稀土改性对SO42-/ZrO2固体酸催化剂结构与催化性能的影响

采用共沉淀法和浸渍法在不同条件下制备了稀土-SO₄^2-/ZrO₂系列固体酸催化剂。使用废油脂与甲醇的酯交换反应评价了催化剂活性,并通过X射线衍射、红外光谱、比表面积测定表征方法考察了催化剂结构和性能的关系。结果表明,La摩尔掺杂量4%、焙烧温度600℃时制得的SO₄^2-/ZrO₂-La₂O₃催化剂活性最高,此时脂肪酸甲酯的产率为64.68%,且具有较好的重复使用性。稀土的引入使活性四方相ZrO₂更加稳定,600℃焙烧使催化剂既具有较多活性四方相ZrO₂,又具有较大比表面积,从而提高了催化剂活性。催化剂中形成了固体超强酸结构,且改性后酸强度增大,催化剂活性中心数目增加。     

Al源种类对微乳液法制备固体超强酸催化剂异构化性能的影响

分别以拟薄水铝石、γ-Al₂O₃、Al₂O₃、Al(NO₃)₃·9H₂O为Al源,通过微乳液法制备了一系列Pt-S₂₈O^2-/ZrO₂-Al₂O₃催化剂,并利用XRD、FT-IR、BET、H₂-TPR等手段对其进行了表征,考察了Al源种类对Pt-S₂₈O^2-/ZrO₂-Al₂O₃固体超强酸催化剂结构和酸性的影响,并以正戊烷异构化反应为探针,考察了Al源种类对催化剂异构化性能的影响。结果表明,不同Al源制备的催化剂均能够稳定ZrO₂四方晶相,增大催化剂的比表面积;除以拟薄水铝石为Al源制备的催化剂外,其他催化剂的氧化还原性能均有所提高。以Al(NO₃)₃·9H₂O为Al源制备的催化剂具有最大的比表面积和更多的超强酸,表现出最佳的异构化性能,在反应压力2.0 MPa、氢烃物质的量比4∶1、质量空速(WHSV)1.0 h^-1、反应温度220 ℃条件下,异戊烷产率达到59.5%。     

基于钛锡载体的SCR低温脱硝催化剂的表面性质研究

采用共沉淀法制备TiO₂-SnO₂固溶体,浸渍法负载CeO₂得到一系列xCeO₂/TiO₂-SnO₂负载型催化剂,在模拟NH₃选择性催化还原NO_x(NH₃-SCR)反应条件下考察催化剂低温脱硝活性。通过X射线衍射(XRD)、比表面积测定(BET)、程序升温还原(H₂-TPR)、程序升温脱附(NH₃-TPD)、高分辨率透射电子显微镜(HRTEM)、原位漫反射傅里叶变换红外光谱(in situ DRIFTS)等表征技术,研究了氧化铈负载后催化剂的微观结构、表面物种的存在状态、表面酸位等表面性质及NH₃吸附特性。结果表明,Ce:Ti物质的量比为0.1时,催化剂催化脱硝反应活性最高,同时具有较宽的温度窗口(250~300℃)和热稳定性;铈的过量负载会导致催化剂比表面积减小、活性窗口变窄,同时其氧化还原能力和NH₃吸附能力也减弱。NH₃-TPD结果显示,CeO₂的负载导致催化剂NH₃在弱酸及中等酸位的吸附显著增强,与催化剂NH₃-SCR最佳反应物温度降低有关。in situ DRIFTS表明,xCeO₂/TiO₂-SnO₂催化剂的Lewis酸位和Brønsted酸位强度均明显增强,同时,在1657~1666cm^-1处出现新的Brønsted酸位,参与SCR反应的主要物质是NH₄⁺分子。     

MnOx/SAPO-11催化剂的制备、表征及其低温NH3-SCR活性

分别采用浸渍法、柠檬酸络合法以及沉淀法在SAPO-11分子筛上负载MnO_x,制备了一系列MnO_x/SAPO-11催化剂。考察了催化剂的低温NH₃选择性催化还原(SCR) (NH₃-SCR) NO_x的性能。结果表明,沉淀法制备的负载量为20%(w)的MnO_x/SAPO-11催化剂表现出最优异的低温NH₃-SCR性能及N₂选择性。通过X射线衍射(XRD)、扫描电镜(SEM)、能量散射谱(EDS)、原子吸收光谱(AAS)、N₂吸附-脱附、X射线光电子能谱(XPS)、H₂程序升温还原(H₂-TPR)、NH₃程序升温脱附(NH₃-TPD)以及NO/O₂程序升温脱附-质谱(NO/O₂-TPD-MS)等多种表征手段对催化剂的结构及表面性质进行分析。表征结果显示,采用不同方法制备催化剂时,其表面MnO_x的存在形式和晶相结构不同。沉淀法制备的催化剂表面存在无定型态MnO_x以及MnO₂晶型,具有较大的介孔及外表面积、更多比例的Mn⁴⁺和化学吸附氧,同时表面存在对反应有利的中强酸以及强酸。因此,催化剂在低温SCR反应阶段能够生成重要中间产物NO₂,从而表现出最佳低温活性。同时,三种制备方法均能使MnO_x相对均匀分散在SAPO-11表面。SAPO-11对催化剂表面MnO_x物种的形成具有一定的影响,从而影响催化剂的酸性,拓宽了MnO_x的活性温度窗口,提高了催化剂的N₂选择性。     

磁性纳米固体超强酸的合成、表征及性能

首次制备了SO₄^2-/Co_0.5Fe_2.5O₄-ZrO₂磁性固体超强酸,利用TEM,DTA,XRD和FTIR等手段研究了Co_0.5Fe_2.5O₄磁性基质对ZrO₂的粒子大小、晶化温度与结构的影响.考察了磁性固体超强酸的催化性能及催化剂的寿命、回收率和磁性.结果表明,引入Co_0.5Fe_2.5O₄磁性基质不但赋予催化剂以磁性,而且在固体超强酸形成过程中延迟了ZrO₂由四方晶相向单斜晶相的转变,有助于稳定样品表面的含硫物种,磁性固体超强酸对酯化反应具有较高的催化活性,可活化再生,并保持磁性.     

综合创新设计实验:“均相反应、异相回收”[PIMPS]H2PW12O40双功能催化剂在酯化、氧化反应中的应用*

磺酸类离子液体及多酸催化剂是近年来应用广泛的2类高效环境友好型催化剂,实现2类催化剂组装成单组分双功能化环保型催化剂并运用到大学有机化学实验中,替代现行实验中常用的强腐蚀性、强氧化性的浓硫酸,是未来实验内容改革的方向之一。本实验合成的[PIMPS]H₂PW₁₂O₄₀(PIMPS=1-丙基-3-磺酸基丙基咪唑磺酸盐)催化剂经¹H NMR、IR确证了结构,并将其应用于苯甲酸乙酯合成、苯甲硫醚氧化反应中。实验结果表明,此单组分催化剂具有酸催化、氧化催化双功能特性,催化效果良好,具有可重复使用、无腐蚀性等显著优点。在催化反应中兼具均相催化和非均相催化特点,催化剂能够实现在反应体系中的均相反应、异相回收。通过此实验的开展,培养了学生依据绿色化学理念发现问题、解决问题的创新能力和创新意识,有利于学生深入理解单组分双功能催化剂的概念,有效地达到理论和实践的有机结合。     

PW/SBA-15负载型催化剂的性能研究

合成、表征了一系列SBA-15负载H₃PW₁₂O₄₀(PW)催化剂.负载量高达60%以上时,XRD仍未检测到催化剂上有PW晶相峰.负载后PW保持其Keggin结构,但与载体之间存在较强的相互作用.通过改变PW负载量可调变催化剂的酸性,制得适用于中强酸和弱酸性催化反应的介孔固体酸催化剂.     

载体物化性质对锰铈催化剂NH3-SCR脱硝性能的影响

选取TiO₂、SAPO-34、Al₂O₃三种常用载体,通过浸渍法以Mn-Ce-O为活性组分制备了负载型MnCeO_x脱硝催化剂。采用XRD、BET、H₂-TPR、XPS、Py-FTIR等手段对催化剂的固相结构、比表面积、还原性能、表面元素及酸量进行表征分析。结果表明,MnCeO_x/SAPO-34催化剂具有最大的比表面积（439.87 m²/g）,酸量适中,还原性能最差;MnCeO_x/Al₂O₃催化剂中Mn⁴⁺、Ce³⁺所占比例较高,但酸性最弱;MnCeO_x/TiO₂催化剂还原性能最优,表面Mn、Ce元素浓度最高,并具有大量Lewis酸性位。通过气固相催化反应装置对催化剂性能进行了NH₃-SCR脱硝评价,结果表明,MnCeO_x/TiO₂催化剂具有较好的脱硝性能,反应温度为280 ℃时,NO转化率达100%（空速为42000 h^-1）;与催化剂物化性质对比分析,催化剂的氧化还原能力和Lewis酸性位对其脱硝性能至关重要。     

疏水双功能介孔固体酸的合成及其在乙酸乙酯酯化反应中的应用

通过水热合成法一步合成了具有不同疏水基团－CH₃ 、－(CH₃)₂ 和－(CH₃)₃的双功能介孔固体酸SBA-15-SO₃H－(CH₃)_x催化剂。通过X射线粉末衍射(XRD)、N₂吸脱附、元素分析等方法对催化剂进行了表征,并在乙酸乙酯酯化反应中进行催化性能评价。结果表明,随着疏水前驱体中甲基数的增加,样品的疏水性增强。SBA-15-SO₃H-(CH₃)_x催化剂的催化活性随着疏水性的增强而提高,而具有较强疏水性的材料SBA-15-SO₃H-(CH₃)₃在反应中具有较高的催化性能。以SBA-15-SO₃H-(CH₃)₃为催化剂,酯化反应的最优条件为：温度为120℃,乙酸与乙醇摩尔比为4∶1,催化剂质量分数为1 %,反应时间为1h。在此条件下,乙醇的转化率和乙酸乙酯的选择性分别为93%和100%。     

多酸基复合光催化剂的合成及其太阳光驱动CO2制甲酸研究在实验教学中的设计与探究

温和条件下将二氧化碳(CO₂)高效转化为高值化学品,不仅可以实现碳资源的循环利用,也对减缓温室效应具有重要意义。本实验基于多酸(POMs)复合催化剂制备及其应用于光催化CO₂加氢制甲酸的创新性研究成果,设计了适合本科实验教学的综合创新实验。实验采用浸渍法将Anderson型多酸[H₆(CrO₆)Mo₆O₁₈]^3-分散到TiO₂表面形成多酸复合光催化剂CrMo₆/TiO₂,通过X射线粉末衍射和红外光谱解析了催化剂的结构。利用气相色谱和液相色谱对光催化产物进行分析检测,结果显示,光照条件下CrMo₆/TiO₂复合光催化剂可催化CO₂高选择性转化为液体产物甲酸。紫外-可见光谱分析证实,多酸的修饰减小了TiO₂能带间隙,增加了光谱的吸收范围,提升了光催化性能。本实验内容涵盖了无机材料合成、仪...     

Hydration of dimethyl ether to methanol over solid acids

The hydration of dimethyl ether (DME) to methanol over various solid acids was studied. The acidity of the catalysts is determined by FTIR spectroscopy. The hydration is found to occur predominantly on the Br?nsted acid sites. Among the catalysts studied, WO_x/ZrO₂ and H-ZSM-5 appeared to be most active and selective.     

Sol–Gel Entrapped Lewis Acids as Catalysts for Biodiesel Production

Replacing fossil fuels with biodiesel enables the emission of greenhouse gases to be decreased and reduces dependence on fossil fuels in countries with poor natural resources. Biodiesel can be produced by an esterification reaction between free fatty acids (FFAs) and methanol or by transesterification of triglycerides from oils. Both reactions require homogeneous or heterogeneous catalysis. Production of biodiesel catalyzed by heterogeneous catalysts seems to be the preferred route, enabling easy product separation. As we have previously shown, the Lewis acids AlCl₃ and BF₃ can serve as highly efficient catalysts under ultrasonic activation. The present study focused on the development of oleic acid (OA) esterification with methanol by the same catalysts immobilized in silica matrices using the sol–gel synthesis route. During the course of immobilization, AlCl₃ converts to AlCl₃ × 6H₂O (aluminite) and BF₃ is hydrolyzed with the production of B₂O₃. The immobilized catalysts can be reused or involved in a continuous process. The possibility of biodiesel production using immobilized catalysts under ultrasonic activation is shown for the conversion of FFAs into biodiesel in batch and continuous mode.     

Modulation of Self-Separating Molecular Catalysts for Highly Efficient Biomass Transformations

The energetically viable fabrication of stable and highly efficient solid acid catalysts is one of the key steps in large-scale transformation processes of biomass resources. Herein, the covalent modification of the classical Dawson polyoxometalate (POMs) with sulfonic acids (-SO₃H) is reported by grafting sulfonic acid groups on the POM's surface followed by oxidation of (3-mercaptopropyl)trimethoxysilane. The acidity of TBA₆-P₂W₁₇-SO₃H (TBA=tetrabutyl ammonium) has been demonstrated by using ³¹P NMR spectroscopy, clearly indicating the presence of strong Brønsted acid sites. The presence of TBA counterions renders the solid acid catalyst as a promising candidate for phase transfer catalytic processes. The TBA₆-P₂W₁₇-SO₃H shows remarkable activity and selectivity, excellent stability, and great substrate compatibility for the esterification of free fatty acids (FFA) with methanol and conversion into biodiesel at 70 °C with >98 % conversion of oleic acid in 20 min. The excellent catalytic performance can be attributed to the formation of a catalytically active emulsion, which results in a uniform catalytic behavior during the reaction, leading to efficient interaction between the substrate and the active sites of the catalyst. Most importantly, the catalyst can be easily recovered and reused without any loss of its catalytic activity owing to its excellent phase transfer properties. This work offers an efficient and cost-effective strategy for large-scale biomass conversion applications.     

Carbonylation of tert-butyl alcohol over H-zeolites

The Koch-type carbonylation of tert-butyl alcohol was studied over H-type zeolites. It was found that the catalytic carbonylation of a large amount of tert-butyl alcohol relative to the acidic sites of the H-zeolites in organic solvents requires an elevated temperature and CO pressure, although previous solid state NMR studies have revealed that the transformation of tert-butyl alcohol of an amount comparable to the acidic sites into 2,2-dimethylpropanoic acid proceeds just upon the CO co-adsorption in the H-zeolites at room temperature and atmospheric pressure. The catalytic performance of different H-zeolites and the influence of CO pressure, H₂O addition and solvent effects on the carbonylation of tert-butyl alcohol have been investigated. H-ZSM-5 gives the highest selectivity for 2,2-dimethylpropanoic acid due to its adequate pore dimensions. The present work indicates the possible industrial application of solid acids as carbonylation catalysts instead of liquid acids for the Koch reaction to produce tert-carboxylic acids.     

Heterogeneous catalysts based on B/P/O for the monoetherification of 1,2-dihydroxybenzene in the gas phase

Boron–phosphorus mixed oxides were tested as heterogeneous catalysts for the gas-phase etherification of catechol (1,2-dihydroxybenzene) with methanol, aimed at the production of guaiacol (1-methoxyphenol). This reaction represents an alternative to the etherification processes which makes use of homogeneous catalysts in the liquid phase. The activity of the catalysts was found to depend considerably on the B/P atomic ratio. A catalyst having B/P = 1.0, made of BPO₄, exhibited the best results in terms of (i) conversion of catechol, (ii) selectivity to guaiacol, and (iii) steadiness of performance with time-on-stream. Characterisation of the catalyst using TPD of NH₃ evidenced that this catalyst has the optimal surface acidity, which makes the undesired reactions of tar formation and ring-alkylation slower. Supporting the B/P/O catalysts on α-Al₂O₃ resulted in lower activity, but the catalytic performance was less dependent on the B/P ratio. Doping with potassium resulted in a lowering of the number of acid sites; however, small amounts of dopant led to an increase in activity, possibly due to a co-operation effect between basic and acid sites.     

From Waste Biomass to Solid Support: Lignosulfonate as a Cost‐Effective and Renewable Supporting Material for Catalysis

Lignosulfonate (LS) is an organic waste generated as a byproduct of the cooking process in sulfite pulping in the manufacture of paper. In this paper, LS was used as an anionic supporting material for immobilizing cationic species, which can then be used as heterogeneous catalysts in some organic transformations. With this strategy, three lignin‐supported catalysts were prepared including 1) lignin‐SO₃Sc(OTf)₂, 2) lignin‐SO₃Cu(OTf), and 3) lignin‐IL@NH₂ (IL=ionic liquid). These solid materials were then examined in many organic transformations. It was finally found that, compared with its homogeneous counterpart as well as some other solid catalysts that are prepared by using different supports with the same metal or catalytically active species, the lignin‐supported catalysts showed better performance in these reactions not only in terms of activity but also with regard to recyclability.     

One-Pot Reactions with Sol-Gel Entrapped Catalysts, Acids and Bases

Silica sol-gel entrapped acids, bases and organometallic catalysts are used successfully in one-pot reactions without interfering with each other. Both physically and covalently entrapped acids and bases were employed in these processes, including polystyrene sulfonic acid, 1-propane sulfonic acid, molybdosilicic acid (SiO₂-MoO₃), poly[(vinylbenzyltrimethyl)ammonium] hydroxide and 1,5,7-triazabicyclo[4.4.0]decene. The entrapped metal-based catalysts are Rh₂Co₂(CO)₁₂ and RuCl₂(PPh₃)₃. The one-pot reactions carried out with these heterogenized reagents and catalysts include formation of alkenes under acidic and basic conditions, C—C bond formation by condensation reactions with an -carbon to a carbonyl, hydroformylation and hydrogenation.     

Design of Water-Tolerant Solid Acids: A Trade-Off Between Hydrophobicity and Acid Strength and their Catalytic Performance in Esterification

Water, as a byproduct in esterification, tends to adsorb on solid acid catalysts, causing loss of active components or decomposition of framework and thereby decreasing their reactivity and durability, while the development of water-tolerant solid acids is expected to solve these problems. In this review, the recent developments of major kinds of water-tolerant solid acids including zeolite, mesoporous silica, metal organic framework-based catalyst, magnetic nanoparticles, and polymeric catalyst are discussed in detail. Special attention has been paid to understand the role of hydrophobicity, acid strength, and structure of water-tolerant solid acids in catalytic performance and their stability. From the literature survey, it is found that despite the modified zeolites have a water contact angle as large as 160°, but their acid strength need to be improved and their small micropore sizes restrict their use in catalyzing the esterification of bulky molecules. In contrast, solid acids with abundant acid sites, suitable hydrophobicity, and abundant mesopores or macropores usually exhibit high activity and reusability. Among all the known solid acids, polystyrene-supported acidic ionic liquid catalysts (PS-CH₂-[SO₃H-pIM] [HSO₄]) show a high yield of n-butyl acetate with 99.1% and high reusability of 13 times, which is a breakthrough over the traditional. This review aims to offer a comprehensive understanding for the water-tolerant solid acid catalysts in esterification.

Graphic Abstract

     

Efficient hydrolyzation of cellulose in ionic liquid by novel sulfonated biomass-based catalysts

A green and effective approach for comprehensive hydrolyzation of cellulose has been described. Several carbon-based solid acids were successfully prepared using various biomass (glucose, microcrystalline cellulose, bamboo, and rice husk) and used to catalyze cellulose hydrolysis. The acid groups (–SO₃H and –COOH) were successfully introduced onto the surface of the carbon-based solid acid catalysts as evidenced by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The structure of the prepared catalysts was characterized by scanning electron microscope and X-ray diffraction. The catalysts showed excellent catalytic performance for hydrolysis of cellulose. To improve the reaction efficiency, ball-milling and solubilization in ionic liquids of cellulose were adopted. A maximum total reducing sugar yield of 81.8 % was obtained in ionic liquid 1-butyl-3-methyl imidazolium chloride at 125 °C for 90 min when the water addition was 10 % of ionic liquid. This study provided a promising strategy to synthesize solid acids from lignocelluloses, which were further used to convert biomass into biofuels and platform chemicals.     

Effects of acyl donor type, catalyst type, and reaction conditions on the activity and selectivity of Friedel-Crafts acylation

Acylation of anisole and 3-methylanisole was performed with several acylating reagents (acetylation by AcCl and Ac₂O and bromoacetylation by BrAcCl and (BrAc)₂O) over different solid acid catalysts. The reaction conditions were optimized with respect to the acylation reagent, overall yield, solid acid catalyst, and the products selectivities. While acylation of anisole with acetyl chloride or acetic anhydride resulted in its full conversion to para-substituted acetophenone, the use of bromoacetyl bromide or bromoacetic anhydride yielded also the ortho-substituted product. Acylation of 3-methylanisole also yielded both para- and ortho-substitutions, and the products distribution was affected by the reaction conditions and catalyst type. It was found that while more acidic catalysts (caesium salt of heteropolyacid and zeolites) were the most active towards anisole acylation, the most active catalysts for the acylation of 3-methylanisole were ion-exchange catalysts. Employing HY-740 zeolite resulted in the highest ortho-selectivity in the acylation of anisole with bromoacetyl bromide and bromoacetic anhydride and in the acylation of 3-methylanisole with acetic anhydride.