Adsorption of reformer off-gas on NaX zeolite and metal organic framework (mil53(AI)): Equilibria and kinetics

Thesis (Doctoral)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2013Includes bibliographical references (leaves: 90-96)Text in English; Abstract: Turkish and Englishx, 96 leavesSynthetic gas produced from steam methane reforming (SMR off -gas) is a mixture of H2, CO, CO2, and CH4 can be used in fuel cell after purification. In this study adsorption as a purification tool was used to obtain high H2 content of gas mixture from SMR off gas. Zeolites and metal organic framework were used as an adsorbent. CO2 equilibrium studies on K rich NaX zeolites, prepared with ultrasonic and traditional methods, and metal organic framework MIL53 (Al) shows high adsorption on zeolites than MIL53(Al) up to 1 atm. K rich zeolites give lower adsorption than NaX zeolite. Adsorption isotherms obtained for MIL53 (Al) is linear ( favorable for zeolites). This makes MIL53(Al) is an promising adsorbent for high pressure application. Adsorption equilibrium at 5 atm shows that NaX zeolite is good adsorbent for the SMR off gas with the following orders: CO2>CH4>CO> H2. Kinetics of SMR off gas in MIL 53 (Al) were studied by using Zero Length Column (ZLC) method. The results show that the calculated diffusivities are strongly dependent on temperature but weakly dependent on purge flow rate. The study reveals that transport is controlled by intracrystalline diffusion. The activation energy on diffusion are nearly same (about 41 kJ/mol) and not change with respect to kinetic diameter of SMR off gases. Heat of SMR off gas adsorption on MIL53(Al) obtained from Henry’s constant shows that adsorption is exothermic. The study shows that the ZLC method is an effective tool to investigate the diffusion kinetics of SMR off-gas gases in MIL53(Al)

Effects of Isothermal and Adiabatic Thermal Loadings on Size and Strain Rate Dependence of Copper Nanowire

In the present paper, the size and strain rate effects on ultra-thin <100>/{100} Cu nanowires at an initial temperature of 10 K have been discussed. Extensive molecular dynamics (MD) simulations have been performed using Embedded atom method (EAM) to investigate the structural behaviours and properties under high strain rate. Velocity-Verlet algorithm has been used to solve the equation of motions. Two different thermal loading cases have been considered: (i) Isothermal loading, in which Nose-Hoover thermostat is used to maintain the constant system temperature, and (ii) Adiabatic loading, i.e., without any thermostat. Five different wire crosssections were considered ranging from 0.723 x 0.723 nm2 to 2.169 x 2.169 nm2. The strain rates used in the present study were 1 x 109 s-1, 1 x 108 s-1, and 1 x 107 s-1. The effect of strain rate on the mechanical properties of copper nanowires was analysed, which shows that elastic properties are independent of thermal loading for a given strain rate and cross-sectional dimension of nanowire. It showed a decreasing yield stress and yield strain with decreasing strain rate for a given cross-section. Also, a decreasing yield stress and increasing yield strain were observed for a given strain rate with increasing cross-sectional area. Elastic modulus was found to be ~ 100 GPa, which was independent of processing temperature, strain rate, and size for a given initial temperature. Reorientation of <100>/ {100} square cross-sectional copper nanowires into a series of stable ultra-thin pentagon copper nanobridge structures with dia of ~ 1 nm at 10 K was observed under high strain rate tensile loading. The effect of isothermal and adiabatic loading on the formation of such pentagonal nanobridge structure has been discussed.Defence Science Journal, 2009, 59(3), pp.252-259, DOI:http://dx.doi.org/10.14429/dsj.59.151

Manyetik nano atom kümelerinin moleküllerle ve yüzeyle etkileşmesinin yoğunluk fonksiyonel teori ile incelenmesi

Platin atom kümelerinin elektronik özellikleri, yoğunluk fonksiyonel teori (YFT) kullanılarak genelleştirilmiş gradyent yaklaşımı ile gamma noktasında incelenmiştir. Platin kümeleri için, bağlanma enerjileri, manyetizasyonları, bağ uzunlukları, en yüksek dolu moleküler orbital enerjisi (HOMO), en düşük boş moleküler orbital enerjisi (LUMO), HOMO-LUMO fark (HLG) değerleri boyuta bağlı olarak hesaplandı. Ptn kümelerinin, atom sayısının artması ile birlikte 3 boyutlu yapıyı tercih ettiği gözlemlenlendi. Ptn atom kümelerinin elektronik özelliklerini belirleyebilmek için durum yoğunluğu hesabı da yapıldı. H2 (Hidrojen) ve NH3 (Amonyak) molekülü tutunmuş platin atom kümeleri YFT kullanılarak genelleştirilmiş gradyent yaklaşımı ile incelendi. H2 ve NH3 tutunmuş platin atom kümelerinin tutunma enerjisi, HOMO, LUMO, manyetizasyon ve bağ uzunlukları, kararlı tutunma durumları için artan atom sayısına göre incelendi. Platin ile azot atomları arasında güçlü bir etkileşme bulundu. NH3 tutunmuş Pt14 atom kümesindeki NH3 molekülünde ayrışma gözlemlendi. H2 tutunmuş platin atom kümelerinin Pt3 atom kümesi dışındakilerin tümünde H2 molekülünün ayrıştığı bulunmuştur. Her bir H atomunun, farklı platin atomlarıyla bağ yapmayı tercih ettiği görünmektedir. NH3 ve H2 tutunmuş platin atom kümelerinde Fermi seviyesi yakınında, platinin d orbitalinin baskın olduğunu gözlemlendi. Platin atom kümelerinin metalik ve iletkenlik özelliklerinin NH3 ve H2 molekülleri tutunmasıyla değişmiştir. NH3 tutunmuş Pt2 atom kümesi yarı metalik özellik gösterebilir. NH3 ve H2 tutunmuş Pt atom kümelerinin HLG değerleri hesaplandı. H2 ve NH3 molekülünün Pt atomuna tutunmasında elde dilen sonuçlar gösteriyorki, Pt atomundan H atomuna yük geçişi ve Pt ve N atomları arasında kutuplanma meydana gelmiştir. Bu elde eldilen sonuçların Löwdin analizi ile uyumlu olduğu görülmüştür. MoSe2 tek tabakası ile Fe, Mn atomları arasındaki etkileşmeler incelendi. Fe ve Mn atomları tek tabakada Mo üzerinden bağlanmayı tercih etti.The electronic properties of platinum clusters are investigated at gamma point by using density functional theory (DFT) within generalized gradient approximation. The size dependence of binding energy, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), magnetization, and bond length values are calculated for platinum clusters. It is observed that Ptn clusters prefer to form 3D structures with increasing number of atoms., The electronic density of states is also calculated to explore the electronic properties of Ptn clusters. The NH3 and H2 molecules adsorbed Ptn clusters are investigated by DFT calculations within generalized gradient approximation. The adsorption energy, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), HOMO-LUMO gap (HLG), magnetization, and bond length values of H2 ve NH3 adsorbed platinum clusters are investigated as a function of atom number for the stable adsorption site . A strong interaction is found between Pt and N atoms. It is surprisingly observed that NH3 dissociation occurs at Pt14 cluster. We found that H2 molecule dissociates at different adsorption sites for all clusters except Pt3 cluster. Each of H atom seems to prefer to bound different Pt atoms. We see that d orbital of Pt is dominant near the Fermi level in NH3 and H2 adsorbed Ptn clusters. Metallic and conductivity properties of Ptn clusters change with adsorption of NH3 and H2 molecules. NH3 adsorbed Pt2 cluster can show half metallic properties. HOMO-LUMO gap (HLG) values for NH3 and H2 adsorbed Ptn clusters are evaluated. The results also imply charge transfer from Pt to H atoms in H2 adsorbed Ptn clusters and apolarization between Pt and N atoms in NH3 adsorbed clusters. These results also comply with Lowdin analysis. The interactions between MoSe2 monolayer and Fe, Mn atoms are investigated. Fe and Mn atoms prefer to bound to Mo atom in MoSe2

The influence of cations on the dipole moments of neighboring polar molecules

It is shown that the dipole moment of polar (water, methanol, formamide, acetone and acetonitrile) molecules in the neighborhood of a cation is increased primarily by polarization from the bare electrostatic charge of the cation, although the effective value of the latter is somewhat reduced by "back donation" of electrons from neighbouring polar molecules. In other words, the classical picture may be viewed as if a point charge slightly smaller than the nominal charge of the cation would be placed at the cation site. It was found that the geometrical arrangement of the polar molecules in the first solvation shell is such that their mutual polarization reduces the dipole moments of individual molecules, so that in some cases they become smaller than the dipole moment of the free protic or aprotic molecule. We conjecture that this behavior is essentially a manifestation of the Le Chatellier-Braun principle

Atomistic Approaches for the Analysis, Design, and Simulation of Nanosensors and Nanocatalysts

Using ideas of materials genome initiative, it is possible to create new materials with tailored properties for applications in nanoelectronics, sensing, and catalysis among other fields. The contamination of groundwater due to accidental leakage of radioactive wastes poses a grave danger to the environment and human life and hence trace characterization of these radioactive materials is of paramount importance in nuclear forensics and reprocessing. The presence of uranium and plutonium complexes in contaminated soil and water around nuclear processing facilities especially after a nuclear accident would provide us with critical information to guide a proper and timely response. We examine the applicability of graphene-based nanosensor for detection of these radionuclides based on ab initio density functional theory and Green’s function theory. Changes in the molecular electrostatic potential due to presence of a foreign moiety near graphene can be transduced and amplified into current-voltage characteristics at nanoscale. By comparing the change in current due to presence of U or Pu complexes near a graphene-based sensor, we should be able to detect trace amounts of these radionuclides. The DNA origami has emerged as a new and promising method to create nanostructures with precise atomistic tailored geometries. In addition, these origamis can be functionalized or impregnated with specialized single stranded DNA/RNA chains (known as aptamers) in order to convert them into biosensors. Thrombin is an enzyme directly involved in formation of blood clot which is a major cause of heart attack. We perform molecular dynamics simulations to determine the relative energetics associated with the capture of thrombin by a novel biosensor assembly consisting of two aptamers attached to a rectangular DNA origami. In addition to developing nanosensors, we also apply multi-scale computational approach to develop nanocatalysts and describe catalytic reactions happening at the surface to design more efficient catalysts. Molybdenum disulfide, (MoS2) being a very versatile material for several applications, is an industrial catalyst for hydrotreating processes in petroleum refineries. We perform MD simulations on a typical middle distillate fraction of crude oil containing thiophene and dibenzothiophene molecules in order to determine their relative positions with respect to the catalytic surface previous to possible reactions that are then studied with DFT. Furthermore, we analyze MoS2- graphene and MoS2-boron nitride clusters as possible hydrodesulfurization catalysts

Fabrication of YBCO thin flims by pulsed laser deposiyion technique and their charcterization

Thesis (Master)--Izmir Institute of Technology, Physics, Izmir, 2010Includes bibliographical references (leaves: 63-66)Text in English; Abstract: Turkish and Englishxi, 66leavesThis thesis focuses on pulsed laser deposition (PLD) system, fabrication of high temperature superconducting YBCO thin films and their characterization. In this study, the electrical and structural studies performed on laser deposited YBCO films have shown that films produced by PLD. The thin films were characterized in detail by employing structural XRD, SEM, EDX and AFM and electrical ( R-T) measurements. During this work, pulsed laser deposition system used to grow superconducting thin film on MgO single crystal substrate. Firstly PLD system was carried out by using different growth parameters. Deposited films was cooled down in situ under an oxygen atmosphere at a given pressure. The deposition tecnique has emerged as a very powerful method to make composition and microstructure controlled superconducting YBCO films.Thanks to rapid heating and evaporation of the target and interaction of the laser beam with evaporated materials leading to formation of a high temperature plasma PLD system is different from other thin film growth system.However, major problem was particulates emmission which was shown SEM,we solved this problem by chaning distance between target and substrate, and laser power. Furthermore Electron Dispersive X-Ray Spectroscopy (EDX) method was used to identify the chemical contents of the films.The relation between critical temperature and oxygen deficieny was investigated by means of electrical resistance R(T) and x-ray diffraction measurements.Finally, our results were compared to literature and explanied similarites.Text in English; Abstract: Turkish and English