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H2 Uptake (h2 + uptake)

Distribution by Scientific Domains

Polymers and Materials Science	50%
Chemistry	50%

Selected Abstracts

The Role of Amine,B(C6F5)3 Adducts in the Catalytic Reduction of Imines with H2: A Computational Study

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2009
Timofei Privalov
Abstract This study thoroughly examines the potential energy surfaces (PESs) of two possible mechanisms for reduction of imines by B(C6F5)3 and H2. The key reaction steps of the first catalytic mechanism, which is the focus of our study, are: (i) the uptake of H2 by a thermally activated amine,B(C6F5)3 species; (ii) proton transfer from the NH2+ moiety of [RNH2CH2R,]+[HB(C6F5)3], to the imine; (iii) nucleophillic attack of the C-center of the iminium ion by the BH, group. The potential energy barriers of the latter, as determined by calculating the evolution of the H-bonded complex of an imine and [RNH2CH2R,]+[HB(C6F5)3], in toluene, are around 10 kcal,mol,1 each. In the second mechanism, only imines serve as basic partners of B(C6F5)3 in the H2 activation, which affords an [RN(H)CHR,]+[HB(C6F5)3], ion pair; direct reduction then proceeds via nucleophilic attack of the C-center by the BH, in [RN(H)CHR,]+[HB(C6F5)3],. This route becomes catalytic when the product amine is released into the solvent and B(C6F5)3 is re-used for H2 activation. Upon taking into account the association energy of an amine,B(C6F5)3 adduct [,9.5 kcal,mol,1 for tBuN(H)CH2Ph and B(C6F5)3 in toluene], the potential energy barrier for H2 uptake by an imine and B(C6F5)3 increases to 14.5 kcal,mol,1. We report a somewhat lower potential energy barrier for H2 uptake by thermally activated amine,B(C6F5)3 adducts [12.7 kcal,mol,1 for the B-N adduct of tBuN(H)CH2Ph and B(C6F5)3 in toluene], although the difference between the two H2 activationbarriers is within the expected error of the computational method. Two catalytic routes are compared based on B3LYP-computed PESs in solvent (toluene).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Amorphous Infinite Coordination Polymer Microparticles: A New Class of Selective Hydrogen Storage Materials,

ADVANCED MATERIALS, Issue 11 2008
You-Moon Jeon
A new class of micrometer-sized amorphous infinite coordination particles is selectively prepared from the coordination chemistry of a metallo-salen building block and Zn2+ ions. The particles show moderately high H2 uptake and almost no N2 adsorption, even though they are amorphous and do not have the well-defined channels typically used to explain such selectivity in metal,organic framework systems. [source]

Alumina-Supported Ni,Au: Surface Synergistic Effects in Catalytic Hydrodechlorination

CHEMCATCHEM, Issue 2 2009

Abstract Catalytic gas-phase hydrodechlorination (HDC) of 2,4-dichlorophenol (2,4-DCP) has been investigated over Ni/Al2O3 and Au/Al2O3 prepared by impregnation, and Au,Ni/Al2O3 prepared by reductive deposition of Au onto Ni. Catalyst activation by temperature-programmed reduction is examined and the activated catalysts are characterized in terms of H2 chemisorption, XRD and TEM-energy dispersive X-ray (EDX) measurements. Ni/Al2O3 (<1,10,nm) and Au/Al2O3 (<1,15,nm) exhibit a relatively narrow metal size distribution while Au,Ni/Al2O3 bore larger particles (1,30,nm) with variable surface Ni/Au ratios. Au/Al2O3 exhibits low H2 uptake and low HDC activity to generate 2-chlorophenol (2-CP) as the sole product. H2 chemisorption on Au,Ni/Al2O3 was approximately five times lower than that recorded for Ni/Al2O3 but both catalysts delivered equivalent initial HDC activities. Ni/Al2O3 exhibits an irreversible temporal deactivation where partial dechlorination to 2-CP is increasingly favored over full dechlorination to phenol. In contrast, thermal treatment of Au,Ni/Al2O3 in H2 after reaction elevates HDC activity with a preferential full HDC to phenol. This response is linked to a surface reconstruction resulting in a more homogeneous combination of Ni and Au. This result was also achieved by a direct treatment of Au,Ni/Al2O3 with HCl. A parallel/ consecutive kinetic model is used to quantify the catalytic HDC response. [source]

High-Surface-Area Nanoporous Boron Carbon Nitrides for Hydrogen Storage

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2010
David Portehault
Abstract Nano- and mesoporous boron carbon nitrides with very high surface areas up to 1560,m2,g,1 are obtained by pyrolysis of a graphitic carbon nitride mpg-C3N4 infiltrated with a borane complex. This reactive hard-templating approach provides easy composition and texture tuning by temperature adjustment between 800 and 1400,°C. The process yields BxCyNzOvHw materials as direct copies of the initial template with controlled compositions of 0.15,,,x,,,0.36, 0.10,,,y,,,0.12, 0.14,,,z,,, 0.32, and 0.11,,,v,,,0.28. The nano and mesoporosities can also be tuned in order to provide hierarchical materials with specific surface areas ranging from 610 to 1560,m2,g,1. Such high values, coupled with resistance against air oxidation up to 700,°C, suggest potential materials for gas storage and as catalyst supports. Indeed, it is demonstrated that these compounds exhibit high and tunable H2 uptakes from 0.55 to 1.07,wt.% at 77,K and 1 bar, thus guiding further search of materials for hydrogen storage. [source]