Evaluating Diatomaceous Earth for Long-Term Use in Hydrogen Storage.

Efficient hydrogen storage is essential for its use as a sustainable energy carrier. Diatomaceous earth, a high-surface-area siliceous geomaterial, shows potential as a physisorption material for hydrogen storage. This study analyzes diatomaceous earth's long-term characteristics when subjected to high-pressure hydrogen injection. The diatomaceous earth was subjected to a hydrogen pressure of 1200 psi for a period of 80 days at room temperature. Neither notable morphological or mineralogical changes were observed. Nevertheless, there was a slight reduction in fine particles and a slight increase in larger particles. The Brunauer-Emmett-Teller (BET) surface area decreased slightly with a significant decrease in pore width. However, the hydrogen adsorption at 77 K temperature was increased significantly (45.5%) after the hydrogen storage test. Moreover, there was a delayed release of molecular water as the temperature increased. These changes suggest that a condensation reaction has occurred involving some of the opal-A silanol groups (Si-O-H), producing molecular water. Bonding through siloxane bridges (Si-O-Si) results in a significant decrease in pore width and increased hydrophobicity (i.e., the interaction between diatomaceous surface and H2 was increased), thereby enhancing hydrogen adsorption capacity. These findings indicate that diatomaceous earth holds promise as a material for hydrogen storage, with the potential for its hydrogen adsorption capacity to improve over time.

Techno-Environmental Evaluation of Alkaline Treatment in Flax Reinforced Thermoplastics.

A combination of thermoplastics and natural fiber reinforcements is considered an ideal choice to mitigate environmental impacts and enhance recyclability or reusability. Chemical treatments are often employed to enhance the thermomechanical properties of natural fiber-reinforced plastics. Nevertheless, it is of paramount importance to assess the techno-economic impact of such chemical treatments and environmentally friendly materials for their implementation in mass productions on an industrial scale. In this work, high-density polyethylene is reinforced with sodium hydroxide (NaOH)-treated and untreated flax fibers to study its impact on mechanical and environmental properties. The composites treated with NaOH exhibited a 37% increase in tensile strength. However, life cycle assessment performed on the NaOH-treated samples showed that they had a global warming potential of 5.8 kg of CO2, a terrestrial acidification potential of 0.0269 kg of SO2, and a human carcinogenic toxicity of 0.031 kg of 1,4-DCB compared to the untreated samples. In summary, the techno-environmental analysis reveals a novel approach to identifying chemical treatments based on their technical and environmental effects.

CO2 Adsorption on Biomass-Derived Carbons from Albizia procera Leaves: Effects of Synthesis Strategies.

CO2 capture is a useful strategy for controlling the risks associated with global warming. The design of an adsorbent is essential for clean and potentially energy-efficient adsorption-based carbon capture processes. This study reports a facile and moderately temperature single-stage combined pyrolysis and activation strategy for the synthesis of nitrogen-doped carbons for high-performance CO2 capture. Using nitrogen-rich Albizia procera leaves as the precursor and carrying out single-stage pyrolysis and activation at temperatures of 500, 600, and 700 °C in the presence NaHCO3 as an activating agent, carbons with different surface characteristics and ultrahigh weight percentage (22-25%) of nitrogen were obtained. The subtle differences in surface characteristics and nitrogen content had a bearing on the CO2 adsorption performance of the resultant adsorbents. Outstanding results were achieved, with a CO2 adsorption capacity of up to 2.5 mmol/g and a CO2 over N2 selectivities reaching 54. The isotherm results were utilized to determine the performance indicators for a practical vacuum swing adsorption process. This study provides a practical strategy for the efficient synthesis of nitrogen-doped carbons for various adsorption applications.

Unveiling meta-Alkyloxy/-Silyloxy-Substituted N-Aryl PNP Ligands for Efficient Cr-Catalyzed Ethylene Tetramerization.

Novel N-aryl-functionalized PNP ligands (1-4) bearing m-alkyloxy/-silyloxy substituents were prepared and evaluated for chromium-catalyzed ethylene oligomerization using MMAO-3A as an activator. The selected Cr/PNP system under optimized condition exhibited high 1-octene-selective (up to 70 wt %) ethylene tetramerization at a remarkable rate (over 3000 kg gCr-1 h-1). More importantly, the undesirable polyethylene selectivity was restricted to a minimum level of ∼1-2 wt % for pre-catalysts derived with ligands 1 and 2. Employing chlorobenzene as a reaction medium yielded best productivity in conjunction to the total α-olefin (1-C6 + 1-C8) selectivity (∼88 wt %). N-aryl PNP ligands (3 and 4) incorporating m-silyloxy substituents in the phenyl ring exhibited relatively poorer tetramerization performance while yielding higher PE fraction as compared to their m-alkyloxy derivatives. A detailed molecular structure of the best-performing pre-catalyst 1-Cr was established by single-crystal X-ray diffraction analysis. The stability of 1/Cr-based catalyst system was investigated for a reaction time of up to 2 h under optimized condition.

A rational approach towards selective ethylene oligomerization via PNP-ligand design with an N-triptycene functionality.

Novel PNP ligands bearing an N-triptycene backbone were developed and evaluated for selective ethylene oligomerization. Upon activation with MMAO-3A, the pre-catalyst mixture containing Cr(acac)3/ligand efficiently promotes ethylene tetramerization with remarkably high productivities (up to 1733 kg gCr-1 h-1) and C8 olefin selectivities (up to 74.1 wt%). More importantly, ligands with a PNP moiety connecting at the 1- or 1,4-position of the triptycene molecule could achieve exceptionally high alpha (1-C6 + 1-C8) selectivities, exceeding 90 wt%, as a result of high 1-C6 purity (>90 wt%) in the C6 fraction. Based on comparative catalytic studies employing various PNP ligands with or without an N-triptycene backbone, we illustrate the fact that a rational design of PNP ligands with an optimum degree of steric profile around the N-center could provide C6 cyclics controlled highly α-selective ethylene oligomerization.

Highly Efficient Ethylene Tetramerization Using Cr Catalysts Constructed with Trifluoromethyl-Substituted N-Aryl PNP Ligands.

Tetramerization of ethylene by chromium catalysts stabilized with functionalized N-aryl phosphineamine ligands C6H4(m-CF3)N(PPh2)2 (1), C6H4(p-CF3)N(PPh2)2 (2), C6H4(o-CF3)N=PPh2-PPh2 (3), and C6H3(3,5-bis(CF3))N(PPh2)2 (4) was evaluated. The parameter optimization includes temperature, co-catalyst, and solvent. Upon activation with MMAO-3A, the new catalyst system especially with m-functional PNP ligand (1) exhibited high 1-octene selectivity and productivity while giving minimum undesirable polyethylene and C10 + olefin by-products. Using PhCl as a solvent at 75 °C led to a remarkable α-olefin (1-C6 + 1-C8) selectivity (>90 wt %) at a reaction rate of 2000 kg·gCr -1·h-1. Under identical conditions, analogous PNP ligands bearing -CH3, -Et, and -Cl functional moieties at the meta position of the N-phenyl ring displayed significantly lower reactivity. The catalyst with p-functional ligand (2) exhibited lower activity and comparable selectivities, while the Cr/PPN (with ligand 3) system gave no noticeable reactivity. The molecular structure of the precatalyst (1-Cr), exhibiting a monomeric structural feature, was elucidated with the aid of single-crystal X-ray diffraction study.

Early Metal Di(pyridyl) Pyrrolide Complexes with Second Coordination Sphere Arene-π Interactions: Ligand Binding and Ethylene Polymerization.

Early metal complexes supported by hemilabile, monoanionic di(pyridyl) pyrrolide ligands substituted with mesityl and anthracenyl groups were synthesized to probe the possibility of second coordination sphere arene-π interactions with ligands with potential for allosteric control in coordination chemistry, substrate activation, and olefin polymerization. Yttrium alkyl, indolide, and amide complexes were prepared and structurally characterized; close contacts between the anthracenyl substituents and Y-bound ligands are observed in the solid state. Titanium, zirconium, and hafnium tris(dimethylamido) complexes were synthesized, and their ethylene polymerization activity was tested. In the solid state structure of one of the Ti tris(dimethylamido) complexes, coordination of Ti to only one of the pyridine donors is observed pointing to the hemilabile character of the di(pyridyl) pyrrolide ligands.