Zeolites and Related Materials as Catalyst Supports for Hydrocarbon Oxidation Reactions

Abstract

Catalytic oxidation is a key technology for the conversion of petroleum-based feedstocks into useful chemicals (e.g., adipic acid, caprolactam, glycols, acrylates, and vinyl acetate) since this chemical transformation is always involved in synthesis processes. Millions of tons of these compounds are annually produced worldwide and find applications in all areas of chemical industries, ranging from pharmaceutical to large-scale commodities. The traditional industrial methods to produce large amounts of those compounds involve over-stoichiometric quantities of toxic inorganic reactants and homogeneous catalysts that operate at high temperature, originating large amounts of effluents, often leading to expensive downstream processes, along with nonrecovery of valuable catalysts that are loss within the reactant effluent. Due to the increasingly stringent environmental legislation nowadays, there is considerable pressure to replace these antiquate technologies, focusing on heterogeneous catalysts that can operate under mild reactions conditions, easily recovered, and reused. Parallelly, recent advances in the synthesis and characterization of metal complexes and metal clusters on support surfaces have brought new insights to catalysis and highlight ways to systematic catalysts design. This review aims to provide a comprehensive bibliographic examination over the last 10 years on the development of heterogeneous catalysts, i.e., organometallic complexes or metal clusters immobilized in distinct inorganic supports such as zeolites, hierarchical zeolites, silicas, and clays. The methodologies used to prepare and/or modify the supports are critically reviewed, as well as the methods used for the immobilization of the active species. The applications of the heterogenized catalysts are presented, and some case-studies are discussed in detail.

Multifunctional Mesoporous Silica Nanoparticles for Oral Drug Delivery

“…Silica based nano carriers for delivery of drugs, biomolecules, and food are an emerging highlight. The silica based oral delivery system includes non-porous silica nanoparticles, mesoporous silica nanoparticles, hybrid silica nanoparticles, and diatom silica nanoparticles [12,18,30,63,68,72,78,80]. Of these, the mesoporous silica nanoparticle is most commonly used.…”

“…Medications are delivered via the SBA-15, SBA-16, MCM-41, and MCM-48 which are all commonly utilized [16]. [17], published by MDPI, 20 [18], published by MDPI, 2022, [19], published by MDPI, 2013, [20], published by MDPI, 2020 MSNs have quite good physicochemical properties and are tunable. The high porosity of MSNs allows the lodging and release of a wide range of biomolecules and medicinal substances.…”

“…The rate of hydrolysis, the interaction between a constructed template and silica polymer, and condensation of the silica source are all variables that impact the size and form of mesoporous silica nanoparticles. By changing the pH, we can regulate the above variables using various templates and co-solvents [18]. Biological variables such as blood circulation time, in vivo distribution, and excretion rate can be influenced by particle size [15].…”

“…Types of mesoporous silica nanoparticles. Adapted from[17], published by MDPI, 20[18], published by MDPI, 2022,[19], published by MDPI, 2013,[20], published by MDPI, 2020…”

Nitrogen- and Halogen-Free Multifunctional Polymer-Directed Fabrication of Aluminum-Rich Hierarchical MFI Zeolites

“…Furthermore, apart from acidity, accessibility to acid sites is also crucial for the conventional microporous Al-rich ZSM-5 zeolite that suffers from diffusion limitation leading to rapid deactivation in the practical applications because of coke deposition. However, the accessibility to acid sites can be improved by creating mesopores in the microporous zeolites [ 13 , 14 , 15 , 16 ]. Post-synthetic desilication of Al-rich ZSM-5 zeolites (Si/Al ratio < 25) to generate additional mesopores is relatively unexploited because the high Al concentration in the framework hinders the extraction of silicon from the zeolite structure [ 17 ].…”