Single-step preparation and catalytic activity of mesoporous MCM-41 and SBA-15 silicas functionalized with perfluoroalkylsulfonic acid groups analogous to Nafion®

MAO- and Borate-Free Activating Supports for Group 4 Metallocene and Post-Metallocene Catalysts of α-Olefin Polymerization and Oligomerization

Modern industry of advanced polyolefins extensively uses Group 4 metallocene and post-metallocene catalysts. High-throughput polyolefin technologies demand the use of heterogeneous catalysts with a given particle size and morphology, high thermal stability, and controlled productivity. Conventional Group 4 metal single-site heterogeneous catalysts require the use of high-cost methylalumoxane (MAO) or perfluoroaryl borate activators. However, a number of inorganic phases, containing highly acidic Lewis and Brønsted sites, are able to activate Group 4 metal pre-catalysts using low-cost and affordable alkylaluminums. In the present review, we gathered comprehensive information on MAO- and borate-free activating supports of different types and discussed the surface nature and chemistry of these phases, examples of their use in the polymerization of ethylene and α-olefins, and prospects of the further development for applications in the polyolefin industry.

Solid acid catalysts produced by sulfonation of petroleum coke: Dominant role of aromatic hydrogen

Carbon based solid waste materials have been intensively investigated for the preparation of solid acid catalysts through sulfonation, but the acidity varies significantly depending on the material. In this study, the role of aromatic hydrogen in sulfonation with concentrated H₂SO₄ was investigated using petroleum coke (petcoke), graphite, and biochar as the carbon materials. Through ball milling and calcination, the amount of aromatic hydrogen on the petcoke could be increased or decreased, respectively. After sulfonation at 80 °C with concentrated H₂SO₄, the produced acidity (i.e., -SO₃H groups) increased as the amount of aromatic hydrogen increased from essentially no acidity on graphite to 0.55 mmol/g on biochar and 1.25 mmol/g on petcoke (particle sizes of 45-90 μm) indicating the importance of aromatic hydrogen during sulfonation. Calcination (350 °C for 1 h) of the petcoke before sulfonation decreased the acidity to 0.59 mmol/g, while ball milling (with isopropanol and silica for 24 h) increased the acidity to 3.73 mmol/g. The sulfonated petcoke samples were used as catalysts for the esterification reaction between octanoic acid and methanol at 60 °C and the turnover frequencies were 48-85 h^-1. The results give insights on the preparation of solid acid catalysts from carbon materials and highlight the application of petcoke without activation as a feedstock for esterification catalysts.

Solvent-Free Production of Isosorbide from Sorbitol Catalyzed by a Polymeric Solid Acid

A series of polymeric solid acid catalysts (PDSF-x) is prepared by grafting strong electron-withdrawing groups (-SO₂ CF₃ ) on a sulfonic acid-modified polydivinylbenzene (PDS) precursor synthesized hydrothermally. The effect of acid strength on sorbitol dehydration is investigated. The textural properties, acidity, and hydrophobicity are characterized by using Brunauer-Emmett-Teller analysis, elemental analysis, and contact angle tests. The results of FTIR spectroscopy and X-ray photoelectron spectroscopy show that both -SO₃ H and -SO₂ CF₃ are grafted onto the polymer network. We used solid-state ³¹ P NMR spectroscopy to show that the acid strength of PDSF-x is enhanced significantly compared with that of PDS, especially for PDSF-0.05. As a result, PDSF-0.05 exhibits the highest isosorbide yield up to 80 %, a good turnover frequency of 231.5 h^-1 (compared to other catalysts), and excellent cyclic stability, which is attributed to its large specific surface area, appropriate acid strength, hydrophobicity, and stable framework structure. In addition, a plausible reaction pathway and kinetic analysis are proposed.

Developing two-dimensional solid superacids with enhanced mass transport, extremely high acid strength and superior catalytic performance

Solid acids have been widely used as heterogeneous catalysts in developing green and sustainable chemistry. However, it remains a challenge to improve the mass transport properties and acid strength of solid acids simultaneously. Herein, we report a class of two dimensional (2D) layered hybrid solid acids with outstanding mass transfer and extremely high acid strength by incorporating sulfonated polymers in-between montmorillonite layers. The 2D layered structure and broad distribution of pore sizes allow for highly efficient mass transport of substrate molecules into and out of the solid acids. The acid strength of these solid acids was found to be stronger than that of 100% H₂SO₄, H₃PW₁₂O₄₀ and any other reported solid acids to date, as determined by ¹H and ³¹P solid-state NMR. These 2D solid acids show extraordinary catalytic performance in biomass conversion to fuels, superior to that of H₃PW₁₂O₄₀, HCl and H₂SO₄. Theoretical calculations and control experiments reveal that H-bond based interactions between the polymer and montmorillonite facilitate the unusually high acid strengths found in these samples.

Development of Sulfonic-Acid-Functionalized Mesoporous Materials: Synthesis and Catalytic Applications

Sulfonic acid based mesostructures (SAMs) have been developed in recent years and have important catalytic applications. The primary applications of these materials are in various organic synthesis reactions, such as multicomponent reactions, carbon-carbon bond couplings, protection reactions, and Fries and Beckman rearrangements. This review aims to provide an overview of the recent developments in the field of SAMs with a particular emphasis on the reaction scope and advantages of heterogeneous solid acid catalysts.

Synthesis and characterization of sulfur-containing hybrid materials based on sodium silicate

An original method for the one-stage synthesis of sulfur-containing silica of SBA-15 type is developed and described. Instead of tetraethylorthosilicate (TEOS) typically used as a source of silica, the inexpensive sodium metasilicate has been applied in our method. The mesoporous silica material was first functionalized with thiol groups then oxidized by concentrated nitric acid to produce sulfonic groups. The samples obtained possess developed specific surface area (S_sp = 320–675 m² g⁻¹) and porous structure with an effective pore diameter of 3.5–5.7 nm. The orderliness of the structure and presence of surface sulfur-containing acidic groups of various natures in the synthesized materials were determined using XRD, TEM, N₂ adsorption, conductivity and potentiometric titration methods. Based on the results of the measurements of the zeta potential vs. pH and electrolyte concentration, conclusions about the electro-surface properties and aggregation stability of sample dispersion have been drawn. The obtained samples are environmentally-friendly and could be used in green chemistry.

Hybrid Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> Si(CH₂)₃SH–SBA-15 and Si(CH₂)₃SO₃H–SBA-15 silicas were obtained with developed specific surface area and an effective pore diameter of 3.5–5.7 nm.

Silica-immobilized Aquivion PFSA superacid: application to heterogeneous direct etherification of glycerol with n-butanol

Silica-immobilized Aquivion® resin with high mesoporosity and acid-site accessibility demonstrated good activity, selectivity and reusability for glycerol etherification withn-butanol.

Direct templating assembly route for the preparation of highly-dispersed vanadia species encapsulated in mesoporous MCM-41 channel

Understanding the nature of active sites, including the number and dispersion on the surface of a support, is essential to improve the catalytic activity.

An ordered, extra-large mesoporous ceramic acid with strong Brönsted acid sites and excellent thermal/hydrothermal stability

A thermal and hydrothermal stable mesoporous ceramic acid (mCA) was synthesized by uniform coating of a WZrO(x) layer onto the internal surface of extra-large mesoporous silica (EP-FDU-12). Its ordered mesoporous structure and strong Brönsted acid sites display excellent thermal (1000 °C, air, 5 h) and hydrothermal (water steam, 300 °C, 24 h) stability.

Proteins in mesoporous silicates

Mesoporous silicates (MPS) have an ordered pore structure with dimensions comparable to many biological molecules. They have been extensively explored as supports for proteins and enzymes in biocatalytic applications. Since their initial discovery, novel syntheses methods have led to precise control over pore size and structure, particle size, chemical composition, and stability, thus allowing the adsorption of a wide variety of biological macromolecules, such as heme proteins, lipases, antibody fragments, and proteases, into their structures. This Review discusses the application of ordered, large-pore, functionalized mesoporous silicates to immobilize proteins for biocatalysis.