介孔硅铝酸盐的合成及其在傅克反应中的催化性能

采用溶胶凝胶法合成了一系列有序性好且酸性较强的介孔硅铝酸盐材料。利用X射线粉末衍射(XRD)、透射电镜(TEM)、²⁷Al核磁共振(²⁷Al NMR)、氨气程序升温脱附(HN₃-TPD)及吡啶吸附红外光谱(Py-FT-IR)对制备的介孔硅铝酸盐材料的结构和性能进行表征,并考察了材料在苯甲醚和苯甲醇的傅克烷基化反应中的催化活性。实验结果表明：合成过程中,表面活性剂的用量、硅铝物质的量的比会影响材料结构的有序性,醋酸用量对材料结构有序性影响很小;进一步研究结果表明,n_Si / n_Al比会影响材料的酸催化活性,当n_Si / n_Al=10时材料的酸催化活性最高。氨气程序升温脱附和吡啶吸附红外光谱表明n_Si / n_Al=10的材料含有最多的B酸酸量。     

一种新型介孔磷酸硅铝(SAPO)分子筛的合成及表征

以Silicate-1晶种为硅源,水热合成了一种新型介孔磷酸硅铝(SAPO-1)分子筛,并且通过X射线粉末衍射、红外光谱、透射电镜、扫描电镜、热重分析、N2吸附/脱附和氨气程序升温脱附(NH₃-TPD)等多种手段对产物进行了表征.红外光谱表明,Silicate-1导向剂成功地引入了介孔骨架;氨气程序升温脱附(NH₃-TPD)结果表明,SAPO-1具有较强的酸性.催化结果表明,SAPO-1在大分子催化反应中有较高的活性.     

不同硅铝比Cu-ZSM-5纳米片上N2O催化分解

以双季铵盐表面活性剂为模板剂,水热条件下合成了硅铝比(nSi/nAl)为18、26和95的ZSM-5沸石纳米片,采用离子交换方法制备了铜改性的ZSM-5纳米片样品,并测试了其催化分解N_2O性能。结合X射线衍射(XRD)、N_2吸附/脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)、透射电镜(TEM)、氢气程序升温还原(H_2-TPR)、氧气程序升温脱附(O_2-TPD)和原位红外漫反射光谱(CODRIFT)等表征结果 ,探讨了沸石硅铝比对于催化剂N_2O分解性能的影响及其原因。结果表明,ZSM-5纳米片硅铝比越低,CuZSM-5纳米片催化剂的活性越高。催化活性的提高归因于低硅铝比催化剂上Cu~+活性物种可还原性的增强和吸附氧脱附能力的提高。     

具有多级孔的SAPO-34-H分子筛的合成与表征

以一种多功能长链有机硅为唯一硅源合成了多级孔材料SAPO-34-H(Hierarchical),并对其结构和性质进行了表征.氮气吸附和透射电镜(TEM)照片显示,SAPO-34-H样品不仅拥有常规的微孔体系,还有孔径在5.1nm左右的介孔体系.氨气程序升温脱附表征(NH3-TPD)结果显示,与传统的SAPO-34相比,该材料在引入介孔的同时酸性有所降低.     

超声溶胶-凝胶法制备强酸性介孔材料

 在不使用有机模板剂和孔调节剂的情况下,以无机盐为原料制备了锆和钛修饰的硅铝介孔材料及担载铂的电子-酸性双功能介孔材料. 激光粒度仪和N2吸附-脱附等温线表征的结果显示,制备方法对溶胶的粒度分布和材料的结构性质有较大的影响. 吡啶吸附-脱附的红外光谱表明所得材料具有强的表面酸性,利用XPS和H2-TPR等表征手段确定了材料强表面酸性的来源. 1-己烯加氢异构反应表明所合成的材料具有良好的催化活性.     

磺酸化手性向列型介孔二氧化硅的制备及其催化合成龙脑

通过溶胶凝胶法制备了手性向列型介孔二氧化硅(CNMS)和用浸渍法制备了磺酸化手性向列型介孔硅(CNMS-SO₃H)固体酸催化剂。 通过比表面积分析(BET)、X射线衍射仪(XRD)、红外吸收光谱分析法(FT-IR)、氨-程序升温脱附(NH₃-TPD)和吡啶吸附红外光谱(Py-FTIR)等技术手段表征催化剂的结构和性质。 结果表明,在α-蒎烯与无水草酸物质的量比为1∶0.4,CNMS-SO₃H催化剂用量与松节油的质量比为7∶100。 温度为100 ℃,时间为8 h,龙脑的收率最高为49.89%,α-蒎烯转化率为100%,正龙脑的量是异龙脑的4倍。 固体酸催化剂具有很好的催化活性和稳定性,在重复使用8次之后,α-蒎烯转化率在99%以上。     

中空介孔硅铝球形分子筛的制备及催化裂解性能

利用沸石前驱体溶液和介孔硅球(MSS)为原料,通过水热法成功制备了具有中强酸性介孔壳的中空介孔硅铝球形分子筛(HMAS)。利用透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)、N2-吸脱附、27Al核磁共振(27Al NMR)及NH3程序升温脱附(NH3-TPD)对材料的结构和性能进行了表征。研究结果表明,在MSS的中空过程中伴随有物质再分配和介孔结构的逐渐演变。MSS介孔孔道中的十六烷基三甲基溴化铵(CTAB)分子,一方面保护MSS免遭强碱性沸石前驱体溶液的溶蚀,另一方面作为形成HMAS介孔壳层的模板剂。在此CTAB分子的作用下,沸石前驱体结构单元被引入到HMAS的介孔球壳上。所得材料具有介孔结构和中强酸性,在催化裂解1,3,5-三异丙苯反应中表现出优异的催化性能。     

AlMCM-41介孔分子筛的合成及表征

以拟薄水铝石为铝源、水玻璃为硅源、十六烷基三甲基溴化铵为模板剂,在110℃时水热晶化合成了含Al的MCM-41介孔分子筛.采用X射线衍射(XRD)、N2吸附-脱附、固体29Si、27Al魔角旋转核磁共振技术(MASNMR)、扫描电镜(SEM)及吡啶吸附傅里叶变换红外(FTIR)光谱技术对AlMCM-41分子筛进行了表征.结果表明:AlMCM-41分子筛具有六方排列的孔道结构,同时具有很高的相对结晶度、比表面积和孔容,且孔分布单一;AlMCM-41分子筛中Si原子在骨架内键合的程度更高,使AlMCM-41分子筛具有更好的骨架晶化程度;同时具有四配位骨架铝,使AlMCM-41介孔分子筛具有适当的酸性.     

热处理对HZSM-5结构、酸性及催化乙醇脱水反应性能的影响

对商用HZSM-5分子筛进行高温热处理,利用X射线衍射(XRD)、核磁共振波谱法(²⁷Al-MAS NMR)低温氮吸附、电感耦和等离子体放射光谱(ICP-AES)、氨-程序升温脱附(NH₃-TPD)和吡啶吸附傅里叶变换红外(FT-IR)光谱等技术对高温热处理改性前后样品进行了表征,并考察了高温热处理对分子筛的结构、酸性及催化乙醇脱水制乙烯反应性能的影响。结果表明,热处理改性后的HZSM-5分子筛发生骨架脱铝,B酸减少,L酸增多,孔容增大,出现新的介孔;适中的酸性位和复合型的介-微双孔道结构使其减少了反应中的副反应,乙烯的选择性得到提高,催化剂寿命显著提高。     

铈掺杂的介孔分子筛的水热合成与结构性能

以硅酸钠、硝酸铈铵为原料,十六烷基三甲基溴化铵为模板剂,通过水热法合成铈掺杂的介孔分子筛CeMCM-41.分别采用X射线粉末衍射(XRD)、透射电子显微镜(TEM)、红外光谱(FT-IR)、紫外-可见分光光度计(UV-Vis)和N2吸附-脱附等技术对产物的晶相、结构、形貌、比表面积和孔径进行表征.同时研究硅铈物质的量比对合成材料结构性能的影响.实验结果表明:水热条件下成功合成出铈掺杂的MCM-41介孔分子筛,其比表面积为480.5～1 295.2m2/g,平均孔径在2.70～6.29 nm之间.随着稀土元素铈的掺杂量的增加,CeMCM-41介孔分子筛的比表面积和孔体积变小,介孔有序性变差.     

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。     

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。     

高酸位多级孔超稳Y型沸石的制备及催化性能

以表面活性剂十六烷基三甲基溴化铵（CTABr）为模板剂,在水热体系对水蒸气处理后的超稳Y型（USY）沸石进行晶化处理,获得高酸量和高水热稳定性的USY-c-w样品。利用X射线衍射、扫描电子显微镜、透射电子显微镜、固态核磁共振、N₂吸附-脱附、NH₃-程序升温脱附、傅里叶变换红外光谱及吡啶红外对所制备催化剂的物化性质进行详细表征。选用1,3,5-三异丙苯（TIPB）催化裂化作为探针反应,研究制备的催化剂的催化性能,并与工业USY沸石进行对比。结果表明,再次水热晶化后,样品的硅铝骨架局部重构,非骨架铝重新进入沸石骨架,合成样品的硅铝比（n_SiO2/n_Al2O3）由10降至3.0;再晶化后的USY沸石,不仅具有丰富的介孔结构,并且具有更多的弱酸和中强酸位点。在TIPB裂解反应中,再晶化后的USY沸石表现出比原样品更优异的催化性能。     

康熙《皇城宫殿衙署图》解读(下)*

以尿素为沉淀剂,采用负压沉积沉淀法将Au负载于不同载体,分别制备了Au/HZSM-5、 Au/SiO_2及Au/Al_2O_3催化剂.采用X射线粉末衍射、透射电镜、 NH_3-程序升温脱附、红外羟基和原位吸附吡啶红外羟基等技术对催化剂进行了表征,探究了Au对不同载体的作用,并用脉冲微反装置评价了催化剂对正丁烷脱氢反应的性能.结果表明,相较于其他载金催化剂, Au/HZSM-5酸性较强, Au与HZSM-5相互作用后会形成Si-O(H)-Au基团,该活性相对正丁烷脱氢起到一定的促进作用.     

Hydrolytic vs. Nonhydrolytic Sol-Gel in Preparation of Mixed Oxide Silica–Alumina Catalysts for Esterification

The development of green and sustainable materials for use as heterogeneous catalysts is a growing area of research in chemistry. In this paper, mesoporous SiO₂-Al₂O₃ mixed oxide catalysts with different Si/Al ratios were prepared via hydrolytic (HSG) and nonhydrolytic sol-gel (NHSG) processes. The HSG route was explored in acidic and basic media, while NHSG was investigated in the presence of diisopropylether as an oxygen donor. The obtained materials were characterized using EDX, N₂-physisorption, powder XRD, ²⁹Si, ²⁷Al MAS-NMR, and NH₃-TPD. This approach offered good control of composition and the Si/Al ratio was found to influence both the texture and the acidity of the mesoporous materials. According to ²⁷Al and ²⁹Si MAS NMR analyses, silicon and aluminum were more regularly distributed in NHSG samples that were also more acidic. Silica–alumina catalysts prepared via NHSG were more active in esterification of acetic acid with n-BuOH.     

MnOx/Al-SBA-15的结构性质及低温NH3选择性催化还原NOx

采用后合成法制备MnO_x/Al-SBA-15催化剂, 考察了催化剂的低温NH₃选择性催化还原(SCR)NO_x的性能. 利用傅里叶透射红外变换(FTIR)光谱、N₂吸附-脱附、X射线衍射(XRD)、扫描电镜(SEM)、拉曼光谱(Raman)、X射线光电子能谱(XPS)及NH₃程序升温脱附(NH₃-TPD)的表征手段, 对催化剂的结构性质和SCR性能进行了系统分析. 结果表明, 适量Al的掺杂能提高MnO_x/SBA-15催化剂的SCR活性, 当硅铝摩尔比为50时, 催化剂活性最佳. 表征结果显示, Al掺杂后, 催化剂仍保持良好的骨架结构, 较大比表面、孔容和孔径, 并且Mn在催化剂表面富集, 由低价态转化为高价态, MnO₂为催化剂的主要活性相. 此外, Al的掺杂使MnO_x在催化剂表面高度分散, 表面酸性增强, 从而提高了催化剂的SCR活性.     

Effect of small amounts of Al on the surface silanol structure and their correlation to the improved catalytic performances of WOx/SiO2–Al2O3 in the propene self-metathesis

Surface silanol structures, acid properties, and tungsten dispersion of the sol-gel-derived 7W/SiO₂–xAl₂O₃ (x = 0.2–23 wt%) were investigated by means of ²⁹Si, ²⁷Al, and ¹H MAS NMR, NH₃-TPD, in-situ NH₃-IR spectroscopy, XRD, and Raman spectroscopy. The surface silanol structure changed upon Al and tungsten loadings; however, loading of 1 wt% Al₂O₃ appeared to be the threshold for preserving the Si(OH)Al with isolated bridge after impregnation of 7 wt% W. The 7W/SiO₂–1Al₂O₃ (1 wt% Al₂O₃) was also found to exhibit the lowest ratio of Bronsted to Lewis acid with the highest amount of Lewis acid sites and the best catalyst performances in propene self-metathesis at 550 °C in terms of both propene conversion and ethylene/butene selectivity. Despite its low tungsten dispersion, the metathesis activity was correlated well with the higher amount of tungsten carbene species, which were formed on the catalysts containing higher isolated bridge silanol and the presence of higher Lewis acid sites.     

Analysis of NH3-TPD Profiles for CuSSZ-13 SCR Catalyst of Controlled Al Distribution – Complexity Resolved by First Principles Thermodynamics of NH3 Desorption,IR and EPR Insight into Cu Speciation**

NH₃ temperature-programmed desorption (NH₃-TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NO_x. Herein, we propose an interpretation of NH₃-TPD results, which takes into account the temperature-induced dynamics of NH₃ interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH₃ adsorption on single Cu²⁺, Cu⁺, [CuOH]⁺ centers, dimeric [Cu-O-Cu]²⁺, [Cu-O₂²⁻-Cu]² species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH₃ desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH₃-TPD experiment. Thus, a rigorous interpretation of the NH₃-TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers.     

Theoretical study of isomerism of carbonand silicon-substituted aluminum clusters M<Subscript>6</Subscript>Al<Subscript>38</Subscript> and M<Subscript>12</Subscript>Al<Subscript>32</Subscript>

More than twenty M₆Al₃₈ isomers and several M₁₂Al₃₂ isomers of carbon- and silicon-substituted aluminum clusters with six and twelve dopant atoms of general formula M_nA_l44–n(M = C and Si, n = 6 and 12) have been studied by the density functional theory method. Calculations predict that, in the lowest-lying M₆Al₃₈, isomer, all substitutions of C atoms for Al are localized in one outer surface layer of the aluminum cage. In the course of optimization, the C atoms with a negative charge of about 1e are incorporated into positions of the intermediate layer to transform it into a 12-atom face composed of three adjacent vertex-sharing six-membered rings with short C–Al bonds. In the favorable isomer of M₆Al₃₈, the dopants are scattered as individual Si atoms located in both outer layers or in the subsurface space between the outer layers and the inner core of the cluster. Optimization of low-lying isomers with twelve starting substitutions of C and Si for Al in both outer layers has localized two preferable C₁₂Al₃₂ isomers. One of them contains three covalently bonded diatomic C₂ anions, which are combined through bridging aluminum atoms in the three-dimensional [C₆Al₇] cluster inside the severely distorted outer cage. In the second, most favorable, isomer, the dopants are distributed as isolated C anions; together with the bridging Al atoms, they form the [M₁₂Al₃₂] inner cage with an unusual dumbbell-like structure. For M₁₂Al₃₂, the aluminum cage undergoes moderate distortions. The silicon atoms remain in the outer layers and form five-membered ring subclusters [Si₅] and [Si₂Al₃] bound to the neighboring intermediate layers through elongated and weakened Si–Al bonds. Evaluation of the energies of the model exchange reactions Al₄₄ + M₆ → M₆Al₃₈ + Al₆ and Al₄₄ + 2M₆ → M₁₂Al₃₂ + 2A_l6 shows that for M= C both reaction are exothermic, whereas for M = Si the former reaction is nearly isothermal and the second reaction is endothermic and requires significant energy inputs. The differences between the equilibrium structures and the relative positions on the energy scale of the isomers of the C₆Al₃₈–Si₆Al₃₈ and C₁₂Al₃₈–Si₁₂Al₃₈ clusters are examined.