Influence of Brønsted acid strength on conversion of carbenium ion by molecular simulation

doi:10.11949/j.issn.0438-1157.20170962

Abstract

Abstract:

The influence of Brønsted acid strength on catalytic reactivity of carbenium ion was systematically studied by density functional theory (DFT) calculations. Four typical reactions of C₄ carbenium ion as model compound, including hydrogen transfer, isomerization, β scission, and dehydrogenation, were simulated in five solid acid models with various acid strengths from weak-, strong-, even close to super-acid. The calculation results revealed that the reaction energy barrier decreased exponentially for hydrogen transfer reaction but decreased linearly for other three reactions with the increase of Brønsted acid strength. In weak-acid range, the sensitivities of reactions to acid strength from high to low was:hydrogen transfer > isomerization > β scission > dehydrogenation. Hydrogen transfer reaction had the lowest sensitivity in the strong-acid range. Calculation on ionic character of the organic fragments in transition states showed that reaction sensitivity to acid strength could be related to Mulliken charges of the transition state. The transition state with more Mulliken charge lead to stronger interaction with acid such that the activation energy barrier could be effectively reduced by increasing acid strength. The calculation was consistent with experimental conclusion and explained acid strength on production yield at the atomic level, which is of great significance to the development of new catalytic materials and modification of current catalysts.

Key words: Brønsted acid strength, carbenium ion, molecular simulation, Mulliken charge, catalysis, chemical reaction

摘要：

采用密度泛函理论（DFT）系统地研究了Brønsted酸强度与催化反应过程中正碳离子转化活性之间的关系。通过调整B酸模型电子分布构建5种酸强度模型，其酸强度范围覆盖弱酸、强酸以及超强酸。将C₄正碳离子作为模型化合物，计算其氢转移、异构化、脱氢、β断裂4种反应。计算结果表明氢转移的反应能垒与酸强度呈指数关系，其他3个反应能垒与酸强度呈线性关系。在弱酸范围内各反应对酸的敏感度由高到低排列如下：氢转移反应 > 异构化反应 > β断裂反应 > 脱氢反应，而在强酸范围内氢转移的酸敏感度最低。通过计算过渡态离子携带的电荷可知，反应活性对酸的敏感度与过渡态离子携带的Mulliken电荷有关。过渡态离子携带电荷越多，与酸性位的相互作用越强，所以提高酸强度时能更有效地降低反应能垒。该反应规律与实验结论相匹配，并且从原子层面解释了不同酸强度时实验产率变化的原因，对开发新型催化材料或者催化剂改性有重要意义。

关键词: Brø, nsted酸强度, 正碳离子, 分子模拟, Mulliken电荷, 催化, 化学反应

CLC Number:

TQ461.1

FU Jia, FENG Xiang, LIU Yibin, YANG Chaohe. Influence of Brønsted acid strength on conversion of carbenium ion by molecular simulation[J]. CIESC Journal, 2018, 69(2): 725-732.

付佳, 冯翔, 刘熠斌, 杨朝合. Brønsted酸强度对正碳离子转化方向影响的分子模拟[J]. 化工学报, 2018, 69(2): 725-732.

References 31

[1]	MACHT J, JANIK M J, NEUROCK M, et al. Mechanistic consequences of composition in acid catalysis by polyoxometalate keggin clusters[J]. Journal of the American Chemical Society, 2008, 130(31):10369-10379.
[2]	SONG W, NICHOLAS J B, HAW J F. A persistent carbenium ion on the methanol-to-olefin catalyst HSAPO-34:acetone shows the way[J]. Journal of Physical Chemistry B, 2001, 105(19):4317-4323.
[3]	HAW J F, ZHANG J, SHIMIZU K, et al. NMR and theoretical study of acidity probes on sulfated zirconia catalysts[J]. Journal of the American Chemical Society, 2000, 122(50):12561-12570.
[4]	YANG G, ZHOU L, HAN X. Lewis and Brönsted acidic sites in M4+-doped zeolites (M=Ti, Zr, Ge, Sn, Pb) as well as interactions with probe molecules:a DFT study[J]. Journal of Molecular Catalysis A Chemical, 2012, s 363/364:371-379.
[5]	胡思, 张卿, 尹琪, 等. 氢氧化钠-氟硅酸铵改性HZSM-5催化甲醇制丙烯[J]. 物理化学学报, 2015, 31(7):1374-1382. HU S, ZHANG Q, YIN Q, et al. Catalytic conversion of methanol to propylene over HZSM-5 modified by NaOH and (NH4)2SiF6[J]. Acta Physico-Chimica Sinica, 2015, 31(7):1374.
[6]	王彬, 王剑福, 张晓菲, 等. 二核铌钼硫簇NbMoSn-/0(n=3~7)掺杂体系的结构与成键性质的理论研究[J]. 化学学报, 2017, 75(3):307-320. WANG B, WANG J F, ZHANG X F, et al. Theoretical investigations on the structures and the chemical bonding of NbMoS n-/0(n=3-7) clusters[J]. Journal of Acta Chimica Sinica, 2017, 75(3):307-320.
[7]	FU J, FENG X, LIUBIN Y, CHAOHE Y. Effect of pore confinement on the adsorption of mono-branched alkanes of naphtha in ZSM-5 and Y zeolites[J]. Applied Surface Science, 2017, 423:131-138.
[8]	CHU Y, HAN B, FANG H, et al. Influence of acid strength on the reactivity of alkane activation on solid acid catalysts:a theoretical calculation study[J]. Microporous & Mesoporous Materials, 2012, 151(11):241-249.
[9]	FANG H, ZHENG A, LI S, et al. New insights into the effects of acid strength on the solid acid-catalyzed reaction:theoretical calculation study of olefinic hydrocarbon protonation reaction[J]. Journal of Physical Chemistry C, 2010, 114(22):54-81.
[10]	ZHENG X, BLOWERS P. An ab initio study of ethane conversion reactions on zeolites using the complete basis set composite energy method[J]. Journal of Molecular Catalysis A:Chemical, 2005, 229(1):77-85.
[11]	DELLEY B. From molecules to solids with the DMol3 approach[J]. Journal of Chemical Physics, 2000, 113(18):7756-7764.
[12]	ZHAO Y, TRUHLAR D G. A new local density functional for main-group thermochemistry, transition metal bonding, thermochemical kinetics, and noncovalent interactions[J]. Journal of Chemical Physics, 2006, 125(19):194101.
[13]	ZHAO Y, TRUHLAR D G. Improved description of nuclear magnetic resonance chemical shielding constants using the M06-L meta-generalized-gradient-approximation density functional[J]. Journal of Physical Chemistry A, 2008, 112(30):6794-9.
[14]	ZHAO Y, HOU T, HANSON E. Benchmark data for noncovalent interactions in HCOOH… benzene complexes and their use for validation of density functionals[J]. Journal of Chemical Theory and Computation, 2009, 5(10):2726-2733.
[15]	EYRING H. The activated complex in chemical reactions[J]. Journal of Chemical Physics, 1935, 3(2):107-115.
[16]	JANIK M J, MACHT J, IGLESIA E, et al. Correlating acid properties and catalytic function:a first-principles analysis of alcohol dehydration pathways on polyoxometalates[J]. Journal of Physical Chemistry C, 2009, 113(5):1872-1885.
[17]	CHU Y, HAN B, ZHENG A, et al. Influence of acid strength and confinement effect on the ethylene dimerization reaction over solid acid catalysts:a theoretical calculation study[J]. Journal of Physical Chemistry C, 2012, 116(23):12687-12695.
[18]	BRAND H, CURTISS L, ITON L E. Ab initio molecular orbital cluster studies of the zeolite ZSM-5(I):Proton affinities[J]. Journal of Physical Chemistry, 1993, 97(49):12773-12782.
[19]	HAW J F. Zeolite acid strength and reaction mechanisms in catalysis[J]. Cheminform, 2003, 34(3):5431-5441.
[20]	STEPANOV A G, ZAMARAEV K I. 13C solid state NMR evidence for the existence of isobutyl carbenium ion in the reaction of isobutyl alcohol dehydration in H-ZSM-5 zeolite[J]. Catalysis Letters, 1993, 19(2):153-158.
[21]	SAZAMA P, KAUCKY D, MORAVKOVA J. Superior activity of non-interacting close acidic protons in Al-rich Pt/H-* BEA zeolite in isomerization of n-hexane[J]. Applied Catalysis A:General, 2017, 533:28-37.
[22]	ASENSI M, CORMA A, MARTINEZ A. Skeletal isomerization of 1-butene on MCM-22 zeolite catalyst[J]. Journal of Catalysis, 1996, 158(2):561-569.
[23]	?EJKA J, WICHTERLOVA B, SARV P. Extent of monomolecular and bimolecular mechanism in n -butene skeletal isomerization to isobutene over molecular sieves[J]. Applied Catalysis A:General, 1999, 179(1/2):217-222.
[24]	BORONAT M, VIRUELA P, CORMA A. The skeletal isomerization of but-1-ene catalyzed by theta-1 zeolite[J]. Physical Chemistry Chemical Physics, 2001, 3(15):3235-3239.
[25]	MULLER S, LIU Y, KIRCHBERGER F M. Hydrogen transfer pathways during zeolite catalyzed methanol conversion to hydrocarbons[J]. Journal of the American Chemical Society, 2016, 138(49):15994-16003.
[26]	BORONAT M, VIRUELA P, CORMA A. Theoretical study on the mechanism of the hydride transfer reaction between alkanes and alkylcarbenium ions[J]. Journal of Physical Chemistry B, 1997, 101(48):386.
[27]	CARR R T, NEUROCK M, IGLESIA E, et al. Catalytic consequences of acid strength in the conversion of methanol to dimethyl ether[J]. Journal of Catalysis, 2011, 278(1):78-93
[28]	MACHT J, CARR R T, IGLESIA E. Consequences of acid strength for isomerization and elimination catalysis on solid acids[J]. Journal of the American Chemical Society, 2009, 131(18):6554-6565.
[29]	张剑秋. 降低汽油烯烃含量的催化裂化新材料探索[D]. 北京:石油化工科学研究院, 2001. ZHANG J Q. Novel catalytic materials for gasoline olefin reduction in the catalytic cracking process[D]. Beijing:Research Institute of Pertroleum Processing, 2001.
[30]	MARTINEZ-ESPIN J S, DE WISPELAERE K, JANSSENS T V W. Hydrogen transfer versus methylation:on the genesis of aromatics formation in the methanol-to-hydrocarbons reaction over H-ZSM-5[J]. ACS Catalysis, 2017, 7(9):5773-5780.
[31]	YU J G, ZHOU P, LI Q. New insight into the enhanced visible-light photocatalytic activities of B-, C-and B/C-doped anatase TiO2 by first-principles[J]. Physical Chemistry Chemical Physics, 2013, 15(29):12040-12047.