ABSTRACT
Oxygen-containing carbons are promising supports and metal-free catalysts for many reactions. However, distinguishing the role of various oxygen functional groups and quantifying and tuning each functionality is still difficult. Here we investigate the role of Brønsted acidic oxygen-containing functional groups by synthesizing a diverse library of materials. By combining acid-catalyzed elimination probe chemistry, comprehensive surface characterizations, 15N isotopically labeled acetonitrile adsorption coupled with magic-angle spinning nuclear magnetic resonance, machine learning, and density-functional theory calculations, we demonstrate that phenolic is the main acid site in gas-phase chemistries and unexpectedly carboxylic groups are much less acidic than phenolic groups in the graphitized mesoporous carbon due to electron density delocalization induced by the aromatic rings of graphitic carbon. The methodology can identify acidic sites in oxygenated carbon materials in solid acid catalyst-driven chemistry.
ABSTRACT
Ruthenium (Ru) is the one of the most promising catalysts for polyolefin hydrogenolysis. Its performance varies widely with the support, but the reasons remain unknown. Here, we introduce a simple synthetic strategy (using ammonia as a modulator) to tune metal-support interactions and apply it to Ru deposited on titania (TiO2). We demonstrate that combining deuterium nuclear magnetic resonance spectroscopy with temperature variation and density functional theory can reveal the complex nature, binding strength, and H amount. H2 activation occurs heterolytically, leading to a hydride on Ru, an H+ on the nearest oxygen, and a partially positively charged Ru. This leads to partial reduction of TiO2 and high coverages of H for spillover, showcasing a threefold increase in hydrogenolysis rates. This result points to the key role of the surface hydrogen coverage in improving hydrogenolysis catalyst performance.
ABSTRACT
Patterning metal-organic frameworks (MOFs) at submicrometer scale is a crucial yet challenging task for their integration in miniaturized devices. Here we report an electron beam (e-beam) assisted, bottom-up approach for patterning of two MOFs, zeolitic imidazolate frameworks (ZIF), ZIF-8 and ZIF-67. A mild pretreatment of metal oxide precursors with linker vapor leads to the sensitization of the oxide surface to e-beam irradiation, effectively inhibiting subsequent conversion of the oxide to ZIFs in irradiated areas, while ZIF growth in non-irradiated areas is not affected. Well-resolved patterns with features down to the scale of 100 nm can be achieved. This developer-free, all-vapor phase technique will facilitate the incorporation of MOFs in micro- and nanofabrication processes.
ABSTRACT
Vapor-phase treatment of ZIF-8 membranes with manganese(II) acetylacetonate (Mn(acac)2 ) allows permselectivity tuning. Propylene/propane selectivity increases from 31 to 210 after the Mn(acac)2 treatment at 165 °C for 30â min, while selectivities increase from 14.6 to 242 for H2 /CH4 , from 2.9 to 38 for CO2 /CH4 , from 2.4 to 29 for CO2 /N2 , and from 2.9 to 7.5 for O2 /N2 , after Mn(acac)2 treatment at 175 °C for 30â min. Stable equimolar propylene/propane mixture selectivity of 165 at ambient temperature and 4â bar equimolar feed with a propylene flux of 8.3×10-4 â mol m-2 s-1 is established. A control experiment excludes thermal treatment alone causing these changes. XPS analysis reveals the presence of Mn(acac)2 on the outer surface of the vapor-treated ZIF-8 membranes while no other changes are detectable by X-ray diffraction and infrared spectroscopy.
ABSTRACT
Vapor phase ligand treatment (VPLT) of 2-aminobenzimidazole (2abIm) for 2-methylimidazole (2mIm) in ZIF-8 membranes prepared by two different methods (LIPS: ligand induced permselectivation and RTD: rapid thermal deposition) results in a notable shift of the molecular level cut-off to smaller molecules establishing selectivity improvements from ca. 1.8 to 5 for O2 /N2 ; 2.2 to 32 for CO2 /CH4 ; 2.4 to 24 for CO2 /N2 ; 4.8 to 140 for H2 /CH4 and 5.2 to 126 for H2 /N2 . Stable (based on a one-week test) oxygen-selective air separation performance at ambient temperature, 7â bar(a) feed, and 1â bar(a) sweep-free permeate with a mixture separation factor of 4.5 and oxygen flux of 2.6×10-3 â mol m-2 s-1 is established. LIPS and RTD membranes exhibit fast and gradual evolution upon a 2abIm-VPLT, respectively, reflecting differences in their thickness and microstructure. Functional reversibility is demonstrated by showing that the original permeation properties of the VPLT-LIPS membranes can be recovered upon 2mIm-VPLT.
ABSTRACT
In this work, batch-adsorption experiments and molecular simulations are employed to probe the adsorption of binary mixtures containing ethanol or a linear alkane-1,n-diol solvated in water or ethanol onto silicate-1. Since the batch-adsorption experiments require an additional relationship to determine the amount of solute (and solvent adsorbed, as only the bulk liquid reservoir can be probed directly, molecular simulations are used to provide a relationship between solute and solvent adsorption for input to the experimental bulk measurements. The combination of bulk experimental measurements and simulated solute-solvent relationship yields solvent and solute loadings that are self-consistent with simulation alone, and allow for an assessment of the various assumptions made in literature. At low solution concentrations, the solute loading calculated is independent of the assumption made. At high concentrations, a negligent choice of assumption can lead to systematic overestimation or underestimation of calculated solute loading.
