A Theoretical Investigation of Cu+ , Ni2+ and Co2+ -Exchanged Zeolites for Hydrogen Storage.

This study investigates the H2 adsorption on Cu+ , Ni2+ and Co2+ -exchanged SSZ-13 (CHA) and SSZ-39 (AEI) using periodic DFT computations. The most stable Cu+ position was found to be the 6-membered-ring window for both zeolites. Similarly, for the investigated Ni2+ and Co2+ loadings on 6-membered-ring windows, the third nearest neighbor Al positions, i. e., Al-O-Si-O-Si-O-Al coordination, was found to be the most stable position. H2 adsorption was investigated for all the Cu+ , Ni2+ and Co2+ centers. AEI and CHA resulted in similar H2 -Cu interactions for the Al and B substituted structures. H2 adsorption on Cu+ located in the 8-membered-ring gave the highest adsorption energy for both frameworks. Replacing Al with B in the framework increased the electron back donation from Cu+ (3d) orbitals to H2 antibonding orbital (σH2 * ). The H2 adsorption energies on the Ni2+ and Co2+ -exchanged zeolites were found to be between -15 and -44 kJ/mol. Higher energy values were observed on the AEI framework, especially when two Al atoms have the Al-O-Si-O-Al configuration. Lesser interaction of the d-orbitals in the case of the Co2+ and Ni2+ cations resulted in heat of H2 adsorption close to optimum values required for H2 storage on porous materials.

CO2 hydrogenation to methanol and dimethyl ether at atmospheric pressure using Cu-Ho-Ga/γ-Al2O3 and Cu-Ho-Ga/ZSM-5: Experimental study and thermodynamic analysis.

CO2 valorization through chemical reactions attracts significant attention due to the mitigation of greenhouse gas effects. This article covers the catalytic hydrogenation of CO2 to methanol and dimethyl ether using Cu-Ho-Ga containing ZSM-5 and g-Al2O3 at atmospheric pressure and at temperatures of 210 °C and 260 °C using a CO2:H2 feed ratio of 1:3 and 1:9. In addition, the thermodynamic limitations of methanol and DME formation from CO2 was investigated at a temperature range of 100-400 °C. Cu-Ho-Ga/g-Al2O3 catalyst shows the highest formation rate of methanol (90.3 µmolCH3OH/gcat/h ) and DME (13.2 µmolDME/gcat/h) as well as the highest selectivity towards methanol and DME (39.9 %) at 210 °C using a CO2:H2 1:9 feed ratio. In both the thermodynamic analysis and reaction results, the higher concentration of H2 in the feed and lower reaction temperature resulted in higher DME selectivity and lower CO production rates.

A potential catalyst for continuous methane partial oxidation to methanol using N2O: Cu-SSZ-39.

Continuous catalytic methanol production from methane is reported on Cu-SSZ-39 using N2O as an oxidant. Through optimization of CH4, N2O and H2O partial pressures, a methanol formation rate of 499 µmolCH3OH g-1 h-1 and a methanol selectivity of 34% is achieved.

One-step synthesis of hierarchical [B]-ZSM-5 using cetyltrimethylammonium bromide as mesoporogen.

One-step facile synthesis of boron containing ZSM-5 microspheres is developed using 1,6-diaminohexane as the structure-directing agent and cetyltrimethylammonium bromide as the mesoporogen. High boron incorporation up to Si/B ratio of 38 is achieved and evidenced by the stretching vibrations of B-O-Si at 667 cm-1 and 917 cm-1 using Fourier-transform infrared spectra. The morphology of the crystals resembles berry-like spheres with sizes approximately 15 µm, which is composed of aggregated nanocrystals having sizes around 450 nm, is observed using scanning electron microscopy. The textural properties, i.e. the surface areas and pore volumes are investigated using N2 adsorption at -196 °C. t-plot micropore volume of 0.11 cm3/g and mesopore volume of 0.14 cm3/g are obtained applying this synthesis method for mesopores having pore diameters within the range of 2-10 nm.

Rotational dynamics of organic cations in the CH3NH3PbI3 perovskite.

Methylammonium lead iodide (CH3NH3PbI3) based solar cells have shown impressive power conversion efficiencies of above 20%. However, the microscopic mechanism of the high photovoltaic performance is yet to be fully understood. Particularly, the dynamics of CH3NH3(+) cations and their impact on relevant processes such as charge recombination and exciton dissociation are still poorly understood. Here, using elastic and quasi-elastic neutron scattering techniques and group theoretical analysis, we studied rotational modes of the CH3NH3(+) cation in CH3NH3PbI3. Our results show that, in the cubic (T > 327 K) and tetragonal (165 K < T < 327 K) phases, the CH3NH3(+) ions exhibit four-fold rotational symmetry of the C-N axis (C4) along with three-fold rotation around the C-N axis (C3), while in the orthorhombic phase (T < 165 K) only C3 rotation is present. At around room temperature, the characteristic relaxation times for the C4 rotation are found to be τC4 ≈ 5 ps while for the C3 rotation τC3 ≈ 1 ps. The T-dependent rotational relaxation times were fitted with Arrhenius equations to obtain activation energies. Our data show a close correlation between the C4 rotational mode and the temperature dependent dielectric permittivity. Our findings on the rotational dynamics of CH3NH3(+) and the associated dipole have important implications for understanding the low exciton binding energy and a slow charge recombination rate in CH3NH3PbI3 which are directly relevant for the high solar cell performance.