Renju Zacharia

Interlayer cohesive energy of graphite from thermal desorption of polyaromatic hydrocarbons

We have studied the interaction of polyaromatic hydrocarbons ~PAHs! with the basal plane of graphite using thermal desorption spectroscopy. Desorption kinetics of benzene, naphthalene, coronene, and ovalene at submonolayer coverages yield activation energies of 0.50 eV, 0.85 eV, 1.40 eV, and 2.1 eV, respectively. Benzene and naphthalene follow simple first order desorption kinetics while coronene and ovalene exhibit fractional order kinetics owing to the stability of two-dimensional adsorbate islands up to the desorption temperature. Preexponential frequency factors are found to be in the range 10 14 ‐10 21 s 21 as obtained from both FalconerMadix ~isothermal desorption! analysis and Antoine’s fit to vapor pressure data. The resulting binding energy per carbon atom of the PAH is 5265 meV and can be identified with the interlayer cohesive energy of graphite. The resulting cleavage energy of graphite is 6165 meV/atom, which is considerably larger than previously reported experimental values.

Volumetric hydrogen sorption capacity of monoliths prepared by mechanical densification of MOF-177

Bulk powdered MOF-177 is mechanically compressed to prepare monoliths with bulk densities more than three times its crystallographic density, and their excess and total gravimetric and volumetric hydrogen storage capacities are measured over a pressure range of 0–13 MPa at 77 K and room temperature. The maximum excess volumetric hydrogen storage capacity of these monoliths at ∼6 MPa and 77 K is 25.8 ± 1.2 g L−1, which is a 78% increase of that of powdered bulk MOF-177 and 80% of the theoretical maximum excess volumetric hydrogen storage capacity predicted on the basis of the materials crystallographic density. The monoliths show diminishing excess gravimetric capacity with increasing density which is attributed to their decreasing micropore volume, which in turn stems from the progressive collapse of MOF-177 crystals to an amorphous phase when they are subjected to densification. A modified Dubinin–Astakhov (DA) model is adapted to describe the excess gravimetric adsorption of samples with varying bulk densities. The total volumetric capacity of monoliths prepared from MOF-177 is 48.0 ± 2.1 g L−1 at 13 MPa and 77 K; if a complete storage system that does not reduce this capacity by more than 20% is designed, it can then meet the DOE 2015 volumetric system target at 77 K. Under the same conditions, it is easier to meet the DOE 2015 gravimetric system target of 5.5 wt% as the materials total gravimetric storage capacity is ∼10.3 ± 0.3 wt%.

Review of solid state hydrogen storage methods adopting different kinds of novel materials

Overview of advances in the technology of solid state hydrogen storage methods applying different kinds of novel materials is provided. Metallic and intermetallic hydrides, complex chemical hydride, nanostructured carbon materials, metal-doped carbon nanotubes, metal-organic frameworks (MOFs), metal-doped metal organic frameworks, covalent organic frameworks (COFs), and clathrates solid state hydrogen storage techniques are discussed. The studies on their hydrogen storage properties are in progress towards positive direction. Nevertheless, it is believed that these novel materials will offer far-reaching solutions to the onboard hydrogen storage problems in near future. The review begins with the deficiencies of current energy economy and discusses the various aspects of implementation of hydrogen energy based economy.

Simulation of binary CO 2 /CH 4 mixture breakthrough profiles in MIL-53 (Al)

MIL-53 (Al) aluminum terephthalate, a commercial metal-organic framework, has been studied as a potential candidate for pressure swing adsorption separation of CO2/CH4 binary mixtures. Pure gas isotherms of CH4 and CO2 measured over 0-6MPa and at room temperature are fitted with the Dubinin-Astakhov (D-A) model. The D-A model parameters are used in the Doong-Yang Multicomponent adsorption model to predict the binary mixture isotherms. A one-dimensional multicomponent adsorption breakthrough model is then used to performa parametric study of the effect of adsorbent particle diameter, inlet pressures, feed flow rates, and feed compositions on the breakthrough performance. Commercial MIL-53 with a particle diameter of 20 µm renders high tortuous flow; therefore it is less effective for separation. More effective separation can be achieved if MIL-53 monoliths of diameters above 200 µm are used. Faster separation is possible by increasing the feed pressure or if the starting compositions are richer in CO2. More CH4 is produced per cycle at higher feed pressures, but the shortened time at higher pressures can result in the reduction of the CH4 purity.

Nanomaterials for renewable energy storage: synthesis, characterization, and applications

1Department of Chemical and Materials Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 21589, Saudi Arabia 2Gas Processing Center, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar 3Electrochemical Power Systems Division, CSIR-Central Electrochemical Research Institute, Karaikudi 630006, India 4SABIC Chair in Catalysis, King Abdulaziz University, P.O. Box 80204, Jeddah 21589, Saudi Arabia 5Game Lab, Chenergy Group, Department of Applied Science and Technology (DISAT), Politecnico Di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy