （1257350）
