Water-tolerant Solid Acid Catalyst Research Articles

Solids containing Si-O-P bonds: is the hydrolytic sol-gel route a suitable synthesis strategy?

AbstractMaterials based on silicon-phosphorus mixed oxides have traditionally attracted interest in electronics, optics, catalysis, and related fields. The preparation of a solid containing stable Si–O–P linkages is a huge challenge due to their intrinsic instability to hydrolysis in a wet atmosphere. On the other hand, most technological applications of these materials, such as protonic conductive membranes in fuel cells and water-tolerant solid acid catalysts, are related to their interaction with water; consequently, suitable synthesis procedures that positively face this tradeoff are mandatory. Besides the traditional high-temperature techniques, sol-gel synthetic methods represent a viable, low-cost alternative, allowing for the preparation of high-purity materials with a homogeneous distribution of the components at the atomic scale. Si–O–P linkages are easily obtained by nonhydrolytic sol-gel routes, but only in inert and dry atmosphere. Conversely, hydrolytic routes offer opportunities to control the structure of the products in a wide range of processing conditions. The present review aims at providing an overall picture of the research on the sol-gel synthesis of phosphosilicate and related materials and theisr different applications, emphasizing how the interest in these systems is still lively, considering both conventional and emerging applications, such as flame retardance. The incorporation of Si–O–P nanostructures in polymer composites, coatings, and textiles is indeed a promising strategy to improve properties like thermal stability and fire resistance; however, their in-situ synthesis brings about additional difficulties related to the reactivity of the precursors. The perspectives linked with the development of Si–P-based materials are finally outlined. Graphical Abstract

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.

Development of a Novel Hydrophobic ZrO2–SiO2 Based Acid Catalyst for Catalytic Esterification of Glycerol with Oleic Acid

The inevitably low value of glycerol has led to extensive investigations on glycerol conversion to value-added derivatives. The esterification of glycerol with oleic acid is currently a very important industrial process. In this work, a novel heterogeneous acid catalyst featuring hydrophobic surface is developed on modified ZrO2–SiO2 support as water-tolerant solid acid catalyst is vital for biphasic esterification reactions that produce water. The novel ZrO2–SiO2–Me&Et-PhSO3H catalyst was prepared through silication and surface modification with trimethoxymethylsilane and 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane. This work showed that it is possible to control the acidity and hydrophobicity of the catalyst by tailoring the amount of surface modification agents. It was found that the hydrophobicity of the catalyst decreased as its acidity increased. Furthermore, at constant catalyst acidity, the more hydrophobic catalyst showed a better yield.

Insights into deactivation mechanism of sulfonated carbonaceous solid acids probed by cellulose hydrolysis

Sulfonated carbonaceous solid acids are key heterogeneous catalysts and are widely used in acid-catalyzed reactions, especially in biomass transformation. In this work, the sulfonated carbonaceous solid acids were prepared and their stability was examined in cellulose hydrolysis at 170 °C. Their activity decreased largely after the hydrothermal treatment at 170 °C, as a result of the leaching of their SO3H species. Characterizations of the filtrates after the hydrothermal treatment of these solid acid catalysts by NMR and laser scattering demonstrated that the leaching of SO3H sites was not caused by the cleavage of CS bonds, but by the exfoliation of colloidal carbon particles with SO3H sites from the catalysts. Such leaching problem led to significant decrease in SO3H density for the carbon-based solid acids that synthesized by traditional sulfonation methods because of their uneven distribution of SO3H sites. To address this issue, carbon precursors with more free CH sites were applied to regulate the distribution of SO3H sites. As a consequence, the evenly distributed SO3H sites resulted in less change in acid density after the hydrothermal treatment, and maintenance of high SO3H density. This study could provide new guidance to further design of water-tolerant solid acid catalysts, and would promote the development of energetically efficient processes to convert cellulose.

Phosphoric acid functionalized graphene oxide: A highly dispersible carbon-based nanocatalyst for the green synthesis of bio-active pyrazoles

Carbon-based catalysts are gained significant interest for improving a number of catalytic processes due to their unique set of benefits. However, a few of such catalysts are proper for synthesis of organic compounds in water. Therefore, there is a strong need for developing water-tolerant and dispersible catalysts. Here, we demonstrate a simple and efficient method for the preparation of highly dispersible phosphonic acid functionalized carbocatalyst. The applied functionalization method was flexible in controlling the functionalization level. The prepared nanocatalyst exhibited superior catalytic performance toward multicomponent synthesis of pyrano[2,3-c]pyrazole, with 80–90% yield within 15 min in water. Moreover, this water-tolerant solid acidcatalyst could be simply retrieved and after 6 successive cycles of reactions, the reaction time and yield still keeps within the same level.

Sulfanilic acid functionalized mesoporous SBA-15: A water-tolerant solid acid catalyst for the synthesis of uracil fused spirooxindoles as antioxidant agents

Incorporating sulfanilic acid as a hydrophobic Brønsted acid inside the nanospaces of SBA-15 led to a water-tolerant solid acid catalyst, SBA-15-PhSO3H, which showed excellent catalytic performance in synthesis of uracil-fused spirooxindoles in aqueous ethanol. The synthesized compounds were evaluated for their antioxidant activity by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging assay.

Synthesis of aluminium triflate-grafted MCM-41 as a water-tolerant acid catalyst for the ketalization of glycerol with acetone

An aluminium triflate species grafted over MCM-41 (Al(TF)–MS) was synthesized by a novel route as an inexpensive and water-tolerant solid acid catalyst for the ketalization of glycerol with acetone to solketal (solketal synthesis).

Lewis Acid Catalysis of TiO4 Tetrahedra on Mesoporous Silica in Water

TiO4-deposited mesoporous silica (TDMS) was studied as a water-tolerant solid Lewis acid catalyst. TDMS prepared by a simple postgrafting technique using Ti(i-pro)4 has a large BET surface area (ca. 450 m2 g–1) and ordered mesoporous structure. Ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), X-ray absorption near edge structure (XANES), and CO adsorption measurements with Fourier transform infrared (FTIR) spectroscopy revealed that isolated TiO4 tetrahedra on TDMS have Lewis acidity, even in the presence of water. Lewis acid centers on TDMS exhibit higher catalytic performance for the hydride transfer of pyruvaldehyde to lactic acid and the Mukaiyama-aldol condensation of benzaldehyde with 1-trimethylsilyloxy-cyclohexene in water than that of conventional heterogeneous and homogeneous Lewis acids, including scandium(III) triflate (Sc(OTf)3), which also works even in water. The high catalytic performance of TDMS can be attributed to Lewis acid catalysis of isolated TiO4 tetrahedra in water.

Encapsulation of a Polyoxometalate into an Organosilica Microcapsule for Highly Active Solid Acid Catalysis

We have developed a highly active and water-tolerant solid acid catalyst by encapsulating a polyoxometalate into hydrophobic hollow polymethylsiloxane microspherical particles. 12-Tungstophosphoric acid and a cesium salt of a heteropoly acid (Cs2.5H0.5PW12O40, abbreviated as CsPW) were used for this purpose. The encapsulated catalysts were prepared by a sol–gel reaction of methyltrichlorosilane around water droplets containing heteropoly compounds in a water-in-oil emulsion. Both the catalysts were active in the hydrolysis of ethyl acetate in a large excess of water. While the 12-tungstophosphoric acid in the polymethylsiloxane microcapsules leached into the water during the repetition of the reaction, the activity of the CsPW encapsulated catalyst (0.86 mol·(acid-mol)−1·min–1) was maintained. This activity was superior to that of bare cesium salt (0.34 mol·(acid-mol)−1·min–1). To our knowledge, the CsPW encapsulated catalyst exhibits the highest activity among solid acid catalysts with respect to reactio...

Efficient, Stable, and Reusable Silicoaluminophosphate for the One-Pot Production of Furfural from Hemicellulose

Development of stable, reusable, and water-tolerant solid acid catalysts in the conversion of polysaccharides to give value-added chemicals is vital because catalysts are prone to undergo morphological changes during the reactions. With the anticipation that silicoaluminophosphate (SAPO) catalysts will have higher hydrothermal stability, those were synthesized, characterized, and employed in a one-pot conversion of hemicellulose. SAPO-44 catalyst at 170 °C within 8 h could give 63% furfural yield with 88% mass balance and showed similar activity up to at least 8 catalytic cycles. The morphological studies revealed that SAPO catalysts having hydrophilic characteristics are stable under reaction conditions.

Catalytic conversion of bio-oil to oxygen-containing fuels by simultaneous reactions with 1-butanol and 1-octene over solid acids: Model compound studies and reaction pathways

Upgrading bio-oil by addition reactions across olefins represents a route to refine bio-oil to combustible and stable oxygen-containing fuels. Development and application of highly active strong solid acid catalysts with good hydrothermal stability has become a key determinant for success, because bio-oil’s complexity includes large amounts of water. Temperatures of 120°C or more are needed for satisfactory kinetics. Batch upgrading of a model bio-oil (phenol/water/acetic acid/acetaldehyde/hydroxyacetone/d-glucose/2-hydroxymethylfuran) over five water-tolerant solid acid catalysts (Dowex50WX2, Amberlyst15, Amberlyst36, silica sulfuric acid (SSA) and Cs2.5H0.5PW12O40 supported on K-10 clay (Cs2.5/K-10, 30wt.%)) with 1-octene/1-butanol were studied at 120°C/3h. SSA, ▪, exhibited the highest water tolerance and activity. Upgrading using olefin/1-butanol is complex, involving many simultaneous competing esterification, etherification, olefin hydration, phenol alkylation, aldol condensation, sugar dehydration etc. reactions.

Carbocatalytic dehydration of xylose to furfural in water

Graphene, graphene oxide, sulfonated graphene, and sulfonated graphene oxide (SGO) have been prepared, characterized and tested for the dehydration of xylose to furfural in water. In particular, SGO was proven to be a rapid and water-tolerant solid acid catalyst even at very low catalyst loadings down to 0.5 wt.% vs xylose, maintaining its initial activity after 12 tested repetitions at 200 °C, with an average yield of 61% in comparison to 44% for the uncatalyzed system. Raman spectroscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, 13C solid state nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy and surface area analysis suggested that the aryl sulfonic acid groups were the key active sites for high temperature production of furfural in water. They were more thermally stable under the reaction conditions and acidic than other functional groups attached to the graphene surface.

Biorefining: Heterogeneously Catalyzed Reactions of Carbohydrates for the Production of Furfural and Hydroxymethylfurfural

Furfurals are important intermediates in the chemical industry. They are typically produced by homogeneous catalysis in aqueous solutions. However, heterogeneously catalyzed processes would be beneficial in view of the principles of green chemistry: the elimination of homogeneous mineral acids makes the reaction mixtures less corrosive, produces less waste, and facilitates easy separation and recovery of the catalyst. Finding an active and stable water-tolerant solid acid catalyst still poses a challenge for the production of furfural (furan-2-carbaldehyde) and 5-(hydroxymethyl)-2-furaldehyde (HMF). Furfural is produced in the dehydration of xylose, and HMF is formed from glucose and fructose in the presence of an acidic catalyst. Bases are not active in dehydration reaction but do catalyze the isomerization of monosaccharides, which is favorable when using glucose as a raw material. In addition to the desired dehydration of monosaccharides, many undesired side reactions take place, reducing the selectivity and deactivating the catalyst. In addition, the catalyst properties play an important role in the selectivity. In this Review, catalytic conversion approaches are summarized, focusing on the heterogeneously catalyzed formation of furfural. The attractiveness of catalytic concepts is evaluated, keeping in mind productivity, sustainability, and environmental footprint.

Hybrid Sulfonic Acid Catalysts Based on Silica-Supported Poly(Styrene Sulfonic Acid) Brush Materials and Their Application in Ester Hydrolysis

Catalytic conversions involving water as a reactant, product, or solvent are of high importance in biomass conversion into fuels and chemicals. In this context, water-tolerant solid acids are highly valued. Polymer-oxide hybrid materials based on nonporous silica-supported sulfonic acid-containing polymer brush materials are proposed here as a new class of potentially water-tolerant solid acid catalyst. Atom transfer radical polymerization (ATRP), using both (i) an established and (ii) a new ATRP initiator that is designed to improve the hydrolytic stability of the catalyst, leads to creation of poly(styrene) brushes on the surface of fumed silica. These brushes are sulfonated to produce an acid catalyst akin to an acidic Merrifield resin, but with enhanced accessibility of the active sites. The catalysts are evaluated in the hydrolysis of ethyl lactate, with the polymer brush materials having the same activity as a homogeneous catalyst, p-toluenesulfonic acid, and being substantially more active than an ...

Sulfonated graphene as water-tolerant solid acid catalyst

Acid catalysts are essential for various chemical reactions in the industrial hydrocarbon chemistry. Sulfonated carbon has shown promising application as a new, cheap and environmentally friendly solid acid catalyst. In this study, we prepared the sulfonated graphene acid catalyst, and it was characterized by electron microscopy, Raman spectroscopy, solid state 13C MAS NMR, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Catalytic hydrolysis of ethyl acetate shows that the sulfonated graphene has highly catalytic activity and can be repetitively used as a water-tolerant solid acid catalyst.

Efficient Utilization of Nanospace of Layered Transition Metal Oxide HNbMoO6as a Strong, Water-Tolerant Solid Acid Catalyst

Layered HNbMoO6 was found to function as a strong solid acid catalyst, exceeding the activity of zeolites and ion-exchange resins for Friedel-Crafts alkylation. HNbMoO6 also exhibited high catalytic activity for esterification of hydrocarboxylic acid and hydration. The catalytic performance of layered HNbMoO6 is attributed to the intercalation of reactants into the interlayer and the development of strong acidity.

Glucose production from saccharides using layered transition metal oxide and exfoliated nanosheets as a water-tolerant solid acid catalyst

The layered transition-metal oxide HNbMoO(6) is demonstrated to exhibit remarkable catalytic performance for the hydrolysis of saccharides such as sucrose, cellobiose, starch, and cellulose, attributable to water tolerance and the facile accessibility of saccharides into the strong acidic interlayer gallery of the solid.

Preparation and Catalytic Application of Novel Water Tolerant Solid Acid Catalysts of Zirconium Sulfate/HZSM-5

Esterification of acrylic acid(AA) to produce AA esters has widespread application in the chemical industry. A series of water tolerant solid acid catalysts was prepared, and characterized by XRD, nitrogen adsorption, TGA-DTA, XPS, and ammonia adsorption FTIR. The effects of Si/Al ratio, zirconium sulfate(ZS) loading on HZSM-5 and calcination temperature on the esterification were investigated. When 20% (mass fraction) ZS is loaded on HZSM-5, the conversion of AA reaches 100%. XRD analysis indicates that ZS is highly dispersed on HZSM-5 because no crystalline structure assigned to ZS is found. Catalytic activity and hydrophobicity of ZS supported on HZSM-5 are higher compared with those of parent ZS or HZSM-5. Results show that this kind of novel catalysts is an efficient water tolerant solid acid catalyst for esterification reactions.

Supported zirconium sulfate on carbon nanotubes as water-tolerant solid acid catalyst

A new solid acid of zirconium sulfate (CZ) was successfully supported on carbon nanotube (CNT) for esterification reaction. Preparation conditions of the supported CZ have been investigated, to obtain highest catalytic activity for esterification reaction. XRD, TEM, BET, X-ray photoelectron spectra (XPS) and in situ FTIR analysis has also been carried out to understand the characteristics of the catalyst. In the esterification of acrylic acid with n-octanol, the supported CZ exhibited high catalytic activity and stability. The catalytic activity was nearly unchanged during four times of reuse. XRD and TEM analysis indicated that CZ was finely dispersed on CNT. XPS analysis shows that the CZ species was preserved and the chemical environment of the CZ has changed after loaded on CNT. This finding show that CNT as CZ support is an efficient water-tolerant solid acid.