Y分子筛中硅铝桥羟基结构调变规律的理论研究
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摘要
Y分子筛中B酸的酸性在催化过程中起着主要作用,其结构的变化反应了B酸的强弱。采用周期性模型模拟了HY、[AlO]+/HY及[Al(OH)]2+/HY中B酸位置的稳定结构,从第一性原理和分子动力学两方面研究了B酸中心的结构变化与周围微环境的关系。通过几何结构、电子结构和分子力学统计结果发现,非骨架铝物种的加入增加了B酸的强度,且与H原子在12元环上的分布数量有关系,H原子越少,其酸性越强。B酸中心H原子与O原子结合能力越弱,并且H原子失去电子越多,B酸酸性越强。非骨架铝的加入能增强B酸的酸性,且[Al(OH)]2+非骨架铝物种对B酸性质的影响明显。研究可为分子筛B酸调变提供理论支持。
Br?nsted acid in Y zeolite plays a key role in the processes of catalyst,and the structure reflects the strength of B acid.The stable structures of Br?nsted acid sites of HY, [AlO]+/HY, and [Al(OH)]2+/HY were simulated by periotic models. The relationship between the structures of Br?nsted acid sites and its environments was identified by combination of dynamic simulation with DFT calculation. By analyzing the structure and electronic permanent, together with the statistical results of molecular dynamics,it can be found that the strength of Br?nsted acid can connected with the number of H atoms in the 12 membered ring that the small number.The weaker the binding ability of H atoms to O atoms in B acid center is,and the more electrons H atoms lose,the stronger the B acid acidity is.The addition of extra-framework aluminum can enhance the acidity of B acid,and [Al(OH)]2+has more obvious effect on B acid properties.These results can lead the synthetic and modification of B acid site in a theoretical support.
Br?nsted acid in Y zeolite plays a key role in the processes of catalyst,and the structure reflects the strength of B acid.The stable structures of Br?nsted acid sites of HY, [AlO]+/HY, and [Al(OH)]2+/HY were simulated by periotic models. The relationship between the structures of Br?nsted acid sites and its environments was identified by combination of dynamic simulation with DFT calculation. By analyzing the structure and electronic permanent, together with the statistical results of molecular dynamics,it can be found that the strength of Br?nsted acid can connected with the number of H atoms in the 12 membered ring that the small number.The weaker the binding ability of H atoms to O atoms in B acid center is,and the more electrons H atoms lose,the stronger the B acid acidity is.The addition of extra-framework aluminum can enhance the acidity of B acid,and [Al(OH)]2+has more obvious effect on B acid properties.These results can lead the synthetic and modification of B acid site in a theoretical support.
引文
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[18]魏潘鹏,焦健豪,王焕,等.12元环硅铝分子筛酸性及其B酸中心可接近性探究[J].石油化工高等学校学报,2018,31(4):27-31.Wei P P,Jiao J H,Wang H,et al.The acidity and accessibility of aluminosilicate zeolites with 12-ring channels[J].Journal of Petrochemical Universities,2018,31(4):27-31.
[2] Li S,Huang S J,Shen W,et al.Probing the spatial proximities among acid sites in dealuminated HY zeolite by solid-state NMR spectroscopy[J].The Journal of Physical Chemistry C,2008,112(37):14486-14494.
[3]黄朝晖,刘乃旺,姚佳佳,等.USY分子筛表面酸性的调变及其在催化脱除芳烃中烯烃的应用[J].化工进展,2016,35(1):138-144.Huang Z H,Liu N W,Yao J J,et al.Surface acid modification of zeolite and its application in removal of olefins in aromatics[J].Chemical Industry and Engineering Progress,2016,35(1):138-144.
[4]张畅,秦玉才,高雄厚,等.Ce改性对Y型分子筛酸性及其催化转化性能的调变机制[J].物理化学学报,2015,31(2):344-352.Zhang C,Qin Y C,Gao X H,et al.Modulation of the acidity and catalytic conversion properties of Y zeolites modified by cerium catio[J].Acta Physico-Chimica Sinica,2015,31(2):344-352.
[5]于善青,田辉平,朱玉霞,等.稀土离子调变Y型分子筛结构稳定性和酸性的机制[J].物理化学学报,2011,27(11):2528-2534.Yu S Q,Tian H P,Zhu Y X,et al.Mechanism of rare earth cations on the stability and acidity of Y zeolites[J].Acta PhysicoChimica Sinica,2011,27(11):2528-2534.
[6]苏琼,陈辉,陆善祥.催化裂化催化剂的酸性调变方法[J].现代化工,2011,31(S1):43-46.Su Q,Chen H,Lu S X. Different acidity modification methods of FCC catalysts[J]. Modern Chemical Industry,2011,31(S1):43-46.
[7]潘惠芳,苏建明,王彪,等.超稳Y沸石催化剂的积炭行为和酸性调变[J].石油学报(石油加工),1992(3):30-36.Pan H F,Su J M,Wang B,et al.Coking behaviour and acidity accommodations of usy zeolite catalysts with various Si/Al ratios[J].Acta Petrolei Sinica(Petroleum Processing Section),1992(3):30-36.
[8] Li S,Zheng A,Su Y,et al.Br?nsted/Lewis acid synergy in dealuminated HY zeolite:A combined solid-state NMR and theoretical calculation study[J].Journal of the American Chemical Society,2007,129(36):11161-11171.
[9] Bhering D L,Ramírez-Solís A,Mota C J A. A density functional theory based approach to extra-framework Aluminum species in zeolites[J].The Journal of Physical Chemistry B,2003,107(18):4342-4347.
[10] Mota C J A,Bhering D L,Rosenbach N.A DFT study of the acidity of ultrastable Y zeolite:Where is the Br?nsted/Lewis acid synergism[J].Angewandte Chemie International Edition,2004,43(23):3050-3053.
[11] Katada N,Kageyama Y,Takahara K,et al.Acidic property of modified ultrastable Y zeolite:Increase in catalytic activity for alkane cracking by treatment with ethylenediaminetetraacetic acid salt[J].Journal of Molecular Catalysis A:Chemical,2004,211(1-2):119-130.
[12] Liu C,Li G,Hensen E J M,et al.Nature and catalytic role of extraframework aluminum in Faujasite zeolite:A theoretical perspective[J].ACS Catalysis,2015,5(11):7024-7033.
[13] Liu C,Li G,Hensen E J M,et al.Relationship between acidity and catalytic reactivity of Faujasite zeolite:A periodic DFT study[J].Journal of Catalysis,2016,344:570-577.
[14] Perdew J P,Chevary J A,Vosko S H,et al.Atoms,molecules,solids,and surfaces:Applications of the generalized gradient approximation for exchange and correlation[J].Physical Review B,1992,46(11):6671-6687.
[15] Perdew J P,Burke K,Wang Y. Generalized gradient approximation for the exchange-correlation hole of a many-electron system[J].Physical Review B,1996,54(23):16533-16539.
[16] Hammer B,Hansen L B,N?rskov J K.Improved adsorption energetics within density-functional theory using revised PerdewBurke-Ernzerh of functional[J].Physical Review B,1999,59(11):7413.
[17]黄哲,李强,莫周胜,等.密度泛函理论研究Y分子筛的Br?nsted酸性[J].石化技术与应用,2014,32(5):398-403.Huang Z,Li Q,Mo Z S,et al. Study on the Bronsted acidity of Y zeolite by density functional theory[J]. Petrochemical Technology&Application,2014,32(5):398-403.
[18]魏潘鹏,焦健豪,王焕,等.12元环硅铝分子筛酸性及其B酸中心可接近性探究[J].石油化工高等学校学报,2018,31(4):27-31.Wei P P,Jiao J H,Wang H,et al.The acidity and accessibility of aluminosilicate zeolites with 12-ring channels[J].Journal of Petrochemical Universities,2018,31(4):27-31.