Development of Sinter-Resistant Core–Shell LaMn_<i>x</i>Fe_1–<i>x</i>O₃@mSiO₂ Oxygen Carriers for Chemical Looping Combustion

This work investigates the possibility of using LaMn_0.7Fe_0.3O_3.15@mSiO₂ as oxygen carriers for chemical looping combustion (CLC). CLC is a new combustion technique with inherent separation of CO₂ from atmospheric N₂. LaMn_0.7Fe_0.3O_3.15@mSiO₂ core–shell materials were prepared by coating a layer of mesostructured silica around the agglomerated perovskite particles. The oxygen carriers were characterized using different methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ sorption, hydrogen temperature-programmed reduction (H₂-TPR), and temperature-programmed desorption of oxygen (TPD-O₂). The reactivity and stability of the carrier materials were tested in a special reactor, allowing for short contact time between the fluidized carrier and the reactive gas [Chemical Reactor Engineering Centre (CREC) fluidized riser simulator]. Multiple reduction–oxidation cycles were performed. TEM images of the carriers showed that a perfect mesoporous silica layer was formed around samples with 4, 32, and 55 nm in thickness. The oxygen carriers having a core–shell structure showed higher reactivity and stability during 10 repeated redox cycles compared to the LaMn_0.7Fe_0.3O_3.15 core. This could be due to a protective role of the silica shell against sintering of the particles during repeated cycles under CLC conditions. The agglomeration of the particles, which occurred at high temperatures during CLC cycles, is more controllable in the core–shell-structured carriers, as confirmed by SEM images. XRD patterns confirmed that the crystal structure of all perovskites remained unchanged after multiple redox cycles. Methane conversion and partial conversion to CO₂ were observed to increase with the contact time between methane and the carrier. Indeed, more oxygen from the carrier surface, grain boundaries, and even from the bulk lattice was released to react with methane. Upon rising the contact time, less CO was formed, which is desirable for CLC application. Increasing the reaction temperature and methane partial pressure lead to enhanced conversions of CH₄ under CLC conditions

Catalyst-Free Epoxidation of Limonene to Limonene Dioxide

Limonene dioxide is a platform molecule for the production of new biopolymers. First attempts at limonene epoxidation were made by using low-coordination titanium supported on SBA-16 as the catalyst using <i>tert</i>-butyl hydroperoxide as the oxidizing agent, but no limonene dioxide was obtained. When limonene was substituted by 1,2-limonene oxide, the yield of limonene dioxide was only 13% in the same conditions. Two other techniques, both using in situ generated dimethyl dioxirane by the reaction of acetone with Oxone, have been studied and compared. These reactions are carried out in semibatch conditions and at room temperature. The first double epoxidation of limonene was performed in a conventional biphasic organic–water system and the other in excess acetone. The former epoxidation of limonene using ethyl acetate as the organic phase allowed reaching 95% conversion and yielding 33% of limonene dioxide. In comparison, when the reaction was performed in acetone, a limonene dioxide yield of 97% was observed under optimized conditions. The double epoxidation of limonene should be carried out at room temperature with a flowrate of 4 mL min^–1 of aqueous Oxone for a period of 45 min with a stoichiometric excess of 30% of Oxone

Role of Metal–Support Interactions, Particle Size, and Metal–Metal Synergy in CuNi Nanocatalysts for H₂ Generation

Efficient bimetallic nanocatalysts based on non-noble metals are highly desired for the development of new energy storage materials. In this work, we report a simple method for the synthesis of highly dispersed CuNi catalysts supported on mesoporous carbon or silica nanospheres using low-cost metal nitrate precursors. The mesoporous carbon-supported Cu_0.5Ni_0.5 nanocatalysts exhibit excellent catalytic performance for the hydrolysis of ammonia borane and decomposition of hydrous hydrazine with 100% hydrogen selectivity in aqueous alkaline solution at 60 °C. The chemical composition and size of the metal particles, which have a significant influence on the catalytic properties of the supported bimetallic CuNi materials, can readily be controlled by adjusting the metal loading and ratio of metal precursors. An exceedingly high turnover frequency of 3288 (mol_H₂ mol_metal^–1h^–1) and complete reaction within 1 min in dehydrogenation of ammonia-borane were achieved over a tailored-made catalyst obtained through precise monitoring of metal particle size, composition, and support properties

Sorption of Water/Methanol on Teflon and Hydrocarbon Proton Exchange Membranes

The sorption of water and methanol droplets on Teflon films, as well as on various representative classes of hydrocarbon-based proton exchange membranes (PEMs) was investigated using contact angle measurement (drop shape method) during wetting under ambient open-air conditions. Teflon films exhibited constant hydrophobic surfaces when contacted with water, but a significant sorption of methanol. The PEMs showed slow sorption of water, and a significant sorption of methanol. The differences in sorption of water and methanol on Teflon and PEMs arose from the match/compatibility in the surface free energies as well as polarities between a liquid and a membrane. The significant discrepancies in surface free energies and polarities between water (72.0 mJ m^–2 and 70.1%, respectively) and Teflon film (14.0 mJ m^–2 and 4.9%, respectively) lead to a highly hydrophobic surface and no discernible sorption of water on Teflon films, while the relative similarity or minor discrepancy in surface free energies and polarities between methanol (22.5 mJ m^–2 and 17.0%, respectively) and Teflon film (14.0 mJ m^–2 and 4.9%, respectively) results in a significant sorption of methanol on Teflon. The surface free energies of PEMs were calculated using the harmonic-mean approach, based on contact angle measurements using both water and diiodomethane as probes. The results show that PEMs have initial surface free energies ranging from 44.1 to 54.0 mJ m^–2 along with polarities in the range of 20.8 to 29.1%, for a selection of typical sulfonated polymers. The surface free energies of ionomers were principally contributed to by the nonpolar component, but the presence of polar groups in the polymer increased the polar component, leading to an increase in surface free energy. Of the PEMs investigated, sulfonated poly­(aryl ether ether nitrile) has a higher surface energy than those of other ionomers with similar sulfonate contents. The compatibility between water/methanol and PEMs was investigated on the aspect of surface free energies. The present study provides a plausible strategy to prescreen potential PEMs and optimize membrane electrode assembly (MEA) fabrication

Evolution of Functional Groups during Pyrolysis Oil Upgrading

In this work, we examine the evolution of functional groups (carbonyl, carboxyl, phenol, and hydroxyl) during hydrotreatment at 100–200 °C of two typical wood derived pyrolysis oils from BTG and Amaron in a batch reactor over Ru/C catalyst for reaction time of 4 h. An aqueous and an oily phase were obtained. The contents of the functional groups in both phases were analyzed by GC/MS, ³¹P NMR, ¹H NMR, CHN, KF titration, UV fluorescence, carbonyl groups by Faix and phenols by Folin−Ciocalteu method. The consumption of hydrogen was between 0.007 and 0.016 g/(g of oil), and 0.001–0.020 g of CH₄/(g of oil), 0.005–0.016 g of CO₂/(g of oil), and 0.03–0.10 g of H₂O/(g of oil) were formed. The contents of carbonyl, hydroxyl, and carboxyl groups in the volatile GC-MS detectable fraction decreased (80, 65, and ∼70%, respectively), while their behavior in the total oil and hence in the nonvolatile fraction was more complex. The carbonyl groups initially decreased having a minimum at ∼125–150 °C and then increased, while the hydroxyl groups had a reversed trend. This might be explained by the initial hydrogenation of the carbonyl groups to form hydroxyls, followed by continued dehydration reactions at higher temperatures that may have increased their content. The ³¹P NMR analysis was on the limit of its sensitivity for the carboxylic groups to precisely detect changes in the upgraded nonvolatile fraction; however, the more precise titration method showed that the concentration of carboxylic groups in the nonvolatile fraction remains constant with increased hydrotreatment temperature. The UV fluorescence results show that repolymerization increases with temperature, starting as low as 125 °C. ATR-FTIR method coupled with deconvolution of the region between 1490 and 1850 cm^–1 was shown to be a good tool for following the changes in carbonyl groups and phenols of the stabilized pyrolysis oils. The deconvolution of the IR bands around 1050 and 1260 cm^–1 correlated very well with the changes in the ³¹P NMR silent O groups (likely ethers). Most of the H₂O formation could be explained from the significant reduction of these silent O groups (from 12% in the fresh oils, to 6 to 2% in the stabilized oils) most probably belonging to ethers

Hybrid Periodic Mesoporous Organosilicas (PMO-SBA-16): A Support for Immobilization of d-Amino Acid Oxidase and Glutaryl-7-amino Cephalosporanic Acid Acylase Enzymes

This study examined the adsorption and stability of d-amino acid oxidase (DAAO) and glutaryl-7-amino cephalosporanic acid acylase (GL-7-ACA acylase) enzymes using two different types of periodic mesoporous organosilicas PMO-SBA-16 synthesized from 1,2-bis­(trimethoxysilyl)­ethane (BTME) and 1,4-bis­(triethoxysilyl)­benzene (BTEB). Very high loading, specific enzymatic activities, and stabilities have been reached by proper optimization of mesopore structure and morphology

A General Chelate-Assisted Co-Assembly to Metallic Nanoparticles-Incorporated Ordered Mesoporous Carbon Catalysts for Fischer–Tropsch Synthesis

The organization of different nano objects with tunable sizes, morphologies, and functions into integrated nanostructures is critical to the development of novel nanosystems that display high performances in sensing, catalysis, and so on. Herein, using acetylacetone as a chelating agent, phenolic resol as a carbon source, metal nitrates as metal sources, and amphiphilic copolymers as a template, we demonstrate a chelate-assisted multicomponent coassembly method to synthesize ordered mesoporous carbon with uniform metal-containing nanoparticles. The obtained nanocomposites have a 2-D hexagonally arranged pore structure, uniform pore size (∼4.0 nm), high surface area (∼500 m²/g), moderate pore volume (∼0.30 cm³/g), uniform and highly dispersed Fe₂O₃ nanoparticles, and constant Fe₂O₃ contents around 10 wt %. By adjusting acetylacetone amount, the size of Fe₂O₃ nanoparticles is readily tunable from 8.3 to 22.1 nm. More importantly, it is found that the metal-containing nanoparticles are partially embedded in the carbon framework with the remaining part exposed in the mesopore channels. This unique semiexposure structure not only provides an excellent confinement effect and exposed surface for catalysis but also helps to tightly trap the nanoparticles and prevent aggregating during catalysis. Fischer–Tropsch synthesis results show that as the size of iron nanoparticles decreases, the mesoporous Fe–carbon nanocomposites exhibit significantly improved catalytic performances with C₅₊ selectivity up to 68%, much better than any reported promoter-free Fe-based catalysts due to the unique semiexposure morphology of metal-containing nanoparticles confined in the mesoporous carbon matrix