Porous Solid Acid Research Articles

Synergistic activation of hydroxyl groups by hierarchical acid sites and deep eutectic solvents for the dehydration of fructose to 5-hydroxymethylfurfural under mild temperature

The activation of C–OH bond shows great importance for fructose dehydration to produce 5-hydroxymethylfurfural (HMF). In the deep eutectic solvent (DES), the synergistic improvement of surface sulfonic acid groups on hierarchical porous carbon solid acids (HPCSA) and choline chloride (ChCl) on activation of fructose hydroxyl groups was studied to achieve high catalytic performance under mild conditions. The results show a high yield of 90.7 % for HMF at relatively mild temperature of 70 °C. The polarizing effect of ChCl on fructose hydroxyl groups enhances the interaction energy between fructose and sulfonic acid groups on carbon surface, resulting in elongated C–OH bond of fructose from 1.412 Å to 1.456 Å. The hierarchical pore structure can improve the accessibility to acid active sites and increase the quantity of surface sulfonic acid groups by enlarging specific surface areas. A reaction mechanism considering the synergistic effect of various components in DES is proposed to explain the promotion of fructose dehydration under mild conditions. This work provides an effective solution for utilizing biomass to produce renewable energy.

Synthesis of porous polymer-based solid acid and its catalytic activities for biodiesel synthesis from waste oil and tetrahydropyranylation of alcohols

Synthesis of porous polymer-based solid acid and its catalytic activities for biodiesel synthesis from waste oil and tetrahydropyranylation of alcohols

Synthesis of acetylglycerols over hierarchical porous sulfonated polymeric solid acid

Biodiesel is a sustainable and renewable fuel, which is popularly recommended as a substitute for traditional fossil resources. However, the rapidly growing production of biodiesel in past decades has brought the formation of surplus glycerol. In this work, glycerol-derived acetins were synthesized via transesterification of glycerol with methyl acetate over a hierarchical porous polymeric solid acid catalyst (hSPB-x) which was prepared in a facile method. It was found that hSPB-2 was highly active and stable for this transesterification reaction. The highest yield of acetylglycerols reached 126.1 g-acetins/g-cat/h at 100 °C, while the turnover frequency of acid sites in hSPB-2 attained 330.1 h−1 at the beginning of the reaction. And hSPB-2 was stable for 5-time recycles without obvious deactivation. Characterization results indicated that the excellent performance of hSPB-2 could be attributed to its high acidity (2.77 mmol/g), large surface area (872 m2/g), regular hierarchical pore channels, and good thermal stability.

Synthesis of N-Unprotected Diaryl Ketimines and Alkyl Ketimines from Ketones and Ammonia Using Porous Solid Acids with Analysis of Their Adsorption Behavior

Abstract The most atom-efficient synthetic method for N-unprotected ketimines (N-H ketimines) from ketones is the dehydration condensation reaction with ammonia (NH3). However, until now, few synthetic methods for N-H ketimines with high versatility have been known. In this study, we examined various solid acids and found that N-H diaryl ketimines with various functional groups on the aryl groups could be synthesized in high yields from diaryl ketones and NH3 under solvent-free conditions using silica-alumina (SiO2-Al2O3) or proton-exchanged Y-type zeolite (H-Y). Solid-state 13C and 15N NMR measurements indicated that the N-H ketimine formed in the pores of acidic zeolite was coordinated to NH4+ species on the pore surface. By quantum chemical calculations we also discussed the reason why the dehydration-condensation reaction between ketone and NH3, which is an endothermic reaction in a vacuum, was biased toward the product side in the actual experiment. In addition, this synthetic method can be applied to synthesize N-H alkyl ketimines with α-acidic hydrogens, which are less stable and more sensitive to hydrolysis and oligomerization than diaryl ketimines.

Efficient production of 5-hydroxymethylfurfural from fructose catalyzed by acidic ion-functionalized porous carbon solid acid

Efficient production of 5-hydroxymethylfurfural from fructose catalyzed by acidic ion-functionalized porous carbon solid acid

ZrMo oxides supported catalyst with hierarchical porous structure for cleaner and sustainable production of biodiesel using acidic oils as feedstocks

Ameliorating the reactant mass transfer and fabricating the multiple active sites on the catalyst surface are feasible strategies to synthesize efficient and recyclable catalysts for efficient biodiesel production by using acidic oils as feedstocks. Herein, hierarchical porous solid acids with Zr and Mo oxides as active sites were prepared by using polystyrene spheres (PS) and P123 as templates. It was shown that the active species of Zr and Mo oxides were uniformly dispersed on the hierarchical porous silica support, and the solid catalysts featured high surface area and interconnected mesoporous/macropores with high mass diffusive extent, showing improved catalytic performances for the biodiesel production as compared to the control catalyst without hierarchical pores, owing to the mass transfer enhancement and more easily accessible active sites. The transesterification reaction in 93.8% of oil conversion as well as complete conversion of free fatty acids (FFAs) were simultaneously performed by using this solid catalyst, hence achieving one-pot transformation of acidic oils to biodiesel and minimizing the complex and tedious separation process. Moreover, the higher water and FFA-resistance capacity was shown for this solid catalyst, posing its more suitable for the biodiesel production with acidic oils as feedstocks. This hierarchical porous solid catalyst could be facilely recycled using simple filtration, and still maintained high activities after reuse for five runs, which rendered it to have the potential of cost-effective production of biodiesel in particular from low-grade acidic oils.

Direct production of ethyl levulinate from carbohydrates and biomass waste catalyzed by modified porous silica with multiple acid sites

Three modified porous silica solid acid catalysts with multiple acid sites (SO3H-Al/Silica, SO3H-Al-Zr/Silica, and SO3H-Zr/Silica) were prepared and characterized. The Pyridine-infrared spectra showed that both Brønsted (B) and Lewis (L) acid sites were present in all three catalysts. Catalytic acid sites with different acid strengths were also found, including strong sulfonic acids and several weak acids. The prepared solid acid catalysts were used to catalyze the ethanolysis of glucose, glucosyl-based carbohydrates, and starchy food waste to produce ethyl levulinate (EL). The formation of EL was promoted by the synergistic effect between multiple acid sites on the catalysts. A higher B/L ratio and –SO3H amount promoted the production of EL. The catalytic activity was positively correlated to the specific surface area of the catalysts. Promising results were obtained for SO3H-Al/Silica: the maximum EL yield from glucose was 47.9%, and a small amount of 5-ethoxymethylfurfural was detected as a byproduct. Cellobiose, cellulose, expired wheat flour, and kitchen waste were also used as raw materials to produce EL, affording EL yields in the range of 1.6–38.9%. Finally, the stability of the prepared catalysts was explored after reuse and hot filtration.

Hierarchically Ordered Porous Solid Acid: Preparation and Application as a Biodiesel Catalyst

AbstractAcid‐catalyzed esterification of high fatty acid content feedstocks with methanol is an efficient way to prepare biodiesel. In this work, using the dual template method combining the colloidal crystal template and the porogen, a series of hierarchical ordered porous weak cross‐linked polystyrene solid acid catalysts with high mass transfer efficiency and high acid density were successfully prepared. This catalyst displayed stronger acid strength and better swelling properties. The specific surface area of the obtained catalyst is 32 m2 ⋅ g−1, and its acid value reaches 4.11 mmol ⋅ g−1. The effect of the hierarchical porous structure and swelling on the access to the catalytic sites were illuminated. Acid‐catalyzed reactions showed that hierarchically ordered porous cross‐linked polystyrene solid acid catalyst was more active (the efficiency of the esterification of oleic acid and methanol was up to 93.67 %) than Amberlyst‐15 catalyst.

Preparation of the porous carbon-based solid acid from starch for efficient degradation of chitosan to D-glucosamine

Effective degradation of chitosan to D-glucosamine is considered to make a great contribution for the development of the medical industry. To address this issue, a porous carbon-based solid acid catalyst (PCSA) functionalized with -OH, -COOH and -SO3H groups was successfully prepared. Typically, the physicochemical properties of PCSA were deeply determined by a series of characterization technique including FT-IR, TGA, RM, NH3-TPD, SEM and Element Analysis. Moreover, the catalytic performances of PCSA towards to D-glucosamine production from chitosan were evaluated. In particular, the effects of catalyst acid density, ratio of acidic groups, chitosan concentration, reaction temperature, reaction time and catalyst dosage on the yield of D-glucosamine were investigated in detail. Interestingly, the experimental results indicated that a yield of D-glucosamine as high as 90.5% was achieved, and no obvious deactivation occurred even after six consecutive cycles. In light of the advantages of superior activity/recyclability and low cost, the starch-derived solid acid developed in this work might possess the broad industrial application prospects.

Preparation of Porous Macromolecule Oxazine Poly-Ionic Liquid Solid Acid Catalyst and its Application in Esterification Reaction

Preparation of Porous Macromolecule Oxazine Poly-Ionic Liquid Solid Acid Catalyst and its Application in Esterification Reaction

Promotion of sulfonic acid groups on biomass carbons loading ultrafine palladium nanoparticles for the efficient hydrodeoxygenation of vanillin in water

Carbonaceous catalysts with sulfonic acid (-SO3H) groups are showing promising performances in the conversion of mono- and poly-saccharides, however, their applications in the hydrodeoxygenation (HDO) of oxygen-rich lignin derivatives are rarely reported. Herein, we report a facile synthetic approach for one-step preparation of porous carbonaceous solid acids with –SO3H groups (OHCA) where monosaccharide, polysaccharide, and raw biomass can be used as carbon precursors. These porous carbonaceous solid acids supported ultrafine palladium nanoparticles (Pd/OHCA) exhibited excellent performances in the HDO of vanillin (VAN) in water. We found that Pd nanoparticles (Pd NPs) were responsible for the hydrogenation of VAN to vanillyl alcohol (VAL) and acidic groups were crucial for the hydrogenolysis of generated VAL to 2-methoxy-4-methylphenol (MMP). Importantly, VAL once generated can be immediately converted to MMP via synergistic catalysis between acidic groups and Pd NPs, avoiding the formation of by-products. Pd/OHCA catalyst also exhibited excellent stability in the HDO of VAN and retained its activities in the six consecutive runs. The findings of this work provide a new thought for the HDO of biomass derivatives over biomass-based carbon catalysts.

First-Principles Grand-Canonical Simulations of Water Adsorption in Proton-Exchanged Zeolites

Water appears by design or as impurities in many important reactive systems. For those catalyzed by porous solid acids, such as widely used zeolites, experimentally quantifying the amount or elucidating the structure of adsorbed water clusters at reaction conditions is challenging, while computational studies (e.g., first-principles molecular dynamics simulations) often need to assume the loading to examine solvation effects. Here, we perform first-principles grand-canonical simulations to predict water adsorption to H-ZSM-5 zeolites under specified experimental conditions. Presampling with inexpensive force fields and a pool-based parallelization algorithm are used to improve simulation efficiency, while molecular dynamics is used to sample configurations involving hydronium species. We observe that H+ exchange dramatically increases the hydrophilicity of zeolite MFI and an appreciable amount of water is present at very low relative humidities. At all conditions examined, the zeolitic protons are found to dissociate readily from the surface basic sites and become mobile by participating in the hydrogen-bonded chains of adsorbed water molecules.

Introducing hydroxyl groups as cellulose-binding sites into polymeric solid acids to improve their catalytic performance in hydrolyzing cellulose

Effective hydrolysis of cellulose to glucose is a crucial step to produce fuels and chemicals from lignocellulosic biomass. Solid acids are promising alternatives of cellulases and homogenous acids for hydrolyzing cellulose. In this study, porous polymeric solid acids bearing hydroxyl and sulfonic acid groups were fabricated for cellulose hydrolysis in water through the low-cost Friedel-Crafts “knitting” polymerization of hydroxyl-containing aromatic monomers followed by sulfonation. The synthesized bifunctional solid acids could effectively hydrolyze microcrystalline cellulose (Avicel) to glucose by as high as 93 % at 120 °C within 48 h and ball-milled Avicel by 98 % at 120 °C in 24 h. The evidence from this study indicated that the outstanding catalytic performance of the solid acids was attributed to the porous structure (large surface area) and the presence of the hydroxyl (cellulose-binding group) in the solid acids.

Graphene modified porous organic polymer supported phosphotungstic acid catalyst for alkylation desulfurization

A new strategy of using graphene to modify porous organic solid acid catalyst for alkylation desulfurization is proposed by taking advantage of the π-π interaction between graphene and thiophenic sulfur. A graphene-modified sulfonated porous organic polymer (POP) supported phosphotungstic acid (HPW) catalyst (HPW/POP-G-SO3H) is successfully prepared by the solution polymerization-sulfonation-impregnation method. Steam adsorption experiment results show that graphene modification could increase the adsorption capacity of 3- methylthiophene (3-MT), but has little effect on the adsorption of isopentane; therefore, the selective adsorption of 3-MT could be enhanced. DFT calculations plus dispersion corrections also show that the adsorption energy of 3-MT on graphene is higher than that of isopentene on graphene and higher than those of 3-MT and isopentene on sulfonated POP. Subsequently, the catalytic activity test of alkylation desulfurization confirms that graphene-modified supported HPW catalyst shows higher alkylation desulfurization activity. This could support our assumptions. After recycles of 6 times, the 3-MT conversion on HPW/POP-G-SO3H catalyst decreases slightly, which possesses good recycling performance. Therefore, HPW/POP-G-SO3H catalyst will have broad application prospects in the field of alkylation desulfurization.

Efficient solvent-free synthesis of N-unsubstituted ketimines from ketones and ammonia on porous solid acids

We quantitatively synthesized N-unsubstituted (NH) diphenylketimine from benzophenone and ammonia without solvent under ambient conditions on some solid acids, especially the proton-exchanged Y-type zeolite (H-Y), by a simple procedure. Similarly, other N-unsubstituted ketimines were also obtained in high yields by the reaction of alkyl aryl ketones or a dialkyl ketone having α-acidic hydrogens with a large excess of ammonia gas at 1 atm. without a solvent with the aid of the zeolite’s high dehydration ability and stabilization effects.

Efficient, continuous N-Boc deprotection of amines using solid acid catalysts

Rapid, catalytic N-Boc deprotection of aromatic and aliphatic amines is achieved using readily-available porous inorganic solid acids in flow.

MOF-Assisted Synthesis of Highly Mesoporous Cr2O3/SiO2 Nanohybrids for Efficient Lewis-Acid-Catalyzed Reactions.

The facile fabrication of porous solid acids is highly desired for replacing hazardous liquid acids for many acid-catalyzed reactions in the industry. Herein, we present a bottom-up strategy to construct ultrastable mesoporous Cr2O3/SiO2 nanohybrids (denoted as Meso-Cr-Si-O) with highly dispersed Lewis acid sites by pyrolysis of a SiO2@MIL-101 precursor prepared via nanocasting by a reverse double-solvent approach, which can guarantee the efficient encapsulation of SiO2 nanoparticles (NPs) inside the MIL-101 pores. The pore environment of Meso-Cr-Si-O can be well tuned by simply controlling the amount of silica within the MIL-101 pores and the pyrolysis temperature. Pyridine adsorption experiments demonstrate that the density of Lewis acidic sites in the obtained Meso-Cr-Si-O is much higher than that of MIL-101-derived Cr2O3 NPs. Benefitting from its highly mesoporous nanostructure with abundant acid sites, the optimal Meso-Cr-Si-O exhibits a significantly improved catalytic activity for the Lewis-acid-catalyzed Meerwein-Ponndorf-Verley reduction of cyclohexanone with 4.5 times higher yield of cyclohexanol than that of the MIL-101-derived Cr2O3 NPs, representing the first efficient Cr2O3-based catalytic system for this reaction.

A Porous Polymer-Based Solid Acid Catalyst with Excellent Amphiphilicity: An Active and Environmentally Friendly Catalyst for the Hydration of Alkynes

Developing efficient solid acid catalysts for aqueous organic reactions is of great importance for the development of sustainable chemistry. In this work, a porous polymeric acid catalyst was synthesized via a solvothermal copolymerization and a successive ion-exchange method. Physicochemical characterizations suggested that the prepared polymers possessed large Brunauer-Emmett-Teller (BET) surface areas, a hierarchically porous structure, excellent surface amphiphilicity, and nice swelling properties. Notably, an activity test in phenylacetylene hydration indicated that the prepared solid acid exhibited high catalytic activity in water, which outperformed commercial amberlyst-15, sulfuric acid, and benzenesulfonic acid. Moreover, the prepared solid acid can be easily recovered and reused at least four times. Additionally, a variety of aromatic and aliphatic alkynes could be effectively transformed into corresponding ketones under optimal reaction conditions.

Porous and efficient polymeric solid acid synthesized from sulfonation of nanoporous polymer

Efficient nanoporous amberlite (XAD-4) based solid strong acid (XAD-4–SO3H–SO2CF3) has been successfully synthesized by decorating SO2CF3, a strong electron withdrawing group onto the network of nanoporous solid acid of XAD-4–SO3H. N2 sorption isotherms and TG curves show that XAD-4–SO3H–SO2CF3 has large BET surface area and good thermal stability. XPS spectra show that the group of SO2CF3 has been introduced onto the network of XAD-4–SO3H. TEM results shows that the well-dispersion of C, S, and O elements. Catalytic property tests show that XAD-4–SO3H–SO2CF3 exhibits excellent catalytic activities in biomass transformation toward acylation of anisole with acetyl chloride, synthesis of bisphenol-A and esterification of acetic acid with cyclohexanol when compared with those of solid strong acids of Amberlyst-15, SBA-15-0.1–SO3H, H3PW12O40 and XAD-4–SO3H.

Efficient hydrogen production from partial oxidation of propane over SiC doped Ni/Al2O3 catalyst

The composite Ni/Al2O3-SiC catalyst was designed and synthesized for hydrogen production from propane partial oxidation. Through the composite of high thermal conductivity SiC and porous solid acid Al2O3, it improved the shortcoming of sintering and inactivation of high-temperature reaction for Ni-based catalysts. The samples were characterized by X-ray diffraction, N2 physical adsorption, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis etc. From the results, the SiC doped catalyst exhibited superior catalytic properties for hydrogen production by propane partial oxidation. By doping SiC with high thermal conductivity to Al2O3 support, the catalyst was improved for sintering and carbon deposition resistance and reducing the aggregation of Ni active sites reflected by improving the stability of hydrogen production.