Structural and acidic characteristics of Cu-Ni-modified acid-leached mordenites

Two series of dealuminated Na-mordenite zeolites (DML and DMH) were impregnated, in comparison with the parent nondealuminated NaMSP, in aqueous nitrate solutions of Cu and Ni to achieve varying loadings for both of the cations. These samples were characterized by N(2) adsorption, XRD, DSC of ammonia desorption, ammonia volumetric sorption, IR of ammonia adsorption, and FTIR-photoacoustic (FTIR-PAS) techniques. The FTIR-PAS spectrum of CuNi-loaded NaMSP shows a band at 935 cm(-1) ascribed to O(3)Siz.sbnd;Oz.sbnd;SiO(3) linkages produced as a result of dealumination caused by the synergistic effect of Cu and Ni cations under the preparation conditions. As a confirmation, this band was intensified upon acid dealumination (DML) where, at the extent of dealumination (DMH), collapsing of the zeolite structure was obtained subsequent to cation modification. In addition, the dealumination effect was markedly enhanced upon increasing the load of Cu in proportion to Ni. A total erosion of OH group characteristics of Siz.sbnd;(OH)z.sbnd;Al at 3610 cm(-1) was depicted when the Ni content exceed that of Cu where it did not show any change when the Cu content surpasses that of Ni. The amount of adsorbed ammonia measured volumetrically was enlarged after dealumination as well as after increasing the contents of the modificating cations. The IR study of ammonia adsorption revealed a band at 1428 cm(-1), in either nondealuminated or dealuminated-modified samples, assigned to stronger Bronsted acid sites than those at 1455 cm(-1). The band at 1428 cm(-1) was markedly enhanced in the latter samples than in the former. This was due in part to the replacement of the protons by cations, producing sufficiently mobile protons. In conformity, DeltaH values obtained for DSC effects via ammonia desorption were enhanced after dealumination. Other correlations with XRD and surface texturing on one hand and the structural variations following cations incorporation on the other hand are evaluated and discussed.     

脱铝丝光分子筛应用于MTP反应:Al的落位和晶体形貌的影响

甲醇制烯烃/丙烯工艺(MTO/MTP)是当前煤基碳资源绿色催化转化的重要过程之一.在MTO/MTP工艺中,分子筛通常面临低碳烯烃选择性低、水热稳定性差和寿命短等挑战.开发高选择性和高稳定性的分子筛催化剂对煤基乙烯/丙烯等化学品的工业生产具有重要意义.本文选择了具有12元环孔道的低硅丝光分子筛(Si/Al=6)为母体,对其进行脱铝处理制备了一系列不同Al含量的高硅丝光(Si/Al=51?436)催化剂.通过N_2-吸附、NH₃程序升温脱附、羟基红外光谱、CD3CN-IR和Py-IR等技术对脱铝前后分子筛的孔道结构、酸密度、酸强度和铝的落位进行了深入研究,并将其与MTP反应性能进行关联.结果表明,骨架Al的脱除在晶体中引入了介孔.随着Si/Al的提高,分子筛的酸量和酸强度同时降低.深度脱铝后的丝光分子筛中只存在少量位于8元环侧口袋与12元环交叉口处的T2和T4位Al原子.Si/Al高于150的脱铝丝光分子筛在MTP反应中丙烯选择性高达63%,丙烯/乙烯的比值高达10.与低硅丝光分子筛相比,深度脱铝的丝光分子筛表现出更好的稳定性和更长的寿命.相同反应条件下,低硅丝光样品(Si/Al=6)反应2 h后完全失活(转化率低于10%),而高硅丝光样品(Si/Al=274)反应132 h后转化率仍然高于80%.丝光分子筛在脱铝处理后催化性能得到大幅提升的原因为:酸密度和酸强度的降低显著改变了双循环机理历程,反应中芳烃循环的比重下降,烯烃循环得到了增强,进而提高了丙烯选择性并抑制了积碳速率.此外,脱铝后保留下来的Al原子(活性中心)位于12元环孔道,其大孔结构与脱铝引入的介孔孔道为反应物、中间体及产物的扩散提供了充足的空间,进一步抑制了副反应的发生和积碳的生成.进一步研究丝光分子筛形貌对MTP反应的影响发现,丝光分子筛尺寸的变化不改变产物分布,但显著影响催化剂寿命,其原因在于丝光分子筛c-轴长度的增加使得烃池物种的扩散受到限制,导致催化剂的寿命降低.     

Zur Selektivität des Ionenaustausches an unterschiedlich dealuminierten Mordeniten

Selectivity of Ion Exchange on Dealuminated Mordenites Ion Exchange selectivity of Na-mordenites dealuminated by HCl for K⁺, Mg⁺⁺, Ca⁺⁺, and Ba⁺⁺ ions was investigated. Selectivity for K⁺ ions decreases nearly linear with increasing dealumination of mordenite whereas the selectivity for alkaline earth ions increases. Due to dealumination of mordenite its characteristical preference for monovalent towards divalent cationa is reversed.     

~(29)Si MAS-NMR STUDIES ON DEALUMINATION OF MORDENITE

A series of different H-mordenites from acid leaching and steam calcination have beenmeasured with ~(29)Si NMR. Through analysis of these solid-state ~(29)Si NMR spectra, theresults related to dealumination process of mordenite are obtained. It is shown that mor-denite is combined by four kinds of non-equivalent Si (or Al) via oxygen bridges. The deal-umination order is T(1), T(2), T(4) and T(3). The dealuminated amount in the non-equivalentsites during different dealumination processes has also been discussed in detail.     

丝光沸石水蒸气/酸浸渍脱铝的多核固体核磁共振研究

采用¹H,²⁹Si,²⁷Al魔角旋转固体核磁共振(MASNMR)及¹H-²⁹Si交叉极化(CP)技术研究丝光沸石水蒸气/酸浸渍脱铝过程中各种铝物质的结构与性质.结果表明,丝光沸石上骨架铝原子在水分子作用下,生成非骨架四配位铝物质[Al(OH)₃(H₂O)],分别在²⁷Al谱δ45和¹H谱δ3.0处出现共振信号,这种铝物质不同于扭曲四配位铝,在高温下进一步水合生成Al(OH)₃(H₂O)₂和Al(OH)₃(H₂O)₃,即非骨架五配位和六配位铝物质.¹H-²⁹SiCP和¹H谱证实,水蒸气脱铝使丝光沸石产生了大量的硅羟基和铝羟基.     

Catalytic properties of zeolites MCM-22 and NU-87 in disproportionation of toluene

The catalytic properties of MCM-22 and NU-87 were investigated for the disproportionation of toluene to produce benzene and xylene, and the results were compared with those obtained over mordenite, beta and ZSM-5. It turns out that dealumination of MCM-22 removes selectively the acid sites from the external surface and thus suppresses the secondary isomerization of p-xylene, enhancing the para-selectivity. This indicates that the dealuminated MCM-22 is a promising catalyst for the selective formation of p-xylene from toluene disproportionation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Surface photochemistry of Rh(CO)2 on zeolite Y-production of a stable coordinatively unsaturated rhodium monocarbonyl surface species at room temperature

The photochemical production and chemical reactivity of a new coordinatively unsaturated rhodium monocarbonyl species on the surface of dealuminated zeolite Y over a temperature range of 300-420 K and a pressure range from 10(-5) to 20 Torr has been studied. Using high vacuum techniques and transmission infrared spectroscopy, ultraviolet irradiation (350 +/- 50 nm) of supported Rh(CO)(2) surface species led to the production of stable, but reactive, =Rh(CO) surface species, characterized by an infrared band at 2023 cm(-1). The coordinatively unsaturated =Rh(CO) species convert to less reactive and coordinatively saturated Rh(CO) by thermal treatment above 370 K. The Rh(CO) species were characterized by an infrared band at 2013 cm(-1). An explanation of the mode of bonding of the rhodium monocarbonyl species to the zeolite surface is provided. Coordinatively unsaturated =Rh(CO) species captured N(2), H(2), and O(2) gas molecules near room temperature to produce a variety of mixed ligand rhodium surface complexes of the form Rh(CO)(N(2)), Rh(CO)(H(2)), Rh(CO)(H)(2), Rh(CO)(H), Rh(CO)(O), and Rh(O). Infrared band assignments for the new species are provided. The work provides new insight into the photochemical behavior of Rh(CO)(2) species supported on high-area zeolite materials and may improve our understanding of the role of active rhodium monocarbonyl species in the development of heterogeneous photocatalysts.     

Characterization of short-time dealumined HZSM-5 zeolites

Temperature-programmed desorption (TPD) of water was applied to characterize short-time dealuminated HZSM-5 zeolites. Using a regularization method, distribution functions of the effective desorption energy of water were calculated. The results clearly show that during dealumination a new adsorption site is formed which can be attributed to non-framework or transient aluminium species. The highest concentration of these sites was observed for a dealumination time of 25-30 min. NO adsorption studies support this result. Furthermore, it could be concluded that the heterogeneity and the average acid strength of the remaining Si-OH-Al groups of the dealuminated samples do not change compared to the Si-OH-Al groups of the parent HZSM-5 zeolite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intercalation of Methylene Blue into Mordenites: Role of Zeolite Acidity

The intercalation of methylene blue into mordenite zeolite was studied by diffuse reflectance spectroscopy. Methylene blue was incorporated into mordenite by ion exchange in the aqueous phase. Samples of sodium, calcium and protonated mordenite were subjected to methylene blue loading. The DR spectra observed shortly after mixing the dye with sodium mordenite are those of aggregated species adsorbed on the surface. The period of intercalation is very short (1 h) for protonated mordenite and is too long for calcium mordenite (7 days). The hydrated mordenite samples containing intercalated methylene blue show two 660 and 610 nm bands which are assigned to monomeric and dimeric species of methylene blue, respectively. Upon dehydration a new band at 745 nm is observed which corresponds to the protonated dye molecule. The intensity of this band increases with severity of dehydration. Those dehydrated samples containing merely aggregated dye molecules adsorbed on the surface do not show the 745 nm band. The protonation of methylene blue is reversible by the dehydration-hydration process.     

Infrared spectroscopic investigation of CO adsorption on SBA-15- and KIT-6-supported nickel phosphide hydrotreating catalysts

The infrared (IR) spectra of CO adsorbed on 10, 20, and 30 wt % nickel phosphide-containing reduced SBA-15 and KIT-6 mesoporous silica-supported catalysts have been studied at 300-473 K. On the catalysts containing a stoichiometric amount of phosphorus with 20 wt % loading, the most intense IR absorption band was observed at 2097-2099 cm(-1), which was assigned to CO terminally bonded to coordinatively unsaturated Ni(delta+) (0 < delta < 1) sites. The frequency of this band was 15 cm(-1), higher than that in the spectrum of a reduced Ni2P/SiO2 catalyst, indicating a modified Ni-P charge distribution. This band shifted to lower wavenumbers, and its intensity decreased, while the relative intensity of another band at 2191-2194 cm(-1) assigned to CO terminally bonded to P increased going to catalytically less active, excess-P-containing SBA-15-supported catalysts. CO also adsorbed as a bridged carbonyl (1910 cm(-1)) and as Ni(CO)4 (2050 cm(-1)) species, and the formation of surface carbonates was also identified. The nature of the surface acidity was studied by temperature-programmed desorption of ammonia (NH3-TPD). Weak and strong acid sites were revealed, and the high excess-P-containing catalyst released the highest amount of ammonia, indicating that a high concentration of strong acidity can be disadvantageous for reaching high hydrotreating catalytic activity. The modified Ni-P charge distribution, the mode of CO adsorption on surface nickel phosphide sites, as well as the acidity can be directly connected to the catalytic activity of these mesoporous silica-supported catalysts.     

水热脱铝ZSM-5/Y复合分子筛的表征和催化裂化性能

ZSM-5/Y是一种通过原位合成方法制备的新型复合分子筛材料,用XRD、IR光谱、N2吸附／脱附等手段,研究了水热处理对ZSM-5/Y物化性质的影响,并以正己烷为原料考察了样品的催化裂化性能.结果表明,与机械混合样品相比,在550 ℃和700 ℃水热处理条件下,复合分子筛中的Y型沸石相具有更好的结晶保留度.复合分子筛的中孔孔径分布范围大于机械混合分子筛,但复合分子筛样品所表现出的中、大孔体积小于相应的机械混合分子筛.吡啶吸附定量IR研究表明,550 ℃水热处理使复合分子筛的B酸量和L酸量减少;而机械混合样品则是B酸量和L酸量变化很小.进一步700 ℃水热处理则使B和L酸量都大量减少.与氢型样品相比,550 ℃脱铝样品的正己烷裂化活性显著增加,700 ℃脱铝后活性明显降低.产物分布的分析表明活性的提高与反应机理的改变有关.     

β沸石骨架稳定性与表面酸性的红外光谱研究

用红外光谱法研究了真空热脱附和空气中焙烧两种不同的方法脱除模板剂对Hβ沸石骨架结构稳定性和表面酸性的影响.结果表明,在真空条件下加热脱除模板剂,其骨架结构保持完好且质子酸中心最多.而在空气中焙烧脱除模板剂,导致沸石骨架部分脱铝,形成大量的Lewis酸且耐酸性极差.     

脱铝MCM-49分子筛的结构、酸性及苯与丙烯液相烷基化催化性能研究

采用硝酸回流和水蒸气两种处理方法对用动态水热法合成的纳米MCM-49分子筛进行脱铝改性. 用XRD、氮气吸附-脱附、NH3-TPD、FTIR和NMR等技术进行了表征, 并考察了脱铝前后MCM-49分子筛在苯与丙烯液相烷基化反应中的催化性能. 27Al核磁共振谱表明, 硝酸回流和水蒸气处理能有效地脱除MCM-49分子筛的部分骨架铝和非骨架铝. NH3-TPD和FTIR表征结果表明, 脱铝降低了MCM-49分子筛的Brönsted酸和Lewis酸的酸量. 硝酸脱铝未改变分子筛的酸强度分布, 而在600 ℃水蒸气脱铝则造成酸强度的降低. 实验条件下, MCM-49分子筛的丙烯转化率为99.5%, 异丙苯的选择性为73.6%. 脱铝改性降低了烷基化反应活性和异丙苯的选择性, 提高了收率. 与脱铝前MCM-49分子筛相比, 常温下经硝酸处理5 h的脱铝MCM-49分子筛在保持催化活性相当的情况下, 异丙苯收率提高了5.3%.     

High-resolution Fourier-transform infrared spectroscopy of the Coriolis coupled ground state and ν7 mode of ketenimine

High resolution FTIR spectra of the short lived species ketenimine have been recorded in the regions 390-1300 cm(-1) and 20-110 cm(-1) using synchrotron radiation. Two thousand six hundred sixty transitions of the ν(7) band centered at 693 cm(-1) and 126 far-IR rotational transitions have been assigned. Rotational and centrifugal distortion parameters for the ν(7) mode were determined and local Fermi and b-axis Coriolis interactions with 2ν(12) are treated. A further refinement of the ground state, ν(12) and ν(8) parameters was also achieved, including the treatment of previously unrecognized ac-axis and ab-axis second order perturbations to the ground state.     

不同方法制备的脱铝Y沸石的孔结构

Y沸石脱铝有多种方法。由于在脱铝过程中发生水解、聚合、重排等反应,分子筛的孔结构将发生很大的变化,如形成空穴,甚至可导致骨架结构单元的崩塌,形成二次孔。由于不同的脱铝方法的脱铝机理不同,即使它们的脱铝程度一致,产生的孔结构也将不同,这必将导致它们的酸性质和催化性能的差异。目前关于Y沸石孔结构的研究报导还很少,尤其对SSY,US-SSY沸石孔结构的报导更为鲜见。本文用低温N_2吸附-脱附等温线和层厚t等方法,对四种不同方法制备的脱铝Y沸石(USY,DAY,SSY和US-SSY)的微孔、二次孔及其孔径分布(2.0～60.0nm)进行了初步研究,得到了一些有用的信息,为进一步研究其酸性质和催化性能打下了基础。     

超细NaY分子筛的深度脱铝

通过优化和组合不同脱铝补硅方法,依次经氟硅酸铵处理、600oC水热处理、硅溶胶+草酸处理和800oC水热处理过程,成功实现了200nm超细NaY分子筛的深度脱铝,最终产品骨架硅铝比高达27.3,比表面积为581.9m2/g,分子筛结晶度保持在65%以上.结果表明,对于超细NaY分子筛脱铝,第一步采用氟硅酸铵进行部分缺陷修补尤为重要.根据分子筛晶粒尺寸不同,需严格控制氟硅酸铵用量和处理次数.当晶粒为200nm时,氟硅酸铵与分子筛骨架铝的摩尔比为0.16,处理一次较为适宜.在连续脱铝过程中及时补修脱铝产生的缺陷是保障超细NaY分子筛成功脱铝的关键,而采用氟硅酸铵、硅溶胶、800oC高温水热处理,可有效实施这种骨架修正作用.     

Dibenzodioxin adsorption on inorganic materials

Dibenzodioxin adsorption/desorption on solid surfaces is an important issue associated with the formation, adsorption, and emission of dioxins. Dibenzodioxin adsorption/desorption behaviors on inorganic materials (amorphous/mesoporous silica, metal oxides, and zeolites) were investigated using in situ FT-IR spectroscopy and thermogravimetric (TG) analysis. Desorption temperatures of adsorbed dibenzodioxin are very different for different kinds of inorganic materials: approximately 200 degrees C for amorphous/mesoporous silica, approximately 230 degrees C for metal oxides, and approximately 450 degrees C for NaY and mordenite zeolites. The adsorption of dibenzodioxin can be grouped into three categories according to the red shifts of the IR band at 1496 cm(-1) of the aromatic ring for the adsorbed dibenzodioxin: a shift of 6 cm(-1) for amorphous/mesoporous silica, a shift of 10 cm(-1) for metal oxides, and a shift of 14 cm(-1) for NaY and mordenite, suggesting that the IR shifts are proposed to associated with the strength of the interaction between adsorbed dibenzodioxin and the inorganic materials. It is proposed that the dibenzodioxin adsorption is mainly via the following three interactions: hydrogen bonding with the surface hydroxyl groups on amorphous/mesoporous silica, complexation with Lewis acid sites on metal oxides, and confinement effect of pores of mordenite and NaY with pore size close to the molecular size of dibenzodioxin.     

Raman microscopy of selected tungstate minerals

A series of tungstate bearing minerals including scheelite, stolzite, ferberite, hübnerite, wolframite, russellite, tungstenian wulfenite and cuprotungstite have been analyzed by Raman microscopy. The results of the Raman spectroscopic analysis are compared with published data. These minerals are closely related and often have related paragenesis. Raman microscopy enables the selection of individual crystals of these minerals for spectroscopic analysis even though several of the minerals can be found in the same matrix because of the pargenetic relationships between the minerals. The Raman spectra are assigned according to factor group analysis and related to the structure of the minerals. These minerals have characteristically different Raman spectra. The nu1(Ag) band is observed at 909 cm(-1) and although the corresponding nu1(Bu) vibration should be inactive a minor band is observed around 894 cm(-1). The bands at 790 and 881 cm(-1) are associated with the antisymmetric and symmetric Ag modes of terminal WO2. The band at 695 cm(-1) is interpreted as an antisymmetric bridging mode associated with the tungstate chain. The nu4(Eg) band was absent for scheelite. The bands at 353 and 401 cm(-1) are assigned as either deformation modes or as r(Bg) and delta(Ag) modes of terminal WO2. The band at 462 cm(-1) has an equivalent band in the infrared at 455 cm(-1) assigned as delta(as)(Au) of the (W2O4)n chain. The band at 508 cm(-1) is assigned as nu(sym)(Bg) of the (W2O4)n chain.     

Influence of V content on the nature and strength of acidic sites in VSibeta zeolite evidenced by IR spectroscopy

VSibeta zeolites prepared by a two-step postsynthesis method have been characterized by physical techniques. A significant reduction of intensity of the IR band near 3515 cm(-1) after impregnation of dealuminated beta zeolite with aqueous NH4VO3 indicates that V ions specifically react with hydrogen-bonded SiO-H groups of vacant T sites. IR bands at 3618 and 3645 cm(-1) are assigned to SiO-H groups interacting with V and to VO-H groups, respectively. In VSibeta, diffuse reflectance UV-visible data show that below 1.9 wt % V is present as lattice tetrahedral species and at higher content as extra-lattice octahedral species (mononuclear and polynuclear). VSibeta samples are EPR-silent at 298 or 77 K suggesting that there are no paramagnetic VIV ions. IR studies show that V-OH groups are less acidic than Si-OH-Al groups of parent HAlbeta zeolite. IR results of CO adsorption evidence three kinds of Lewis acidic sites, related to lattice mononuclear and extra-lattice mononuclear and polynuclear V species. Quantitative IR studies of ammonia and pyridine adsorption reveal that only about half of V introduced into zeolite is able to form either Br?nsted or Lewis acidic sites.     

Stabilisation of the Secondary Structure of Chitosan Gels during the Preparation of Composites

Summary: Zeolite-chitosan composites have been prepared by encapsulation of zeolites by a gelling solution of chitosan or by in-situ synthesis of zeolites inside a chitosan gel. The preparation of the composite implies modifications of both components. Zeolites are dealuminated by the acid solution in which chitosan is dissolved and the morphology of the chitosan fibrils is stabilized by iniorganic species issued from the dealumination of the zeolites or from their synthesis medium. Zeolite-bearing chitosan xerogels present surface area and porosity similar to the textural properties of chitosan aerogels.