Solid-supported Acid Research Articles

Acidic and basic sites on the surface of sodium montmorillonite active for catalytic transesterification of glycerol to glycerol carbonate

Montmorillonite (Mt) as a solid acid catalyst or support has been widely used in catalytic reactions. However, the existence and catalytic activities of its surface basic sites have rarely been revealed. Here, the surface and structure of Na-Mt are modulated by thermal treatment, providing both acidic and basic sites for the transesterification of glycerol with dimethyl carbonate (DMC) to glycerol carbonate (GLC). The experimental results showed that the thermally activated Na-Mt exhibited bifunctional catalytic properties in glycerol transesterification. The Na-Mt calcined at 400 °C had a basic site density of 1.38 mmol/g and led to a glycerol conversion of 96.8% and a GLC yield of 94.5%. Edge surfaces of Na-Mt provided MII (MIII) atoms as Lewis acidic sites for facilitating the generation of glyceroxide anions from activated glycerol and -M-OH groups as Brønsted and Lewis basic sites for enhancing the carbonyl activation of DMC. This work revealed the co-existence of acidic and basic sites over thermally activated Na-Mt for synergetic catalysis in the transesterification of glycerol to GLC, making the development of Mt-based materials as bifunctional catalysts for one-pot acid-base catalytic processes possible.

Telescoped Continuous Flow Synthesis of 2-Substituted 1,4-Benzoquinones via Oxidative Dearomatisation of para-Substituted Phenols Using Singlet Oxygen in Supercritical CO2

AbstractThis paper describes a continuous multi-step synthesis in supercritical CO2. A continuous flow synthesis of 2-substituted 1,4-benzoquinones is reported, and details of the high-pressure reactors are given. This proceeds via the telescoped dearomatisation of p-substituted phenols using singlet oxygen in supercritical CO2 and an acid-mediated C–C migration. The process has a short residence time of 30 minutes, with overall yields and projected productivities of up to 83% and 9 g/day, respectively. This methodology enables a safe and efficient synthesis of 2-substituted 1,4-benzoquinones from photo-generated singlet oxygen, and cheap and readily available p-substituted phenols. The procedure has high atom efficiency, low photocatalyst loading, and substitutes potentially hazardous and corrosive reagents and solvents for molecular oxygen, CO2, and the less hazardous solid-supported acid Amberlyst-15.

Synthesis and Structural Characterization of 16-Membered Schiff Base Macrocycles

Novel tetraazamacrocyclic complexes of Cu(II), Co(II), Ni(II) and Zn(II) has been synthesized from the reaction of ethylenediamine with Meldrums acid and divalent metal ions using solid-supported perchloric acid (HClO4-SiO2) as a catalyst. The complexes were characterized by IR, 1HNMR, EPR spectra, magnetic moments, conductance, thermal analysis (TGA and DTA), and powder X-ray analysis (XRD). The antimicrobial studies of these complexes against Staphylococcus typhi, Staphylococcus aurieus, Escherichia coli, Bacillus subtilis species by Minimum Inhibitory Concentration (MIC) method revealed that these complexes possess potent antibacterial activity.

A comparative study on energy efficient CO2 capture using amine grafted solid sorbent: Materials characterization, isotherms, kinetics and thermodynamics

Excessive emission of CO2 is the main reason for the greenhouse effect. Amine-functionalized solid sorbents are promising candidates for reducing CO2 emissions, while sorbent quality depends greatly on the support. Herein, a new type of aluminosilicate solid acid support with a high specifical surface area of 412 m2/g and an acid amount of 7.88 mmol/g was fabricated using a low-energy hydrothermal free method. The fabricated aluminosilicate support and a benchmark MCM-41 porous silicate were then functionalized through chemical grafting of (3-Aminopropyl)triethoxysilane (APTES), and subsequently applied for CO2 capture. The results revealed that the amine loading and CO2 adsorption capacity of the fabricated aluminosilicate support were comparable with those of the benchmark MCM-41 porous silicate. Moreover, the fabricated sorbent exhibited low adsorption and desorption activation energy of 14.47 and 51.05 kJ/mol, which were 32% and 20% lower, respectively, than those of the benchmark one. The lower adsorption activation energy was found to be associated with the lower CO2 transfer resistance, whereas the lower desorption activation energy was attributed to the unique catalytic effect induced by the protons and Al atoms of the support. Our results indicate new possibilities in energy saving preparation of amine-based solid sorbent for energy efficient CO2 capture.

Geometric, electronic, and synergistic effect in the sulfonated carbon-supported Pd catalysts for the direct synthesis of hydrogen peroxide

Although carbon-supported palladium catalysts have been generally used for the direct synthesis of H2O2 (DSHP), the low H2O2 selectivity remains a challenge. In this work, it was systematically studied how the sulfonated carbon surface affects the physicochemical properties of Pd during catalyst preparation, and thereby affects the catalytic activity of Pd/C for the DSHP reaction. Nano-sized Pd particles (about 2–3 nm) with a high Pd2+/Pd0 ratio resulted in a high H2O2 selectivity. The sulfonated carbon material acted as an efficient solid acid support and enhanced the H2O2 selectivity. Fine-tuning the Pd properties on the sulfonated carbon support significantly improved the H2O2 selectivity by as much as 87 % in the absence of caustic promoters, which clearly demonstrates that the synergistic combination of the active metal properties and that of the carbon support are extremely important to realize a highly active and selective carbon-supported palladium catalyst for the DSHP reaction.

Methane dehydroaromatization using Mo supported on sulfated zirconia catalyst: Effect of promoters

Methane dehydroaromatization (MDHA) is a direct approach of converting methane to aromatics and H2. Mo doped HZSM-5/HMCM-22 are considered as the most active and stable catalysts for MDHA. It is generally thought to involve a process in which Mo oxides convert to MoCy/MoOxCy active species that activate CH4 to C2Hy dimers. In a final step, C2Hy dimers undergo oligomerization on zeolite Brønsted acid sites. An alternative solid acid support is sulfated zirconia (SZ), which is known to contain strong Brønsted acidity. Carbon deposition is significant. Here, MDHA is compared to Pt, Pd, Cr, W promoters for Mo/SZ catalyst to decrease carbon deposition and increase aromatics selectivity. The catalysts are characterized using BET, SEM-EDS, DRIFTS, Raman Spectroscopy, XRD, XANES and TPO. Activity varied with different promoters. Less carbon deposition and slower deactivation were observed for Pd, Pt and Cr promoted catalysts, while W promotion resulted in more carbon deposition and rapid deactivation Compared to Pd and W promotion, Pt and Cr increased higher aromatics selectivity for Mo/SZ.

Insight into the Selective Conversion via a Steered Adsorption and Protonation from Tantalates‐based Solid Acid's Intrinsic Proton for Hydride‐transfer Reduction

AbstractBrønsted solid acids have popularly been used as catalysts or supports for many hydrogenation reactions, while it is uncertain if their structural H species could significantly enhance velocity and reusability for these reactions. In this work, a series of tantalate‐supported silver catalysts Ag/MxH2–xTa2O6 (M=H, Li, Na, K, Sr) were prepared, along with abundant solid acid catalysts (Ag/Al2O3, Ag/SiO2−Al2O3, Ag/ZrO2−SO42−, and Ag/heteropolyacid). By assessing activity of a model reaction from p‐nitrophenol to the corresponding aniline together with an isotope comparative test (Ag/D2Ta2O6 and Ag/H2Ta2O6), a previously unknown route was uncovered, which involves that intrinsic proton H species of the Brønsted solid acid support directly participate in the formation of products. Meanwhile, Ag NPs could form an embedded distribution by exchanging with structural H species, responsible for the stabilization of catalytic active sites. The results reported here could give a deep understanding on proton chemistry of solid acids in construction of catalysts and/or supports in H‐participating reactions.

Novel Fe3O4/SiO2/PPA Magnetic Nanoparticles: Preparation, Characterization, and First Catalytic Application to the Solvent- Free Synthesis of Tetrahydrobenzo[a]xanthene-11-ones

Novel Fe3O4/SiO2/PPA nanoparticles were used as solid acid support in the solvent-free synthesis of 12-aryl-9,9-dimethyl-8,9,10,12-tetrahydro-11H-benzo[a]xanthen-11-ones via multicomponent condensation of aromatic aldehydes with naphthalen-2-ol and 5,5-dimethylcyclohexane-1,3-dione. The target products were obtained in good to high yields. The Fe3O4/SiO2/PPA nanoparticles were thoroughly characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transform IR spectroscopy, and energy-dispersive C-ray spectroscopy. The new catalyst has a high activity and is environmentally friendly, heterogeneous, easily recoverable, and recyclable without loss of catalytic activity.

Direct synthesis of H2O2 over acid-treated Pd/C catalyst derived from a Pd-Co core-shell structure

Abstract Although a wide range of Pd/C catalysts has been developed for the direct synthesis of H2O2, low H2O2 yields remain a challenging issue. In this study, we propose a novel catalyst design involving the formation of Pd@Co(BO3)2 core-shell nanoparticles (NPs) on an activated carbon support followed by the cobalt borate shell etching with H3PO4. The non-noble metal shell efficiently suppressed unfavorable aggregation of Pd NPs, resulting in the formation of small and monodisperse Pd NPs after stripping the cobalt. The use of H3PO4 was also beneficial to obtain a high H2O2 yield by decreasing the metallic nature of Pd and enabling the acid-treated activated carbon to act as a solid acid support. The features of the acid-treated Pd/C catalyst derived from the Pd@Co(BO3)2 core-shell were superior enough for achieving extremely high activity in the direct synthesis of H2O2. The H2O2 productivity of 5721 mmol-H2O2/g-Pd.h with 88.1% H2O2 selectivity reported herein is one of the best values among Pd/C catalysts developed to date. It was also demonstrated that the cobalt borate shell should be completely removed because cobalt accelerated H2O2 decomposition and hydrogenation.

Controlled Hydrodeoxygenation of Phenolic Components in Pyrolysis Bio-oil to Arenes

Hydrodeoxygenation of phenolic components in pyrolysis bio-oil is considered to be a potential strategy for producing renewable aromatic chemicals. The key issue of this process is the establishment of an effective catalytic system that can cleave the CAr–O bonds without affecting the aromatic structure. To achieve this goal, an efficient heterogeneous catalyst with solid acid support (WOx/ZrO2) and active metal (Ru) was prepared in this study. The Ru–WOx/ZrO2 catalyst can effectively convert model phenolic compounds into aromatic hydrocarbons. For a mixed phenolic sample, the conversion to and selectivity for arenes were all around 90%. The good selectivity was proved to be strongly related to the surface adsorption and acid properties of the catalyst as well as the reaction pathway. Moreover, the hydrodeoxygenation of a pretreated bio-oil was also conducted and presented a satisfactory yield of arenes at 240 °C with 1 MPa of H2 reacted for 5 h. The depolymerization of high-molecular-weight phenolic olig...

Catalytic hydrodeoxygenation of m-cresol over Ni2P/hierarchical ZSM-5

Bifunctional catalysts comprising Ni2P supported over a hierarchical ZSM-5 zeolite (h-ZSM-5) were synthesized and applied to the hydrodeoxygenation (HDO) of m-cresol, a model pyrolysis bio-oil compound. Surface and bulk characterization of Ni2P/h-ZSM-5 catalysts by XRD, TEM, DRIFTS, TPR, porosimetry and propylamine temperature-programmed desorption reveal that Ni2P incorporation modifies the zeolite textural properties through pore blockage of the mesopores by phosphide nanoparticles, but has negligible impact of the micropore network. Ni2P nanoparticles introduce new, strong Lewis acid sites, whose density is proportional to the Ni2P loading, accompanied by new Brönsted acid sites attributed to the presence of POH moieties. Ni2P/h-ZSM-5 is ultraselective (>97%) for m-cresol HDO to methylcyclohexane, significantly outperforming a reference Ni2P/SiO2 catalyst and highlighting the synergy between metal phosphide and solid acid support. m-Cresol conversion was proportional to Ni2P loading reaching 80 and 91% for 5 and 10wt% Ni respectively. Turnover frequencies for m-cresol HDO are a strong function of Ni2P dispersion, evidencing a structure sensitivity, with optimum activity observed for 4nm particles.

Zeolite supported palladium catalysts for hydroalkylation of phenolic model compounds

Bifunctional palladium-based catalysts with zeolite supports were investigated in phenol hydroalkylation, representing high-potential model reaction for transformation of lignocellulose-derived compounds to automotive and jet fuels. Conversion of phenol correlated with the amount of accessible acid sites and textural properties of the solid acid support: under the same reaction conditions and at the same Pd loading. The highest phenol conversions (99–100%) were obtained for large-pore zeolite Beta and mesopore-containing MCM-36/56 materials. The selectivity towards the targeted cyclohexylcyclohexane on different supports decreased in the following order Beta (57%) > MCM-36 (42%) ≈ MCM-56 (37%) > MCM-22 (20%), while the contribution of undesired reaction termination through formation of non-reactive cyclohexane was more pronounced for the expanded MCM-36/56 based catalysts. Substrate consumption after 60 min over the least active MCM-22-based catalysts increased with increasing Pd content as follows 27% (0.3 wt % Pd), 80% (0.5 wt % Pd) and 98% (0.7 wt % Pd). High activity of Pd/Beta catalysts was not vitiated even by sintering effects being the most pronounced for Beta as a support.

A new and efficient synthesis of pyrazole-fused isocoumarins on the solid surface of magnetically separable Fe3O4@SiO2-SO3H nanoparticles

A new and efficient procedure has been developed for the synthesis of a series of pyrazole-fused isocoumarins from easily available ninhydrin and arylhydrazones. In this synthesis the condensations of ninhydrin and arylhydrazones are carried out under solvent free conditions employing magnetically separable Fe3O4@SiO2-SO3H nanoparticles as solid acid support. Some members of pyrazole-fused isocoumarins are known to bind to a GABA receptor.

Direct synthesis of hydrogen peroxide from hydrogen and oxygen over Pd-supported HNb3O8 metal oxide nanosheet catalyst

A two-dimensional layered niobium oxide and its exfoliated nanosheet were examined as potential solid acid supports for direct synthesis of hydrogen peroxide from hydrogen and oxygen under intrinsically safe and noncorrosive reaction conditions. The catalytic performance strongly depended on the acid strength of the support material. The Pd-supported protonated niobium oxide nanosheet catalyst (Pd/HNb3O8-NS) with remarkably enhanced acidity was superior to layered Pd/KNb3O8 or Pd/HNb3O8 to promote the reaction. Hydrogen peroxide decomposition testing revealed that, although HNb3O8 was comparable to its exfoliated counterpart, HNb3O8-NS, in suppressing hydrogen peroxide decomposition without hydrogen, HNb3O8 was virtually ineffective in preventing hydrogen peroxide hydrogenation in the presence of hydrogen. However, compared with HNb3O8, HNb3O8-NS was found to be still effective at suppressing hydrogen peroxide hydrogenation. The different efficiency observed between HNb3O8 and HNb3O8-NS in the prevention of hydrogen peroxide hydrogenation implies that use of a highly acidic support is advantageous to effectively suppress faster and therefore more unfavorable hydrogen peroxide hydrogenation compared with decomposition. This result clearly demonstrates that the highly acidic HNb3O8 nanosheet can serve as an efficient solid acid support for direct synthesis of hydrogen peroxide from hydrogen and oxygen.

ChemInform Abstract: Magnetically Separable Fe3O4—SO3H Nanoparticles as an Efficient Solid Acid Support for the Facile Synthesis of Two Types of Spiroindole Fused Dihydropyridine Derivatives under Solvent Free Conditions.

AbstractDepending on the nature of the N‐substituents of the starting isatins, two different types of products are obtained by three component one‐pot condensation reactions of isatins, indanedione (III), and enamines.

Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen over Pd‐supported Metal‐Organic Framework Catalysts

Pd‐supported metal‐organic framework (MOF) catalysts have been applied for the direct synthesis of H2O2 from H2 and O2 under intrinsically safe and noncorrosive reaction conditions. The catalytic performance was strongly governed by the properties of the support materials, and the Brønsted acid sites newly introduced on the organic linkers of MOF were proven to be more effective than the Lewis acid sites on the open metal sites in enhancing the H2O2 formation and suppressing its decomposition. Pd/MIL‐101‐SO3H was highly efficient in promoting the reaction owing to the contribution from the strong acidity and highly porous nature of the robust MOF support used. The hydrogen peroxide productivity of Pd/MIL‐101‐SO3H catalyst reached 361 mmol H2O2 mmol/Pd/h, which was 2.3 or 1.7 times higher than that of the conventional Pd/HBEA (SAR = 25) or Pd/sulfonated resin catalyst, respectively. This result clearly demonstrates the promising potential of MOF as a solid acid support material.

Continuous-Flow Alcohol Protection and Deprotection Reactions Catalyzed by Silica-Supported Sulfonic Acid

Alcohol protection and deprotection reactions, catalyzed by solid-supported sulfonic acid, have been investigated under continuous-flow conditions. Primary, secondary, benzylic and phenolic alcohols can be protected under these conditions by tetrahydropyranyl and several silyl ether moieties, generating synthetically useful amounts of material in short time. Furthermore, the described setup can be used to deprotect protected alcohols and be used in selective protection reactions. Because the solid-supported acid catalyst is continually reused in a packed-bed approach, workup is greatly simplified and in most cases only solvent removal is necessary, while reaching high turn-over numbers.

Novel synthesis of a series of spiro 1,3-indanedione-fused dihydropyridines through the condensation of a tetrone with N-aryl/alkylenamines in presence of solid support silica sulfuric acid.

A convenient protocol for the library synthesis of biologically important 1-aryl-2',6-spiro(1',3'-indanedione)-1H-indeno[1,2-b]quinoline-5,7-diones has been developed. In this one-pot reaction protocol a tetrone is condensed with various N-aryl/alkylenamines of 1,3-cyclohexadiones on the surface of a solid-supported acid catalyst silica sulfuric acid under solvent-free condition. The significant advantages of this methodology are the use of solvent-free reaction conditions, operational simplicity of the reaction, good yield of the products with high atom economy, and employment of a recyclable catalyst. All these favorable factors make the present method convenient, economic, and 'benign by design'.

Magnetically separable Fe3O4–SO3H nanoparticles as an efficient solid acid support for the facile synthesis of two types of spiroindole fused dihydropyridine derivatives under solvent free conditions

Two types of spiroindole fused dihydropyridine derivatives have been synthesised from isatins under solvent-free conditions using magnetically separable Fe3O4–SO3H nanoparticles.

One-pot SSA-catalyzed β-elimination: an efficient and inexpensive protocol for easy access to the glycal of sialic acid

Neu5Ac2en1Me per-OAc, the fully protected glycal of sialic acid, is a key intermediate in the discovery of therapeutics and diagnostics, including anti-influenza drugs and proteolysis resistant peptidomimetic foldamers. The synthesis of this sialic acid derivative, however, still relies on standard sugar chemistry that utilizes multi-step methodologies. Herein we report a facile and highly efficient microwave-assisted preparation of Neu5Ac1Me using silica sulfuric acid (SSA) as solid-supported acid catalyst that is one- to two-orders of magnitude faster than standard procedures. We also describe the microwave-assisted and SSA-catalyzed one-pot, rapid, solvent free reaction that combines both peracetylation and β-elimination reactions in one step to generate the glycal from Neu5Ac1Me. We coined the term One-pot SSA-catalyzed Technology for β-Elimination Protocol (OneSTEP) to describe this least laborious, most efficient, and practical preparation to date of Neu5Ac2en1Me per-OAc in terms of yield, time, reagent cost, and waste generation.