Cu2+ ions as a paramagnetic probe to study the surface chemical modification process of layered double hydroxides and hydroxide salts with nitrate and carboxylate anions

A layered zinc hydroxide nitrate (Zn5(OH)8(NO3)2.2H2O) and a layered double hydroxide (Zn/Al-NO3) were synthesized by coprecipitation and doped with different amounts of Cu2+ (0.2, 1, and 10 mol%), as paramagnetic probe. Although the literature reports that the nitrate ion is free (with D3h symmetry) between the layers of these two structures, the FTIR spectra of two zinc hydroxide nitrate samples show the C2v symmetry for the nitrate ion, whereas the g ||/A || value in the EPR spectra of Cu2+ is high. This fact suggests bonding of some nitrate ions to the layers of the zinc hydroxide nitrate. The zinc hydroxide nitrate was used as matrix in the intercalation reaction with benzoate, o-chlorobenzoate, and o-iodobenzoate ions. FTIR spectra confirm the ionic exchange reaction and the EPR spectroscopy reveals bonding of the organic ions to the inorganic layers of the zinc hydroxide nitrate, while the layered double hydroxides show only exchange reactions.     

Equilibrium study of selected divalent d-electron metals adsorption on A-type zeolite

The objective of the presented study was to investigate the adsorption of Cu, Co, Mn, Zn, Cd and Mn on A-type zeolite. The isotherms for adsorption of metals from their nitrates were registered. The following adsorption constants K of metals were found: 162,890, 124,260, 69,025, 16,035, 10,254, and 151 [M(-1)] for Cu, Co, Mn, Zn, Cd, and Ni, respectively, for the concentration range 10(-4)-10(-3) M. On the other hand, the investigation of pH influence on the distribution constants of metals showed that the adsorption of metals proceeds essentially through an ion-exchange process, surface hydrolysis, and surface complexation. The supplementary results from DRIFT, scanning electron microscopy, and X-ray diffraction methods confirmed the presumption about the possible connection between the electronic structure of divalent ions and their adsorption behavior, showing that ions with d5 and d10 configurations such as Mn2+, Zn2+, Cd2+, with much weaker hydrolytic properties than Cu2+ and Ni2+, strongly interact with the zeolite framework and therefore their affinity to the zeolite phase is much stronger when compared with that of the Ni2+ ion, but at the same time not as strong as the affinity of the Cu2+ ion, the latter forming a new phase during the interaction with zeolite framework. For Zn2+, during inspection of the correlation between the proton concentration H/Al and zinc concentration Zn/Al on the zeolite surface, the formation of the surface complex [triple bond]S-OZn(OH) was proposed. A correlation between the heterogeneity of proton concentrations H/Al on Me-zeolite surfaces and the hydrolysis constants pKh of Me2+ ions was found.     

Characterization of Zn centers in ZSM-5 zeolites with X-ray absorption spectroscopy

In the analysis of Zn K XANES of a ZnO + Na-ZSM-5 zeolite, the appearance of a solid state ion exchange reaction was shown. The ZSM-5 zeolites modifed by zinc exhibit enhanced catalytic activity.     

高温水蒸气处理对ZnHZSM-5活性中心的影响

应用X-射线衍射、能谱表面分析和吡啶吸附红外光谱研究了高温水蒸气处理对HZSM-5和ZnHZSM-5催化剂的影响，并以丙烷芳构化作为探针反应考查了催化活性中心的变化．高温水蒸气处理对分子筛的结晶度影响不大，但水蒸气处理使得分子筛骨架铝脱出，脱出的铝在表面富集，分子筛锌交换位的骨架铝脱出较难，脱铝导致分子筛的酸性减弱．高温水蒸气处理后的HZSM-5和ZnHZSM-5催化剂的丙烷反应活性都降低，在ZnHZSM－5上丙烯的选择性增加，反映了具有脱氢活性的锌的强L酸中心数目相对B酸中心减少较少，进一步说明了处于离子交换位的锌离子对骨架铝有保护作用     

分子筛表面酸性对微波固相法制备ZnCl2/Y催化剂的影响

 采用XRD和原子吸收光谱法研究了微波作用下分子筛表面酸性对ZnCl2与Y分子筛固态相互作用的影响．结果表明，微波辐射可显著促进ZnCl2在分子筛表面分散，其分散阈值与分子筛表面酸性有关．随着分子筛表面酸量和酸强度增加，ZnCl2在分子筛表面的最大分散量减少，分散的ZnCl2与Y分子筛的固态离子交换量也减少；NaY型分子筛比HY分子筛更容易发生固态离子交换反应．考察了微波固相法制备的ZnCl2／HY催化剂在苯甲醚与乙酰氯酰化反应中的催化性能．结果表明，在分子筛表面分散的ZnCl2具有更高的催化活性及对甲氧基苯乙酮选择性．     

Particle distribution in a microporous material: experiments with zeolite A.

The theory on particle distribution and exchange equilibria in a microporous material is applied to experimental ion-exchange data involving zeolite Na-A and zeolite K-A, with silver ions as the exchanging species. The presented method enables direct evaluation of the measured data and consideration of nonequivalent particle sites. The isotherms of the K+ versus Ag+ exchange in zeolite K-A rise much more steeply, at low exchange degrees, than those of the Na+ versus Ag+ exchange in zeolite Na-A. This result implies a different course of the ion-exchange reactions. Spectroscopic measurements on dehydrated, partly silver-exchanged zeolites Na-A and K-A do indeed show that in zeolite Na-A, the Na+ ions occupying four-ring positions are exchanged faster for Ag+ than the Na+ ions occupying eight- and six-ring positions, while in zeolite K-A the exchange does not start with the four-ring ion but with six-ring ions, followed by the four-ring ion. These findings are consistent with the results obtained from evaluation of the ion-exchange data. The resulting thermodynamic quantities significantly differ from published reference values, which we suggest should be revised.     

Decationization and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff

The paper presents results of investigation of exchange of the clinoptilolite tuff cations with hydrogen ions from HCl solution of concentration 0.1 mmol cm(-3) and ammonium ions solutions of concentrations 0.0071 to 2.6 mmol cm(-3). Molal concentrations, x (mmol g(-1)) of cations exchanged in acid solution and in ammonium ions solutions were compared with molal concentrations of cations obtained by determination of the cation-exchange capacity of clinoptilolite tuff. The obtained results show that at ammonium ion concentrations lower than 0.1 mmol cm(-3), with regard to exchange capacity for particular ions, best exchanged are Na+ ions, followed by Mg2+ and Ca2+ ions, while exchange of K+ ions is the poorest (Na+ > Mg2+ > Ca2+ > K+). At ammonium concentrations from 0.2 to 1 mmol cm(-3) the order is Na+ > Ca2+ > Mg2+ > K+. At concentrations higher than 1 mmol cm(-3) the order is Na+ > Ca2+ > K+ > Mg2+. The results are a consequence of the uptake of hydrogen ions by zeolite samples in ammonium ions solutions at concentrations lower than 1 mmol cm(-3) and indicate the importance of Mg2+ (besides Na+ ions) for the exchange between clinoptilolite cations and H+ ions, in contrast to K+ ions, whose participation in the reaction with H+ ions is the lowest. During decationization of the clinoptilolite in acid solution, best exchanged are Na+, Mg2+, and Ca2+ ions, while exchange of K+ ions is the poorest. Due to poor exchange of K+ and H+ ions and good exchange of Na+, Mg2+, and Ca2+ ions, it is to be assumed that preservation of stability of the clinoptilolite structure is caused by K+ ions present in the channel C. Clinoptilolite is dissolved in the clinoptilolite A and B channels where Na+, Mg2+, and Ca2+ ions are present. On the acid-modified clinoptilolite samples, exchange of ammonium ions is poorer than on natural zeolite. The longer the contact time of the zeolite and acid solution, the worse ammonium ions exchange. It can be assumed that H+ ions exchanged with zeolite cations are consumed for solution of aluminum in the clinoptilolite structure; therefore the concentration of H+ ions as exchangeable cations decreases. In the ammonium ion solution at a concentration of 0.0065 mmol cm(-3), from the acid-modified zeolite samples, Al3+ ions are exchanged best, followed by Na+, Mg2+, Ca2+, and K+ ions. Further to the results, it is to be assumed that exchangeable Al3+ ions available from clinoptilolite dissolution are best exchanged with H+ ions in acid solution.     

Electrospray mass spectrometry of zinc dithiophosphate derivatives and its application to the analysis of engine oil antiwear additives

Electrospray mass spectrometry (ES-MS) has been applied to a variety of zinc O,O′-dialkyldithiophosphate (DTP) derivatives. The neutral Zn(DTP)₂ compounds were converted to the [Zn(DTP)₃]⁻ anions by reaction with excess DTP⁻ and these principal anions are readily observed by ES-MS. Exchange reactions between two different zinc tris(DTP) anions leads to the simultaneous observation of zinc anions containing all possible combinations of ligands even though the species in solution are exchanging rapidly on the NMR timescale. Similar mass spectra are observed upon mixing Zn(DTP)₂ with a different DTP⁻ anion. Reaction of Zn(DTP)₂ with dimethylsulfoxide (DMSO) in methanol solution gives [Zn(DTP)(DMSO)_1,2]⁺ and free DTP⁻ ions which are observed in the positive ion and negative ion ES mass spectra respectively. This latter reaction provides a convenient method for the characterisation and qualitative analysis of engine oil inhibitor and antiwear additives, which contain zinc dithiophosphates with alkyl and aryl substituents.     

Zn物种对乙烯芳构化反应过程的影响

分别采用离子交换法和物理混合法制备了不同Zn含量的ZSM-5分子筛催化剂,采用X射线衍射、扫描电子显微镜、N2物理吸附、氨程序升温脱附、吡啶红外吸附光谱、紫外-可见光谱和X射线光电子能谱等技术研究了催化剂的结构、表面性质及Zn物种种类,探讨了Zn物种存在状态对乙烯芳构化反应的影响。结果表明,引入到HZSM-5中的Zn物种包括三种状态,即ZnO晶体、存在于分子筛孔道中的ZnO团簇以及Zn和分子筛质子酸中心通过固相反应生成的Zn(OH)+物种;不同的制备方法显著影响Zn物种的分布。比较了制备方法和Zn含量对ZSM-5分子筛催化剂在乙烯芳构化反应中性能的影响,发现Zn(OH)+物种是芳构化的主要活性中心,同时ZnO物种的存在有助于乙烯制芳烃反应的发生。     

Intercalation and functionalization of zinc hydroxide nitrate with mono- and dicarboxylic acids

The intercalation of ions derived from succinic, glutaric, and adipic acid into layered zinc hydroxide nitrate by ionic exchange reaction is reported. Different reaction conditions are investigated and the materials are characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis (simultaneous thermogravimetry and differential scanning calorimetry) and elemental analysis. The dicarboxylic acids can be grafted to the matrix slab by one carboxylate group and the second hydrated carboxylate group is hanging between the layers. Benzoate ions have also been intercalated by both ionic exchange reaction and stirring in acetonitrile. The two benzoate-intercalated materials exchange the organic moiety by sulfate ions if stirred in magnesium sulfate solution, but the sample obtained by anion exchange also allows the unusual incorporation of neutral magnesium sulfate in addition to free solvated sulfate ion. A schematic arrangement of the intercalated species between the layers is presented.     

用于乙烯芳构化反应的Zn/HZSM-5催化剂失活机制研究

采用浸渍法制备了Zn负载量（质量分数）分别为1%、2%、3%的Zn/HZSM-5分子筛催化剂,通过XRD、N₂吸附-脱附、NH₃-TPD、Py-FTIR、XPS、TG-DTA等技术,系统考察Zn/HZSM-5分子筛在乙烯芳构化反应的失活机制。结果表明,积炭是催化剂失活的主要原因,HZSM-5中Zn的添加在较大程度上抑制了催化剂的积炭行为;低Zn含量时催化剂失活缓慢,但Zn含量较高时,由于催化剂比表面积和孔体积极剧下降,催化剂失活加剧。反应过程中,分子筛上Zn物种存在迁移和流失行为,迁移行为体现为催化剂表面Zn的富集和相对比例的变化;Zn流失速率在不同反应阶段保持恒定,但受到Zn含量的影响,Zn含量越高、流失速率越大。外表面ZnO是分子筛催化剂Zn流失的主要物种,且随Zn负载量升高变化趋势愈加明显,其含量与积炭速率存在一定关联。     

Reactivity of C1 surface species formed in methane activation on Zn-modified H-ZSM-5 zeolite

Solid-state (13)C magic angle spinning (MAS) NMR spectroscopy investigations identified zinc methyl species, formate species, and methoxy species as C(1) surface species formed in methane activation on the zeolite Zn/H-ZSM-5 catalyst at T≤573 K. These C(1) surface species, which are possible intermediates in further transformations of methane, were prepared separately by adsorption of (13)C-enriched methane, carbon monoxide, and methanol onto zinc-containing catalysts, respectively. Successful isolation of each surface species allowed convenient investigations into their chemical nature on the working catalyst by solid-state (13)C MAS NMR spectroscopy. The reactivity of zinc methyl species with diverse probe molecules (i.e., water, methanol, hydrochloride, oxygen, or carbon dioxide) is correlated with that of organozinc compounds in organometallic chemistry. Moreover, surface formate and surface methoxy species possess distinct reactivity towards water, hydrochloride, ammonia, or hydrogen as probe molecules. To explain these and other observations, we propose that the C(1) surface species interconvert on zeolite Zn/H-ZSM-5. As implied by the reactivity information, potential applications of methane co-conversion on zinc-containing zeolites might, therefore, be possible by further transformation of these C(1) surface species with rationally designed co-reactants (i.e., probe molecules) under optimized reaction conditions.     

Kinetics of proton transfer in the zeolitic tuff

The kinetics of a proton transfer into dilute acid solutions containing natural zeolitic tuff was studied by following the pH evolution of the liquid phase. Four different solutions with tuff contents of 9, 3, 1 and 0.5 (% wt) and three different particle size fractions (≤ 2000 μm) were studied. The proton concentration of the solution was decreased by increasing the zeolite amount and decreasing the particle size fraction. The proton transfer reaction was analyzed with chemical reactions and diffusion model equations. Analysis shows that the adsorption and/or ion exchange are possible mechanisms and are expressed by a second order reaction model.     

ZnHZSM-5上丙烷芳构化的研究-丙烷的活化

研究了HZSM－5、ZnHZSM－5和ZnNaZSM－5上的羟基振动光谱和一氧化碳吸附的红外光谱，以及丙烷的芳构化反应．红外光谱中发现表征强B酸的3610cm－1羟基振动峰相对强度由于锌离子的引入和浸渍氢氧化钠而减小，说明了锌离子和钠离子均进入了分子筛的阳离子位；一氧化碳在锌离子上的吸附峰位在2232cm－1，说明进入阳离子位的锌离子是一种强L酸．反应结果表明，锌离子的引入大大地促进了丙烷的转化和芳烃选择性的提高；在一定范围内，随浸渍氢氧化钠量的增加，丙烷转化率下降，而丙烯的选择性和产率增加，说明了锌组份直接参与了丙烷的脱氢过程．Zn－L酸是丙烷活化脱氢的中心，丙烷在该中心上异裂活化直接脱氢．     

Promoted effect of zinc–nickel bimetallic oxides supported on HZSM-5 catalysts in aromatization of methanol

Zn/ZSM-5(NZ2) and Zn/Ni/ZSM-5(NZ3) as the catalysts for methanol to aromatics(MTA) were synthesized by a simple ultrasonic impregnation. The textural and acid properties of all catalysts were characterized using XRD, HRTEM, NH_3-TPD, Py-IR, XPS, XRF and TG techniques. The XRD and HRTEM results showed that the basic zeolite structures were not affected much with the incorporation of Zn and Ni species. However, great changes have taken place in acid properties. The Py-IR and XPS results indicated that the Zn-Lewis acid sites(ZnOH~+ species), which have stronger interaction with the zeolite framework compared with ZnO species, were generated at the expense of B acid sites with the incorporation of zinc species. Moreover, the product analysis results showed that the incorporation of zinc species promoted the primary aromatization by enhancing the dehydroaromatization and suppressing the cracking and subsequent H-transfer reaction. Furthermore, the addition of Ni species well inhibited the loss of zinc species by converting partial ZnO species to ZnOH~+ species, and thus improved the aromatization activity and catalyst stability. The catalytic performance results showed that the NZ3 possess higher conversion of methanol in a longer time and lower average rate of coke formation compared with NZ2. In addition,the NZ3 also exhibited the highest yield of BTX as the reaction proceeds.     

氢预处理对Zn/HZSM-5分子筛催化乙烯芳构化反应性能的影响

采用浸渍法制备了Zn/HZSM-5分子筛催化剂,进行了不同温度的氢气预处理,通过X射线衍射(XRD)、氮气吸附-脱附、傅里叶变换红外(FT-IR)光谱、NH_3程序升温脱附(NH_3-TPD)、X射线光电子能谱(XPS)等表征技术,系统考察氢气预处理对Zn/HZSM-5分子筛结构、孔道、酸性、Zn存在状态以及在乙烯芳构化反应中的催化性能等的影响。研究结果表明,氢气预处理温度显著影响Zn/HZSM-5中Zn物种的含量和存在状态:600℃以下的氢处理,几乎不影响分子筛上Zn物种的总含量,而600℃以上氢处理时会造成Zn物种的大量流失;XPS研究显示,氢预处理的温度不同,分子筛上ZnOH~+与ZnO的相对比例变化显著。结合乙烯芳构化反应性能,可以发现ZnOH~+物种的含量与芳烃选择性存在较好的线性关系,说明其是促进烯烃脱氢、芳构化的主要活性中心,Zn存在状态的变化使得氢气预处理温度显著影响乙烯芳构化反应产物的分布。     

Chemical formation of mononuclear univalent zinc in a microporous crystalline silicoaluminophosphate

A host-guest compound containing mononuclear univalent Zn+ ions has been prepared through vapor reaction of metallic zinc with protons in the cages of SAPO-CHA, a silicoaluminophosphate molecular sieve. Unlike in fused ZnCl2 salt, the formed Zn+ species are associated with the molecular sieve walls, and this prevents the cations from getting paired to form diamagnetic (Zn-Zn)2+. Electron spin resonance spectroscopy reveals the paramagnetic nature of the Zn+ species which display anisotropic g factors, and the two crystallographically independent Zn+ sites are distinguishable from the ESR signals. The magnetic moments of the univalent zinc in SAPO-CHA interact antiferromagnetically at low temperatures with a Néel point of about 4 K as observed from the temperature dependence plot of the magnetic susceptibility of the host-guest compound.     

Kinetics of the Zn(II)/Zn(Hg) electrode reactions in DMSO solutions of halide ions

The electrode reaction Zn(II)/Zn(Hg) in complex chloride, bromide, and iodide solutions with DMSO as solvent and ammonium perchlorate as supporting electrolyte has been studied at the equilibrium potential by the faradaic impedance method and a square-wave method. Furthermore, double-layer data have been determined by electrocapillary measurements. The results indicate that the zinc chloride and bromide complexes do not contribute noticeably to the exchange current density, while in the iodide system both the solvated zinc ion and the first complex take part in the charge transfer. From the dissimilar results valid for water and DMSO solutions the conclusion is made that probably ligand bridging at the amalgam by the halide ions is operative in water solutions, whereas in DMSO the larger solvent molecules adsorbed can form a steric hindrance to ligand bridging by chloride or bromide ions.     

Design and generation of extended zeolitic metal-organic frameworks (ZMOFs): synthesis and crystal structures of zinc(II) imidazolate polymers with zeolitic topologies

Attempts to create metal-organic frameworks (MOFs) with zeolitic topologies, metal (zinc(II) and cobalt(II)) imidazolates have repeatedly been used as the metal-organic motifs of inorganic silicate analogues. By modulating the synthetic strategy based on the solvothermal and liquid diffusion method, seven further MOFs (including at least three zeolitic MOFs) of zinc(II) imidazolates, [Zn(im)2.x G] (G=guest molecule, x=0.2-1) 1 a-7 a, have been successfully synthesized. Of these, 1 a-3 a are isostructural with the previously reported cobalt analogues 1 b-3 b, respectively, while 4 a-7 a are new members of the metal imidazolate MOF family. Complex 4 a exhibits a structure related to silicate CaAl2Si2O8 of CrB4 topology, but with a higher network symmetry; complex 5 a has a structure with zeolitic DFT topology that was discovered in zeolite-related materials of DAF-2, UCSB-3, and UCSB-3GaGe; complex 6 a demonstrates an unprecedented zeolite-like topology with one dimensional channels with 10-rings; and 7 a displays a structure of natural zeolite GIS (gismondine) topology. All of these polymorphous MOFs were created only by using certain solvents as structure-directing agents (SDAs). Further extensive metal-organic frameworks with zeolitic topologies can be envisaged if other solvents were to be used.     

Distribution of aluminum and boron in the periodical building units of boron-containing Beta zeolites

Various boron only ([B]-BEA) as well as aluminum- and boron-containing beta zeolites ([Al,B]-BEA) have been prepared and modified by ion exchange of ammonium, sodium, and nickel ions. The zeolite samples have been characterized by 11B, 27Al, and 29Si MAS as well as three of them by 11B and 27Al 3Q-MAS NMR spectroscopy. The quantitative contributions of defect-free Si(nX) (n = 2, 1, 0; X = Al, B) and Si(OH)x (x = 2, 1) sites to the NMR signal intensities were calculated from the various Si/(Al + B) ratios and relative 11B, 27Al, and 29Si NMR signal intensities using the special distribution of aluminum and boron in different periodical building units of the zeolite framework. The boron atoms are sitting exclusively in diagonal positions in the four-membered rings of [B]-BEA zeolites, while the aluminum atoms are situated both in diagonal and lone positions in the four-membered rings of [Al,B]-BEA zeolites. A higher part of boron atoms are positioned in framework-related deformed tetrahedral boron species than in lattice positions in the [B]-BEA than in the [Al,B]-BEA zeolites. All extraframework octahedral aluminum species are transformed back to lattice positions due to ion exchange from the protonated form to ammonium-, sodium-, or nickel-ions containing zeolites. Oppositely, trigonal boron leaves the zeolite structure completely during ion exchange.