Diels-Alder Reaction with Transition Metal/Zeolites

Transition metal/Y zeolites were prepared by microwave solid state and aqueous solution ion-exchange methods. The activity of these zeolites was investigated in a Diels–Alder reaction of cyclopentadiene and maleic anhydride, anthracene and maleic anhydride. The yield of these reactions increased in order of (NaY < Fe²⁺Y < Fe³⁺Y < MnY < CuY ≈ NiY < CoY ≈ CrY < ZnY) for both methods. The aqueous solution ion-exchanged zeolites showed higher activity in comparison to solid state exchange. About 65–70% yield was observed for the Diels–Alder reaction with ZnY Zeolite. Endo-selectivity was observed for these reactions. Received in final form: 14 January 2005     

Conversion of acids to benzimidazoles with transition metal/zeolites

Transition metal/Y zeolites were prepared using microwave solid state and aqueous solution ion exchange methods. The activity of these zeolites was investigated in a conversion of acids to benzimidazoles reaction between 4-methyl-1, 2-phenylenediamine and 3-nitrobenzoic acid. The yield of these reactions increased in order of CuY < Fe²⁺Y < NiY < CoY < NaY < CrY < MnY < ZnY for both methods. The solid state ion-exchanged zeolites showed higher activity in comparison to the aqueous solution exchange. Yields of products in the presence of the ZnY zeolite were of the order of 69–83%. It seems that the Lewis sites are better sites compared to the Bronsted sites for this reaction.     

高活性甲醇氧化羰基化CuY催化剂的结构及催化活性中心

采用硝酸铜溶液和NaY分子筛溶液离子交换制备了CuY催化剂,通过加入氨水提高交换溶液的pH值以及高温焙烧活化,显著提高了甲醇氧化羰基化合成碳酸二甲酯的催化活性,与固相离子交换、沉积和浸渍法制备的催化剂相比,虽负载的铜量较低,但催化活性较高. 通过元素分析、XRD、H2-TPR、XPS和AES等对CuY催化剂微观结构的表征表明,在Cu(NO3)2离子交换溶液中加入氨水,促进了Cu2+离子交换的进行,提高了CuY催化剂的Cu交换量,并且交换的Cu2+主要落位于分子筛的超笼中. 在惰性气氛中焙烧活化CuY催化剂,Cu2+自还原为Cu+,氨促进了自还原过程的进行,显著提高了催化剂的活性. 焙烧活化温度越高,越有利于超笼中Cu2+→Cu+的自还原过程,使超笼中Cu+的含量增加, CuY催化活性增加. 进一步研究表明Y分子筛超笼中的Cu+是主要的催化活性中心.     

NaY分子筛的改性及吸附脱氮性能

采用离子交换法用NH⁺₄、Zn²⁺、Cu²⁺、Cr³⁺阳离子改性NaY分子筛,并利用XRD、FT-IR和低温N₂吸附-脱附等方法对改性的分子筛进行了表征。XRD 和FT-IR表征结果表明,改性后的分子筛骨架完好。Cr改性Y分子筛(CrY)的比表面积、孔体积及平均孔径均较小,但存在部分介孔。研究了改性分子筛对含喹啉模拟燃料的吸附脱氮,喹啉分子尺寸的模拟结果为0.711 6 nm×0.500 2 nm,说明其并不易进入Y型分子筛0.74 nm的微孔。吸附脱氮结果表明,CrY的脱氮效果最好,CuY和ZnY次之,NH₄Y效果最差,改性分子筛的吸附脱氮性能与金属离子的价态有关,同价金属离子改性后的分子筛,吸附时间对其影响趋势相同,且金属离子价态越高,改性分子筛的吸附脱氮性能越好。吸附温度对CrY和NH₄Y分子筛吸附脱除喹啉的影响不大,可在室温下使用,但高温有利于CuY和ZnY吸附脱氮。XRD表征结果表明,焙烧后CrY分子筛骨架已完全塌陷失去了绝大部分吸附脱氮性能。     

CuY制备方法对其催化甲醇氧化羰基化活性中心的影响

以Cu(NO₃)₂为铜源,以NaY和HY分子筛为载体,通过溶液离子交换法和等体积浸渍法制备了不同的无氯CuY催化剂,并进行了气相甲醇氧化羰基化催化活性研究。通过浸渍法制备的催化剂Cu含量为10%,而以NaY和铜氨溶液离子交换制备的催化剂Cu含量只有6.3%,但其催化活性和选择性均较好。通过催化剂的Cu元素分析、低温氮吸附-脱附、XRD、H₂-TPR、XPS和TPD等表征表明,溶液离子交换法制备的催化剂,Cu物种以离子的形式高度分散于分子筛骨架结构中,较好地保持了分子筛晶体结构,并对甲醇有较强的吸附能力,催化活性较高,而将等体积浸渍Cu(NO₃)₂溶液后的HY或NaY分子筛,在400 ℃焙烧过程中,发生了固体离子交换反应,形成了连接于分子筛骨架的Cu²⁺,但以HY为载体更容易进行固体离子交换,未交换的铜物种以CuO的形式分散到分子筛表面。在600 ℃高温活化中,催化剂中Cu²⁺可部分还原为活性物质Cu⁺,但以NaY和铜氨溶液离子交换制备的催化剂Cu²⁺自还原能力最大。     

Oxidation of cyclohexane catalyzed by metal-ion-exchanged zeolites

The ion-exchange rates and capacities of the zeolite NaY for the Cu(II), Co(II), and Pb(II) metal ions were investigated. Ion-exchange equilibria were achieved in approximately 72 h for all the metal ions. The maximum ion exchange of metal ions into the zeolite was found to be 120 mg Pb(II), 110 mg Cu(II), and 100 mg Co(II) per gram of zeolite NaY. It is observed that the exchange capacity of a zeolite varies with the exchanged metal ion and the amount of metal ions exchanged into zeolite decreases in the sequence Pb(II) > Cu(II) > Co(II). Application of the metal-ion-exchanged zeolites in oxidation of cyclohexane in liquid phase with visible light was examined and it is observed that the order of reactivity of the zeolites for the conversion of cyclohexane to cyclohexanone and cyclohexanol is CuY > CoY > PbY. It is found that conversion increases by increase of the empty active sites of a zeolite and the formation of cyclohexanol is favored initially, but the cyclohexanol is subsequently converted to cyclohexanone.     

Electrochemical behavior of Ni(II) incorporated in zeolite Y-modified carbon electrode: application for electrocatalytic oxidation of methanol in alkaline solution

Nickel ions were incorporated in NaY zeolite according to cation exchange mechanism. Then NiY zeolite was used as modifier for preparation of modified carbon paste electrode. The electrochemical behavior of NiY-modified carbon paste electrode (NiY/CPE) was studied in alkaline solution using cyclic voltammetry method. Ability of different electrodes containing NiY/CPE, Ni-NiY/CPE, Ni-NaY/CPE, and Ni/CPE for electrocatalytic oxidation of methanol was compared (three last electrodes prepared by open circuit accumulation of Ni(II) ions on the surface of NiY/CPE, NaY/CPE, and bare CPE, respectively). Results show that Ni-NiY/CPE is best catalyst for the electrochemical oxidation of methanol in alkaline solution and both process of earlier Ni ion incorporation through cation exchange in NaY zeolite and open circuit accumulation of Ni ion on the surface of electrode are essential to have good catalyst. Effect of graphite–zeolite ratio on electrocatalytic current was studied and 3:1 ratio of graphite–zeolite was selected as optimum ratio for preparing electrode. Ni-NiY/CPE has very good stability toward the methanol oxidation in concentration range of 0.005 to 0.5 M. Finally, using chronoamperometric method, the catalytic rate constant (k) for methanol was found to be 1.56 × 10⁴ cm³ mol⁻¹ s⁻¹.     

介孔调变对CuY催化剂甲醇氧化羰基化反应活性的影响

碱溶液处理NaY分子筛形成的介孔有利于反应物及产物分子的扩散,调节碱溶液浓度可控制Y分子筛中的介孔结构,通过溶液离子交换法制备CuY催化剂,研究了NaY分子筛介孔结构调变对CuY催化剂催化甲醇氧化羰基化反应活性的影响。通过BET、~(29)Si-NMR、XRD、NH_3/CO-TPD、H_2-TPR和TEM等表征及催化活性分析表明,在碱溶液处理过程中,NaY分子筛骨架中的Si(0Al)和Si(1Al)原子被优先脱除,且笼结构坍塌使得临近超笼连接,逐步形成直径为3.47~3.66 nm,孔容介于0.142~0.226cm~3·g~(-1)的介孔,在提高反应物分子和产物分子扩散性能的同时,提高了活性物种的可接近性。随着碱液浓度的增加,CuY催化剂的催化活性先升高后降低。当碱液浓度为0.2 mol·L~(-1)时,NaY分子筛介孔直径为3.47 nm,孔容达到最大(0.226 cm~3·g~(-1)),相应CuY催化剂DMC的时空收率、选择性和甲醇转化率分别达到204.0 mg·g~(-1)·h~(-1)、67.8%和14.0%,活性最佳。     

Comparative Study of Nickel Catalysts Supported on X- and Y-Zeolites

We have made a comparative study of CO/H₂ reactions over the nickel catalysts supported on X- and Y-zeolites, prepared by incipient-wetness impregnation (W) and ion-exchange (E) methods. The catalysts were characterized by surface area and volumetric chemisorption measurements, temperature programmed reduction profiles, and x-ray diffraction analysis. The results show that the turnover frequency decreases in the order; NiX(W)>NiY(W)>NiY(E)>NiX(E). The metal dispersion and catalytic activity of the catalyst are mainly affected by the support materials, the preparation methods, and the activation procedures. The high activity of NiX(W) was due to its higher reducibility, smaller nickel crystalline size, and better nickel dispersion. The low activity of NiX(E) was attributed to the poor ion-exchange of Ni with NaX, the poor reducibility, the large crystalline size, and the poor nickel dispersion.     

CuY型分子筛制备及吸附脱硫影响因素研究

通过液相离子交换法制备CuY型分子筛,并利用正交实验得到了制备过程中交换时间、交换温度、铜离子浓度的最佳条件。系统研究了CuY分子筛的焙烧温度、吸附时间、吸附温度对其吸附脱除模拟油中二苯并噻吩(DBT)的影响。采用XRD、ICP及BET比表面积分别对不同CuY分子筛的骨架结构及阳离子负载量进行了研究。结果表明,二次交换后,分子筛已达到交换平衡,最佳焙烧温度为450℃,温度过高会破坏分子筛的骨架结构;分子筛上的吸附水对其吸附脱除二苯并噻吩的能力有较大的影响。     

载体H+含量对CuY甲醇氧化羰基化反应性能影响

通过过量浸渍Cu(NO_3)_2溶液于Y分子筛载体上,制备出Cu负载量为6.4%的CuY催化剂,考察了甲醇氧化羰基化反应的催化性能,并采用X射线衍射(XRD)、H2程序升温还原(H2-TPR)、透射电子显微镜(TEM)和NH3程序升温脱附(NH3-TPD)等手段对催化剂表面微观结构进行了表征。研究表明,随Y分子筛载体H+含量的增加,可使更多Cu物种落位于分子筛微孔笼结构中,且高度分散,而笼内未交换的Na+能进一步促进铜物种更多落位于载体超笼结构中,形成更多甲醇氧化羰基化反应的Cu+活性中心。同时随铜物种引入,催化剂中产生了明显的中强酸,酸量随落位于载体笼结构中的Cu物种的增加而增加,催化剂总酸量随之增加,导致甲醇氧化羰基化产物分布发生改变,碳酸二甲酯(DMC)选择性明显降低。对比等体积浸渍法制备的92.3%的高DMC选择性CuY催化剂,以不含H+的NaY分子筛为载体,过量浸渍法制备的CuY催化剂酸量少、Cu物种活性中心多,在保持82.4%的高DMC选择性时,其DMC的时空收率(STY)也高达109.1mg·g~(-1)·h-1。     

酸处理对CuY催化剂孔结构及氧化羰基化性能的影响

对NaY分子筛(n_Si/n_Al=2.65)进行了草酸脱铝处理并作为载体采用液相离子交换法制备CuY催化剂, 应用于常压甲醇氧化羰基化合成碳酸二甲酯(DMC)反应。NaY分子筛及其CuY催化剂通过N₂低温吸附-脱附、透射电子显微镜、X射线衍射、²⁹Si固体核磁共振、NH₃吸附程序升温脱附、吡啶吸附红外光谱、H₂程序升温还原、原子吸收等方法进行表征。研究结果表明, 酸处理NaY分子筛后, 骨架铝被脱除, 导致骨架n_Si/n_Al比增加、相对结晶度降低并产生介孔, 有利于产物分子的扩散, 从而影响催化活性。采用4 h、2 mol·L^-1草酸处理NaY分子筛作为载体制备的CuY催化剂显示出较高的催化性能, DMC时空收率和甲醇转化率分别从103.6 mg·g^-1·h^-1和6.3%增加到184.9 mg·g^-1·h^-1和10.2%。产生的介孔能够促进催化剂中铜活性位的可接近性及反应物分子和产物分子的扩散。     

金属络合物制备分子筛负载金属催化剂的CO加氢反应性能

应用Ｙ分子筛吸附Ｆｅ（ＣＯ）５、Ｃｏ（ＣＯ）３ＮＯ和Ｍｏ（ＣＯ）６的温和热分解制备分子筛负载金属催化剂，从分子筛交换阳离子和吸附金属络合物之间的相互作用说明其ＣＯ加氢产物的分布特点。实验结果表明，分子筛内阳离子和吸附金属络合物间的相互作用显著影响制得催化剂的结构和反应的产物分布。由于金属络合物和分子筛内阳离子间的电子转移，使ＮｉＹ附载金属催化剂显示出高的ＣＯ转化率和甲烷选择性。在ＣｕＹ中，这种电子     

酸处理对CuY催化剂孔结构及氧化羰基化性能的影响

对NaY分子筛(n_Si/n_Al=2.65)进行了草酸脱铝处理并作为载体采用液相离子交换法制备CuY催化剂,应用于常压甲醇氧化羰基化合成碳酸二甲酯(DMC)反应。NaY分子筛及其CuY催化剂通过N₂低温吸附-脱附、透射电子显微镜、X射线衍射、²⁹Si固体核磁共振、NH₃吸附程序升温脱附、吡啶吸附红外光谱、H₂程序升温还原、原子吸收等方法进行表征。研究结果表明,酸处理NaY分子筛后,骨架铝被脱除,导致骨架n_Si/n_Al比增加、相对结晶度降低并产生介孔,有利于产物分子的扩散,从而影响催化活性。采用4 h、2 mol·L^-1草酸处理NaY分子筛作为载体制备的CuY催化剂显示出较高的催化性能,DMC时空收率和甲醇转化率分别从103.6 mg·g^-1·h^-1和6.3%增加到184.9 mg·g^-1·h^-1和10.2%。产生的介孔能够促进催化剂中铜活性位的可接近性及反应物分子和产物分子的扩散。     

CuNaY分子筛的制备及其催化甲醇氧化羰基化

采用多种铜盐溶液与NaY分子筛离子交换制备了CuNaY催化剂,通过加入氨水提高溶液pH值以及高温活化,显著提高了该催化剂对甲醇氧化羰基化合成碳酸二甲酯的反应活性。不同的铜盐水溶液交换制备的CuNaY催化剂催化活性不同,添加氨水将溶液pH值调节为11后,离子交换制备的CuNaY催化剂的催化活性和DMC选择性明显升高且趋于一致。经元素分析、XRD、XPS和H₂-TPR表征可知,加入氨水可促进Cu²⁺离子交换的进行,提高CuNaY催化剂中Cu的交换量,催化剂中约75%的Cu²⁺定位于分子筛的超笼中。     

NiY分子筛表面酸性影响其选择性吸附脱硫性能的机理研究

采用原位红外光谱技术,以噻吩、环己烯和苯为模型探针分子,分别考察单一烃分子在NiY分子筛上的吸附与反应行为以及噻吩与烯烃、芳烃间的竞争吸附和催化反应行为。单一探针分子吸附研究发现,NiY分子筛中与Ni物种相关的Lewis(L)酸位是噻吩的选择性吸附活性位;噻吩和环己烯在NiY分子筛中Brnsted(B)酸位上发生的质子化和低聚反应明显弱于HY分子筛。双探针分子竞争吸附研究发现,环己烯二聚体在NiY中强B酸位上的强化学吸附与噻吩存在显著的竞争吸附行为。另外,苯和噻吩在NiY上的竞争吸附现象在373K时明显减弱。由此,在选择性吸附脱硫过程中,减少吸附剂表面B酸中心可降低烯烃对噻吩的竞争吸附,另外适当提高吸附体系的温度可以有效避免芳烃对噻吩的竞争吸附。     

Etude De L'acidité De Zéolithes Y Modifiées Par Différents Cations. Application à la réaction de reformage sec du méthane

A series of modified zeolite catalysts (HYM) was prepared by ion-exchange of a commercial faujasite Y by various cations (M=Ni, Cr, Fe, Li, Ce). The exchange level was calculated from the chemical analysis results. The acidity of the samples was determined by ammonia adsorption calorimetry which allowed the simultaneous determination of the number and strength of the acid sites. The order of acidity obtained was the following: HYCr>HY>HYNi>HYLi>HYFe>HYCe. These catalysts were tested in the dry reforming reaction of methane by carbon dioxide in the 400–700°C domain, under atmospheric pressure. The best catalytic performances were observed with the HYNi sample which displayed methane and dioxide conversions of 74,1 and 78,5% respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermogravimetric investigation

Ion-exchange of transition metal ions into montmorillonite was investigated using two different ion-exchange procedures. Performing ion-exchange from aqueous solution of the respective metal ion leads to material possessing measurable BrØnsted acidity, while the solid-state exchange materials show predominantly Lewis acidity.Measurements by means of a derivatograph allowed us to construct a feasible reaction mechanism for solid-state ion exchange. Satisfactory correlation was found between the results calculated from the reaction steps assumed and the measurements by means of a derivatograph.Financial support by the Hungarian Research Fund (OTKA T014275) is gratefully acknowledged. The skilful technical assistance of Kati Barna is highly appreciated.     

Photocatalytic isomerization of norbornadiene over Y zeolites

K, Zn, Cs and La ion-exchanged Y zeolites were prepared and used as photocatalysts for the isomerization of norbornadiene. The prepared catalysts were characterized by EDS, XRD, ²⁷Al- and ²⁹Si-NMR, UV-vis and IR. The La-exchanged sample showed the highest degree of exchange, but accompanied with some dealumination. La-exchange generated both B-acid and L-acid sites, whereas other metals produced only L-acid sites. For the photocatalytic isomerization reaction, the activity order was LaY > CsY > ZnY > KY. The heavy atom effect and B-acidity are expected to play important roles in the reaction.     

Production of reducing sugar from corn stover by dilute acid hydrolysis co-catalyzed with metal salts under microwave radiation

Acid hydrolysis of corn stover under microwave radiation by adding four metal salt co-catalysts (ferrous sulfate, copper sulfate, zinc sulfate, and manganese sulfate) to produce reducing sugar was investigated. The influences of microwave power, reaction time, sulfuric acid concentration, and co-catalyst concentration on the yield of reducing sugar were studied. The results show that the catalytic effects of ferrous sulfite and copper sulfate are more obvious for the yield of reducing sugar compared with only dilute acid hydrolysis with microwave radiation. Long-time microwave irradiation resulted in secondary hydrolysis, generating small-molecule compounds and decreasing the yield of reducing sugar. The reducing sugar yield was increased by decreasing the hydrolysis reaction time and microwave radiation power. In terms of reducing sugar yield, the four kinds of metal salt co-catalyst act in the order: ferrous sulfate > copper sulfate > sulfuric acid zinc sulfate > manganese sulfate. At concentration of 3.0 %, the best was ferrous sulfate, producing yield of 35.10 %.