采用Gaussian 03程序中的密度泛函（DFT）理论B3LYP/6-31＋＋G（d,p）方法,对木聚糖一个循环单元的热解机理进行了理论研究.设计了八条热解路径,对每条路径中反应物、中间体、过渡态和产物进行能量梯度全优化,并对过渡态进行了IRC验证,在298～1098 K温度范围内计算了每个路径的热力学及动力学参数.结果表明：Path1,Path2为放热反应,Path3在798 K由吸热反应转变为放热反应,其余路径为吸热反应;室温到798 K,2-糠醛和水的转化率最高,温度高于898 K,Path4成为主反应路径.通过动力学分析给出了木糖分子不同断键方式下的三个最优路径：Path2的控速步为Step5活化能为236.9 kJ/mol;Path6的控速步为Step7,活化能为363.9 kJ/mol;Path7或Path8的控速步为Step15,活化能为336.5 kJ/mol.分析表明,无论热力学或是动力学都优先支持Path2生成2-糠醛和水,其次是Path6生成乙醇醛和甲醛,Path7或Path8生成乙醇醛、乙二醇和一氧化碳.%Eight kinds of paths of possible pyrolysis reactions were designed,and B3LYP/6-31＋＋G（d,p） methods in Gaussian 03 package was used for investigating the pyrolysis reaction mechanism of xylan monomer.The equilibrium geometries of the reactants,transition states,intermediate and products of every reaction path were optimized,and the transition states were checked using IRC method.The standard ther-modynamic and kinetic parameters of every reaction path in 298～1098 K temperature ranges were calcu-lated.The result shows that Path1 and Path2 are exothermic reaction and Path3 turn to exothermic reaction above 898 K and the other Paths are endothermic reaction.When the pyrolysis temperature is below 798 K the convert ratio of 2-furfuraldehyde（P1） and water is the highest.Above 798 K,the main reaction path is Path4.From the kinetic analysis,we get three better path from all the paths of xylose molecule pyrolysis in different bond breaking-way.The rate-determining step of path2 is step5,whose activation energy is 236.9 kJ/mol.The rate-determining step of Path6 is step7,whose activation energy is 363.9 kJ/mol.The rate-determining step of Path7 or Path8 is step15,whose activation energy is 336.5 kJ/mol.According to re-sults of thermodynamic or dynamic analysis,Path1 which produces 2-furfuraldehyde and water is given pri-ority to supporting.Path6 which produces glycolaldehyde and methanal is given secondly supporting.Path7 or Path8 which produces glycolaldehyde,glycol and CO is given last supporting.
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