納米碳催化乙炔氫氯化反應機理的DFT研究
發(fā)布時間：2018-10-10 06:54
【摘要】：聚氯乙烯作為五大工程塑料之一,其單體氯乙烯(VCM)的合成是聚氯乙烯工業(yè)生產(chǎn)中的重要環(huán)節(jié),其中催化劑扮演著至關重要的角色。目前工業(yè)化生產(chǎn)VCM中使用的主要為汞基催化劑,而由于汞的高溫易揮發(fā)性造成嚴重的汞污染以及我國嚴峻的汞資源形勢和國際禁汞的趨勢,新型無汞催化劑的開發(fā)應用已迫在眉睫。本論文基于密度泛函理論,采用計算化學的手段研究乙炔氫氯化反應在兩種非金屬碳基催化劑上的反應機理。分別探索了C原子摻雜的B_(12)N_(12)籠(B11N12C、B12N11C)和三種缺陷石墨烯(單空位石墨烯MVG、雙空位石墨烯DVG和Stone-wales缺陷石墨烯SWDG)上的反應機理,從而為實驗提供理論依據(jù),促進低成本,高穩(wěn)定性的新型非金屬催化劑的開發(fā)。研究結果表明,C摻雜后的B11N12C和B12N11C籠相較于摻雜前對反應物C2H2和HCl的吸附均得到明顯增強,且C2H2在B11N12C上有順式和反式兩種吸附形態(tài),摻雜籠對C2H2的吸附能力遠遠高于對于HCl的吸附,C2H2的吸附能大小順序為B12N11CB11N12C(反式)B11N12C(順式),吸附能依次為-27.58、-25.87和-25.70kcal/mol;HCl的吸附強度順序為B11N12CB12N11C,吸附能依次為-3.06和-1.58 kcal/mol;前線分子軌道理論(FMO)分析結果表明摻雜后,摻雜位點的前線軌道發(fā)生電子云的明顯富集,有利于吸附的發(fā)生;C2H2的吸附形態(tài)引發(fā)的B11N12C上的兩種反應路徑R1(反式)、R2(順式)和B12N11C上的反應路徑中,R1的活化能最低,為36.08kcal/mol,R2和R3分別為49.63和41.41kcal/mol,三種路徑的速率控制步驟均為共吸附態(tài)轉變?yōu)檫^渡態(tài)時HCl分子的解離。缺陷石墨烯中缺陷位的形成改變了石墨烯表面均勻的電子分布,并使電子在缺陷位附近發(fā)生聚集,較完美石墨烯PG增強了石墨烯與反應物的相互作用,特別是DVG對兩種反應物的吸附均強于其他缺陷石墨烯,吸附能大小順序為DVGMVGSWDG。C2H2的吸附能分別為-13.25、-6.22和-1.92kcal/mol,HCl的吸附能分別為-5.08、-4.43和-3.28kcal/mol;三種缺陷石墨烯反應機理十分相似,速率控制步驟均為共吸附態(tài)向過渡態(tài)轉變時HCl的分解,MVG、DVG和SWDG活化能分別為39.46、41.55和41.16kcal/mol,反應活性位點在兩個相連的5元環(huán)和6元環(huán)共有的碳碳鍵上。MVG上的活化能更低,更有利于催化乙炔氫氯化反應的發(fā)生。
[Abstract]:As one of the five engineering plastics, the synthesis of vinyl chloride monomer (VCM) is an important part in the industrial production of PVC, in which the catalyst plays a crucial role. At present, mercury-based catalysts are mainly used in the industrial production of VCM, and the severe mercury pollution caused by the high temperature and volatility of mercury, the severe situation of mercury resources in China and the trend of international mercury ban. The development and application of new mercury-free catalysts is imminent. Based on density functional theory (DFT), the mechanism of hydrogen-chlorination of acetylene over two non-metallic carbon-based catalysts was studied by computational chemistry. The reaction mechanisms of C atom doped B _ (12) N _ (12) cage (B _ (11) N _ (12) C) and three kinds of defective graphene (single vacancy graphene MVG, double vacancy graphene DVG and Stone-wales defect graphene SWDG) were investigated respectively, which provided theoretical basis for experiment and promoted low cost. Development of new non-metallic catalysts with high stability. The results show that the adsorption of C2H2 and HCl in the B11N12C and B12N11C cages after doping with C is obviously enhanced compared with that before doping, and C2H2 has two kinds of adsorption forms on B11N12C: cis and trans-type. The adsorption ability of the doped cages to C2H2 is much higher than that of the adsorbed C _ 2H _ 2 of HCl in the order of B12N11CB11N12C (trans-B11N12C), -27.58 ~ 25.87 and -25.70 kcal / mol 路mol ~ (-1) h ~ (-1), respectively, and the order of adsorption energy is B11N12CB12N11C, and the adsorption energy is -3.06 and -1.58 kcal/mol;, respectively, and the order of adsorption energy is B11N12CB12N11C, and the order of adsorption energy is B11N12CB12N11C and -1.58 kcal/mol;. The results of channel theory (FMO) analysis show that after doping, The electron cloud enrichment occurred in the frontier orbit of the doping site, which is beneficial to the activation energy of the two reaction pathways R1 (trans) R2 (cis) and R1 (cis) on B11N12C initiated by the adsorptive form of C _ 2H _ 2 and the lowest activation energy of R1 in the reaction path on B12N11C, which is beneficial to the adsorption formation of C _ 2H _ 2. The values of R2 and R3 were 49.63 and 41.41 kcal / mol, respectively. The rate control steps of the three paths were the dissociation of HCl molecules when the coadsorption state was transformed into transition state. The formation of defect sites in graphene changed the uniform electron distribution on the surface of graphene and made the electrons gather near the defect site. The perfect graphene PG enhanced the interaction between graphene and reactants. In particular, the adsorption of the two reactants by DVG was stronger than that of other graphene defects, and the adsorption energy of DVGMVGSWDG.C2H2 was -13.25 ~ 6.22 and -1.92 kcal / mol 路mol ~ (-1), respectively, and the adsorption energy of DVGMVGSWDG.C2H2 was -5.08 ~ 4.43 and -3.28 kcal / mol, respectively, and the reaction mechanism of three kinds of defective graphene was very similar. The activation energy of HCl decomposed into transition state is 39.46 渭 g 41.55 and 41.16 kcal / mol, respectively, and the activation energy of the active sites is lower on the carbon / carbon bond shared by the two connected five-member and six-member rings, respectively, when the rate control step is the transition from the co-adsorption state to the transition state, and the activation energy of DVG and SWDG are even lower than that of MVG, and the activation energy of MVG is much lower than that of MVG, and the activation energy of the active sites is even lower. It is more favorable to catalyze the hydrogen chlorination of acetylene.
【學位授予單位】：石河子大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ222.423;O643.36
本文編號：2261056
[Abstract]:As one of the five engineering plastics, the synthesis of vinyl chloride monomer (VCM) is an important part in the industrial production of PVC, in which the catalyst plays a crucial role. At present, mercury-based catalysts are mainly used in the industrial production of VCM, and the severe mercury pollution caused by the high temperature and volatility of mercury, the severe situation of mercury resources in China and the trend of international mercury ban. The development and application of new mercury-free catalysts is imminent. Based on density functional theory (DFT), the mechanism of hydrogen-chlorination of acetylene over two non-metallic carbon-based catalysts was studied by computational chemistry. The reaction mechanisms of C atom doped B _ (12) N _ (12) cage (B _ (11) N _ (12) C) and three kinds of defective graphene (single vacancy graphene MVG, double vacancy graphene DVG and Stone-wales defect graphene SWDG) were investigated respectively, which provided theoretical basis for experiment and promoted low cost. Development of new non-metallic catalysts with high stability. The results show that the adsorption of C2H2 and HCl in the B11N12C and B12N11C cages after doping with C is obviously enhanced compared with that before doping, and C2H2 has two kinds of adsorption forms on B11N12C: cis and trans-type. The adsorption ability of the doped cages to C2H2 is much higher than that of the adsorbed C _ 2H _ 2 of HCl in the order of B12N11CB11N12C (trans-B11N12C), -27.58 ~ 25.87 and -25.70 kcal / mol 路mol ~ (-1) h ~ (-1), respectively, and the order of adsorption energy is B11N12CB12N11C, and the adsorption energy is -3.06 and -1.58 kcal/mol;, respectively, and the order of adsorption energy is B11N12CB12N11C, and the order of adsorption energy is B11N12CB12N11C and -1.58 kcal/mol;. The results of channel theory (FMO) analysis show that after doping, The electron cloud enrichment occurred in the frontier orbit of the doping site, which is beneficial to the activation energy of the two reaction pathways R1 (trans) R2 (cis) and R1 (cis) on B11N12C initiated by the adsorptive form of C _ 2H _ 2 and the lowest activation energy of R1 in the reaction path on B12N11C, which is beneficial to the adsorption formation of C _ 2H _ 2. The values of R2 and R3 were 49.63 and 41.41 kcal / mol, respectively. The rate control steps of the three paths were the dissociation of HCl molecules when the coadsorption state was transformed into transition state. The formation of defect sites in graphene changed the uniform electron distribution on the surface of graphene and made the electrons gather near the defect site. The perfect graphene PG enhanced the interaction between graphene and reactants. In particular, the adsorption of the two reactants by DVG was stronger than that of other graphene defects, and the adsorption energy of DVGMVGSWDG.C2H2 was -13.25 ~ 6.22 and -1.92 kcal / mol 路mol ~ (-1), respectively, and the adsorption energy of DVGMVGSWDG.C2H2 was -5.08 ~ 4.43 and -3.28 kcal / mol, respectively, and the reaction mechanism of three kinds of defective graphene was very similar. The activation energy of HCl decomposed into transition state is 39.46 渭 g 41.55 and 41.16 kcal / mol, respectively, and the activation energy of the active sites is lower on the carbon / carbon bond shared by the two connected five-member and six-member rings, respectively, when the rate control step is the transition from the co-adsorption state to the transition state, and the activation energy of DVG and SWDG are even lower than that of MVG, and the activation energy of MVG is much lower than that of MVG, and the activation energy of the active sites is even lower. It is more favorable to catalyze the hydrogen chlorination of acetylene.
【學位授予單位】：石河子大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ222.423;O643.36
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