Influence of alkali metal doping on surface properties and catalytic activity/selectivity of CaO catalysts in oxidative coupling of methane

Surface properties （viz. surface area, basicity/base strength distribution, and crystal phases） of alkali metal doped CaO （alkali metal/Ca= 0.1 and 0.4） catalysts and their catalytic activity/selectivity in oxidative coupling of methane （OCM） to higher hydrocarbons at different reaction conditions （viz. temperature, 700 and 750 ℃; CH4/O2 ratio, 4.0 and 8.0 and space velocity, 5140-20550 cm^3 ·g^-1·h^-1） have been investigated. The influence of catalyst calcination temperature on the activity/selectivity has also been investigated. The surface properties （viz. surface area, basicity/base strength distribution） and catalytic activity/selectivity of the alkali metal doped CaO catalysts are strongly influenced by the alkali metal promoter and its concentration in the alkali metal doped CaO catalysts. An addition of alkali metal promoter to CaO results in a large decrease in the surface area but a large increase in the surface basicity （strong basic sites） and the C2＋ selectivity and yield of the catalysts in the OCM process. The activity and selectivity are strongly influenced by the catalyst calcination temperature. No direct relationship between surface basicity and catalytic activity/selectivity has been observed. Among the alkali metal doped CaO catalysts, Na-CaO （Na/Ca = 0.1, before calcination） catalyst （calcined at 750 ℃）, showed best performance （C2＋ selectivity of 68.8% with 24.7% methane conversion）, whereas the poorest performance was shown by the Rb-CaO catalyst in the OCM process.     

Nitrate-Bridged "Pseudo-Double-Propeller"-Type Lanthanide(III)-Copper(II) Heterometallic Clusters: Syntheses, Structures, and Magnetic Properties

Two discrete nitrate-bridged novel "pseudo-double-propeller"-shaped hexanuclear Cu/Ln clusters of the formula [Cu(4)Ln(2)L(4)L'(4)(NO(3))(2)(OH(2))(2)]·3NO(3)·4H(2)O [Ln = Dy, Gd; LH = o-vanilin; L'H = 2-(hydroxyethyl)pyridine] were synthesized and characterized. Single-crystal X-ray diffraction studies revealed the trimeric half-propeller-type Cu(2)/Ln core connected to other opposite-handed similar trimers by a bridging nitrate ligand. The Dy analogue, [Cu(4)Dy(2)L(4)L'(4)(NO(3))(2)(OH(2))(2)]·3NO(3)·4H(2)O, shows frequency-dependent out-of-phase alternating-current magnetic susceptibility, which indicates that this novel discrete [Cu(4)Dy(2)] heterometallic cluster may exhibit single-molecule-magnet behavior.     

Energetics during proton transfer process in hydrated zündel ion complex

Zündel ion (H₅O) is one of the two important structures formed during the proton transfer process in aqueous system. This work reports microsolvation of Zündel ion using density functional theory based B3LYP method with aug‐cc‐pVTZ basis set. Interaction of Zündel ion with four water molecules in its first solvation shell is studied using many‐body analysis approach. A change in many‐body energies and their contribution to the binding energy of a complex during the proton transfer process from donor to acceptor water molecule in Zündel ion‐4H₂O complex is obtained. For the hydrated Zündel ion complex, the contribution from total two‐body, three‐body, four‐body, five‐body, and relaxation energy to the binding energy is 84.7, 14, 6.87, 1.6, and 4%, respectively, at B3LYP/aug‐cc‐pVTZ level. Relaxation energy and total five‐body energy have repulsive contribution to the binding energy of a hydrated Zündel ion complex. It is found that the relaxation energy and binding energy of a Zündel‐4H₂O complex is the maximum and minimum, respectively, when a shared proton is at equal distance from oxygen atom of donor and acceptor water molecules. A significant change in two‐body, three‐body, and four‐body energies for which Zündel ion is one of the many‐body terms is observed during the proton transfer process. A change in total two‐body, total three‐body, total four‐body, and relaxation energy is about 2.6, 1.8, 0.4, and 1.1%, respectively, during the proton transfer process. A change in two‐body, three‐body, and four‐body interaction energies between water molecules is very small during the proton transfer process. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012