Synthesis of a nano-crystalline solid acid catalyst from fly ash and its catalytic performance

The synthesis of nano-crystalline activated fly ash catalyst (AFAC) with crystallite size of 12 nm was carried out by chemical and thermal treatment of fly ash, a waste material generated from coal-burning power plants. Fly ash was chemically activated using sulfuric acid followed by thermal activation at 600 °C. The variation of surface and Physico-chemical properties of the fly ash by activation methods resulted in improved acidity and therefore, catalytic activity for acid catalyzed reactions. The AFAC was characterized by X-ray diffraction, FT-IR spectroscopy, N₂-adsorption–desorption isotherm, scanning electron microscopy, flame atomic absorption spectrophotometry and sulfur content by CHNS/O elemental analysis. It showed amorphous nature due to high silica content (81%) and possessed high BET surface area (120 m²/g). The catalyst was found to be highly active solid acid catalyst for liquid phase esterification of salicylic acid with acetic anhydride and methanol giving acetylsalicylic acid and methyl salicylate respectively. A maximum yield of 97% with high purity of acetylsalicylic acid (aspirin) and a very high conversion 87% of salicylic acid to methyl salicylate (oil of wintergreen) was obtained with AFAC. The surface acidity and therefore, catalytic activity in AFAC was originated by increased silica content, hydroxyl content and higher surface area as compared to fly ash. The study shows that coal generated fly ash can be converted into potential solid acid catalyst for acid catalyzed reactions. Furthermore, this catalyst may replace conventional environmentally hazardous homogeneous liquid acids making an ecofriendly; solvent free, atom efficient, solid acid based catalytic process. The application of fly ash to synthesize a solid acid catalyst finds a noble way to utilize this abundant waste material.     

Synthesis and characterization of fly ash supported sulfated zirconia catalyst for benzylation reactions

Synthesis of highly active nano-crystalline, thermally stabilized solid acid catalyst has been reported by loading different weight fractions of sulfated zirconia on chemically activated fly ash through two step sol-gel technique. The catalysts were characterized using powder XRD, FT-IR, N₂-adsorption desorption study, CHNS elemental analysis, SEM-EDAX and their acidity were measured by pyridine adsorbed FTIR. Liquid phase benzylation of benzene and toluene with benzyl chloride was studied as test reaction for catalytic activity of SZF catalysts. A very high conversion of benzene (87%) and toluene (93%) were observed, which is attributed to significant amount of acid site on the catalyst surface. The FTIR study of the pyridine adsorbed samples reflects the presence of Brønsted as well as Lewis acid sites. The catalyst with 12 wt.% zirconia (SZF-12) was regenerated and reused up to four reaction cycles with equal efficiency as in the first run.     

Fly ash supported calcium oxide as recyclable solid base catalyst for Knoevenagel condensation reaction

A new type of solid base catalyst has been prepared by loading of CaO on thermally activated fly ash, with the aim of being used as heterogeneous catalyst for fine chemical production. The prepared fly ash supported calcium oxide catalyst (FAC) was characterized by FT-IR spectroscopy, X-ray diffraction analysis, Scanning Electron Microscopy and atomic absorption spectroscopy. The catalytic activity of FAC was evaluated by Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate as model test reaction under optimized conditions. The catalyst gave very high conversion (87%) of benzaldehyde to desired product ethyl (E)-α-cyanocinnamate with high purity. The catalyst was completely recyclable without significant loss in activity up to three reaction cycles, which confers its stability during reaction unlike commercial catalysts. Moreover this catalyst shows a promising future in providing environmentally clean process for the industrial sector.     

Synthesis and characterization of novel solid base catalyst from fly ash

A new type of solid base catalyst was synthesized by chemical and thermal activation of fly ash, collected from Thermal Super Power Station situated in Kota, Rajasthan, India. The chemical activation was carried out by 50 wt.% NaOH followed by thermal activation at 450 °C. The modified physiochemical property of solid base fly ash (SBFA) was determined by X-ray diffraction, FT-IR spectroscopy, Scanning Electron Microscopy, N₂ adsorption-desorption studies and Flame Atomic Absorption Spectrophotometry. The results reveal that the catalyst is nano-crystalline in nature with crystallite size 11 nm and particle size in the range 840 nm to 6.95 μm. The surface basicity and therefore, catalytic activity in SBFA was originated by increased hydroxyl content as compared to fly ash, suggesting that the catalyst possess higher surface active sites. The basicity of the catalyst was measured by liquid phase, solvent free, single step condensation of benzaldehyde with cyclohexanone giving higher conversion (>70%) and selectivity (>80%) of desired product α,α′-dibenzylidenecyclohexanone. This excellent conversion shows that the catalyst has sufficient basic sites both on the surface and in the bulk, responsible for the catalytic activity. Furthermore, this catalyst may replace conventional environmentally hazardous homogeneous liquid bases making an ecofriendly; solvent free, solid base catalyzed process. The application of fly ash to synthesize a solid base catalyst finds a noble way to utilize this abundant waste material.     

Synthesis of TPA impregnated SBA‐15 catalysts and their performance in polyethylene degradation reaction

Tungstophosphoric acid (TPA)‐containing mesoporous santa barbara amorphous (SBA)‐15 materials were synthesized by impregnation of TPA into hydrothermally synthesized SBA‐15. TPA was incorporated to the porous framework of silica with different W/Si ratios, using TPA hydrate as the acid source. The synthesized materials had a surface area range of 212–825 m² g^?1, depending on the TPA loading and exhibited Type IV adsorption–desorption isotherms. Energy dispersive spectrometry and X‐ray photoelectron spectroscopy (XPS) analyses showed that TPA was successfully penetrated into mesopores of the SBA‐15 material. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis of the pyridine adsorbed synthesized materials revealed the existence of Lewis and Brønsted acid sites in the synthesized materials. Their performances were tested in the degradation of polyethylene by thermogravimetric analysis. An increase in TPA content significantly lowered the degradation temperature and activation energy of the polyethylene degradation reaction. In the presence of TPA‐incorporated SBA‐15 catalyst, activation energy was reduced to approximately half‐value of the value found in the absence of the catalyst. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2466–2472, 2012     

硅烷偶联剂对粉煤灰/废胶粉复合材料性能的影响

在废胶粉和粉煤灰中加入硅烷偶联剂γ-氨丙基三乙氧基硅烷(KH-550)或双-[γ-(三乙氧基硅)丙基]四硫化物(Si-69),制备粉煤灰/废胶粉(FA/URP)复合材料。研究了KH-550和Si-69的用量和加入方式对试样的力学性能及耐热性能的影响。并用扫描电镜(SEM)和红外光谱(FT-IR)进行了表征。结果表明:用Si-69对粉煤灰的改性效果好于KH-550;最佳用量和加入方式为Si-69 1.0份,硅烷偶联剂先与粉煤灰混合,而后再与废胶粉混合。SEM证实Si-69/FA/URP比KH-550/FA/URP的相容性好;FT-IR证明了硅烷偶联剂中的Si—OH和粉煤灰表面的—OH发生脱水缩合,形成了Si—O键;在此条件下制得的粉煤灰/废胶粉复合材料具有很好的力学性能。邵尔A硬度为84度,拉伸强度为6.8 MPa,扯断伸长率为49%,磨耗为1.3 cm3/km,可以作为板材或铺路材料。     

SCR脱硝中催化剂表面NH4HSO4生成及分解的原位红外研究

采用工业用V₂O₅-WO₃/TiO₂催化剂,基于傅里叶原位红外光谱(in situ FT-IR)技术考察了SCR脱硝过程中催化剂表面NH₄HSO₄的生成与分解特性。结果表明:在V₂O₅-WO₃/TiO₂催化剂表面ABS的生成可由催化剂V═O基团上Lewis酸上配位吸附活化态的NH₃在O₂环境中与SO₂反应生成,也可由SO₂与催化剂表面反应生成的吸附态金属硫酸盐中间物VOSO₄与气态NH₃直接反应生成;NO能通过与NH₄HSO₄中的NH₄⁺直接反应来降低NH₄HSO₄降解的温度窗口,促进其在催化剂表面的分解行为,NO的脱除与NH₄HSO₄的生成是相互抑制关系;NH₄HSO₄本身的负载量影响其分解与挥发行为。     

蒙脱土负载型固体酸催化剂的烷基化性能与结构研究

以酸化后蒙脱土为载体，采用浸渍蒸发法制备了环境友好的蒙脱土负载znCl2型固体酸催化剂。研究了蒙脱土酸化处理、ZnCl2负载量及活化温度对催化剂烷基化活性的影响，并初步考察了催化剂的稳定性，比较了几种不同酸催化剂的烷基化活性。利用XRD、BET、TG—DTA、吡啶吸附FTIR对催化剂的结构进行了表征和测定；结果表明，蒙脱土酸化处理后形成的孔道有利于负载ZnCl2，ZnCl2与蒙脱土的羟基之间存在着化学键合，经活化后转化成Zn(0H)C1。蒙脱土负载ZnCl2后明显地提高蒙脱土表面的总酸量，催化剂活性与其表面总酸量之间有关，催化剂表面L酸与B酸的共存有利于其烷基化活性的提高。实验条件下，蒙脱土负载ZnCl2型催化剂在苯与氯节的烷基化反应中表现出较高的催化活性，二苯甲烷的收率最高可达83．6％。与其它Lewis酸试剂及酸化蒙脱土相比，蒙脱土负载型催化剂催化活性大有提高。     

Synthesis and application of a novel strong and stable supported ionic liquid catalyst with both Lewis and Brønsted acid sites

Poly(4-vinylpyridine)-supported ionic liquid with both Lewis and Brønsted acid sites was easily prepared from its starting materials and used as a novel and highly efficient heterogeneous catalytic system for the synthesis of biscoumarins by two-component one-pot domino Knoevenagel-type condensation/Michael reaction between various aliphatic and aromatic aldehydes with 4-hydroxycoumarin. The Lewis and Brønsted acidic sites loading in [P₄VPy-BuSO₃H]Cl-X(AlCl₃) were found to be 2.15 and 0.9 mmol per gram of catalyst, respectively. The effect of the simultaneous presence of Lewis and Brønsted acid sites was evaluated. The catalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), elemental analysis, and atomic absorption technique. The catalyst is stable (as a bench top catalyst) and reusable.     

Conversion of Fly Ash—An Environmentally Detrimental Waste to Zeolite Beta (BEA) for Commercial Catalytic Applications

Zeolite beta (BEA) was synthesized hydrothermally using fly ash as a combined source of alumina and silica. The overall crystallization period required to obtain pure crystalline BEA zeolite was found to be slightly longer when fly ash was used. The physicochemical properties of BEA phases obtained using fly ash (FLBEA) and conventional source materials (CONBEA) were compared. The H/FLBEA catalyst has exhibited excellent catalytic performance in commercially important benzene isopropylation process. These results have demonstrated that converting fly ash into BEA zeolite not only alleviates the disposal problem but also turns an otherwise waste material into a marketable commodity.     

破乳法合成N掺杂TiO2/粉煤灰及其可见光催化性能研究

粉煤灰表面负载TiO2制备光催化材料是粉煤灰高附加值资源化应用的一种新途径,通过破乳的方法在粉煤灰表面负载TiO2是一种新的尝试.以十二烷基苯磺酸钠改性的粉煤灰为载体,纳米TiO2胶体为钛源,NaOH为破乳剂,尿素为氮源,在反应釜中通过破乳的方法成功合成了N掺杂的TiO2/粉煤灰复合材料.通过扫描电子显微镜(SEM)、...     

MnOx/WO3/TiO2低温选择性催化还原NOx机理的原位红外研究

浸渍法制备15% MnO_x/5% WO₃/TiO₂低温脱硝催化剂,利用原位傅里叶变换红外（in situ FT-IR）设计包括多种吸附反应以及不同预处理方式的微观暂态试验与微观稳态试验,研究其NH₃-SCR脱硝反应机理,并推测反应路径。结果表明,催化剂的NH₃-SCR反应主要以Eley-Rideal机理方式进行,仅在一定温度条件下可以看到Langmuir-Hinshclwood反应路径。催化剂表面Lewis酸位的NH₃吸附是还原剂的主要来源,Brønsted酸位吸附的NH₄⁺随温度上升参与反应的比例略有提高。NH₃的吸附活化是整个反应的控制步骤,吸附态NH₃更易与NO₂发生反应,NO与催化剂表面的相互作用明显弱于NO₂。NO会在催化剂表面氧化活性中心形成大量双齿配位型硝酸盐,阻碍NH₃的吸附和活化,O₂存在条件下促进NH₃-SCR反应进行,阻止NO在催化剂表面形成双齿硝酸盐。NO与NH₃在催化剂表面存在吸附竞争,NO的吸附作用强于NH₃,温度达到100℃后吸附的NH₃方可大量活化并与NO_x发生进一步反应。     

On the catalytic nature of Mn/sulfated zirconia for selective reduction of NO with methane

In this work, the catalytic nature of Mn loaded sulfated zirconia (SZ) catalysts for the selective catalytic reduction (SCR) of NO with methane was investigated by a combination of reactions and characterizations such as FT-IR spectroscopy, H₂-TPR, UV–vis diffuse reflectance spectroscopy (DRS) and NO-TPD. It was found from the results of reactions and FT-IR spectra that the strong Brønsted and Lewis acid sites in the Mn/SZ catalysts were essential for the SCR of NO with methane. The loading of Mn increased the number of strong Lewis acid sites on the surface of SZ catalyst, which is one reason for its promoting effect. On the other hand, FT-IR spectra, H₂-TPR and UV–vis DRS of the catalysts demonstrated that the presence of the SO₄²⁻ species occupied the terminal OH sites on the surface of ZrO₂ support and thereby restrained the formation of more oxidative and nonstoichiometrically dispersed MnO_x (1.5 < x < 2) phase. Such an effect of SO₄²⁻ suppressed the combustion reaction of CH₄ by O₂ and increased the selectivity towards NO reduction. The NO-TPD showed that the loading of Mn increased the adsorption of NO over SZ catalyst, which is another reason for the promoting effect of Mn.     

固体酸催化F-C酰基化反应脱除焦化苯中的噻吩

采用Friedel-Craft反应,乙酸酐作为酰化剂,对焦化苯进行脱硫精制。通过对比MCM-41、HZSM-5和Mont-K10及其负载型催化剂的催化活性,发现未负载型Mont K10具有最高的催化活性,并且随着ZnCl₂负载量的增大,催化活性反而降低。采用FT-IR对固体酸催化乙酰化反应机理进行探讨,发现固体酸表面的L酸是此反应的活性中心,负载ZnCl₂不仅能改变酸位的数量而且能改变酸的强度。通过对反应条件进行优化,转化率可以达到99.4 %。对Mont-K10催化寿命的考察结果表明,经过3次再生还原,催化剂的催化活性仍能恢复,转化率仍在90 %以上,只不过处理量减少为原来的一半。     

Reactivity and surface properties of silica supported molybdenum oxide catalysts for the transesterification of dimethyl oxalate with phenol

A series of MoO₃/SiO₂ catalysts were prepared with Mo loadings ranging from 1 to 16 wt% and applied to the transesterification of dimethyl oxalate (DMO) with phenol. The results showed that the catalyst of MoO₃/SiO₂ with 1 wt% Mo content performed best, giving 54.6% conversion of DMO and 99.6% selectivity to target products, methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). The surface properties were investigated by means of X-ray diffraction (XRD), X-ray photoelectron (XPS), BET specific surface area, temperature-programmed desorption (TPD) of ammonia, and FTIR analysis of adsorbed pyridine. XPS and XRD analyses indicated that Mo(VI) species was highly dispersed at low Mo loading and MoO₃ of the crystal structure appeared at higher loading. NH₃-TPD characterization and FTIR analysis of adsorbed pyridine demonstrated that only Lewis weak acids were present on catalyst surface and the amount of Mo loading has little effect on the strength of the surface acid on MoO₃/SiO₂. The catalytic results exhibited that the synergetic effect of Mo active centers with weak Lewis acid sites catalyzed transesterification of DMO with phenol.     

Synthesis of Hf/SBA-15 Lewis acid catalyst for converting glycerol to value-added chemicals

Hf/SBA-15 catalyst containing highly ordered two-dimensional hexagonal mesoporous silica with a large surface area is prepared in a facile one-step sol–gel method with hafnia content ranging from 2.5 to 10%. The synthesized catalyst is characterized by X-ray diffraction analysis, N₂ adsorption–desorption isotherm, scanning electron microscope and transmission electron microscope. The oxidation state and Lewis acidic properties of 10% Hf/SBA-15 are investigated by diffuse reflectance UV–Vis technique, X-ray photoelectron spectroscopy and pyridine-adsorbed FT-IR analysis. The catalytic activity of Hf/SBA-15 is employed in the acetalization of glycerol with acetophenone and benzaldehyde, order of activity of the catalyst is 10 > 5 > 2.5% Hf/SBA-15. The 10% Hf/SBA-15 is given 43 and 21% selectivity of six-membered (1,3-dioxane) and five-membered (1,3-dioxolane) acetals. Hence, this catalyst is further exploited in the acetalization of glycerol with substituted acetophenone and benzaldehyde. The catalyst could be recycled for five times without a significant decrease in activity.     

Direct synthesis of carbon nanofibers from South African coal fly ash

Carbon nanofibers (CNFs), cylindrical nanostructures containing graphene, were synthesized directly from South African fly ash (a waste product formed during the combustion of coal). The CNFs (as well as other carbonaceous materials like carbon nanotubes (CNTs)) were produced by the catalytic chemical vapour deposition method (CCVD) in the presence of acetylene gas at temperatures ranging from 400°C to 700°C. The fly ash and its carbonaceous products were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), laser Raman spectroscopy and Brunauer-Emmett-Teller (BET) surface area measurements. It was observed that as-received fly ash was capable of producing CNFs in high yield by CCVD, starting at a relatively low temperature of 400°C. Laser Raman spectra and TGA thermograms showed that the carbonaceous products which formed were mostly disordered. Small bundles of CNTs and CNFs observed by TEM and energy-dispersive spectroscopy (EDS) showed that the catalyst most likely responsible for CNF formation was iron in the form of cementite; X-ray diffraction (XRD) and Mössbauer spectroscopy confirmed these findings.     

Selective catalytic reduction of NO by ammonia with fly ash catalyst

This paper investigates the selective catalytic reduction (SCR) of NO with NH₃ using fly ash catalyst. The catalytically active elements investigated here included Fe, Cu, Ni and V. The results indicated that fly ash, after pre-treatment, can be reasonably used as the SCR catalyst support to remove NO from flue gas. Cu gave the highest catalytic activity and NO conversion, compared with Fe, Ni and V. In the pre-treatment process, the nitric acid treatment and drying temperatures for the fly ash particles had little effect on the NO conversion. However, the calcination temperature had an important effect on the catalyst preparation process.     

The effect of mechanically and chemically activated fly ashes on mortar properties

Fly ash is a waste material from coal-burning power plants that consume pulverized solid fuels. Two fly ashes from Asturias (Spain) were activated mechanically by wet milling and chemically by leaching with sulfuric acid. The activated fly ashes were characterized in terms of physico-chemical characterization, granulometry, density, blaine, BET, XRD and SEM.A comparative study was carried out of several mortars, in some cases using different additions of silica fume or activated fly ash. The influence that these additives have on the mechanical resistance of the mortars was studied. As well as the possible use of these activated fly ashes as a replacement for silica fume in producing high-strength mortar or concrete. It was found that mortars containing activated fly ash presented higher compressive strengths.A mercury intrusion porosimetry study was carried out on cement mortars made with mineral additives such as silica fume and activated fly ashes. In general, the porosities values of these mortars showed that mineral admixtures improved mechanical resistance due to the decrease in pore size.     

Novel Solid Acid Catalyst,Bentonite-Supported Polytrifluoromethanesulfosiloxane for Friedel–Crafts Acylation of Ferrocene

Solid acid catalyst, bentonite-supported polytrifluoromethanesulfosiloxane (B-PTFMSS) has been for the first time prepared and used in the Friedel–Crafts acylation of ferrocene with various acyl chlorides. The catalytic activities were influenced by reaction time, reaction temperature, solvent and loaded amount of B-PTFMSS. It was found that the new catalyst B-PTFMSS possessed the advantages of high activities giving similar yield of aliphatic acyl ferrocene (>70%) as conventional Lewis acid catalyst aluminum chloride and it can be used repeatedly and easily regenerated. B-PTFMSS has also been characterized by IR spectra, pyridine adsorbed IR, specific surface area and XRD.