共查询到19条相似文献,搜索用时 109 毫秒
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稀土改性沸石除磷作为一种高效的除磷吸附剂已经被广泛地关注。但是,La和Ce改性沸石在吸附性能和除磷机制上的差异却未见报道。通过制备La和Ce改性商业购天然斜发沸石颗粒用于废水除磷,比较了二者的吸附能力、吸附动力学、物理性质、晶型、表面特征。研究表明:经过La和Ce改性的沸石吸附量提高了将近10倍,Ce改性沸石的吸附量略高于La改性沸石的吸附量。动力学拟合结果表明:La改性沸石对磷的吸附更符合伪二级动力学方程,而Ce改性沸石对磷的吸附更符合伪一级动力学。电镜和能谱分析发现Ce的负载量高于La的负载量。La和Ce都堆积在沸石表面,并未浸渍到沸石的孔径中。由于Ce在沸石表面的大量堆积增加了其比表面积,提高了其对磷的吸附能力。La和Ce改性沸石都形成了相同的晶体,二者具有相同的除磷机制。 相似文献
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非晶质的氧化硅-氧化铝和晶质的丝光沸石催化剂的表面上都有表面OH。可用硅烷偶联剂进行表面改性。由于催比剂的孔径不同以及硅烷偶联剂分子尺寸差异,对氧化硅-氧化铝的改性是在整个内、外表面上进行;而对丝光沸石,由于偶联剂分子不能进入沸石的内孔道中,所以这种改性只能在沸石窗口及外表面上进行。另外,沸石催化剂上酸量适中,酸中心分布较为理想,所以改性的沸石催化剂的选择性,总是比硅铝催化剂有较大增高。改性用的硅烷偶联剂以二甲基二乙氧基硅烷较为适宜。改性后的非晶质硅铝催化剂的对二甲苯选择性由14.6增到34.0%,晶质丝光沸石催化剂改性后由33.3增到43.7%。增加催化剂用量可提高对二甲苯的摩尔百分数到23%,接近它的理论值。 相似文献
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不同孔结构两亲性沸石的制备及其对相界面反应的催化性能 总被引:3,自引:0,他引:3
通过三甲基氯硅烷(TMS)对沸石表面进行修饰,制得了两亲性沸石样品TMS-Hβ, TMS-HY和TMS-HZSM-5,并采用X射线衍射、红外光谱、水饱和吸附量测定和酸碱滴定等手段对改性样品进行了表征. TMS对这三种母体沸石的改性结果有所不同: 对于HZSM-5沸石, TMS仅在外表面修饰; 对于Hβ沸石,少量TMS进入沸石孔道; 而对于HY沸石, TMS则导致沸石结构部分坍塌. 两亲性TMS-HZSM-5和TMS-Hβ沸石在乙酸异戊酯相界面水解反应中表现出明显优于各自母体沸石的催化性能. 两亲性沸石表面硅烷基的稳定性对其催化性能有一定的影响. 相对于TMS-HZSM-5沸石, TMS-Hβ沸石表面硅烷基的稳定性较强; 在较高的相界面反应温度下, TMS-Hβ样品仍能维持两亲性能,表现出较高的催化活性. 相似文献
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采用XRD表征了水蒸气和磷联合改性的HZSM-5沸石分子筛的结构.通过NH3-TPD和N2吸附脱附研究了样品的酸性和比表面.采用正庚烷的裂化反应研究了样品的裂化活性,研究结果表明,磷改性样品与母体样品相比,经过水蒸气处理后显示出较高的酸量和正庚烷裂化活性.上述结果首次用模型簇和计算量子化学方法进行了解释.采用Gaussian94软件包和PM3半经验量子化学方法对模型簇进行了全优化和频率分析.计算结果显示磷改性后样品的脱铝补硅反应热大于母体样品脱铝补硅反应热,从而显示出磷对骨架的稳定化作用. 相似文献
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新型两亲性HZSM-5沸石催化剂对环己烯水合相界面反应的催化研究 总被引:8,自引:0,他引:8
采用三甲基氯硅烷对HZSM-5沸石样品进行外表面修饰,制得两亲性沸石样品,该类两亲性沸石能分布于水、油两相界面处.改性后样品的红外光谱中末端硅羟基峰的强度明显降低,并出现CH3基团的C_H伸缩振动吸收峰,证实部分亲水性表面硅羟基被亲油性硅烷基团取代.这类两亲性样品在不加共溶剂及静置条件下,对环己烯水合相界面催化反应的催化活性远远高于改性前的HZSM-5沸石.由于该相界面反应是以孔道内为主的反应,三甲基氯硅烷经改性制备出的亲油性HZSM-5沸石也呈现出较高的活性. 相似文献
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A new strategy, releasing nitric oxide (NO) and adsorbing nitrosamines simultaneously by zeolitic materials in the digestive system, is validated in this paper. Three types of moisture-saturated molecular sieves, HZSM-5 zeolite, mesoporous zeolite, and mesoporous silica MCM-41, are used as NO-delivery vessels in mimic gastric juice after modification of γ-aminopropyltriethoxysilane (APTES). APTES modification dramatically increased the capability of zeolite and mesoporous silica in NO release in acidic solution, because more NO can be adsorbed in the composite and stored in the form of nitrite. Some composites released the NO 10 times more than their parent materials, and synchronously captured the carcinogen nitrosamines in mimic gastric juice. The influences of APTES modification on the porous structure and surface state of zeolite and mesoporous silica were investigated by XRD, N(2) adsorption, and FTIR tests, through which the mesoporous zeolite is proven to be the optimal support. With this hierarchical material a controllable APTES modification is realized in which a lot of aminopropyl groups are grafted in mesopores while the zeolitic structure is maintained, so the resulting sample exhibits a high capability in releasing NO and adsorbing nitrosamines. This investigation provides a clue for elevating the efficiency of zeolites in the application of life science. 相似文献
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Suppression of methane formation during Fisher-Tropsch synthesis using manganese-cobalt oxide supported on H-5A zeolite as a catalyst 下载免费PDF全文
In Fischer-Tropsch synthesis reaction, methane formation is one of the side reactions which must be suppressed in order to get better catalytic selectivity for light olefins. In the present study, we have modified cobalt based Fischer-Tropsch catalyst and developed a process to minimize methane production, consequently to produce maximum yield of light olefins. Manganese-cobalt oxide supported on H-5A zeolite catalyst was synthesized using modified H-5A zeolite, to increase its surface acid sites. Increased acidity of zeolite plays a major part in the suppression of methane formation during the Fischer-Tropsch reaction. The modified zeolite results in the electronic modification of catalyst surface by creating new active catalytic sites. The results are compared with other supported catalysts along with unmodified zeolite. Appreciable reduction in methane formation is achieved on modified zeolite supported catalyst in comparison with unsupported catalyst. 相似文献
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化学液相沉积法改性HY沸石及其对萘与叔丁醇择形烷基化反应的催化性能 总被引:1,自引:0,他引:1
采用化学液相沉积法,经异丁基三乙氧基硅烷修饰并用高温水蒸气处理得到了改性HY沸石.采用X射线衍射、低温N2吸附和脉冲式质量分析技术研究了改性样品骨架结构、比表面积、孔结构参数和吸附性质的变化,并考察了HY沸石及其改性后样品对萘与叔丁醇烷基化制备2,6-二叔丁基萘(2,6-DTBN)反应的催化性能.结果表明,改性后HY沸石的骨架结构基本不变,但比表面积增大,平均孔径缩小,孔口尺寸得到了一定调变.在改性后HY沸石催化剂上萘与叔丁醇烷基化反应活性下降,但催化剂择形性能明显提高,其2,6-DTBN/2,7-DTBN比可以达到6.62。 相似文献
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Frédéric Lefebvre Piotr Putaj Jean-Marie Basset XuXu Wang XianZhi Fu 《中国科学:化学(英文版)》2010,53(9):1862-1869
This review describes the work of two laboratories in the field of the modification of micro- and mesoporous molecular sieves through reactions with organometallic complexes. The modification of zeolites can occur inside the pore channels or on the external surface, depending on the size of the organometallic complex. When the modification occurs on the external surface, it results in a decrease of the pore entrance, which will lead in turn to a modification of the sorption properties of the zeolite, by decreasing the rate of the adsorption (mainly by a kinetic control). Such a material can be also used in catalysis, because the external acid sites, which are responsible for side-reactions, have been removed upon grafting. When small organometallic complexes are used, they can fill the channels and cages of the zeolite and react with internal hydroxyl groups. Due to the high acidity of zeolites, the reaction occurs very easily (for example at ?100 °C on faujasite), in contrast to what is observed on the external surface, therefore leading to high metal loadings. In that case, the modification of the sorption properties will be mainly related to a thermodynamic control. The resulting materials can be useful in catalysis, by combining the activity of the organometallic complex and properties (for example shape-selectivity) of the zeolite. Modification of mesoporous molecular sieves occurs always in the pores and results in altering of the sorption properties of the solid, by changing the interaction type between the sorbent and the sorbate. For example the sorption isotherm of alkanes is changed from type II to type III according to the IUPAC nomenclature. 相似文献
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Guocheng Lv Wei-Teh Jiang Shangping Xu Travis E. Larson 《Green Chemistry Letters and Reviews》2014,7(2):191-198
This study focused on using imidazolium of different chain lengths to modify the negatively charged zeolite. The modification involves a cation exchange process of the organic cations of ionic liquids (ILs) for the alkali and alkaline earth elements on zeolite surfaces. X-ray diffraction analyses revealed that the uptake of ILs was on the external surfaces. Fourier transform infrared analyses showed that different mechanisms were attributed to IL uptake on zeolite at below and above the external cation exchange capacity. After modification, the zeolite reversed its surface charge to positive, thus enhancing adsorptive removal of anionic contaminants such as chromate from water. At the same time, the modified zeolite increased their total organic carbon content, and thus could promote better adsorptive removal of hydrophobic organic contaminants from water, too. These features enable IL-modified zeolite to be used as inexpensive sorbents for the removal of multi-types of contaminants from water simultaneously. 相似文献