原位红外光谱法测定介孔材料表面酸性

采用原位红外光谱技术研究介孔材料表面酸性,结果表明吡啶同酸性中心作用最佳实验条件为：真空度10-3Pa,活化温度400℃,室温吸附30min。该实验条件下,测得MCM-41介孔分子筛表面B酸位和L酸位同时存在,脱附温度升高时B酸向L酸转化。     

H2O2处理对HZSM-5分子筛结构及催化环己烯水合性能的影响

利用H2O2对HZSM-5分子筛进行处理,并采用X射线衍射、N2低温吸附、扫描电子显微镜、NH3-TPD和吡啶吸附-脱附红外光谱等方法进行表征.考察H2O2处理对HZSM -5结构以及催化环己烯水合反应活性的影响.结果表明,处理后分子筛的颗粒变小,颗粒尺寸(0.5～0.7) μm,酸量下降,L酸中心数减少,B酸增强.H...     

乙醇辅助剂对MCM-22分子筛结构及催化性能的影响

以六亚甲基亚胺为模板剂,乙醇为有机辅助剂,采用动态水热法合成了一系列MCM-22分子筛,利用X射线衍射(XRD)、氨程序升温脱附(NH3-TPD)、傅里叶变换红外光谱(FT-IR)和电子扫描显微镜(SEM)等表征手段考察了乙醇辅助剂对MCM-22分子筛的结构及酸性的影响.结果表明,添加适量的乙醇可以有效调控分子筛结构性能和结晶度,分子筛的强酸位的强度适度增强,弱酸位的强度减弱,总酸量和B酸中心数增大,而L酸中心数减少,且晶粒尺寸减小,比表面积增加,但过量的乙醇会导致ZSM-5分子筛的生成.以苯和丙烯烷基化合成异丙苯为模型反应,评价对所制备的分子筛催化性能,发现添加合适的乙醇得到的MCM-22分子筛具有更高的催化活性和选择性.     

改性NaY分子筛上多乙苯和苯烷基转移反应性能

为了提高烷基转移催化剂性能性,以不同骨架硅铝比的NaY分子筛为原料,利用"两交-水热-焙烧"后改性工艺得到了一系列USY分子筛。通过X射线衍射(XRD)、N_2-物理吸附、扫描电镜(SEM)、氨气程序升温脱附(NH_3-TPD)、吡啶吸附红外光谱(Py-IR)等表征手段研究了各USY分子筛的骨架硅铝比、孔结构特征以及酸性质,考察了各USY分子筛上苯与多乙苯烷基转移反应性能。结果表明:以骨架硅铝比为5.9的NaY分子筛为原料进行水热处理改性,有利于保持微孔结构且制得的USY分子筛比表面积和介孔量大、所含强B酸中心比例较高(B酸/L酸比为1.01),提高了活性位的可接近性及扩散能力,而且强B酸中心为苯与多乙苯烷基转移反应提供比较充足的活性位。在反应温度170℃、反应压力3 MPa、苯与多乙苯质量比2、质量空速为3.3 h~(-1)的实验条件下,二乙苯转化率和三乙苯转化率分别达到了67%和55%以上,乙苯选择性达到了99%以上。因此进一步调变NaY分子筛的合成工艺,合成具有较高骨架硅铝比的Y型分子筛可提高烷基转移催化剂的活性。     

氧化镁改性HZSM-5分子筛的酸性及在合成气直接制二甲醚反应中的应用——镁前驱体的影响

以乙酸镁为前驱体采用浸渍法制备了一系列不同氧化镁(MgO)含量(0%～20%)的镁改性HZSM-5分子筛,并采用X射线衍射(XRD)、N2吸附、X射线光电子能谱(XPS)、氨程序升温脱附(NH3-TPD)和吡啶吸附红外光谱(Py-IR)方法对其结构和酸性进行了表征.在连续流动加压固定床反应器中及温度260℃、压力4 Mpa和气体空速1500 mL·gcat·h)-1条件下,考察了以上述HZSM-5分子筛为甲醇脱水活性组分与铜基甲醇合成活性组分(CuO-ZnO-Al2O3)所组成的双功能催化剂对合成气直接制二甲醚反应的催化性能.结果表明,HZSM-5分子筛经适量的MgO改性后,产物中二甲醚的选择性由49.1%提高到68%以上,而二氧化碳和烃类副产物的选择性则分别由37.1%和9.3%降低到27%和0.1%以下.烃类和二氧化碳副产物减少的原因是MgO改性降低了HZSM-5分子筛强酸中心的酸量,尤其是减少了强Br?nsted酸的酸量.另外,与以硝酸镁为前驱体制备的MgO/HZSM-5不同,MgO在较大的范围(2.5%～20%)内对其催化性能几乎无影响.     

Selective synthesis of p-xylene by alkylation of toluene with dimethyl carbonate over magnesium acetate-modified ZSM-5

以乙酸镁为前体,采用等体积浸渍法制备不同负载量的MgO/ZSM-5催化剂,在气相连续流动固定床反应器上对甲苯与碳酸二甲酯（DMC）择形烷基化合成对二甲苯进行了研究。采用XRD、NH₃-TPD、吡啶吸附红外和2,4-二甲基喹啉吸附红外等手段对催化剂进行了表征。结果表明：B酸中心是甲苯与DMC烷基化反应的活性中心;随着MgO负载量的增加,甲苯转化率下降,对二甲苯的选择性上升;当MgO负载量大于9%时,甲苯转化率和对二甲苯选择性基本保持不变。2,4-二甲基喹啉吸附红外表征结果表明,乙酸镁在改性过程中未进入ZSM-5孔道内,焙烧分解生成的MgO主要分布在分子筛的外表面,分子筛孔内酸位并未受到影响。随着MgO负载量的增加,催化剂外表面的B酸位数量下降,当负载量大于9%时,外表面的B酸位基本消失。     

AgNaZSM-5分子筛催化剂的酸性质表征

采用离子交换法制备AgNaZSM-5分子筛催化剂,并利用吡啶吸附红外光谱(Py-IR)、氨程序升温脱附(NH_3-TPD)实验和正己烷裂解反应研究AgNaZSM-5催化剂被氧化还原后的酸性质。结果表明;催化剂中的Ag~+很容易被氢气或正己烷还原成Ag,分子筛的阳离子位变成了质子,从而起酸催化作用;在氧化性气氛中,Ag物种以Ag~+形式位于阳离子位上。     

不同硅铈比Ce-MCM-41介孔分子筛酸性及结构表征

采用水热法合成了不同硅铈比的Ce-MCM-41介孔分子筛,并采用X射线衍射(XRD)、NH3程序升温脱附(NH3-TPD)、吡啶吸附红外光谱(PY-IR)、透射电镜(TEM)、X射线光电子能谱(XPS)和N2吸附-脱附等手段对Ce-MCM-41介孔分子筛的介孔结构、表面酸性、铈元素的含量和化学态进行表征。结果表明:当Si与Ce的物质的量之比(n(Si/Ce)由100减小至30时,Ce-MCM-41介孔分子筛仍具有典型的六方介孔结构特征,样品表面都存在B酸和L酸中心;当n(Si/Ce)为10时,样品结构有序性下降,B酸含量最多,分子筛中引入的金属Ce元素以Ce3+和Ce4+共存于催化剂中,但主要以Ce4+为主。     

纳米级ZSM-12分子筛的合成及表征

采用双季铵盐模板剂溴代1,4-二氮甲基哌啶基-丁烷,通过动态水热晶化法成功制备了纳米级ZSM-12分子筛。采用X射线衍射、扫描电镜、透射电镜、红外光谱分析及N2吸附-脱附技术等测试方法对所得颗粒进行了研究。所合成的颗粒呈长条形状,长约150 nm,宽约30 nm。所得的ZSM-12沸石结晶体结构完整,无明显骨架缺陷,富含微孔和介孔孔隙。介孔孔隙来源于ZSM-12纳米晶粒之间的堆积孔隙。在酸分布上,所得的HZSM-12分子筛的中强酸及B酸比例较多,使得该沸石在催化反应中具备优良的反应活性。     

Nb-SBA-15的制备及吸附脱氮性能

以SBA-15介孔分子筛为载体,采用浸渍法制备了Nb-SBA-15介孔分子筛,采用X射线衍射、BET、Fourier变换红外光谱、热重–差热分析和吡啶吸附红外光谱分析等测试手段对其进行分析,用喹啉的十二烷溶液为模型化合物,采用静态吸附法在间歇式反应器中对其吸附脱氮性能进行评价。结果表明:Nb-SBA-15分子筛具有高度有序的二维六方介孔结构,并且具有一定的酸性,焙烧温度为300℃,铌酸负载量(质量比)为10%时,Nb-SBA-15具有最高的吸附脱氮率,为65.19%。     

Modification of pillared MFI zeolite nanosheets by nitridation with tailored activity in benzylation of mesitylene and benzyl alcohol

The modification of pillared MFI zeolites was performed by nitridation of silica pillared MFI zeolite nanosheets under NH₃ atmosphere with different time. The resultant zeolites were characterized by a complementary combination of X-ray power diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), pyridine-IR spectroscopy and N₂ adsorption–desorption isotherms. The analyses showed that the nitridation didn't destroy the crystallinity and specific surface area of zeolites, and the acidity of zeolites can be tailored by tuning the time of nitridation, resulting in the different concentration ratios of Brønsted-to-Lewis (B/L) acid sites. Moreover, the nitrided zeolites exhibited high selectivity to 2-benzyl-1,3,5-trimethylbenzene than parent silica pillared MFI zeolite nanosheets in benzylation of mesitylene with benzyl alcohol. A balance between Brønsted acid sites and Lewis acid sites can inhibit the self-etherification of benzyl alcohol and enhance the selectivity of alkylated product. These experimental data implied that nitridation was an effective method to modulate the acidity of zeolites and the synergy between Brønsted acid sites and Lewis acid sites was a decisive factor to determine the selectivity.     

几种沸石分子筛的催化裂化性能研究:1孔结构和酸性

采用X-射线衍射、X射线荧光光谱、N2吸附、吡啶吸附红外光谱和NH3程序升温热脱附研究了分子筛RE-HY,HZSM-5和Hβ的基本物理化学性质。N2吸附结果表明,三维孔道结构的REHY分子筛和Hβ分子筛具有相近的孔半径和吸附量;与HZSM-5和Hβ分子筛相比,高温条件下,REHY分子筛具有较多的Brφsted酸中心和较少Lewis酸中心。NH3程序升温热脱附表明,三种分子筛中,HZSM-5分子筛的强酸中心最多。     

含氮杂原子B-Beta分子筛的制备及其对Knoevenagel缩合反应的催化性能

水热合成杂原子B-Beta分子筛,低温氮化二次处理制备N掺杂的新型碱催化剂,利用Knoevenagel缩合反应进行碱性催化性能评价,考察氮化温度、反应时间、不同氮化前驱体及催化剂稳定性对反应的影响.结果表明,采用低温500℃氮化处理的杂原子B-Beta分子筛催化剂具有优异的催化活性,苯甲醛转化率及产物选择性均接近100...     

Effects of the Nitridation of Y and USY Zeolites on their Catalytic Activity for the Base Catalyzed Knoevenagel Condensation

This contribution reports on the preparation, physicochemical characterization and catalytic performances of nitrided zeolites in the Knoevenagel condensation reaction. These basic materials were prepared by subjecting one Y zeolite (Si/Al ratio of 2.6) and two ultrastable Y zeolites (Si/Al ratio of 13 and 37) to nitridation, i.e., treatment with ammonia at high temperature. Both the amount and the chemical nature of incorporated nitrogen species were controlled by the nitridation temperature. Namely, an increase of the temperature induces an increase of the nitrogen content and the appearance of nitrogenous species in the following order of increasing temperature: NH₄ ⁺, adsorbed NH₃, –NH₂, >NH and >N–. The nitridation occurred practically in the same manner whatever the Si/Al ratio of the starting material. However, from a catalytic point of view different behavior was observed. No direct correlation was found with the nitrogen content of the samples. Nitrided zeolites were found to exhibit catalytic activity as long as the zeolitic framework was maintained.     

NH3-TPD and FTIR spectroscopy of pyridine adsorption studies for characterization of Ag- and Cu-exchanged X zeolites

Pure crystalline NaX zeolites with Si/Al = 1.2 is prepared by the hydrothermal method. The modification is achieved by following the conventional ion-exchange technique to obtain Ag- and Cu-exchanged forms of NaX zeolite with different metal loadings ranging from low to high exchange. Compositional and structural investigations of all samples are performed by atomic absorption spectrometry, elemental analysis, powder XRD, and nitrogen adsorption porosimetry. The acidity of all exchanged zeolites is investigated using both the ammonia temperature-programmed desorption (NH₃-TPD) carried out by microbalance, and the pyridine adsorption performed via Fourier transform infrared spectroscopy (FTIR). XRD analysis shows the global conservation of the zeolitic structure after ionic exchange. The crystallinity loss is more important for zeolites exchanged at high degree of copper. Porosity measurements indicate a decrease of the porous volumes and the specific surface areas when the Ag or Cu exchange degree is raised. Mesopores particularly appear at high exchange degree of copper. NH₃-TPD indicates that the increase of Ag and Cu-exchange degrees leads to an increase of the global acidity, which is more pronounced for Cu-exchanged zeolites. The strength of acid sites for Ag-exchanged zeolites is weaker than for Cu-exchanged zeolites. The FTIR spectroscopy analysis by pyridine adsorption confirms the formation of extra framework aluminum (EFAL) species, inducing an increase in the concentration and the strength of the Lewis acidity. The formation of EFAL is more important for Cu-exchanged zeolites.     

Molecular models of catalytically active sites in zeolites. Quantum chemical approach

A brief review of quantum chemical studies of different active sites in zeolites is presented. Various factors that significantly affect the strength of Brønsted acid sites in zeolites are discussed. An interaction of zeolite protons with entrapped metal particles is considered as a reason of electron-deficiency of metal clusters in zeolite cavities on the Pd and Pt species as an example. Probable precursors of Lewis acid sites (LAS) and reliable molecular models of the LAS in zeolites are discussed on the basis of quantum chemical analysis. Transition metal ions can be catalytically active in the lattice or extra-lattice zeolite positions and the two possibilities are considered for selective oxidation site in titanium silicalite and FeZSM-5 zeolite catalysts, respectively.     

The acidity and catalytic behavior of Mg-ZSM-5 prepared via a solid-state reaction

A series of Mg-ZSM-5 zeolite catalysts with different content of magnesium were prepared via a solid-state reaction of HZSM-5 with magnesium chloride at 327°C. X-ray determinations demonstrated that the structure and crystallinity of the catalysts were not changed as compared with HZSM-5 zeolite. The acidity of the catalysts was characterized by temperature programmed desorption of ammonia and infrared spectra of pyridine adsorption. The studies indicated that their Brønsted acid sites decreased and Lewis acid sites slightly increased with increasing magnesium amount in the zeolites. The catalytic properties of the catalysts have been examined by choosing the alkylation of toluene with methanol as probe reaction. The results showed that the modified zeolite catalysts significantly improved the initial activity and lifetime. Para-selectivity also increases to a level of 80–90%. These results indicate that the solid-state reaction is an effective and convenient route for modification of the zeolite.     

Dinitrogen as a probe of acid sites of zeolites

Nitrogen adsorption on H-ZSM-5 and H-Y zeolites at low temperatures were studied by in situ FT-IR spectroscopy. For each zeolite, two absorption bands were observed at around 2334 and 2352 cm^–1 in thev(NN) region and were assigned to thev(NN) mode of dinitrogen species adsorbed on Brønsted and Lewis acid sites of the zeolites, respectively. These results and previous results for H-mordenite suggest that dinitrogen serves as a probe of acid sites and its advantages as probe are discussed.     

用NH3-TPD研究改性HY沸石的表面酸性

利用NH3-TPD（Temperature—Programmed Desorption）技术对盐酸、草酸和酒石酸化学脱铝改性及无水AlCl3负载改性后的HY型沸石分子筛的表面酸性进行了表征，考察了脱铝改性用酸的浓度、种类对HY沸石表面酸性的影响规律。研究结果表明：酸脱铝改性可以调节HY沸石的酸强度、酸量和强酸与弱酸中心的比例，无水AlCl3负载后催化剂的表面总酸量减少，L酸比例增大。     

A novel method for enhancing on-stream stability of fluid catalytic cracking (FCC) gasoline hydro-upgrading catalyst: Post-treatment of HZSM-5 zeolite by combined steaming and citric acid leaching

This article describes a novel modification method consisting of steaming and subsequent citric acid leaching to finely tune acidity and pore structure of HZSM-5 zeolite and thereby to enhance the on-stream stability of the zeolite derived fluid catalytic cracking (FCC) gasoline hydro-upgrading catalyst. A series of dealuminated HZSM-5 zeolites and their derived catalysts were prepared and characterized by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), ²⁷Al MAS NMR, nitrogen adsorption, temperature programmed desorption of ammonium (NH₃-TPD) and infrared (IR) spectroscopy of chemisorbed pyridine. The results showed that the citric acid leaching could preferentially remove the extra-framework Al (EFAl) species formed by steaming treatment and thus reopen the EFAl-blocked pore channels of the steamed zeolite. The steaming treatment at a suitable temperature and subsequent citric acid leaching not only decreased the strength of acid sites to a desirable degree but also increased the ratio of medium and strong Lewis acidity to medium and strong Brönsted acidity, both of which conferred the resulting catalyst with superior selectivity to aromatics, good hydroisomerization activity and gasoline research octane number (RON) preservability, as well as enhanced on-stream stability. The results fully demonstrated that the treatments by steaming and followed citric acid leaching can serve as an important method for adjusting the physicochemical properties of HZSM-5 zeolite.