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Herein, we aimed to synthesize three organic–inorganic hybrids (DILPOM-1/2/3), developed from the assembly of –SO3H-functionalized dicationic imidazolium ionic liquids having variable methylene connecting spacers with inorganic 12-molybdophosphoric acid. The hybrids DILPOM-1/2/3 were 2-methyl-1-(3-(2-methyl-3-sulfo-1H-imidazol-3-ium-1-yl)propyl)-3-sulfo-1H-imidazol-3-ium phosphomolybdate, 2-methyl-1-(4-(2-methyl-3-sulfo-1H-imidazol-3-ium-1-yl)butyl)-3-sulfo-1H-imidazol-3-ium phosphomolybdate, and 2-methyl-1-(12-(2-methyl-3-sulfo-1H-imidazol-3-ium-1-yl)dodecyl)-3-sulfo-1H-imidazol-3-ium phosphomolybdate. The incorporation of various lengths of connecting spacers made their thermal stability window wider, as verified by thermogravimetric analysis, and thus, they could be used as efficient catalysts in high-temperature reactions. The extent of hydrogen bond interactions within the –SO3H group and the PMo12O403− anion strategically controlled the acidic sites and together with the methylene linkages provide a heterogeneous nature to the hybrids, making them easily recyclable and thermally stable acid catalysts. The hybrid with the longest methylene connecting spacer (n = 12) was found to be more efficient as an acid catalyst than the shorter ones in the solvent-free Michael-like addition of indole with chalcones obtained via Claisen–Schmidt condensation. [ABSTRACT FROM AUTHOR]

Pt/C and SO42−/ZrO2 were mechanically mixed as the catalysts for p-aminophenol synthesis by catalytic transfer hydrogenation of nitrobenzene in water with formic acid as the hydrogen source. The effect of Pt loading and the solid acid on the reaction was investigated. PAP selectivity reached a maximum at a loading of 1 wt%. The characterization results revealed the presence of three valence states of Pt. Pt0 was beneficial for the nitrobenzene hydrogenation, while higher valence Pt contributed to the formic acid decomposition. The catalytic performance of different solid acid catalysts, including HZSM-5, Hβ, SO42−/ZrO2 and SO42−/TiO2, was compared. It was found that Lewis acid sites with strong acid strength were favorable for p-aminophenol formation, and SO42−/ZrO2 showed higher catalytic activity for the reaction. Using Pt/C + SO42−/ZrO2 as the catalyst, the reaction conditions were optimized. Under the optimal reaction conditions, the nitrobenzene conversion and the p-aminophenol selectivity were 80.0% and 47.6%, respectively. The reaction mechanism was also proposed based on the main by-products of the reaction. [ABSTRACT FROM AUTHOR]

Supported Au colloidal nanoparticles have been prepared in the presence of stabilising polymers, such as, PVA, PVP and PEG (polyvinylalcohol, polyvinylpyrrolidone, polyethylene glycol). The effect of the polymer to Au weight ratio was investigated, for the synthesis of Au nanoparticles with varying particle size and particle size distribution. By varying the polymer/Au wt/wt ratio, Au nanoparticles with mean diameters from 3 to 8 nm were synthesised. The synthesised Au catalysts were studied in the liquid phase oxidation of glucose to glucaric acid under alkaline conditions. We demonstrated that the choice of polymer and polymer to Au weight ratio, have an important influence in terms of catalytic activity and yield to glucaric acid. The highest yield to glucaric acid (22%) was obtained using Au–PVA catalysts. A strong deactivation was observed using Au catalysts. Further evaluation of the possible reasons for deactivation were investigated using experimental, computational and NMR relaxation studies. [ABSTRACT FROM AUTHOR]

The conversion of biomass resources into 5-hydroxymethylfurfural (5-HMF) is of great significance for the valorization of biomass into key chemicals and fuels. However, designing heterogeneous catalysts with controllable Brønsted and Lewis acid sites for achieving high yields of 5-HMF remains a challenge. Herein, a highly efficient SAPO-34 nanocrystallites catalyst has been synthesized by a facile strategy, employing commercial low-cost organosilane [3-glycidoxypropyltrimethoxysilane (AC-230)] together with seeds and microporous template triethylamine. The complex functionalities of AC-230 were investigated by conditional experiments and systematic characterizations. The resultant SAPO-34 nanocrystallites (SP-MS) have an ultra-high external surface area (180 m2 g−1), large mesopore volume (0.51 cm3 g−1), a high amount of accessible Brønsted/Lewis acid, and good hydrophilicity. For the conversion of mono-, di-and poly-saccharides into 5-HMF, SP-MS exhibited remarkable activity. Typically, an 81% yield of 5-HMF with a complete glucose conversion was achieved in a biphasic NaCl–H2O/methyl isobutyl ketone solvent system at 170 °C within 45 min, obviously better than other heterogeneous acid catalysts. According to the kinetic study, the Lewis acid sites over SP-MS decreased the apparent activation energy (85 kJ mol−1) of glucose isomerization, and then the abundant Brønsted acid sites boosted the 5-HMF yields. More attractively, the catalytic activity can be restored after at least four cycles. This work is anticipated to provide insights into designing efficient and robust SAPO catalysts for 5-HMF production. [ABSTRACT FROM AUTHOR]

A palladium diphosphine pincer complex H3(PNNNP-PdI) has been encapsulated in the benzotriazolate metal-organic framework MFU-4l-OH ([Zn5(OH)4(btdd)3], btdd2− = bis(1,2,3-triazolo)dibenzodioxin), and the resulting materials were investigated as Lewis acid catalysts for cyclization of citronellal to isopulegol. Rapid catalyst immobilization is facilitated by a Brønsted acid–base reaction between the H3(PNNNP-PdI) benzoic acid substituents and Zn–OH groups at the framework nodes. Catalyst loading can be controlled up to a maximum of 0.5 pincer complexes per formula unit [ PdI-x , Zn5(OH)4−nx(btdd)3(H3−nPNNNP-PdI)xx = 0.06–0.5, n ≈ 2.75]. Oxidative ligand exchange was used to replace I− with weakly coordinating BF4− anions at the Pd–I sites, generating the activated PdBF4-x catalysts (x = 0.06, 0.10, 0.18, 0.40). The Lewis acid catalytic activity of the PdBF4-x series decreases with increasing catalyst density as a result of the appearance of mass transport limitations. Initial catalytic rates show that the activity of PdBF4-0.06 approaches the intrinsic activity of a homogeneous PNNNP-PdBF4 catalyst analogue. In addition, PdBF4-0.06 exhibits better catalytic activity than the metallolinker-based MOF Zr-PdBF4 and was not subject to leaching or catalyst degradation processes observed for the homogeneous analogue. [ABSTRACT FROM AUTHOR]

Two lanthanide-coordination polymers (Ln-CPs) containing benzophenone-4,4′-dicarboxylate (bpndc2−) linker, namely [Er2(bpndc)3(DMF)2] (1) and [Yb2(bpndc)3(DMF)2] (2) were synthesized and characterized using X-ray crystallography and spectroscopic methods. The topological analysis revealed that both compounds are chiral three-dimensional uninodal 5-connected net of type yfh. These Ln-CPs showed good stability and thus were used as heterogeneous catalysts for the acetalization of glycerol. This study provides some further evidence supporting the effectiveness of Ln-CPs as potential Lewis acid catalysts for chemical transformations. [ABSTRACT FROM AUTHOR]

Naturally occurring 2-picolinic acid was uncovered as an off-the-shelf, non-toxic, commercially available, cost-effective and sustainable hydrogen bond donor (HBD) catalyst with a suitable halide co-catalyst for the cycloaddition of CO2 to both terminal and internal epoxides to prepare cyclic carbonates. The catalytic ability of the 2-picolinic acid/n-Bu4NI binary system was noticed when it was used to induce the insertion of CO2 into internal di-substituted epoxides as substrates. This is a rare instance of naturally sourced hydrogen bond donor catalyzed cycloaddition of CO2 to internal epoxides. Notably, 8 crucial internal di-substituted epoxides were converted to the corresponding cyclic carbonates with up to 97% yield and >99% selectivity with only 2 mol% catalyst loading. Additionally, 15 terminal mono-substituted epoxides were transformed under mild reaction conditions in the presence of CO2 (1 bar) to the related cyclic carbonates with up to 98% yield and >99% selectivity, with a low catalyst loading (1 mol%) and high turnover numbers (TON) and frequencies (TOF); TON/TOF (h−1) up to 97/5.4. The catalyst reusability experiment in which the reuse of 2-picolinic acid up to 5 times without significant loss of reactivity and a scale-up reaction with only 1 mol% catalyst loading was performed to highlight the practicality of this catalytic system. Density functional theory (DFT) calculations provided the reaction barriers for the different pyridine carboxylic acid catalysts employed in the title reaction and revealed that finding a suitable hydrogen bond donor catalyst hinges upon the interplay between the acidic strength and catalytic activity. [ABSTRACT FROM AUTHOR]

Oxidative desulfurization (ODS) has been become an important technical route for the production of ultralow-sulfur fuel. This work focuses on a deep understanding of the roles of structural defects, surface acidity and catalytic properties of phosphotungstic acid grafted on Zr-doped MCM-41 catalysts in the oxidation of 4,6-dimethyldibenzothiophene (4,6-DMDBT) in a model diesel. Two kinds of Zr-MCM-41 mesoporous solids (termed ZrM-I and ZrM-II) were synthesized with different methods and their structural defects and surface acidity were investigated. When H3PW12O40 (termed HPW) was grafted on the ZrM solids, their dispersion and structural deformation were largely governed by the interaction with the ZrM support. Three types of HPW nanoparticles, confirmed by 31P-NMR-MAS spectra, were formed, which were related to the unchanged, deformed and defective Keggin units. The amount of total surface acidity was 227 μmol g−1 for HPW/ZrM-I and 307 μmol g−1 for the HPW/ZrM-II catalyst. For 4,6-DMDBT oxidation, the pore regularity and structural defects of the ZrM supports and the surface acidity of the HPW/ZrM catalysts played the key roles. The HPW/ZrM-II catalyst showed higher catalytic activity, due to its larger number of surface acid sites resulting from the greater amount of deformed and defective Keggin-type nanoclusters. The 4,6-DMDBT conversion reached nearly 100% over the HPW/ZrM-II catalyst under optimal condition (reaction temperature: 70 °C; reaction time: 60 min; catalyst concentration: 0.3 g L−1; H2O2/4,6-DMDBT molar ratio: 8; HCOOH/H2O2 molar ratio: 1.5). The 4,6-DMDBT oxidation was sterically favored on the combined Lewis (L) and Brønsted (B) acid sites in the catalysts. L acid sites were the centers for 4,6-DMDBT adsorption and the neighboring B acid sites participated in the transfer of protons and oxygen atoms between adsorbed sulfur compounds and the surface peroxophosphotungstate complex, benefiting the 4,6-DMDBT oxidation. [ABSTRACT FROM AUTHOR]

MIL-101(Cr)-SO3H has excellent thermal and chemical stabilities, making it an ideal porous acid catalyst for many organic reactions and petrochemical industries. However, there are some disadvantages such as the fact that it is not easy to mass produce crystalline MIL-101(Cr)-SO3H and it is time-consuming to purchase the starting organic ligand of 2-sulfoterephthalate monosodium (sTA-Na). In this study, readily available p-xylene (1,4-dimethylbenzene) was used as the raw material for the lab-synthesis of sTA-Na. Some optimal conditions were studied and established to obtain a maximum sTA-Na yield of ∼75%. The prepared sTA-Na was characterized by FT-IR, PXRD, FE-SEM, NMR and MS spectroscopies, showing that its functional groups, molecular structure, and molecular weight are the same as those of the commercial counterpart from TCI company; however, their particle shapes and crystal phases are different. Then, the MIL-101(Cr)-SO3H powder was prepared from the lab-synthesized sTA-Na and used as a catalyst in ethylene dichloride (EDC) cracking to produce a vinyl chloride monomer (VCM). The catalytic activity test in the EDC cracking showed that the reaction temperature can be lowered to 255 °C from 550 °C, while the percentage conversion (∼75%) and the selectivity (99.8%) remain unchanged or even better than those in current industrial processes, indicating that MIL-101(Cr)-SO3H is a promising catalyst applied as an energy efficiency technology in the EDC cracking to produce VCM. [ABSTRACT FROM AUTHOR]

Catalysts of zirconium-exchanged proton-containing tungstophosphoric acid (TPA) supported on β-zeolites were prepared by an impregnation method for the selective alcoholysis of furfuryl alcohol into ethyl levulinate. The prepared catalysts were characterized by different spectroscopic techniques. The results indicated the existence of a Keggin ion structure of TPA after its modification with Zr ions and successive dispersion on β-zeolites. The introduction of Zr in TPA generated Lewis acidic sites in the catalyst. Pyridine-adsorbed FT-IR confirmed the presence of both Brønsted and Lewis acidic sites in catalysts. The catalytic activity for the alcoholysis of furfuryl alcohol depends on the strength of both Brønsted and Lewis acids of the catalyst. Among these catalysts, 20%Zr0.75TPA/β-zeolite was active for the alcoholysis of furfuryl alcohol with a 96% yield of ethyl levulinate. Optimal conditions were established to obtain maximum yield. A plausible reaction mechanism was also proposed. The catalyst was reused without any appreciable loss of activity. [ABSTRACT FROM AUTHOR]

A novel carbon-based solid acid catalyst (SC-GCa-800) was prepared by the carbonization of calcium gluconate at high-temperature followed by sulfonation with 4-diazoniobenzenesulfonate at room temperature. The catalyst was characterized by FT-IR, XPS, TEM, SEM, TGA, N2 adsorption–desorption and elemental analysis to reveal its physical and chemical properties. Furthermore, the effects of reaction temperature, retention time, substrate concentration, catalyst loading and solvent types were investigated. It was demonstrated that SC-GCa-800 is an efficient solid acid catalyst for furfural production obtained from xylose in 1,4-dioxane. A 76.9% furfural yield can be achieved from 100 mg xylose at 140 °C in 40 min by using a 50 mg catalyst. The catalyst showed high stability and could be recycled five times without a significant loss of catalytic activity. The results indicated that the high catalytic activity of SC-GCa-800 was dependent on its high acidity, BET surface and pore structure. More importantly, the furfural can be obtained at low temperature (100–140 °C) and separated easily from the solvent due to the low boiling point of 1,4-dioxane. [ABSTRACT FROM AUTHOR]

An efficient and versatile synthesis of ortho-iodobiphenylboronic acids via the highly regioselective metal–iodine exchange (MIE) of 2,3-diiodobiphenyls is reported. The site-selectivity is very much controlled by the size of the biphenyl fragment, providing only the terminal arylboronic acid derivatives in excellent site-selectivity. The nature of the substituents (R1 and R2) on the biphenyls is found to have an influence on the reactivity but not on the regioselectivity. The best reactivity and the highest isolated yields were furnished with products bearing electron-donating groups. The synthesized derivatives were also tested for in vitro antimicrobial activity against four strains of bacteria and one fungal strain. This revealed that (2-iodo-4′-isopropyl-[1,1′-biphenyl]-3-yl)boronic acid 6A and (3-(benzo[d][1,3]dioxol-5-yl)-2-iodo-5-methoxyphenyl)boronic acid 22A possess the most potent antibacterial and antifungal activity with MICs of 0.10 and 0.3 mg mL−1 for B. cereus and C. albicans respectively. The catalytic activity was also examined towards an amidation reaction at ambient temperature and this revealed a new optimal catalyst, (2-iodo-4′,5-dimethoxy-[1,1′-biphenyl]-3-yl)boronic acid 19A providing a remarkable increase in the amide yields, including α-aminoacids. This work discloses a protocol for the first synthesis of hitherto unknown ortho-iodobiphenylboronic acid derivatives that is scalable, and general in scope, where no chromatographic purification is necessary and the products are indeed potential organocatalysts. [ABSTRACT FROM AUTHOR]

A clay mineral-type modified bentonite, produced via delamination and subsequent incorporation of AlZr and AlCe species to modulate their acid properties, was used to obtain bifunctional catalysts with the incorporation of NiMo, CoMo, NiW and CoW. The catalysts were characterized using X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), temperature-programmed reduction (H2-TPR) and diffuse reflectance infrared Fourier-transform spectra with a probe molecule (NH3-DRIFTS). The catalytic performance was evaluated in the hydroconversion of decane. The main differences in catalytic performance were attributed to the reductive and acid properties of the catalysts. Indeed, when Mo was used, there was a higher conversion compared to W catalysts, which correlated with the greater number of reducible species at lower temperatures. Solids with a promoter/metal ratio of 0.4 presented the best catalytic performance, which is attributed to the fact that this ratio improves the formation of NiW, NiMo, CoW and CoMo species on the surface of solids. On the other hand, the catalysts obtained from the mineral modified with AlCe showed better catalytic activity compared to catalysts containing AlZr as an acidity enhancer. The different processes and elements used give us information to carry out controlled processes for the generation of acid sites that respond to a specific orientation of the decane hydroconversion reaction. [ABSTRACT FROM AUTHOR]

Tungstated metal phosphate (WOx/MP; M = Al, Zr and Ti) solid acid catalysts were examined for vapor phase glycerol dehydration to acrolein and hydroxyacetone. The physico-chemical characteristics of the samples were explored using X-ray diffraction (XRD), N2 sorption, Fourier-transform infrared spectroscopy (FT-IR), UV-visible diffuse reflectance spectroscopy (UV-DRS), and ex situ FT-IR investigation of the adsorbed pyridine and ammonia temperature programmed desorption (NH3-TPD) analysis to gain an understanding of the impact of the structural and acidic nature of the catalysts upon changing the metal component. The catalytic activity and selectivity functionalities were interpreted in terms of the acidity and structural properties of the WOx/MP catalysts. The outcomes demonstrated that WOx/TiP was the most selective and stable catalyst during the catalytic dehydration of glycerol owing to the acceptable amount of surface acidity and the substantial number of pores available on its surface. A detailed study on WOx/TiP was also performed to understand the interaction between the tungsten and the TiP support. [ABSTRACT FROM AUTHOR]

Friedel–Crafts alkylation of resorcinol with methyl tertiary butyl ether was carried out over sulfated zirconia (SZ) catalysts in the liquid phase. The SZ catalysts were synthesized by an impregnation method with different sulfur amounts and characterized by XRD, FT-IR, nitrogen sorption, XPS, SEM, pyridine-FTIR, and NH3-TPD. The effect of the sulfur loading on the total acidity and catalytic activity was investigated. The influence of the nature of the solvents on the alkylation reaction was inspected in terms of their acceptor and donor numbers. The sulfur loading, amount of solvent, temperature, catalyst amount, mole ratio and reusability of the catalyst were examined. The SZ catalyst synthesized by impregnating 1 N sulfuric acid was found to be highly selective for the monoalkylation to 4-tertiary butyl resorcinol (72%) with a resorcinol conversion of ∼70%. The catalyst was recycled thrice with a negligible decrease in the yield for 4-tertiary butylresorcinol. The SZ exhibited the best performance at low temperature (60 °C) among the different types of solid acid catalysts studied so far. [ABSTRACT FROM AUTHOR]

We report on a new route to produce hexane-1,2,5,6-tetrol (tetrol) from cellulose-derived levoglucosanol (lgol). We investigate the reaction intermediates formed over metal and acid catalysts, and propose a reaction network for this process. Lgol is converted to tetrol in up to 90% yield over a bifunctional Pt/SiO2-Al2O3 catalyst at 150 °C. High tetrol yields are maintained at lgol concentrations of up to 21 wt% in water. threo- and erythro-lgol first undergo hydrolysis to 3,4-dideoxymannose (DDM) and 3,4-dideoxyglucose (DDG), respectively. This reaction can be carried out selectively over an Amberlyst 70 acid catalyst at a temperature of 100 °C. At a higher temperature of 150 °C with no added catalyst, DDM and DDG undergo aldose-ketose isomerization to 3,4-dideoxyfructose (DDF). DDM is hydrogenated to c/s-tetrol over a Pt/ SiO2 catalyst, while DDG is hydrogenated to trans-tetrol. Formation of DDF erases the stereocenter at the C2 position of lgol, and hydrogenation of DDF produces a nearly 1:1 mixture of c/s- and trans-tetrol. This catalytic approach to produce tetrol from biomass opens the door to sustainable chemicals derived from tetrol. [ABSTRACT FROM AUTHOR]

Functionalized metal–organic frameworks (MOFs) have been used in a wide range of applications. Although the development of functionalized MOFs with plentiful open metal sites (defects) provides an avenue for targeted reactions, creating such defects remains challenging. Herein, a UiO-type MOF with hierarchical porosity and plentiful Zr–OH/OH2 sites (capping 35% Zr coordination sites) was synthesized within 40 min by a solid-phase synthesis route without the use of solvent and template. The optimal sample converted 5.7 mmol benzaldehyde to (dimethoxymethyl)benzene within 2 min at 25 °C. The turnover frequency number and activity per unit mass reached 2380 h−1 and 8568 mmol g−1 h−1, respectively, outperforming all previously reported catalysts at room temperature. This excellent catalytic activity was correlated with the defect density in functionalized UiO-66(Zr) and the accessibility of plentiful Zr–OH/OH2 sites as acid sites. [ABSTRACT FROM AUTHOR]

We report that the catalytic activity for benzoic acid hydrogenation to cyclohexanecarboxylic acid was positively correlated with the initial surface fraction of Pd2+ in the utilized Pd nanoparticles. Additionally, the mechanism for deactivation of Pd/C as a benzoic acid hydrogenation catalyst was proposed to involve a decrease in the Pd2+ fraction in a strongly reducing atmosphere. [ABSTRACT FROM AUTHOR]

Conversion of 5-hydroxymethylfurfural (HMF) into 5-ethoxymethylfurfural (EMF) and ethyl levulinate (EL) is an attractive biomass transformation due to its potential application in the energy and chemical industries. Here, we report on the conversion with MOF-based polyoxometalate [Cu–BTC][HPM] (NENU-5) as the catalyst. The homogeneous distribution of HPM in the pores of Cu–BTC makes the composite combine the properties of the catalytic activity of HPM and the insolubility, large surface area and hierarchical pores of Cu–BTC. The catalyst demonstrates reusability and catalytic activity with 55% yield of EMF and 11% yield of EL. [ABSTRACT FROM AUTHOR]

The effect of partial substitution of La by Ca and Sr in the catalytic activity of lanthanum cobaltite (LaCoO3) was studied. Two series of La1−xCaxCoO3 and La1−xSrxCoO3 (x = 0, 0.2, and 0.4) reduced perovskites were prepared, characterized and evaluated in the succinic acid conversion at 200 °C and 6 MPa. The characterization results showed a larger Ca substitution in the La1−xCaxCoO3 series, whereas carbonates as segregated phases up to x = 0.2 of Sr were obtained in the La1−xSrxCoO3 series. In the Sr substituted perovskites, the oxidation of Co3+ to Co4+ neutralizes the electronic instability, whereas in the Ca substituted perovskites the presence of Ca2+ generates oxygen vacancies. The succinic acid conversion forms mainly succinic anhydride and 2-hydroxy-tetrahydrofuran by dehydration and hydrogenation processes. The highest initial rate of the reduced LaCoO3 was attributed to the smallest Co crystal size with no segregated phases, compared to substituted catalysts. [ABSTRACT FROM AUTHOR]

γ-Valerolactone (GVL) is an important lignocellulosic platform molecule with huge potential for various industrial and chemical applications, which is usually produced using levulinic acid (LA) or its esters as raw materials. However, a two-step reaction process in which hydrogenation of the carbonyl groups on metal sites and subsequent lactonization catalyzed by acidic sites over multiple catalysts has generally been needed to realize this synthesis. In this work, a hierarchically multifunctional single catalyst of Ru/phosphotungstic acid/hierarchically porous UiO-66 (Ru/HPW/HP-UiO-66), simultaneously integrated with acidic and metal sites, has been fabricated via a simple strategy and successfully applied in the one-pot synthesis of GVL using methyl levulinate (ML) as the raw material. The hierarchically porous and nanosized (∼15 nm) HP-UiO-66 can not only provide sufficient space for the mass transfer of substrates but also favors the loading of bulk HPW molecules, which can effectively mediate the catalytic activities and stability of Ru NPs using the confined pore effect of UiO-66 and the strong interaction between HPW and Ru. When applied in the one-pot synthesis of GVL, the hierarchical Ru/HPW/HP-UiO-66 catalyst showed excellent catalytic activity (>97% yield) and stability (maintained after 7 successive cycles) for GVL. More importantly, the hierarchical catalyst also exhibited an extraordinary performance in the hydrogenation of different unsaturated hydrocarbons in aqueous solution. It is expected that our study offers a novel route to biomass upgrades involving metal/acid bifunctional synergistic catalysts. [ABSTRACT FROM AUTHOR]

Various erbium ion-exchanged montmorillonite K10 materials were prepared by an ion exchange method and were found to act as efficient solid acid catalysts. The catalytic materials synthesized in this work were characterized using a combination of X-ray fluorescence spectroscopy, N2 adsorption, powder X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy and NH3 temperature-programmed desorption, as well as by FT-IR spectra analysis following pyridine adsorption. These catalysts were also evaluated with regard to the hydrothermal conversion of cellulose to lactic acid. Lactic acid yields as high as 67.6% were obtained when reacting 0.3 g cellulose, 0.1 g catalyst and 30 mL water at 240 °C under 2 MPa N2 for 30 min. Upon recycling of the catalyst, the lactic acid yields decreased from 67.6 to 58.7 to 55.9% during the first, second and third trials. Beginning with the second trial the catalyst behaved as a true heterogeneous catalyst for the conversion of cellulose to lactic acid. The observed decreases in catalytic activity during recycling could be due to a combination of erbium ion leaching, deposition of carbon species in pores and partial structural changes in the catalyst. [ABSTRACT FROM AUTHOR]

Useful bio-products are obtainable via the catalytic conversion of biomass or derived intermediates as renewable carbon sources. In particular, furanic ethers and levulinate esters (denoted bioEs) have wide application profiles and can be synthesised via acid-catalysed reactions of intermediates such as fructose, 5-hydroxymethyl-2-furaldehyde (HMF) and furfuryl alcohol (FA) with ethanol. Solid acid catalysts are preferred for producing the bioEs with environmental benefits. Furthermore, the versatility of the catalyst in obtaining the bioEs from different intermediates is attractive for process economics, and in the case of porous catalysts, large pore sizes can be beneficial for operating in the kinetic regime. Carbon-based materials are attractive acid catalysts due to their modifiable surface, e.g. with relatively strong sulfonic acid groups (SO3H). Considering these aspects, here, we report the preparation of mesoporous (SO3H)- functionalised-carbon/silica (C/S) composites with large pores and high amounts of acid sites (up to 2.3 mmol g-1), and their application as versatile solid acid catalysts for producing bioEs from fructose, HMF and FA. The mesoporous composites were prepared by activation of an organic compound deposited on the orderedmesoporous silicas MCF (mesostructured cellular foam) and SBA-15, where the organic compound (p-toluenesulfonic acid) acted simultaneously as the carbon and SO3H source. The atomic-level characterisation of the acid nature and strengths was performed by 31P solid-state NMR studies of an adsorbed base probe, in combination with FT-IR and XPS. Comparative catalytic studies showed that the C/S composites are interesting catalysts for obtaining bioEs in high yields, in comparison with classical solid acid catalysts such as sulfonic acid resin Amberlyst™-15 and nanocrystalline (large pore) zeolite H-beta. [ABSTRACT FROM AUTHOR]

We demonstrate a facile synthesis method of a porous ionic crystal (PIC) composed of the little-known δ-Keggin-type cationic polyoxoaluminum cluster ([δ-Al13O4(OH)24(H2O)12]7+, δ-Al13) with an oppositely-charged polyoxometalate, which enabled us to investigate the activity as a solid acid. The δ-Al13 based PIC exhibited much higher activity in pinacol rearrangement, a typical acid-catalyzed reaction, than the PIC based on the well-known and thermodynamically stable rotational isomer (ε-Al13). This work is a rare example of rotational isomers of polyoxoaluminum clusters exhibiting remarkably different catalytic activities. [ABSTRACT FROM AUTHOR]