Facile synthesis of hierarchical NaX zeolite from natural kaolinite for efficient Knoevenagel condensation

Zeolite catalysts have found extensive applications in the synthesis of various fine chemicals.However,the micropores of zeolites impose diffusion limitations on bulky molecules,greatly reducing the catalytic efficiency.Herein,we explore an economic and environmentally friendly method for synthesizing hierarchical NaX zeolite that exhibits improved catalytic performance in the Knoevenagel condensation reaction for producing the useful fine chemical 2-cyano-3-phenylacrylate.The synthesis was achieved via a low-temperature activation of kaolinite and subsequent in-situ transformation strategy without any template or seed.Systematic characterizations reveal that the synthesized NaX zeolite has both intercrystalline and intra-crystalline mesopores,smaller crystal size,and larger external specific surface area compared to commercial NaX zeolite.Detailed mechanism investigations show that the inter-crystalline mesopores are generated by stacking smaller crystals formed from in-situ crystallization of the depolymerized kaolinite,and the intra-crystalline mesopores are inherited from the pores in the depolymerized kaolinite.This synthesis strategy provides an energy-saving and effective way to construct hierarchical zeolites,which may gain wide applications in fine chemical manufacturing.

Production of linear alkylbenzene over Ce containing Beta zeolites

Ce-encapsulated Beta zeolite was synthesized by a one-pot hydrothermal method with citric acid complexing Ce in the absence of Na species.Additional citric acid can effectively prevent the deposition of Ce species during the hydrothermal synthesis of zeolites,leading to uniform distribution of Ce cluster in the framework of Beta zeolites.Moreover,the sodium-free synthesis system resulted that the Brønsted acid sites were mainly located on the straight channels and external surface of Beta zeolites,improving the utilization of Brønsted acid sites.In addition,Ce encapsulated Beta zeolites showed enhanced activity and robust stability in the alkylation of benzene with 1-dodecene based on the synergistic effect between Ce species and Brønsted acid sites,which pave the way for its practical application in the production of alkylbenzene.

Efficient nitric oxide capture and reduction on Ni-loaded CHA zeolites

As a prominent contributor to air pollution,nitric oxide(NO)has emerged as a critical agent causing detrimental environmental and health ramifications.To mitigate emissions and facilitate downstream utilization,adsorption-based techniques offer a compelling approach for direct NO capture from both stationary and mobile sources.In this study,a comprehensive exploration of NO capture under oxygen-lean and oxygenrich conditions was conducted,employing Ni ion-exchanged chabazite(CHA-type)zeolites as the adsorbents.Remarkably,Ni/Na-CHA zeolites,with Ni loadings ranging from 3 to 4 wt%,demonstrate remarkable dynamic uptake capacities and exhibit exceptional NO capture efficiencies(NO-to-Ni ratio)for both oxygen-lean(0.17-0.31 mmol/g,0.32-0.43 of NO/Ni)and oxygen-rich(1.64-1.18 mmol/g)under ambient conditions.An NH3 reduction methodology was designed for the regeneration of absorbents at a relatively low temperature of 673 K.Comprehensive insights into the NO_(x) adsorption mechanism were obtained through temperature-programmed desorption experiments,in situ Fourier transform infrared spectroscopy,and density functional theory calculations.It is unveiled that NO and NO_(2) exhibit propensity to coordinate with Ni^(2+) via N-terminal or O-terminal,yielding thermally stable complexes and metastable species,respectively,while the low-temperature desorption substances are generated in close proximity to Na^(+).This study not only offers micro-level perspectives but imparts crucial insights for the advancement of capture and reduction technologies utilizing precious-metal-free materials.

Pervaporation performance and characterization of hydrophilic ZSM-5 zeolite membranes for high inorganic acid and inorganic salts

The hydrophilic ZSM-5 zeolite membranes are applied to separate the inorganic acid solutions and inorganic acid/inorganic salt mixtures by pervaporation,and the membrane presents good stability,dehydration,and desalination performance.Influences of inorganic acid type(H_(2)SO_(4),H_(3)PO_(4),HNO_(3),and HCl),H_(2)SO_(4)concentration(1-6 mol·L^(-1)),test temperature(60-90℃)and inorganic acid/inorganic salt type(2 mol·L^(-1)H_(2)SO_(4)and sulfate,2 mol·L^(-1)H3PO4 and phosphate)on the pervaporation performance are investigated in this work.Either for concentrating 3%(mass)H_(2)SO_(4)solution or consecutive dehydrating 20%(mass)H_(2)SO_(4)solution,the hydrophilic ZSM-5 zeolite membrane has a good dehydration performance and stability.Even though the H_(2)SO_(4)concentration and test temperature are increased to 6 M and 90℃,only H_(2)O molecules could pass through the membrane and pH value of the permeation is kept neutral.Besides,the membrane has good dehydration and desalination performance for H_(2)SO_(4)/sulfates and H_(3)PO_(4)/phosphate mixtures,and the rejection of natrium salt,molysite,and magnesium is almost 100%.

Synthesis of NaY zeolite from a submolten depolymerized perlite:Alkalinity effect and crystallization kinetics

NaY zeolites are synthesized using submolten salt depolymerized natural perlite mineral as the main silica and alumina sources in a 0.94 L stirred crystallizer.Effects of alkalinity ranging from 0.38 to 0.55(n(Na_(2)O)/n(SiO_(2)))on the relative crystallinity,textural properties and crystallization kinetics were investigated.The results show that alkalinity exerts a nonmonotonic influence on the relative crystallinity and textural properties,which exhibit a maximum at the alkalinity of 0.43.The nucleation kinetics are studied by fitting the experimental data of relative crystallinity with the Gualtieri model.It is shown that the nucleation rate constant increases with increasing alkalinity,while the duration period of nucleation decreases with increasing alkalinity.For n(Na_(2)O)/n(SiO_(2))ratios ranging from 0.38 to 0.55,the as-synthesized NaY zeolites exhibit narrower crystal size distributions with the increase in alkalinity.The growth rates determined from the variations of average crystal size with time are 51.09,157.50,46.17 and 24.75 nm·h^(-1),respectively.It is found that the larger average crystal sizes at the alkalinity of 0.38 and 0.43 are attributed to the dominant role of crystal growth over nucleation.Furthermore,the combined action of prominent crystal growth and the longer duration periods of nucleation at the alkalinity of 0.38 and 0.43 results in broader crystal size distributions.The findings demonstrate that control of the properties of NaY zeolite and the crystallization kinetics can be achieved by conducting the crystallization process in an appropriate range of alkalinity of the reaction mixture.

Designing zeolites for the removal of aqueous PFAS:a perspective

Zeolites possess unique sieving properties that offer a high selectivity for removing pollutants,such as perand polyfluoroalkyl substances(PFAS).However,there are limited studies examining the efficacy of zeolites as PFAS sorbents.Previous literature explores the effects of certain frameworks and the silica alumina ratio(SAR),and only one study has shown the effect of silanol defects on the hydrophobicity of the adsorbent.Since most zeolites are synthesized in hydroxide media,this leads to formation of silanol defects,which increase hydrophilicity with a greater effect than the inclusion of non-Si T atoms.It is critical that specific characterizations be performed to demonstrate the specific effects of different properties of the zeolites.In particular,synthesis,modification,and/or repair in fluoride media can be used to increase the hydrophobicity of zeolites by reducing silanol defects,and increasing Lewis acidity.

Adsorptive and catalytic properties in the removal of volatile organic compounds over zeolite-based materials

Volatile organic compounds（VOCs） are a major component in air pollutants and pose great risks to both human health and environmental protection. Currently, VOC abatement in industrial applications is through the use of activated carbons as adsorbents and oxide-supported metals as catalysts. Notably, activated carbons easily adsorb water, which strongly hinders the adsorption of VOCs; conventional oxides typically possess relatively low surface areas and random pores, which effectively influence the catalytic conversion of VOCs. Zeolites, in contrast with activated carbons and oxides, can be designed to have very uniform and controllable micropores, in addition to tailored wettability properties, which can favor the selective adsorption of VOCs. In particular, zeolites with selective adsorptive properties when combined with catalytically active metals result in zeolite-supported metals exhibiting significantly improved performance in the catalytic combustion of VOCs compared with conventional oxide-supported catalysts. In this review, recent developments on VOC abatement by adsorptive and catalytic techniques over zeolite-based materials have been briefly summarized.

Ni/β-Zeolite催化合成管径均匀的MWNTs

采用化学气相沉积法 (CCVD) ,用乙炔为原料气 ,在 β Zeolite负载的镍基催化剂上成功地合成了外径 30～ 4 0nm ,内径 2～ 3nm ,长度达四十几微米管径均匀的多层碳纳米管 (MWNTs) .研究了MWNTs从分子筛中分离和纯化的方法 .

Synthesis of zeolite Beta containing ultra-small CoO particles for ethylbenzene oxidation

Zeolite Beta containing ultra-small CoO particles was synthesized from a one-step hydrothermal process. The synthesis route involves the pre-mixture of hydrofluoric acid with tetraethylammo- nium hydroxide （in a molar ratio of 1.3-1.5：1） before the addition of a silicon and cobalt source.Investigations by scanning electron microscopy, X-ray diffraction, UV-Vi s spectroscopy, X-ray pho-toelectron spectroscopy, H 2 -temperature-programmed reduct i on and transmi ssi on el ectron mi -croscopy confirm the presence of ultra-small CoO particles in the zeolite Beta structure. The ul-tra-small CoO particles in zeolite Beta present high stability against both oxidation and reduction atmospheres at high temperatures. The catalytic performance of the CoO-containing zeolite Beta catalysts was compared with other Co-containing zeolites by evaluating ethylbenzene oxidation reactivity. The CoO-containing zeolite Beta exhibits high ethylbenzene conversion and high selectiv-ity to acetophenone and 1-phenylethanol. The high activity of this catalyst system can be attributed to the high dispersion of the ultra-small CoO particles in the Beta structure.

The structure-directing role of heterologous seeds in the synthesis of zeolite

Zeolites have been widely used as catalysts,ion-exchangers,and adsorbents in chemical industries,detergent industry,steel industry,glass industry,ceramic industry,medical and healthfield,and environmentalfield,and recently applied in energy storage.Seed-assisted synthesis is a very effective approach in promoting the crystallization of zeolites.In some cases,the target zeolite cannot be formed in the absence of seed zeolite.In homologous seed-assisted synthesis,the structure of the seed zeolite is the same to that of the target zeolite,while the structure of the seed zeolite is different to that of the target zeolite in the heterologous seed-assisted synthesis.In this review,we briefly summarized the heterologous seed-assisted syntheses of zeolites and analyzed the structure-directing effect of heterologous seeds and surveyed the“common composite building units(CBUs)hypothesis”and the“common secondary building units(SBUs)hypothesis”.However,both hypotheses cannot explain all observations on the heterologous seed-assisted syntheses.Finally,we proposed that the formation of the target zeolite does need nuclei with the structure of target zeolite and the formation of the nuclei of the target zeolite can be promoted by either the undissolved seed crystals with the same CBUs or SBUs to the target zeolite or by the facilitated appropriate distribution of the specific building units due to the presence of the heterologous seed that does not have any common CBUs and SBUs with the target zeolite.

Dealuminated Hβ zeolite for selective conversion of fructose to furfural and formic acid

The fructose-to-furfural transformation is facing major challenges in the selectivity and high efficiency. Herein, we have developed a simple and effective approach for the selective conversion of fructose to furfural using Hβ zeolite modified by organic acids for dealuminization to regulate its textural and acidic properties. It was found that citric acid-dealuminized Hβ zeolite possessed high specific surface areas, wide channels and high Brønsted acid amount, which facilitated the selective conversion of fructose to furfural with a maximum yield of 76.2% at433 K for 1 h in the γ-butyrolactone(GBL)-H_(2)O system, as well as the concomitant formation of 83.0% formic acid. The^(13)C-isotope labelling experiments and the mechanism revealed that the selective cleavage of C1–C2 or C5–C6 bond on fructose was firstly occurred to form pentose or C5 intermediate by weak Brønsted acid, which was then dehydrated to furfural by strong Brønsted acid. Also this dealuminized Hβ catalyst showed the great recycling performance and was active for the conversion of glucose and mannose.

Simultaneous removal of ammonium and phosphate by zeolite synthesized from coal fly ash as influenced by acid treatment

Zeolite synthesized from fly ash （ZFA） without modification is not efficient for the purification of NH4＋ and phosphate at low concentrations that occur in real effluents, despite the high potential removal capacity. To develop an effective technique to enhance the removal efficiency of ammonium and phosphate at low concentrations, ZFA was modified with acid treatment and the simultaneous removal of ammonium and phosphate in a wide range of concentration was investigated. It was seen that when compared with untreated ZFA, only the treatment by 0.01 mol/L of H2SO4 significantly improved the removal efficiency of ammonium at low initial concentrations. The behavior was well explained by the pH effect. Treatment by more concentrated H2SO4 led to the deterioration of the ZFA structure and a decrease in the cation exchange capacity. Treatment by 0.01 mol/L H2SO4 improved the removal efficiency of phosphate by ZFA at all initial P concentrations, while the treatment by concentrated H2SO4 （≥0.9 mol/L） resulted in a limited maximum phosphate immobilization capacity （PIC）. It was concluded that through a previous mild acid treatment （e.g. 0.01 mol/L of H2SO4）, ZFA can be used in the simultaneous removal of NH4＋ and P at low concentrations simulating real effluent.

NiMo/Al_2O_3 catalyst containing nano-sized zeolite Y for deep hydrodesulfurization and hydrodenitrogenation of diesel

Two mixed-matrix NiMo/Al2O3 catalysts containing nano-and micro-sized zeolite Y have been prepared to explore the size effect of zeolite Y particle on the hydrodesulfurization（HDS）and hydrodenitrogenation（HDN）activities of fluid catalytic cracking（FCC）diesel.They were characterized by SEM,BET,XRD,H2-TPR,NH3-TPD and HRTEM.The results show that the catalyst containing nano-sized zeolite Y possesses larger average pore diameter,higher pore volume,weaker and lesser acid sites,more easily reducible metal phases,shorter MoS2 slabs and more slab layers than the catalyst containing micro-sized zeolite Y.The catalysts were also evaluated with a high-pressure fixed-bed reactor using real FCC diesel as feed.The results display that the catalyst containing nano-sized zeolite Y bears higher HDS and HDN activities and exhibits higher relative rate constant for the removal of total sulfur or nitrogen than the one containing micro-sized zeolite.

Evaluation of zeolites synthesized from fly ash as potential adsorbents for wastewater containing heavy metals

The pure-form zeolites （A and X） were synthesized by applying a two-stage method during hydrothermal treatment of fly ash prepared initial Cu and Zn gel. The difference of adsorption capacity of both synthesized zeolits was assessed using Cu and Zn as target heavy metal ions. It was found that adsorption capacity of zeolite A showed much higher value than that of zeolite X. Thus, attention was focused on investigating the removal performance of heavy metal ions in aqueous solution on zeolite A, comparing with zeolite HS （hydroxyl-solidate） prepared from the residual fly ash （after synthesis of pure-form zeolite A from fly ash） and a commercial grade zeolite A. Batch method was used to study the influential parameters of the adsorption process. The equilibrium data were well fitted by the Langmuir model. The removal mechanism of metal ions followed adsorption and ion exchange processes. Attempts were also made to recover heavy metal ions and regenerate adsorbents.

Ammonium removal by modified zeolite from municipal wastewater

Ammonium removal by modified zeolite, H-form and Na-form zeolite, were examined by batch-type methods. The adsorption of ammonium on modified zeolite was exothermic process. The saturation adsorption capacity of ammonium on H-form and Na-form zeolite were 21.23 and 41.15 mg/g, respectively. After ten times adsorption-desorption-readsorption cycles the standard deviations of H-form and Na-form zeolite were 6.34% and 6.59%. The zeolite adsorption process has proved cost effective and practical in reducing ammonium by H-form and Na-form zeolite in municipal wastewater from concentration 27.68 mg/L to 2.80 mg/L and 5.91 mg/L.

Zeolite P synthesis based on fly ash and its removal of Cu(Ⅱ) and Ni(Ⅱ) ions

Zeolite P was synthesized through hydrothermal method based on a kind of Class C fly ash(FA). X-ray diffraction(XRD), scanning electron microscopy(SEM), and Brunauer–Emmett–Teller(BET) were used to analyze and characterize the synthetic sample. The kinetics and thermodynamics of copper and nickel ions removed by the zeolite samples were experimentally explored in detail. The results of kinetic treatment showed the second-order exchange second-order saturation model(SESSM) can well describe the removal process of copper ions, while the first-order empirical kinetic model(FEKM) is the best kinetic model for nickel ions. Langmuir and Freundlich isotherms were used to fit the equilibrium concentration of Cu(Ⅱ) or Ni(Ⅱ) under certain conditions. Whether for copper or nickel ion, the Langmuir model is in good agreement with the experimental equilibrium concentration.The apparent theoretical removal capacities for Cu(Ⅱ) and Ni(Ⅱ) can reach to 138.1 mg·g^(-1) and 77.0 mg·g^(-1),respectively.

Aromatization over nanosized Ga-containing ZSM-5 zeolites prepared by different methods:Effect of acidity of active Ga species on the catalytic performance

Nanosized Ga-containing ZSM-5 zeolites were prepared via isomorphous substitution and impregnation followed by characterized using various techniques. The catalytic performance of the zeolites for the aromatization of 1-hexene was investigated. The results indicate that isomorphous substitution promotes the incorporation of Ga heteroatoms into the framework along with the formation of extra-framework GaO;species（[GaO;]a） that have stronger interactions with the negative potential of the framework. In addition, based on the Py-IR results and catalytic performance, the [GaO;]aspecies with stronger Lewis acid sites produced a better synergism with moderate Br?nsted acid sites and thus improved the selectivity to aromatic compounds. However, the impregnation results in the formation of Ga;O;phase and small amounts of GaO;species that are mainly located on the external surface（[GaO;];）, which contribute to weaker Lewis acid sites due to weaker interactions with the zeolite framework. During 1-hexene aromatization, the nanosized Ga isomorphously substituted ZSM-5 zeolite samples（Gax-NZ5） exhibited better catalytic performance compared to the impregnated samples, and the highest aromatic yield（i.e.,65.4 wt%） was achieved over the Ga4.2-NZ5 sample, which contained with the highest Ga content.

Influence of synthesis parameters on the crystallinity and Si/Al ratio of NaY zeolite synthesized from kaolin

Well-crystallized high-silica NaY zeolites （Si/Al〉2.5） were prepared from a reaction mixture consisting of metakaolin, sodium silicate solution and seed solution via optimization of the mixture composition and reaction conditions. The transformation from kaolin to high-silica NaY zeolite was confirmed by XRD, SEM and IR techniques. Subsequently, the influence of synthesis parameters, i.e. initial SIO2/Al2O3, initial Na2O/SiO2, initial H2O/SiO2, aging time of the seed solution, crystallization temperature and crystallization time, on the NaY growth was investigated in terms of crystallinity and Si/Al ratio. The results showed that the effects of initial SiO2/Al2O3, initial Na2O/SiO2 and initial H2O/ SiO2 on the crystaIlinity and Si/Al ratio of NaY zeolite are similar to those observed in the conventional syntheses of NaY zeolites only using sodium silicate solution as silicon source. However, due to the use of metakaolin as the main silicon and aluminum sources in the present study, a long crystallization induction period of 20 h was achieved, which can be attributed to the dissolution of metakaolin. In addition, different from the conventional syntheses of zeolite NaY, pure NaY zeolites （i.e. without NaP zeolite impurity） were still obtained even at 120℃ because of the use of a large quantity of seed solution （23 wt%） in the reaction mixture. As the aging time of the seed solution increased from 3.5 h to 22 h, the relative crystallinity of the NaY zeolite first increased sharply and then reached a plateau, while the Si/Al ratio first increased rapidly up to a maximum value of 2.75 corresponding to an aging time of 6.5 h, and then decreased sharply with the aging time.

EDTA-LDH/zeolite制备及其对重金属离子的吸附

用水热法和焙烧还原法两步合成了乙二胺四乙酸-水滑石/沸石(EDTA-LDH/zeolite)复合材料,并将其用于去除水溶液中的Cd^(2+)、Pb^(2+)、Cu^(2+),系统研究不同条件下EDTA-LDH/zeolite对单一及混合重金属离子溶液中Cd^(2+)、Pb^(2+)、Cu^(2+)的吸附效果与吸附机制。结果表明,当EDTA-LDH/zeolite投加量为0.05 g、重金属离子浓度为1500 mg/L、pH值为6.5、吸附时间为24 h时,EDTA-LDH/zeolite吸附性能最佳。重金属离子间存在竞争吸附,EDTA-LDH/zeolite对Cd^(2+)、Pb^(2+)、Cu^(2+)的最大吸附容量分别为65.33、98.35和108.51 mg/g。去除过程中沉淀作用、表面络合、螯合反应等多种机制协同作用,去除行为均符合Langmuir等温模型与拟二阶动力学模型。

Ni元素质量分数对65Mn钢木工圆锯片性能的影响

高质量、高效率的木材切削工艺对于提高木材资源的利用率以及提升木质产品的品质具有重要意义。目前,木工圆锯片常用钢材65Mn存在硬度和抗拉强度等力学性能欠佳的问题,为此通过添加镍(Ni)元素对65Mn钢进行改性。采用原料熔炼、浇筑试棒、锻造加工以及热处理等步骤制备Ni改性65Mn钢,并对改性前后的65Mn钢进行显微硬度、冲击韧性和拉伸强度测试。同时运用金相显微镜(metallographic)及扫描电镜(SEM)剖析65Mn钢改性前后的组织构造差异。研究结果表明,1)添加Ni元素后,65Mn钢回火后的组织由回火屈氏体改变为淬火马氏体与回火马氏体的混合体,且当Ni元素质量分数达到0.9%时,出现残余奥氏体;2)在相同热处理工艺条件下,Ni元素对材料的硬度和抗拉强度的影响均呈现出先增大后降低的趋势,冲击韧性较未改性的65Mn钢有所降低。其中,添加质量分数为0.7%Ni元素的65Mn钢的硬度和抗拉强度最优,较未改性的65Mn钢分别增加了10.18%、35.40%(室温)。研究结果为后续木工圆锯片钢材的改良提供了新的思路和方法,有望推动木质加工工具行业的进一步发展。