CAJ | 학술논문

4,4?-二甲基联苯(4,4?-DMBP)是生产高性能聚合物材料的重要前驱体,可以通过4-甲基联苯(4-MBP)甲基化制得.本文采用“our own-N-layered integrated molecular orbital+molecular mechanics”(ONIOM)和密度泛函理论(DFT)方法研究H-ZSM-5分子筛孔内4-MBP和甲醇择形甲基化的反应机理,考虑了分步和协同反应机理.分步机理的活化能低于协同机理.在两种反应机理中,4,4?-DMBP为动力学优先生成产物.过渡态择形的特征也使甲基化更容易生成4,4?-DMBP.在分子筛孔内,4-MBP 异构化生成3-甲基联苯(3-MBP)的反应被抑制.在分子筛外表面,4-MBP异构化生成3-MBP比甲基化反应更有动力学优势,导致4,4?-DMBP选择性降低.对外表面进行改性将会抑制4-MBP异构化反应,并使反应在分子筛孔内进行,因此可以提高4,4?-DMBP的选择性. H-ZSM-5催化择形和非择形反应的计算结果与实验现象一致.
4,4?-이갑기련분(4,4?-DMBP)시생산고성능취합물재료적중요전구체,가이통과4-갑기련분(4-MBP)갑기화제득.본문채용“our own-N-layered integrated molecular orbital+molecular mechanics”(ONIOM)화밀도범함이론(DFT)방법연구H-ZSM-5분자사공내4-MBP화갑순택형갑기화적반응궤리,고필료분보화협동반응궤리.분보궤리적활화능저우협동궤리.재량충반응궤리중,4,4?-DMBP위동역학우선생성산물.과도태택형적특정야사갑기화경용역생성4,4?-DMBP.재분자사공내,4-MBP 이구화생성3-갑기련분(3-MBP)적반응피억제.재분자사외표면,4-MBP이구화생성3-MBP비갑기화반응경유동역학우세,도치4,4?-DMBP선택성강저.대외표면진행개성장회억제4-MBP이구화반응,병사반응재분자사공내진행,인차가이제고4,4?-DMBP적선택성. H-ZSM-5최화택형화비택형반응적계산결과여실험현상일치.
The methylation of 4-methylbiphenyl (4-MBP) can yield 4,4?-dimethylbiphenyl (4,4?-DMBP), an important precursor for advanced polymers. The reaction mechanism of the shape-selective methylation of 4-MBP with methanol within the pores of H-ZSM-5 zeolite was studied, using“our own-N-layered integrated molecular orbital+molecular mechanics”(ONIOM) and density functional theory (DFT) methods. Stepwise and concerted mechanisms were considered, with the former having a lower activation energy. 4,4?-DMBP is kinetical y favored by both mechanisms. Transition state selectivity accounts for the preferential methylation to 4,4?-DMBP. The isomerization of 4-MBP to 3-methylbiphenyl (3-MBP) is restricted within the zeolite. The isomerization of 4-MBP to 3-MBP is kinetically favored over methylation on the external zeolite surface, which causes a decrease in 4, 4?-DMBP selectivity. Passivating the external surface wil suppress 4-MBP isomerization, therefore increasing 4,4?-DMBP selectivity by restricting reaction within the zeolite. The computational results of shape-selective and non-selective reactions over H-ZSM-5 zeolite well account for the experimental observations.