B、Al、Ga同晶取代丝光沸石的从头计算

用从头计算Hartree Fock方法研究了B、Al、Ga等同晶取代进入丝光沸石骨架后可能存在的位置,确定了与电荷平衡质子结合的氧位置,考察了B、Ga等杂原子进入骨架对丝光沸石Brnsted酸性的影响.能量分析表明B、Al、Ga在丝光沸石骨架中最容易进入T3和T4位;当Al、Ga在T4位时,质子与O10结合为能量最低即最稳定结构,而当B在T4位时,质子与O2或O10结合比较稳定.质子亲合势分析表明与硅铝丝光沸石相比, B和Ga进入骨架导致丝光沸石分子筛的Brnsted酸性有所减弱,其酸性依次为：B ZSM 5Ga ZSM 5< Al ZSM 5.     

预吸附吡啶增强二甲醚在丝光沸石上羰基化反应的稳定性

 对比研究了二甲醚在氢型丝光沸石和吡啶修饰的氢型丝光沸石上的二甲醚羰基化反应. 结果表明, 吡啶预吸附大大提高了二甲醚羰基化反应的稳定性, 并且在 473 K 反应 48 h 能够保持约 30% 的乙酸甲酯收率. 原位红外光谱和 NH3 程序升温脱附研究发现,吡啶吸附在 12 元环内, 而 8 元环内的酸性位基本不受干扰. 129Xe 核磁共振研究表明, 未经修饰的丝光沸石反应后孔道严重堵塞, 而吡啶修饰的分子筛反应后孔道基本不变. 因此, 12 元环内酸性位是积炭失活位, 吡啶吸附抑制了 12 元环内积炭的生成, 二甲醚羰基化反应能够在 8 元环内活性位上顺利进行.     

空间位阻对吡啶过度修饰导致丝光沸石二甲醚羰基化酸性位中毒后 再生的诱导作用

当今世界环境与能源问题日益加剧,乙醇作为一种重要的清洁燃料和化学品受到广泛关注,迫切需要探索高效的乙醇合成方法,以满足日益增长的市场需求.其中,将煤炭、生物质、页岩气等为原料合成的二甲醚通过羰基化反应制乙酸甲酯、乙酸甲酯加氢制乙醇的串联式绿色乙醇合成路线具有重要的工业应用前景.然而,在二甲醚羰基化过程中,丝光沸石分子筛易积碳失活,阻碍了其工业应用.吡啶改性可以毒化丝光沸石12元环孔道中的酸性位,抑制积碳的形成,进而大幅度提高该催化剂的稳定性,但同时会使其催化活性降低约40%–50%.为了解决这一难题,本文从分子水平上研究了吡啶吸附行为以及分子筛骨架空间位阻对丝光沸石催化剂上二甲醚羰基化反应的影响.通过解析丝光沸石的骨架结构,我们发现位于8元环侧袋和12元环孔道共用孔壁处O_2位置上的酸性位是二甲醚羰基化反应的活性位,但它们在吡啶修饰过程中易被毒化而使催化剂活性下降.密度泛函理论计算结果表明,吡啶分子因受分子筛骨架空间位阻的影响,在O_2处酸性位上的吸附较弱.而实验结果也表明,通过673 K热处理可以再生被吡啶毒化的O_2活性位,而并不影响12元环孔道中其它吡啶分子的吸附.因此,该热处理方法可以使丝光沸石催化剂保持高稳定性的同时,将二甲醚羰基化反应催化活性提高约60%.本文从分子水平证明了丝光沸石中O_2活性位对二甲醚羰基化反应的重要作用,为绿色乙醇合成技术研究提供了新的思路,也为其它高效分子筛催化体系设计提供了有益的参考.     

纳米丝光沸石分子筛的合成及表征

在水热条件下制备丝光沸石的纳米晶.研究了合成条件、不同添加剂、动态晶化等对沸石粒径的影响.结果表明,反应物中较高的碱度,较低的晶化温度,加入NaCl和Na2SO4金属盐做成核助剂,及动态晶化有利于纳米丝光沸石分子筛的合成.     

以水玻璃为原料合成丝光沸石

丝光沸石是一种高硅分子筛,其结构与A、X、Y型分子筛不同,它有比例很大的五元环,且成对地相互并联。它的主孔道是呈直筒形的十二元环,其截面成椭圆形,平均直径为6.6,化学组成可表示为:M_2/_nO·Al_2O_2·WSiO_2·XH_2O。上式中,M是可进行离子交换的金属阳离子,n是金属阳离子M的价数;W是丝光沸石的硅铝比(SiO_2/Al_2O_3克分子),其值约为10～12,X约6～7。丝光沸石耐酸、耐热及催化活性都显著超过X、Y型分子筛,可以用作干燥剂、吸附剂和烃类转化的催化剂。目前丝光沸石已在工业上用于硝酸厂尾气氧化氮的吸附回     

Fe在丝光沸石骨架中取代位置的DFT研究

用密度泛函理论(DFT)方法研究了Fe同晶取代进入丝光沸石骨架后可能存在的位置,并确定了与电荷平衡质子结合的氧位置.能量分析表明Fe在丝光沸石骨架中最容易进入T2和T4位;当Fe分别在T2和T4位时,电荷平衡质子与O2和O10结合的可能性最大.     

双阳离子体系高通量丝光沸石膜的合成及其乙酸脱水应用（英文）

采用多种表征技术详细研究了碱金属阳离子对丝光沸石分子筛膜生长和渗透汽化性能的影响。结果表明,Li~+、Na~+、K~+和Cs~+以及Na~+-Li~+、Na~+-K~+和Na~+-Cs~+的不同离子组合对丝光沸石分子筛膜的形貌和性能有很大影响。研究发现,碱金属阳离子通过促进硅在初始凝胶中的溶解,在硅铝酸盐的重排过程中起到结构导向作用,进而起到构筑丝光沸石晶体骨架结构的作用。Na~+对丝光沸石晶体的结晶有明显的促进作用,而Li~+、K~+和Cs~+在相同的结晶时间内表现出较慢的结晶速率。在合成凝胶中用K~+代替少量Na~+可以显著改善膜表面的亲水性。特别是合成凝胶中Na~+/K~+比(n_(Na~+)/n_(K~+))为2时,形成了更致密、更亲水的丝光沸石分子筛膜,显示出更高的渗透汽化性能。对于90℃下HAc质量分数为90%的HAc/H_2O混合物的分离,该膜显示出2.67 kg·m~(-2)·h~(-1)的高渗透通量和约为4 000的分离因子。此外,最优条件下合成的丝光沸石分子筛膜在90℃下长达240 h渗透汽化分离90%的HAc/H_2O混合物依然显示优越的酸稳定性。     

丝光型Si-Fe沸石表面酸碱性的研究

本文藉助红外光谱(IR)、程序升温脱附—质谱(TPD—MS)等手段研究了丝光型Si—Fe沸石分子筛表面的酸碱性质。结果表明:丝光沸石骨架中的铝原子被铁原子取代以后,其表面酸性大为减弱,但其碱性相对增强,Si—Fe沸石分子筛大部分表面羟基的酸性很弱,仍有一定量的L酸中心存在于沸石的表面上。     

氨在丝光沸石位置(Ⅵ)上的吸附

用量子化学近似方法,CNDO/2方案,在选取原子簇(AO)_3SiO~*HAl(OA)_2OSi(OA)_3的基础上,采用“氢键式”的吸附模型,计算了NH_3在丝光沸石位置(Ⅵ)上的吸附。结果表明:稳定吸附距离约为2.3A到2.75A(O与N间),其中2.5A为最优吸附位置,它联系着表征Bronsted酸强度的最大吸附热33.80kcal/mol(计算值)、最低的质子迁移势垒及OH振动频率向低频的最大位移。这些结果定性地与文献报道的实验事实一致。     

小晶粒丝光沸石合成的研究

丝光沸石早在20世纪40年代就由Barfer首次合成出来，由于丝光沸石具有高的硅铝比，因而有优良的耐热、耐酸性能，工业上广泛用作气体或液体混合物分离的吸附剂及石油化工与精细化工催化剂．相对于常规粒度分子筛，小晶粒分子筛具有独特的结构特性，如：更大的外表面积、更多的外表面活性中心和暴露在外的晶胞、短而规整的孔道，从而决定了其具有更大的转化大分子能力，及在其上合成后改性技术更易实现．这些特性使得小晶粒分子筛用于催化裂化、加氢裂化、链烷烃的加氢异构化等炼油工业过程中．因此，如何合成粒径更小以至成为纳米级的丝光沸石近年来引起了人们极大的兴趣，成为催化领域目前受重视的研究课题．     

改性丝光沸石上甲醇胺化的研究─—水汽处理对沸石性能的影响

采用吡啶饱和中毒、ＮＨ３－ＴＰＤ、静态吸附、ＩＲ、ＸＲＤ和分子探针反应等方法，研究了用于甲醇胺化反应的改性丝光沸石催化剂性质．结果发现，丝光沸石水汽处理脱铝后的孔道结构基本不变，晶胞的收缩和非骨架铝在孔道内的沉积，不足以严重限制甲醇胺化产物三甲胺在孔道内的进出；且在改性后，由于非骨架铝在孔道内的沉积，分子筛内表面的微环境发生了变化，致使有些活性位不利于三甲胺的吸附和生成，从而有利于进一步提高目的产物二甲胺的选择性．     

Dynamics of sorption of cyclopropane in various H- and Na-zeolites

The frequency response (FR) method has been applied to study the dynamics of cyclopropane adsorption in faujasite, mordenite, beta and ZSM-5 zeolites containing Brönsted or Lewis acid sites in the concentration range of 0.586-0.772 meq/g.     

碱处理丝光沸石的表征及其催化合成乙基叔丁基醚的性能

 研究了碱处理对丝光沸石物相、酸性质和催化合成乙基叔丁基醚(ETBE)性能的影响,并采用XRD,NH3-TPD,吡啶吸附的IR,SEM和N2吸附等方法对其进行了表征. 结果表明,碱处理含有模板剂的丝光沸石的相对结晶度、酸量、比表面积和孔容都增大. 碱处理已脱除模板剂的丝光沸石的相对结晶度、酸量、比表面积和孔容都减小. 碱处理含有模板剂的丝光沸石催化合成ETBE的活性明显高于碱处理已脱除模板剂的丝光沸石,在80 ℃左右即可达到最高活性点,其催化异丁烯的最高转化率为58%,比未经碱处理样品上异丁烯的最高转化率高约13%.     

A density functional theory study of molecular and dissociative adsorption of H2 on active sites in mordenite

Adsorption and chemisorption of H2 in mordenite is studied using ab initio density functional theory (DFT) calculations. The geometries of the adsorption complex, the adsorption energies, stretching frequencies, and the capacity to dissociate the adsorbed molecule are compared for different active sites. The active centers include a Br?nsted acid site, a three-coordinated surface Al site, and Lewis sites formed by extraframework cations: Na+, Cu+, Ag+, Zn2+, Cu2+, Ga3+, and Al3+. Adsorption properties of cations are compared for a location of the cation in the five-membered ring. This location differs from the location in the six-membered ring observed for hydrated cations. The five-membered ring, however, represents a stable location of the bare cation. In this position any cation exhibits higher reactivity compared with the location in the six-membered ring and is well accessible by molecules adsorbed in the main channel of the zeolite. Calculated adsorption energies range from 4 to 87 kJ/mol, depending on electronegativity and ionic radius of the cation and the stability of the cation-zeolite complex. The largest adsorption energy is observed for Cu+ and the lowest for Al3+ integrated into the interstitial site of the zeolite framework. A linear dependence is observed between the stretching frequency and the bond length of the adsorbed H2 molecule. The capacity of the metal-exchanged zeolite to dissociate the H2 molecule does not correlate with the adsorption energy. Dissociation is not possible on single Cu+ cation. The best performance is observed for the Ga3+, Zn2+, and Al3+ extraframework cations, in good agreement with experimental data.     

The interaction mechanisms between aqueous solutions of137Cs and134Ba radionuclides and local natural zeolites for an deactivation scenario

¹³⁷Cs and¹³⁴Ba were removed from synthetic aqueous solutions by means of natural zeolites of Slovakian origin. The equilibrium sorption behavior of Cs and Ba ions onto clinoptilolite and mordenite were studied under static as well as dynamic experimental conditions. Both Freundlich and Langmuir isotherms describe satisfactory by Cs and Ba adsorption on the zeolites studied. The elution of Cs and Ba ions from zeolite columns after the loading cycle was undertaken additionaly, in order to compare column operating runs of various exchanged zeolite forms.     

Superior Storage Performance for NO in Modified Natural Mordenite

Natural mordenite (NMOR), modified by acid treatment and ion‐exchange, was employed for NO adsorption in the present study. The NO storage capacity of modified NMOR was greatly improved compared with its original correspondents, mainly due to the preservation of crystalline structure and the improvement of surface area of NMOR. Among all the modified NMOR, Ni‐NMOR exhibited the highest adsorption capacity for NO (1.20 mmol·g^?1) in the presence of 10% O₂ at 308 K. The influence of the main ingredients in flue gas on the storage capacity of NMOR for NO had also been investigated. In general, H₂O, CO₂ and SO₂ all displayed negative impact on NO adsorption due to their competitive adsorption on the surface of NMOR with NO, while the presence of O₂ greatly improved the adsorption of NO because of the formation of NO₂ and N₂O₃. Moreover, Ni‐NMOR exhibited high efficiency for NO_x removal through the NO_x adsorption‐plasma discharge process.     

甲胺化反应催化剂稀土改性丝光沸石的研究

研究了稀土改性丝光沸石催化剂对常压固定床上甲胺化反应的活性及选择性的影响，结果表明，以钇改性丝光沸石催化剂的活性及对二甲胺的选择性最佳。催化剂表征结果表明，稀土改性丝光沸石主要是引起丝光沸石中Ｂ酸中心发生变化，而对丝光沸石的晶体结构及表面硅铝原子比基本不产生影响。稀土改性能增强催化剂的热稳定性，延长催化剂的寿命。     

Evaluation of cesium sorption on natural mordenite

The kinetic and equilibrium sorption behaviors of Cs⁺ on mordenite, a zeolite which can sorb cesium well, were investigated by using the batch method. Cesium-137 and the stable CsNO₃ were used as tracer and carrier to study the influences on Cs⁺ sorption behaviors by changing Cs⁺ initial concentration, pH value, particle size of mordenite and experimental temperature. The equilibrium was reached in 3 days and the saturated amount of cesium sorbed is about 0.19 kg Cs/kg NM. The sorption data at 25°C and 90°C were fitted to Freundlich sorption model and nonlinear isotherms were found. However, linear isotherm was applicable with a Cs⁺ initial concentration less than 10^–3M. The decrease of Cs⁺ sorption at elevated temperature suggested the sorption reaction was exothermic. The use of centrifugation to separate the liquid from solid phases in traditional batch techniques was not suitable to the kinetic experiment of Cs sorbed by mordenite for lower concentrations.     

表面富硅型ZSM-5分子筛的甲醇制对二甲苯联产低碳烯烃催化性能

通过表面化学改性制备表面富硅型ZSM-5分子筛,采用XRD、N2等温吸附-脱附、TEM、NH3-TPD和Py-FTIR等手段对其孔结构和酸性质进行了表征,考察其甲醇制对二甲苯联产低碳烯烃反应的催化性能。结果表明,引入Zn使催化剂中一部分强酸转变为中强酸,并增加了具有脱氢作用的Zn-L酸中心,提高乙烯和丙烯的选择性;Mg改性不仅可以调节孔道的择形性,而且增加了L酸中心的数量,有利于PX的生成;不同硅源的多次硅沉积使得SiO_2可以更均匀地沉积在外表面,调变催化剂的酸性质和孔结构,从而进一步提高对二甲苯及乙烯和丙烯的选择性。最终,二甲苯中对位选择性可达到87.1%,二甲苯及乙烯和丙烯的选择性达到61%,乙烯在C_2烃类的选择性高达97.8%,丙烯在C_3烃类中选择性高达90.6%。     

Adsorption Characteristics of Natural Erionite, Clinoptilolite and Mordenite Zeolites from Mexico

Nitrogen sorption properties inherent to some natural zeolites from Mexico, such as erionites, clinoptilolites and mordenites, are determined and compared with corresponding sorption properties of homologous synthetic or acid modified forms. The mineralogies of natural zeolites are determined by X-ray analysis. N₂ low-pressure hysteresis loops are displayed by some substrata while are absent in others; key factors for this phenomenon to occur are the micropore structure and the ion-exchange treatment to which the natural precursors are subjected. Argon sorption at 76 K on selected samples evidence further the strong adsorption and the pore blocking effects at pore necks in the zeolites.