<p>In recent years, first principles periodic Density Functional Theory (DFT) calculation</p><p>has been used to investigate heterogeneous catalytic reactions and examine catalyst</p><p>structures as well as adsorption properties in a variety of systems. The increasing</p><p>contribution to give detailed understanding of elementary reaction mechanism is critical to</p><p>provide fundamental insights into the catalyst design. It is a link to the fundamental</p><p>knowledge and a bridge to the practical application. DFT calculations is also a powerful</p><p>tool to predict and yield promising catalysts which is time- and cost-saving in the practical</p><p>end.</p><p>Because of the recent boom in natural shale gas deposit, there is an increasing interest</p><p>in developing more efficient ways to transform light alkanes into desired and high-value</p><p>chemicals, such as propylene. Propylene is a valuable raw material in the petrochemical</p><p>application to make value-added commodities, such as plastics, paints, and fibers, etc. The</p><p>conventional cracking, steam cracking (SC) and fluid catalytic cracking (FCC), could not</p><p>meet the growing demand of propylene. Thus, it has motivated extensive research of</p><p>production technologies. On the other hand, the abundance of light alkanes extracted from</p><p>the shale gas makes on-purpose production an appealing method which is economically</p><p>competitive. Non-oxidative dehydrogenation of propane (PDH) is a one of ways to make</p><p>up the supply and solve the issue.</p><p>xiii</p><p>According to the current research and industrial work, platinum (Pt) shows promising</p><p>performance for the PDH. However, it suffered from some major drawbacks, such as</p><p>thermodynamic limitation, rapid deactivation leading to poor catalytic performance and</p><p>frequent regeneration. In addition, it is a relatively high cost noble metal. Consequently,</p><p>many efforts have been devoted to the enhancement of the catalytic performance. It was</p><p>found that the stability and the selectivity of Pt-based catalysts can be improved via</p><p>modifying its properties with transition metals as promoters.</p><p>In this thesis, DFT calculations were performed for propane dehydrogenation over</p><p>two different catalyst systems, bimetallic platinum-zinc alloy and monometallic platinum</p><p>catalysts. The work provides insights into the catalyst crystal structures, the adsorption</p><p>characteristics of diverse adsorbates as well as the energy profiles regarding to the</p><p>selectivity of the propane dehydrogenation. Bulk calculation signifies a stable tetragonal</p><p>configuration of the PtZn catalyst which is in accordance with the experimental result. The</p><p>thermodynamic stability regarding to the stability of bulk and surface alloys are studied</p><p>with the consideration of physical constrains. We have identified the thermodynamic</p><p>stability of several PtZn low-index surface facets, (101), (110), (001), (100) flat surfaces</p><p>and stepped surface (111), at certain chemical potential environmental conditions through</p><p>the surface energy phase diagram. Stoichiometric and symmetric (101) slab is</p><p>thermodynamically stable under the region of high Pt chemical potential, and the offstoichiometric</p><p>and symmetric (100 Zn-rich) slab under the low Pt chemical potential.</p><p>In this work, PtZn(101) is used as a model surface to demonstrate the effect on the</p><p>catalytic performance with zinc promotion of platinum. In comparison with Pt(111) surface,</p><p>an elimination of 3-fold Pt hollow site on PtZn(101) is of important and it leads to the</p><p>xiv</p><p>change of binding site preferences. The divalent groups (1-propenyl, 2-propenyl) change</p><p>from Pt top site on PtZn(101) to 3-fold site on Pt(111), which is because of the lack of Pt</p><p>3-fold site on alloyed surface. As for propylene, it changes from di-σ site on PtZn to 𝜋 site</p><p>on Pt. The surface reaction intermediates are found to bond more weakly on PtZn(101)</p><p>than on the Pt surface. Especially, the binding energy of propylene reduces from -1.09 to -</p><p>0.16 eV. The weaker binding strength facilitates the activity of propylene on alloyed</p><p>surfaces.</p><p>Through a complete and classic reaction network analysis, the introduction of Zn</p><p>shows an increase in the endothermicity and the energy barrier of each elementary reaction</p><p>on the alloy surface. With the consideration of entropy for kinetic under real experimental</p><p>condition, the alloying of Zn is found to lower the energy barrier for the propylene product</p><p>desorption and increases that for propylene dehydrogenation. Meanwhile, the competition</p><p>between desired C-H and undesired C-C cleavages is investigated. It is found that the</p><p>cleavage of C-H is energetically favorable than that of C-C. These positive factors</p><p>potentially lead to a high selectivity toward propylene production on PtZn(101).</p><p>Subsequently, Microkinetic modeling is performed to estimate kinetic parameters</p><p>including the reaction order, rate-determining step to build a possible reaction mechanism.</p><p>Finally, conclusions brought out about the comparison between bimetallic and</p><p>monometallic catalyst, and suggestions for future work are presented.</p>

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Na reação de desidrogenação oxidativa de propano (ODHP), propano reage com oxigênio da superfície de metais de transição para produzir propeno e água, em temperaturas de 300-700C. Porém, o propeno pode facilmente oxidar, formando CO e CO2. Assim, busca-se catalisadores que promovam a seletividade do propeno. Compostos tipo hidrotalcitas estão sendo apontados como catalisadores de grande potencial para a reação. Portanto, o principal objetivo desse trabalho foi sintetizar precursores tipo hidrotalcitas (contendo íons Ni2+, Mg2+ e Al3+ e tereftalato, heptamolibdato e decavanadato como ânions de compensação) para serem testados na reação de desidrogenação oxidativa de propano. Esses precursores foram sintetizados com uma razão Al/(Al+Ni+Mg)=0,5, variando a razão de Ni/Mg. Além disso, realizou-se a troca iônica do tereftalato (TA) por heptamolibdato (Mo7O24) e decavanadato (V10O28). Esses compostos foram calcinados, obtendo-se assim, óxidos mistos de NiMgAl, NiMgAlMo e NiMgAlV que foram testados como catalisadores na reação de ODHP. Para a determinação das propriedades dos catalisadores foram usadas as técnicas de caracterização: DRX, TGA, volumetria de N2, TPR, Raman e FTIR e ICP. Os resultados indicaram que os materiais tipo hidrotalcita foram obtidos com sucesso. No caso dos precursores preparados por troca iônica a cristalinidade foi menor que os da série NiMgAl-TA. Estes mesmos precursores quando calcinados apresentaram áreas muito altas. Nas três séries, os precursores calcinados são constituídos por óxidos mistos como NiO, NiMoO4, Ni2V2O7 cristalinos e espécies de alumínio e magnésio não detectados na DRX. No teste catalítico de ODHP, observou-se que com o aumento da conversão diminuía a seletividade de propeno, para os óxidos mistos que não continham molibdênio. Os catalisadores da série molibdênio foram os que obtiveram melhor desempenho com altas seletividades, mesmo em altas conversões e a série de cujo precursor foi o tereftalato foi a que exibiu maiores conversões, mas com seletividades menores que da série de Mo / In the reaction of oxidative dehydrogenation of propane (ODHP), propane reacts with oxygen in the transition metal surface to produce propylene and water at temperatures of 300-700 C. However, the propylene can easily oxidize, forming CO and CO2. Thus, catalysts that promote the selectivity of propylene are being searched. Hydrotalcites type compounds are identified as potential major catalysts for the reaction. Therefore, the main objective of this work was to synthesize precursors hydrotalcites type (containing Ni2+, Mg 2+ and Al 3+ ions and terephthalate, heptamolybdate and decavanadate as compensation anions) to test in the reaction of oxidative dehydrogenation of propane.These precursors were synthesized with Al/(Ni+Mg+Al) = 0.5 for different ratios of Ni/Mg. In addition, there was the ion exchange terephthalate (TA) by heptamolybdate (Mo7O24) and decavanadate (V10O28). These compounds were calcined, to obtain NiMgAl, NiMgAlMo and NiMgAlV mixed oxides and tested as catalysts in the ODHP reaction.For determining the properties of the catalysts the following characterization techniques were used: XRD, TGA, N2 volumetry, TPR, ICP, FTIR and Raman spectroscopy. The results indicated that the hydrotalcite-like materials were successfully obtained. In the case of the precursors prepared by ion exchange crystallinity was lower than those of NiMgAl-TA series. These same precursors when calcined had very high areas. In three series, the calcined precursors are comprised by mixed oxides such as crystalline NiO, NiMoO4, Ni2V2O7 and Al an Mg species not detected by XRD. In ODHP catalytic test, it was observed that with increasing conversion the propylene selectivity decreased to the mixed oxides containing no molybdenum. The catalysts of molybdenum series were those who performed better with high selectivity even at high conversions and the terephthalate precursor series shows the highest conversions, but with lower selectivity than Mo series

Effective analytical techniques need to be developed to characterize the products of lignin degradation experiments to be able to generate renewable products from lignin. Mass spectrometry is an valuable analytical approach for lignin characterizaion, but it is hindered by lignin’s poor ionization efficiency, especially in the positive ion mode. In this work, we attempt to improve lignin’s ionization by utilizing electrospray and laser desorption mass spectrometry coupled with the addition of cations and chemical derivatives. We confronted the ionization problem from both a top-down and bottom-up analytical approach by analyzing synthesized monomers, dimers, and polymers along with natural lignin extracts from switchgrass. We also utilized tandem mass spectrometry to sequence lignin dimers and determine their bonding motifs from their fragmentation patterns. We believe that resolving the ionization issues with lignin will open the door for easier and more efficient lignin break-down techniques and ultimately more accessible renewable products from lignin.

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第23991号 / 人博第1043号 / 新制||人||245(附属図書館) / 2022||人博||1043(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 藤田 健一, 教授 小松 直樹, 教授 津江 広人, 教授 大江 洋平 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

The present work reports a study of the effects of the compositions, and various catalytic additives and nanostructuring by high-energy ball milling, on the hydrogen storage properties of LiBH4, NaBH4, LiNH2 and LiAlH4 complex hydrides and their composites. The composites of (NaBH4+2Mg(OH)2) and (LiBH4+2Mg(OH)2) without and with nanometric nickel (n-Ni) added as a potential catalyst were synthesized by ball milling. The effect of the addition of 5 wt.% nanometric Ni on the dehydrogenation behavior of both the NaBH4-and LiBH4-based composites is rather negligible. In the (LiNH2+nMgH2) system, the phase transformations occurring as a function of the ball milling energy injected into the hydride system (LiNH2+nMgH2), having molar ratios n=0.5 to 2.0, have been thoroughly studied. The milling energy is estimated by a semi-empirical method. The results show that for the molar ratios n<1.0 three new phases such as LiH, amorphous Mg(NH2)2 (a-Mg(NH2)2) and Li2Mg(NH)2 are formed during ball milling depending on the injected energy. For the molar ratios n≥1.0 the new phase of MgNH forms whose formation is accompanied by a profound release of hydrogen. Addition of 5 %wt. KH can improve desorption rate of the LiNH2+0.5 MgH2 system. Furthermore this hydride system can be nearly fully rehydrogenated at 200°C and 50 bar H2 pressure. LiAlH4 containing 5 wt.% of nanometric Fe and Ni shows a profound mechanical dehydrogenation by continuously desorbing hydrogen (H2) during ball milling. X-ray diffraction studies show that Fe and Ni ions dissolve in the lattice, replacing the Al ions and forming a substitutional solid solution. Both Fe and Ni decrease the activation energies of stage I and II , but stage I is more sensitive to the particle size . The addition of 5 wt.% nano-size “interstitial compound” (n-TiC, n-TiN and n-ZrC) shows a continuous desorption of H2 is observed during high energy milling. Mechanical dehydrogenation rate of the doped samples increases noticeably during high-energy ball milling in the order of TiN > TiC > ZrC. The interstitial compound additives are able to strongly reduce the activation energy of Stage II dehydrogenation but do not substantially affect the apparent activation energy of Stage I .

Amine boranes have recently been considered as solid hydrogen storage materials with high capability of hydrogen storage. Dimethylamine borane is one of the promising amine boranes with high theoretical gravimetric capacity of 16.9 wt%. Dimethylamine borane can undergo dehydrogenation only in the presence of a suitable catalyst at moderate temperature. In this project, throughout the dehydrogenation of dimethylamine borane (DMAB), the catalytic activity of ruthenium(III) acetylacetonate was examined for the first time. During the catalytic reaction, formation of a new in-situ ruthenium(II) species, [Ru{N2Me4}3(acac)H], is observed. Mercury poisoning experiment indicates that the in-situ ruthenium(II) species is a homogeneous catalyst in the dehydrogenation of dimethylamine borane. Kinetics of catalytic dehydrogenation of dimethylamine borane starting with ruthenium(III) acetylacetonate was investigated depending on catalyst concentration, substrate concentration and temperature. As a result, the hydrogen generation rate was found to be first-order with respect to catalyst concentration and zero-order regarding the substrate concentration. Besides, evaluation of the kinetic data yielded that the activation parameters for dehydrogenation reaction: the activation energy, Ea = 85 &plusmn / 2 kJ&bull / mol-1 / the enthalpy of activation, DH# = 82 &plusmn / 2 kJ&bull / mol-1 and the entropy of activation / DS# = -85 &plusmn / 5 J&bull / mol-1&bull / K-1. Additionally, before deactivation, [Ru{N2Me4}3(acac)H] provides 1700 turnovers over 100 hours in hydrogen evolution from the dehydrogenation of dimethlyamine borane. [Ru{N2Me4}3(acac)H] complex formed during the dehydrogenation of dimethylamine borane was isolated and characterized by UV-Visible, FTIR, 1H NMR, and Mass Spectroscopy. The isolated ruthenium(II) species was also tested as homogeneous catalyst in the dehydrogenation of dimethylamine borane.

The production of transition metal(0) nanoparticles with controllable size and size distribution are of great importance in catalysis since their catalytic activity decreases as nanoparticles aggregate into clumps and ultimately to the bulk metal. Reducing the particle size of heterogeneous catalyst provides a significant rise in its activity as the fraction of surface atoms increases with decreasing particle size. Therefore, transition metal(0) nanoparticles need to be stabilized to certain extend in their catalytic applications by strong stabilizers. In this regard, tert-butylammonium octanoate [(CH3)3CNH3+][CH3(CH2)6COO-] seems to be an appropriate stabilizer for rhodium(0) nanoparticles since octanoate anion and its associated tert-butylammonium cation can provide a sufficient protection for rhodium(0) nanoparticles against aggregation by the combined electrostatic and steric effects. We report herein the preparation and characterization of rhodium(0) nanoparticles stabilized by tert-butylammonium octanoate and their catalytic use in the dehydrogenation of ammonia borane, H3NBH3, which appears to be the most promising hydrogen storage material due to its high hydrogen content (19.6 wt %). Rhodium(0) nanoparticles stabilized by tert-butylammonium octanoate were reproducibly prepared by the reduction of rhodium(II) octanoate dimer with tert-butylamine borane in toluene at room temperature and characterized by EA, XRD, ICP/OES, TEM, HRTEM, STEM, FTIR, XPS, UV-VIS and NMR spectroscopy. The new rhodium(0) nanoparticles is the first example of well-defined, reproducible, and isolable true heterogeneous catalyst used in the dehydrogenation of ammonia borane. They show record catalytic activity in the dehydrogenation of ammonia borane at room temperature with an apparent initial TOF value of 342 h-1 and TTO value of 1100.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 173-183).

The demands on Hydrogen fuel based technologies is ever increasing for substitution or replacing fossil fuel due to superior energy sustainability, national security and reduced greenhouse gas emissions. Currently, the polymer based proton exchange membrane fuel cell (PEMFC), is strongly considered for on-board hydrogen storage vehicles due to low temperature operation, efficiency and low environmental impact. However, the realization of PEMFC vehicles must overcome the portable hydrogen storage barrier. DOE and FreedomCAR technical hydrogen storage targets for the case of solid state hydrides are: (1) volumetric hydrogen density > 0.045 kgH2/L, (2) gravimetric hydrogen density > 6.0 wt%, (3) operating temperature < 150 degrees C, (4) lifetimes of 1000 cycles, and (5) a fast rate of H2 absorption and desorption. To meet these targets, we have focused on lithium borohydride systems; an alkali metal complex hydride with a high theoretical hydrogen capacity of 18 wt.%. It has been shown by Vajo et al. that adding MgH2, improves the cycling capacity of LiBH4. The pressure-composition-isotherms of the destabilized LiBH4 + MgH2 system show an extended plateau pressure around 4-5 bars at 350 degrees C with a good cyclic stability. The mentioned destabilizing mechanism was successfully utilized to synthesize the complex hydride mixture LiBH4 + 1/2MgH2 + Xmol% ZnCl2 catalyst (X=2, 4, 6, 8 and 10) by ball milling process. The added ZnCl2 exhibited some mild catalytic activity which resulted in a decomposition temperature reduction to 270 degrees C. X-ray powder diffraction profiles exhibit LiCl peaks whose intensity increases proportionately with increasing ZnCl2 indicating an interaction between catalyst and hydride system, possibly affecting the total weight percent of desorbed hydrogen. Thermal gravimetric analysis profiles for MgH2 + 5mol% nanoNi and LiBH4 + ZnCl2 + 3mol% nanoNi indicate that small concentrations of nano-nickel acts as an effective catalyst that reduces the mixture desorption temperature to around 225 degrees C and 88 degrees C, respectively. Future work will be focused on thermodynamic equilibrium studies (PCT) on the destabilized complex hydrides.

The present work reports a study of the effects of the compositions, and various catalytic additives and nanostructuring by high-energy ball milling, on the hydrogen storage properties of LiBH4, NaBH4, LiNH2 and LiAlH4 complex hydrides and their composites. The composites of (NaBH4+2Mg(OH)2) and (LiBH4+2Mg(OH)2) without and with nanometric nickel (n-Ni) added as a potential catalyst were synthesized by ball milling. The effect of the addition of 5 wt.% nanometric Ni on the dehydrogenation behavior of both the NaBH4-and LiBH4-based composites is rather negligible. In the (LiNH2+nMgH2) system, the phase transformations occurring as a function of the ball milling energy injected into the hydride system (LiNH2+nMgH2), having molar ratios n=0.5 to 2.0, have been thoroughly studied. The milling energy is estimated by a semi-empirical method. The results show that for the molar ratios n<1.0 three new phases such as LiH, amorphous Mg(NH2)2 (a-Mg(NH2)2) and Li2Mg(NH)2 are formed during ball milling depending on the injected energy. For the molar ratios n≥1.0 the new phase of MgNH forms whose formation is accompanied by a profound release of hydrogen. Addition of 5 %wt. KH can improve desorption rate of the LiNH2+0.5 MgH2 system. Furthermore this hydride system can be nearly fully rehydrogenated at 200°C and 50 bar H2 pressure. LiAlH4 containing 5 wt.% of nanometric Fe and Ni shows a profound mechanical dehydrogenation by continuously desorbing hydrogen (H2) during ball milling. X-ray diffraction studies show that Fe and Ni ions dissolve in the lattice, replacing the Al ions and forming a substitutional solid solution. Both Fe and Ni decrease the activation energies of stage I and II , but stage I is more sensitive to the particle size . The addition of 5 wt.% nano-size “interstitial compound” (n-TiC, n-TiN and n-ZrC) shows a continuous desorption of H2 is observed during high energy milling. Mechanical dehydrogenation rate of the doped samples increases noticeably during high-energy ball milling in the order of TiN > TiC > ZrC. The interstitial compound additives are able to strongly reduce the activation energy of Stage II dehydrogenation but do not substantially affect the apparent activation energy of Stage I .