Mesoporous Solid Acid Catalysts Research Articles

Ordered mesoporous zirconium oxophosphate supported tungsten oxide solid acid catalysts: the improved Brønsted acidity for benzylation of anisole

A series of WO3 supported on ordered mesoporous zirconium oxophosphate solid acid catalyst was employed in benzylation reaction.

Improving the Selectivity toward Three‐Component Biginelli versus Hantzsch Reactions by Controlling the Catalyst Hydrophobic/Hydrophilic Surface Balance

AbstractThe catalytic activities and selectivities of two kinds of mesoporous solid acids SBA‐15‐PrSO3H 1, SBA‐15‐Ph‐PrSO3H 2, and a periodic mesoporous organosilica (PMO) based solid acid Et‐PMO‐Me‐PrSO3H 3 that comprise different physicochemical surface properties were compared in an environmentally benign one‐pot, three‐component Biginelli reaction of aldehydes, β‐ketoesters and urea or thiourea under solvent‐free conditions. Among these mesoporous solid acid catalysts, 3, which has a hydrophobic/hydrophobic balance in the nanospaces (mesochannels) in which the active sites are located, is found to be a significantly more selective catalytic system in the Biginelli reaction; it produces the corresponding 3,4‐dihydropyrimidin‐2‐one\thione (DHPM) 5 derivatives in good to excellent yields and excellent selectivities. Notably, in the case of conducting the three‐component coupling reaction of benzaldehyde, metylacetoacetate and urea in the presence of 1 result in the generation of a mixture of Hantzsch dihydropyridine 4 (≈37 %) and Biginelli dihydropyrimidinone 5 (≈49 %), whereas the same reaction with 2 (catalyst loading of 1 mol % as well) furnishes the corresponding aldolic product methyl‐2‐benzylidene‐3‐oxobutanoate 6 as the major product (≈80 %) with concomitant formation of small amounts of 5 (<10 %) under essentially the same reaction conditions that are employed with catalyst 3. Water adsorption–desorption analysis of the catalysts is employed to possibly relate the observed selectivity to the difference in physicochemical properties of the materials.

Single step esterification of algae oil using mesoporous solid acid catalyst

Algae oil is an underutilized carbon neutral oil that is considered to be a drop-in replacement for transportation fuels in the future. In this work, an acid-catalyzed esterification process which uses an acid loaded KIT-5 mesoporous material was investigated for the production of algal biodiesel. The optimum conditions for transesterification of algal oil with methanol, using mesoporous framework loaded with acid catalyst, were found to be 60°C reaction temperature, 6hour reaction time, 1:2vol/vol ratio of algal oil to methanol and 1.5% catalyst (w/w). Under these optimal conditions, the use of 35% phosphotungstic acid loaded KIT-5 catalyst led to a 98% conversion of algal oil to fatty acid methyl esters. Catalyst recycling and regeneration studies were also conducted.

Transesterification Catalyzed by Superhydrophobic–Oleophilic Mesoporous Polymeric Solid Acids: An Efficient Route for Production of Biodiesel

We report here an efficient mesoporous polymeric solid acid catalyst (p-PDVB-SO3H) with superhydrophobic–oleophilic properties synthesized from copolymerization of divinylbenzene (DVB) with sodium p-styrene sulfonate under solvothermal conditions. N2 isotherm showed that p-PDVB-SO3H has large BET surface area and uniform mesopore. Contact angle tests showed that p-PDVB-SO3H exhibits superhydrophobic–oleophilic property for triolein and methanol, which results in its good miscibility and high exposition degree of active sites for various organic reactants. Catalytic tests showed that p-PDVB-SO3H has much better catalytic activities and recyclability toward transesterification to biodiesel than those of H-form mesoporous ZMS-5 zeolite, carbon solid acid and commercially acidic resin of Amberlyst 15, which will be very important for its wide applications for biodiesel production in industry. Superhydrophobic–oleophilic mesoporous solid acid of p-PDVB-SO3H exhibits very good wettability for methanol and plants oil, further leading to its high exposition degree of active sites, which results in its excellent catalytic activity toward transesterification to biodiesel.

Organic/inorganic MCM-41 magnetite nanocomposite as a solid acid catalyst for synthesis of benzo[α]xanthenone derivatives

In the present study, for the first time the synthesis of organic–inorganic MCM-41 mesoporous magnetite nanoparticles (MNPs@MCM-41) as a new class of solid acid catalyst with large density of sulfonic acid groups was suggested. The specific surface area and textural property of synthesized nanoparticles were improved through the coupling of inorganic and organic components by template synthesis on the magnetite nanoparticle surface. The new solid acid catalyst was prepared in three steps: (i) preparation of colloidal iron oxide magnetite nanoparticles (Fe3O4MNPs) with particle size lower than 8.0nm, (ii) development of an organic–inorganic MCM-41 mesoporous structure with thiol groups on the surface of MNPs (Fe3O4@MCM-41SH) and (iii) oxidation of thiol groups to sulfonic acid (Fe3O4@MCM-41SO3H). The incorporation of sulfonic acid as a functional group on the surface of MNPs@MCM-41 was achieved by simultaneous reaction of condensable inorganic silica species and thionilayted organic compounds (co-condensation, one-pot synthesis) that lead to magnetite mesoporous solid acid catalyst. The properties of prepared magnetite nanocomposite were characterized by FT-IR, XRD, UV-DRS, TEM, VSM and titration. Finally, the applicability of the synthesized nanocomposites was tested as heterogeneous solid acid catalyst for one-pot three component synthesis of aryl benzo[α]xanthenone derivatives in room temperature and solvent free conditions.

Synthesis of novel pyrazolylbiscoumarin derivatives using FeTUD-1 as a mesoporous solid acid catalyst

A series of novel pyrazolyl biscoumarins was synthesized at 80 °C in a one pot procedure using an Fe3+ incorporated mesoporous silicate catalyst (FeTUD-1). The wormhole structured FeTUD-1 catalyzed the condensation of pyrazole aldehyde (1,3-diphenyl-1H-pyrazole-4-carbaldehyde) and 4-hydroxy coumarin to give the product in ∼85% yield. XRD and N2 sorption studies of FeTUD-1 confirmed its amorphous, mesoporous nature, which possessed a large surface area of 638 m2 g−1 and a pore diameter of 9.4 nm. The nature of Fe3+ ion co-ordination within the silica matrix was evaluated by different techniques including diffuse reflectance UV-Vis, FTIR, and EPR. FeTUD-1 possessed both Bronsted and Lewis acidity, as measured by FTIR of pyridine adsorption, that are responsible for the observed activities.

The influence of hydrophobic/hydrophilic balance of the mesoporous solid acid catalysts in the selective dehydration of fructose into HMF

The application of a number of mesoporous sulfonic acids including MCM-41–PrSO3H (1a), MCM-41–Ph–PrSO3H (1b), SBA-15–PrSO3H (2a), SBA-15–Ph–PrSO3H (2b), SBA-15–EtPhSO3H (3a), and SBA-15–Ph–EtPhSO3H (3b) with different surface hydrophobicity in acid-catalyzed dehydration of fructose into 5-hydroxymethylfurfural (HMF) in a water–nitromethane solvent mixture was investigated. Among the studied mesoporous solid acids, the catalysts with lower surface hydrophobicity and relative acidity were found to be more selective and efficient catalytic system for HMF production. Our studies showed that the hydrophilic surface of the employed solid acids might indeed provide a means of faster departure of HMF from the system mesopores as soon as it forms, thus retarding the rehydration of HMF to unwanted by-products and improving the HMF selectivity. HMF selectivity of 75% was reached in 93% fructose conversion in a water–NM system at 140 °C within 30 min in the presence of catalyst 2a, which is comparable or even superior to other systems which employ MIBK–2-butanol or other organic co-solvents.

Benzylation of Toluene over Iron Modified Mesoporous Ceria

Green chemistry has been looked upon as a sustainable science which accomplishes both economical and environmental goals, simultaneously.With this objective, we developed an alternative process to obtain the industrially important benzyl aromatics by benzylation of aromatics using benzyl chloride, catalysed by mesoporous solid acid catalysts. In this work mesoporous ceria is prepared using neutral surfactant which helped the calcination possible at a lower temperature enabling a higher surface area. Mesoporous ceria modified with Fe can be successfully utilized for the selective benzylation of toluene to more desirable product methyl diphenyl methane with 100% conversion and selectivity in 2 hours using only 50mg of the catalyst under milder condition. The reusability, regenerability, high selectivity, 100% conversion, moderate reaction temperature and absence of solvent, etc. make these catalysts to be used in a truly heterogeneous manner and make the benzylation reaction an environment friendly one. © 2012 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Ordered organo-inorganic hybrid mesoporous solid acid catalysts (Zr–TMS–TFA) for Michael addition of indoles with α,β-unsaturated carbonyl compounds under environmentally benign solvent free conditions

The trifluoromethanesulfonic (trflic) acid functionalized Zr–TMS materials were synthesized and characterized by powder XRD, N2-sorption, elemental analysis, FTIR spectroscopy, NH3–TPD, and 13C CP MAS NMR techniques. The samples with different loadings of triflic acid (TFA) over Zr–TMS (5–25wt.%) were synthesized. The acid density of TFA functionalised Zr–TMS (Zr–TMS–TFA) materials increased with loading of TFA from 5 through 25wt.%. The catalytic performance of Zr–TMS–TFA catalysts was evaluated in Michael addition of 3-methylindole to α,β-unsaturated ketones under liquid phase and solvent free reaction conditions. For example, the conversion of 3-methylindole increased with increasing loading of TFA from 38 through 87%. The selectivity of C2-adduct compared to that of N-adduct also increased with increasing loading of TFA. The higher conversion was observed in the case of electron-withdrawing group containing indoles with higher selectivity of C-adduct. The catalysts were found to be reusable.

Mesoporous solid acid catalysts of sulfated zirconia/SBA-15 derived from a vapor–induced hydrolysis route

Mesoporous solid acid catalyst, sulfated zirconia loaded mesoporous silica, was reported here by a facile vapor–induced hydrolysis method. The zirconia precursor of Zr(SO4)2 was introduced into the mesopore of SBA-15 by impregnation, and then hydrolyzed under a NH3/H2O vapor ambience to form a thin zirconia layer coated on the pore surface of SBA-15, which was followed by the sulfation of SO42− ions with calcinations. The catalyst was characterized by powder X-ray diffraction, N2 adsorption–desorption, transmission electron microscopy and infrared spectroscopy, and the results indicated that the catalyst retained the ordered mesoporous structure, high BET surface area, connected pore channel without pore blocking and a 0.7nm thin layer of sulfated zirconia coated on the pore surface. This super acid catalyst showed much higher activity compared with those of unloaded sulfated zirconia and sulfated zirconia loaded SBA-15 hydrolyzed by ammonia aqueous solution, for catalyzing the esterification reaction of oleic acid and methanol. The experimental parameters including the molar ratio of reactants and reaction time were optimized, and approximately 70% of acid sites were remained after three cycles.

Design and Synthesis of Mesoporous Polymer-Based Solid Acid Catalysts with Excellent Hydrophobicity and Extraordinary Catalytic Activity

Novel excellent hydrophobic- mesoporous- polymer-based solid acid catalysts have been successfully synthesized by copolymerization of divinylbenzene (DVB) with sodium p-styrene sulfonate (H-PDVB-x-SO3H's) under solvothermal conditions. N2 isotherms and TEM images showed that H-PDVB-x-SO3H's have high BET surface areas, large pore volumes, and abundant mesoporosity; CHNS element analysis and acid–base titration technology showed that H-PDVB-x-SO3H's have adjustable sulfur contents (0.31–2.36 mmol/g) and acidic concentrations (0.26–1.86 mmol/g); TG curves showed that H-PDVB-x-SO3H's exhibited much higher stability of the active site (372 °C) than that of the acidic resin of Amberlyst 15 (312 °C); contact angle and water adsorption tests showed that H-PDVB-x-SO3H's exhibited excellent hydrophobic properties. Catalytic tests in esterification of acetic acid with cyclohexanol, esterification of acetic acid with 1-butanol, and condensation of benzaldehyde with ethylene glycol showed that H-PDVB-x-SO3H's were more active than those of Amberlyst 15, SO3H-functionalized ordered mesoporous silicas, and beta and USY zeolites, which were even comparable with that of homogeneous H2SO4. The superior hydrophobicity of solid acid catalysts would be favorable for achieving excellent catalytic performance because water usually acts as a byproduct in various acid-catalyzed reactions, which can easily poison the acid sites and result in opposite reactions. Synthesis of porous solid acid catalysts with good hydrophobicity would be very important for their applications.

Catalytic Hydrothermal Saccharification of Rice Straw Using Mesoporous Silica-based Solid Acid Catalysts

Catalytic hydrothermal saccharification of rice straw was carried out in the presence of sulfonated mesoporous silica (SBA-15) -based solid acid catalysts. Effects of reaction time, reaction temperature and weight ratio of solid acid catalyst to rice straw on the saccharification of rice straw were investigated. With increasing reaction time and reaction temperature, the yield of monosaccharide initially increased and then decreased, but the yield of byproducts increased. With increasing weight ratio of solid acid catalyst to rice straw up to 25 %, the yield of monosaccharide initially increased and then remained almost constant. The yield of monosaccharide was 38 % for the saccharifi cation of rice straw carried out at 180 ℃ for 1 h with the weight ratio of rice straw/distilled water/ solid acid catalyst equal to 3/30/0.5 (g/g/g). The composition of rice straw and crystallinity index of cellulose in rice straw before and after the saccharifi cation were determined, respectively. Based on the composition analysis, most xylan and glucan derived from hemicellulose were decomposed, but glucan derived from cellulose was little decomposed via catalytic hydrolysis at 180 ℃ and below. On the other hand, xylan and glucan derived from hemicellulose were almost completely decomposed, and part of glucan derived from cellulose was also decomposed at 200 ℃ and above. At the same time, some ash and lignin in rice straw were removed in all the reactions.

Direct conversion of cellulose to glucose and valuable intermediates in mild reaction conditions over solid acid catalysts

The direct hydrolysis of cellulose to glucose, HMF and other soluble by-products at 190 °C in water solution using zeolites (H-BEA, H-MOR), sulphated zirconia supported over mesoporous silica (SBA-15), Amberlyst ®15, heteropolyacids and AlCl 3·6H 2O as acid catalysts was studied using a high cellulose to catalyst ratio (10), not-pretreated (neither mechanically nor chemically) cellulose and a static (not mixed) autoclave. Under these conditions, not usually considered, but relevant for industrial applications, micro and mesoporous solid acid catalysts are active in the direct hydrolysis of cellulose to glucose, HMF and other soluble by-products. The reactivity in crystalline cellulose conversion is determined on one side from the need to realize an efficient solid–solid interaction between the external surface of the catalyst and the crystalline cellulose, and on the other side on the need to limit the secondary reactions of the formed products. Microporous materials, due to the presence of shape-selectivity effects limiting the polymerization of glucose to humic-type species show the highest formation of glucose and HMF with respect to the sulphated zirconia supported over mesoporous silica (SBA-15) and homogeneous heteropoly acids.

Direct syntheses of sulfonated mesoporous SiO2-TiO2-SO3H materials as solid acid catalysts

A facile one-step approach for a mesoporous solid acid catalyst SiO2-TiO2-SO3H network was developed by the simple chelation of a benzene disulfonate compound to the Ti ion. The resulting catalyst showed excellent catalytic performance for esterification.

Isobutane/butenealkylation on microporous and mesoporous solid acid catalysts: probing the pore transport effects with liquid and near critical reaction media

The alkylation of isobutane with 1-butene was investigated on microporous (β-zeolite) and mesoporous (silica supported heteropolyacids) catalysts in a slurry reactor. The reaction was investigated in the range of 25–100 bar and 15–95 °C in liquid phase and in near critical reaction media with either dense CO2 or dense ethane as diluent, partially replacing the excess isobutane. At 75 °C, the selectivity towards trimethylpentanes (TMP) in the liquid phase is 70%+ initially, but decreases with time on all the catalysts investigated. While near-critical reaction mixtures were employed in order to enhance pore diffusion rates, the conversion and selectivity profiles obtained with such mixtures are comparable to those obtained with liquid phase reaction mixtures in both microporous and mesoporous catalysts. This implies that pore diffusion effects play a limited role at higher temperatures (75–95 °C). In contrast, the liquid phase results at sub-ambient temperatures indicate that the catalyst is deactivated before the TMPs diffuse out of the pores, indicating that pore diffusion effects play an important role in the deactivation process at low temperatures. Our results suggest that novel approaches that enhance the pore-diffusion rates of the TMPs at lower temperatures must be pursued.

Acidity Control of Al-SBA-15 and Its Effect on the Catalytic Performance for Steam Reforming of Dimethyl Ether

Steam reforming (SR) of dimethyl ether (DME) seems to proceed via a successive two step mechanism: hydrolysis of DME over solid acid catalysts, followed by methanol SR over copper-based catalysts. Since the DME hydrolysis is rate-controlling, it is desirable to continue more systematic study concerning the solid acids for better production of hydrogen. In this work, the composites of mesoporous solid acid catalysts (Al-SBA-15) and copper-based catalysts (Cu/ZnO/Al2O3) made the hybrid catalysts, and they were used for DME SR. Acidity of Al-SBA-15 was controlled by tuning Si/Al ratio, which should vary the number of acidic sites. The reducibility of hybrid catalysts was varied with different weight ratio between Al-SBA-15 and Cu/ZnO/Al2O3. The catalytic activity of DME SR was analyzed in terms of acid amount and copper reducibility.

Diels-Alder Cycloaddition of Cyclopentadiene with Ethylacrylate Catalyzed by Mesoporous Al-MCM-48 and Al-MCM-41 Catalysts

In the present work, Diels-Alder reaction of cyclopentadiene with ethylacrylate has been carried out by using two types of mesoporous solid acid catalysts (Al-MCM-41, Al-MCM-48) with different pore structures. The specific topology of Al-MCM-48 (cubic Ia3d structure composed of two independent 3-D channel systems) exhibit higher activity and stereo-control than those of Al-MCM-41 (hexagonal packing of 1-D channels). The physical properties of Al-MCM-48 catalyst, such as high accessibility of reactants to the acid sites, spatial confinement in the nanoscopic reactors, and 3-D channel network structure that are effective adsorption and diffusion of reactants, play a crucial role in the present study.

Novel Mesoporous Nanocomposite WOx-Silicate Acidic Catalysts: Ethylene and Diethylether from Ethanol

Solid acid catalysts are extensively used in a number of industrially important catalytic reactions. Here, water-insoluble novel mesoporous solid acid catalysts, with a unique structure composed of WOx nanorods and W nanoballs within an amorphous silicate lattice, were synthesized following a one-pot hydrothermal route, using silicotungstic acid (STA) as the active component. Surface area of these catalysts are more than 2 orders of magnitude higher than that of pure STA, and they showed very high activity for the simultaneous production of ethylene and diethylether (DEE), which is an attractive transportation fuel alternate, from a nonpetroleum feedstock, namely ethanol. Depending upon the operating conditions, ethylene or DEE selectivities approaching 1.0 or 0.8 were obtained, respectively.

Green Synthesis of Benzylated Aromatics Using Iron Loaded Mesoporous Materials

Syntheses of benzylated aromatics like diphenylmethane and its derivatives by the condensation of benzene or toluene or o‐xylene with benzylchloride or 4‐methylbenzylchloride in the presence of a catalytic amount of various iron loaded mesoporous solid acid catalysts such as Fe/Al‐MCM‐41 (Si/Al=25), Fe/Al‐MCM‐41 (Si/Al=50) and Fe/Al‐MCM‐41 (Si/Al=100) are reported.

Catalytic activities and properties of sulfated zirconia supported on mesostructured γ-Al2O3

Abstract A novel mesoporous solid acid catalyst system was designed by loading sulfated zirconia into mesostructured γ-Al2O3. Their catalytic activities for conversion of n-pentane, Friedel–Crafts benzoylation of anisole with benzoyl chloride and dealkylation of 1,3,5-tri-tert-butyl-benzene were investigated. For comparison, sulfated zirconia and MCM-41 supported sulfated zirconia were also examined. Textural and structural characterizations of the catalysts were performed by means of N2 adsorption, X-ray diffraction and diffuse reflectance UV–vis spectroscopy. Temperature programmed desorption of ammonia and FTIR spectra of adsorbed pyridine were used to determine the acid properties. The results show that novel mesoporous solid acids exhibit superior catalytic performances to sulfated zirconia and MCM-41 supported sulfated zirconia. The enhanced performances of the novel mesoporous acid catalysts can be attributed to more acid sites and/or stronger acid strength.