Browsing by Subject "catalysis"
Now showing 1 - 14 of 14
Results Per Page
Sort Options
Item Advances in Synthesis of Co- and Ter- Polycarbonates and Polyesters from Non-Petroleum Feedstocks and Kinetic Studies of Ligand Substitution from Manganese Half-Sandwich Complexes(2012-07-16) Poland, Ross RiversThis dissertation is written in two parts. The first pertains to polycarbonate and polyester synthesis using relatively benign processes. The synthesis of polycarbonates from the coupling of CO2 and epoxides catalyzed by transition metal catalysts has long been studied in the DJD group. The benefits of this process are that it utilizes comparatively benign reagents, can be performed using no extraneous solvent, and is 100% atom efficient. A method potentially useful for achieving more desirable polycarbonate properties is to produce an epoxide A/epoxide B/CO2 terpolymer, thus allowing more fine "tuning" of properties to what one may desire while simultaneously influencing relative epoxide reactivity to potentially increase catalytic turnovers. Specifically, the coupling of propylene oxide and cyclohexene oxide with CO2 to yield a random copolymer with tunable properties has been studied via a Fineman-Ross analysis. Propylene oxide was found to be incorporated into the resultant polymer chain with anywhere from 4-10 times the preference of cylcohexene oxide. Although it has been reported as early as 1969, the copolymerization of epoxides and cyclic anhydrides catalyzed by transition metal complexes to yield polyesters via a chain-growth mechanism has recently gained much attention. This robust method of polyester synthesis can utilize rather inexpensive reagents to synthesize an array of polyester products which have a wide range of Tg values (-30 degrees C ? 90 degreesC), achievable through simple monomer selection. The second part of this dissertation deals with the kinetic study of ligand substitution from manganese carbonyl metal fragments. Some time ago it was postulated that complexes of the (Cp)M(CO)2L variety undergo ligand substitution via a associative mechanism allowed by a haptotropic eta5-eta3 shift in the eta5 ligand. Through kinetic studies and theoretical modeling, an approximate activation energy barrier of ~34 kJ/mol has been calculated for the ring slip of (2,5-dimethylpyrrole)Mn to occur. Additionally, further kinetic studies were performed in which Tp, a ligand electronically similar to Cp, was compared to MnCp complexes.Item Dendrimer-encapsulated metal nanoparticles: synthesis, characterization, and applications to catalysis(Texas A&M University, 2004-09-30) Niu, YanhuiThe research in this dissertation examines the chemistry and applications of dendrimers in homogeneous catalysis. We examined interactions between dendrimers and charged probe molecules, prepared dendrimer-encapsulated metal nanoparticles in organic solvents, studied size-selectivity of dendrimer-encapsulted catalysts, and designed molecular rulers as in-situ probes to measure the location of dendrimer-encapsulted metal nanoparticles. The intrinsic proton binding constant and a constant that characterizes the strength of electrostatic interactions among occupied binding sites in poly(amidoamine) (PAMAM) dendrimers have been obtained by studying the effect of solution pH on the protonation of the dendrimers. The significant finding is that these two factors are greatly modulated by the unique and hydrophobic microenvironment in the dendrimer interior. Hydrophilic poly(propylene imine) (PPI) dendrimers were modified with various hydrophobic alkyl chains through an amide linkage and were then used as templates for preparing intradendrimer copper nanoclusters. The main driving force for encapsulating metal-ions was found to be the differences in metal-ion solubility between the solvent and the interior of the dendrimer. Nanometer-sized metal particles are synthesized and encapsulated into the interior of dendrimers by first mixing together the dendrimer and metal ion solution and then reducing the composite chemically, and the resulting dendrimer-encapsulated metal nanoparticles can then be used as catalysts. By controlling the packing density on the dendrimer periphery using either different dendrimer generations or dendrimer surface functionalities, it is possible to control access of substrates to the encapsulated catalytic nanoparticle. Molecular rulers consisting of a large molecular "stopper", a reactive probe and a linker were designed as in-situ probes for determining the average distance between the surface of dendrimer-encapsulated palladium nanoparticles and the periphery of their fourth-generation, hydroxyl-terminated PAMAM dendrimer hosts. By doing so, we avoid having to make assumptions about the nanoparticle size and shape. The results suggest that the surface of the encapsulated nanoparticle is situated 0.7 ? 0.2 nm from the surface of the dendrimer.Item Designing phase selective soluble polymers for applications in organic chemistry(Texas A&M University, 2004-09-30) Li, ChunmeiSoluble polymers as supports are gaining more attention now. Developing new polymers, new reagents and catalysts, new separation systems are thus of great interest as these sorts of materials' applications in synthesis and catalysis increase. The work described in the succeeding chapters describes my efforts to synthesize new catalysts that can be attached to polymer supports, to study their catalytic activity and to study separation efficiency. Most of the work focus is on polyacrylamide polymers. Both organometallic catalysts and organic catalysts have been studied. Liquid/liquid separation was the technique mainly investigated. In addition, a new separation scheme called latent biphasic system which is a new liquid/liquid separation method is described. Finally, studies with the Cremer group where the LCST behavior of polyacrylamides was studied using dark field methods are also discussed.Item DEVELOPMENT AND MECHANISTIC STUDIES OF THE CHROMIUM TETRAMETHYLTETRAAZAANNULENE CATALYST SYSTEM FOR THE COPOLYMERIZATION OF CARBON DIOXIDE AND EPOXIDES(2010-07-14) Fitch, ShawnA prominent goal of scientists is to develop products and processes to meet the ever-growing needs of society. Today's needs include products that are economical, specialized, and made through processes with minimal impact on the environment. One such product that serves an important and widespread need is poly(bisphenol A carbonate) for its physical properties and ease of synthesis and processing. However, this polymer does not meet the growing need of being environmentally benign as production involves carcinogenic, chlorinated solvents and toxic monomers that can leach out from the polymer product. An answer to this new demand is the development of a different process for the production of polycarbonate plastics utilizing carbon dioxide and epoxides. Carbon dioxide is an attractive monomer that is cheap and nontoxic, and its utilization signifies an important contribution to counteract global greenhouse emissions. The stability of carbon dioxide has posed a significant and complex challenge towards its utilization. Epoxides are attractive since they are synthesized from a wide variety of olefins, both naturally occurring and those derived from petroleum. The exploration of catalysts to facilitate the coupling of epoxides to carbon dioxide to afford polycarbonates has been under investigation in the Darensbourg lab for fifteen years, and has lead to the development of several successful systems such as zinc bisphenoxides and chromium salens. This dissertation focuses on the development of another successful catalyst system, chromium tetramethyltetraazaannulene, and further elucidation of the mechanism by which polycarbonates are formed. Herein, aspects of the copolymerization process using this system will be discussed in detail, such as cocatalyst and pressure dependence, catalyst derivatization, and kinetic and mechanistic investigations. The end result of these investigations is the development of the most active chromium-based catalyst for the copolymerization of cyclohexene oxide and carbon dioxide and a better understanding of how the copolymer product is produced.Item Fundamental Studies towards Transistion Metal Catalysis and Application of Chromium Salen Complexes for the Synthesis of Polymers(2010-07-14) Andreatta, Jeremy R.?The body of this work spans both fundamental organometallic chemistry and the application of previously studied catalyst systems to produce new polymeric materials. The cone angle of triphenylphosphite was estimated to be 128 degrees by Tolman in the late 70s; however, metal complexes bearing this ligand undergo cis/trans isomerization via a mechanism indicative of greater steric requirements. X-ray crystallographic studies coupled with data compiled from the Cambridge Crystallographic Database, were used to more accurately calculate the steric demand of this wieldy used ligand to be approximately 140 degrees. Additionally, in depth kinetic studies of the interaction of furan ligands with electron deficient manganese and chromium metal centers were performed. Data collected from timescales ranging from minutes to microseconds was utilized to calculate the bond dissociation energy of both 2,3-dihydrofuran (DHF) and furan. The aromatic furan ligand was found to bind to the both metals 7-10 kcal mol-1 weaker than DHF. Additionally, the more electron rich chromium center was found to bind both ligands ?weaker than the manganese center implying a minimization of the M-L pie -back bonding interaction. Solution studies coupled with DFT calculations were utilized to estimate the extent that the furan ligand is dearomatized by approximately 50% upon interaction with the metal center. Application-based studies of the separation of polymer catalyst mixtures were also undertaken. The addition of the 1000 Dalton poly(isobutylene) arms to the salen ligand in (salen)CrCl complexes yielded a catalyst that could be extracted from the reaction mixture containing poly(cyclohexene carbonate) via the addition of heptane. Another approach, not requiring catalyst modification, utilized a secondary amine to facilitate the purification of the polymer product. The reaction of an amine with CO2 to form an ionic liquid resulted in the precipitation of the polymer while the catalyst and byproducts remained in the liquid carbamate phase. Both approaches provided improvements over the long standing method of precipitating the polymer using methanol and strong acid. Lastly, the previous work of the Darensbourg group utilizing (salen)CrCl catalyst to produce polycarbonates from CO2 and epoxides was employed to synthesized sulfur rich poly(thiocarbonate)s. The effects of both CS2 loading and temperature on the copolymerization of CS2 and cyclohexene oxide were studied. Optimal conditions of 1 equivalent of CS2 and 50 degrees C were found to selectively produce the desired polymeric material. The observation of multiple thiocarbonate as well as carbonate functionalities, led to a detailed study of the reaction byproducts to gain insight into the copolymerization process.Item Mechanisms of transition-metal catalyzed additions to olefins(Texas A&M University, 2005-08-29) Nowlan, Daniel ThomasTransition metal catalyzed reactions have an important place in synthetic chemistry, but the mechanistic details for many of these reactions remain undetermined. Through a combination of experimentally determined 13C kinetic isotope effects (KIEs) and density functional theory (DFT) calculations, some of these reactions have been investigated. The cyclopropanation of an olefin catalyzed by rhodium (II) tetrabridged complexes has been shown to proceed through an asynchronous, but concerted mechanism. DFT does not provide an accurate transition structure for the reaction of an unstabilized carbenoid with an olefin, but it does predict an early, enthalpically barrierless transition state which is consistent with the reactivity of unstabilized carbenoids. For the case of stabilized carbenoids, the theoretical structures predict the KIEs accurately and a new model is proposed to explain the selectivity observed in Rh2(S-DOSP)4-catalyzed cyclopropanations. The chain-elongation step of atom transfer radical polymerization (ATRP) has been shown to be indistinguishable from that of free radical polymerization (FRP) for the CuBr/2,2??-bipyridine system. While DFT calculations predict an earlier transition state than observed, the calculations suggest that with increasing levels of theory the predicted KIEs come closer to the observed KIEs. A recently proposed [2 + 2] mechanism for the cyclopropenation of alkynes catalyzed by Rh2(OAc)(DPTI)3 has been shown not to be a viable pathway. Rather, the experimental KIEs are predicted well by canonical variational transition state theory employing the conventional mechanism for cyclopropenation via a tetrabridged rhodium carbenoid. DFT calculations also suggest an alternative explanation for the observed enantioselectivity. The 13C KIEs for metal-catalyzed aziridination have been measured for three separate catalytic systems. While the KIEs do not completely define the mechanism, all of the reactions exhibit similar KIEs, implying similar mechanisms. A surprising feature of this system is the presumed nitrene intermediate??s triplet spin state. This complicates the DFT analysis of this system.Item N-heterocyclic carbene catalysis: expansion of(2009-05-15) Ogle, James WilliamAsymmetric hydrogenation as a general route to polypropionates has been explored for allylic alcohols, acids, and derivatives, which has led to the generation of 2,4-dimethylated hexane derivatives. Quantitative yields in most cases and enantioselectivities greater than 98% were obtained. A remarkable stereofacial inversion was observed when an ester or acid was present in the allylic position instead of an alcohol or alcohol derivative. This led to the construction of all four diastereomers of the hexanol series from a single enantiomer of hydrogenation catalyst. Also described are an attempted synthesis of (-)-lardolure, a formal synthesis of the methyl ester portion of the preen gland extract from the domestic goose Anser anser, and a total synthesis of an extract from the fungi A. cruciatus. The synthesis of these compounds demonstrated shortcomings of the known catalyst system showing enantioselectivities for polymethylated compounds was high, while diastereoselectivity was low. Methodology to develop new N-heterocyclic carbene catalysts was developed using the cyanide coupling of aldimines to generate electronically tunable 1,3,4,5-tetraaryl complexes, and X-ray, IR, and calculations were used to elucidate their electronic characteristics. These studies indicate that the 4,5-positions have as great an influence on the metal-ligand bond as the 1,3-positions. In addition, they are among the most electron-donating 2- metalated N-heterocyclic carbenes found thus far. An intrinsic relationship between catalytic activity and electron donating ability was found in transfer hydrogenations.Item Phase selectively soluble polymer supports to facilitate homogeneous catalysis(2009-05-15) Ortiz-Acosta, DenisseSoluble polymers that have phase selective solubility are useful in synthesis because they simplify purification and separation. Such selectively soluble polymers simplify catalyst, reagent, and product recovery and enable the use of Green chemistry principles in homogeneous catalysis. However, while homopolymers have been reported that have excellent thermal and phase-dependent solubility, less is known about copolymers. Also, less is known about the phase selective solubility of polar aprotic N,N-dialkyl polyacrylamides. This work describes a library synthesis of dye-labeled poly(N-n-octadecylacrylamide-co-N-n-butylacrylamide) copolymers and study of the effects of polymer composition in phase selective solubility of these copolymers. To study the relative importance of n-octadecyl versus n-butyl groups, copolymers with different ratios of n-octadecylacrylamide and n-butylacrylamide but with similar degrees of polymerization and polydispersity were prepared by a split-pool synthesis using a highly soluble poly(N-acryloxy-2-dodecylsuccinimide) as the precursor. Polymer sequestrants were used to remove excess amines and the byproduct N-hydroxyl-2- dodecylsuccinimide without fractionation of the polyacrylamides. Results demonstrated that poly(N-n-octadecylacrylamide-co-N-n-butylacrylamide) copolymers? phase selective solubility is equally dependant of the polar n-butyl and nonpolar n-octadecyl groups on the copolymers. Dye-labeled poly(N,N-dialkylacrylamide)s prepared by the polymerization of N,N-dialkylacrylamides monomers with methyl, ethyl, propyl, butyl, hexyl, and dodecyl N-alkyl groups in a variety of thermomorphic or latent biphasic polar/nonpolar solvent mixtures were also prepared. Studies showed that poly(N,N-dialkylacrylamide)s have phase selective solubility that is highly dependent of the size of the N-alkyl group. Soluble polymers are known to be useful supports for catalysts. This thesis also describes approaches to immobilization of a variety of catalysts on polyisobutylene (PIB). The most effective of these catalysts were analogs of pyridyl N-oxides that have been used as organocatalysts for the catalytic allylation of a variety of aromatic aldehydes. PIB-supported N-oxide promoted the allylation of aldehydes in up to 99% isolated yield. The products were isolated in the polar phase of a thermomorphic system and the catalyst was recycled through five cycles.Item Structure-function relationships in dendrimer-encapsulated metal nanoparticles(Texas A&M University, 2006-04-12) Wilson, Orla MaryThe synthesis, characterization and structure-function relationships of mono- and bimetallic dendrimerencapsulated nanoparticles (DENs) are described. Control over the factors influencing the structure of bimetallic DENs has been attained for PdAu and AuAg systems. The bimetallic DENs are characterized by UV-vis, HRTEM, and single-particle energy dispersive x-ray spectroscopy (EDS). In addition, we use catalysis and selective extraction to chemically probe the surface structure. The fabrication of TiO2-supported Pd, Au and PdAu nanocomposites from DEN precursors is shown to be a viable route for the synthesis of catalytically active, reasonably monodisperse heterogeneous catalysts. Using the dendrimer-templating synthesis, tight control over the size of 1- 2 nm Pd DEN catalysts has led to the observation of a particle-size effect for the hydrogenation of allyl alcohol. We have proposed that for particles with diameters between 1.5? 1.9 nm the reaction occurs preferentially on the exposed face atoms.Item Studies of the relationship of protein structure to regulation and catalysis in tyrosine hydroxylase(Texas A&M University, 2007-09-17) Sura, Giri RajuTyrosine hydroxylase (TyrH) catalyzes the rate-limiting step in the synthesis of the catecholamine neurotransmitters dopamine, epinephrine, and norepinephrine. Phosphorylation of Ser40 of rat TyrH activates the enzyme by decreasing the affinity for catecholamines. In humans, there are four different TyrH isoforms with varying lengths for the regulatory domain. DOPA and dopamine binding studies were performed on the phosphorylated and unphosphorylated human isoforms. The Kd for DOPA was increased two times upon phosphorylation of hTyrH1, but no change was seen for hTyrH4; the Kd value decreased with the increase in the size of regulatory domain. The small effect on the Kd value for DOPA upon phosphorylation of hTyrH suggests that DOPA does not regulate the activity of hTyrH. Dopamine binds very tightly and upon phosphorylation the affinity for dopamine is decreased. This Kd value decreases with the increase in the length of the regulatory domain. The crystal structures of substrate complexes of the homologous enzyme phenylalanine hydroxylase (PheH) show a large movement of a surface loop (residues 131-155) upon amino acid binding. The corresponding loop residues (175-200) in TyrH play an important role in DOPA formation. This conformational change in TyrH loop was studied with fluorescence anisotropy. Three tryptophan residues in the TyrH, at positions 166, 233, and 372, were mutated to phenylalanine, and Phe184 was mutated to tryptophan. An increase in anisotropy was observed in the presence of phenylalanine and 6-methyl-5-deazatetrahydropterin (6M5DPH4), but the magnitude of the change of anisotropy with 6M5DPH4 was greater than that with phenylalanine. Further characterization of the sole tryptophan in the loop showed a decrease in the amplitude of the local motion only in the presence of 6M5DPH4 alone. The conformational change in wild type TyrH was examined by H/D exchange LC/MS spectroscopy in the presence of the natural ligands. Time-course dependent deuterium incorporation into the loop in the presence of ligands indicated that the pterin alone can induce the conformational change in the loop irrespective of whether iron is reduced or oxidized. From these results, one can conclude that the loop undergoes a conformational change upon pterin binding, making the active site better for amino acid binding.Item Supramolecules with dimolybdenum or chiral dirhodium units(Texas A&M University, 2007-04-25) Yu, RongminThis dissertation concerns the syntheses and characterization of supramolecules with quadruply bonded Mo2 4+ units, Mo2(DAniF)3 + (DAniF = N,N'-di-p-anisylformamidinate) or cis- Mo2(DAniF)2 2+, and chiral organometallic Rh2 4+ units, including racemic cis-Rh2(C6H4PPh2)2 2+ and pure enantiomers of cis-Rh2(C6H4PPh2)2 2+. Molecular pairs of dimolybdenum units in which Mo2(DAniF)3 + units are linked by cyclic diamidate anions or dioxolene anions have been investigated. Linkers impact the electronic communication between the dimetal units in various ways. The symmetry and the energy of the frontier orbitals of the linker are among the factors which influence significantly the properties of the molecular pairs. Nature has provided us a great opportunity to study quantitatively the equilibrium between neutral supramolecules with cis-Mo2(DAniF)2 2+ units. Studies of the concentrationdependent and temperature-dependent equilibria between a molecular triangle and square as well as a molecular loop and triangle using 1H and 19F NMR spectra provide quantitative values for the thermodynamic equilibrium constant K, as well as ??????H????, and ??????S???? for the equilibria. The synthesis and characterization supramolecular compounds containing chiral cis- Rh2(C6H4PPh2)2 2+ units, including three racemic triangles and pure enantiomers of three triangles, a carceplex with T symmetry and two loops are also presented.Item Surface spectroscopic characterization of oxide thin films and bimetallic model catalysts(2009-05-15) Wei, TaoOxide thin films and bimetallic model catalysts have been studied using metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), low energy ion scattering spectroscopy (LEISS), X ? ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD) under ultra high vacuum (UHV) conditions. Of particular interest in this investigation was the characterization of the surface morphology and electronic/geometric structure of the following catalysts: SiO2/Mo(112), Ag/SiO2/Mo(112), Au?Pd/Mo(110), Au?Pd/SiO2/Mo(110), and Pd? Sn/Rh(100). Specifically, different types of oxide surface defects were directly identified by MIES. The interaction of metal clusters (Ag) with defects was examined by work function measurements. On various Pd related bimetallic alloy surfaces, CO chemisorption behavior was addressed by IRAS and TPD. Observed changes in the surface chemical properties during the CO adsorption-desorption processes were explained in terms of ensemble and ligand effects. The prospects of translating this molecular-level information into fundamental understanding of ?real world? catalysts are discussed.Item The Development of Werner-type Cobalt Complexes in Enantioselective Hydrogen Bond Mediated Catalysis(2013-12-03) Lewis, KyleChiral-at-metal Werner complexes of the type (?/?)-[Co(1,2-diamine)_(3)]^(3+) 3X^(?)have long been a cornerstone of coordination chemistry. However, despite being inexpensive and readily available in enantiopure form, they have had no applications in enantioselective organic synthesis. This derives from their poor solubility in organic solvents and the fact that the chelating ligands are non-labile, preventing metal based substrate activation. However, it was conceived that the abundant nitrogen-hydrogen bonds of the diamine ligands could activate Lewis basic substrates towards nucleophilic addition via hydrogen bonding. Towards this end, the diastereomeric trications ?-[Co((S,S)-dpen)_(3)]^(3+) and ?-[Co((S,S)-dpen)_(3)]^(3+) (dpen = diphenyl ethylenediamine) were prepared by stereoselective syntheses. Incorporation of the lipophilic Bar_(f)^(?) (B(3,5-CF_(3)-C_(6)H_(3))_(4)^(?)) anion, among others, afforded the organic-soluble mixed salts ?-[Co((S,S)-dpen)_(3)]^(3+) 2X^(?) BAr_(f)^(-) and ?-[Co((S,S)-dpen)_(3)]^(3+) 2X^(?) Bar^( ?)(X = Cl^(?), BF_(4)^(?), PF_(6)^(?)). These Werner complexes were then applied as hydrogen bond mediating catalysts for enantioselective Michael additions of dialkyl malonates to nitroolefins. The catalyzed Michael addition of dimethyl malonate (15a) to trans-?- nitrostyrene was optimized with respect to solvent, temperature, and catalyst counteranion and then extended to a range of nitroolefin substrates. Under optimized ? conditions, ?-(S,S)-3^(3+) 2BF_(4)^(?) Bar_(f)^(-) (10 mol%) catalyzes the Michael addition of 15a to 2-benzyloxy-trans-?-nitrostyrene in acetone at 0 ?C in the presence of Et_(3)N (1.0 equiv) to afford dimethyl 2-(2-nitro-1-(2 benzyloxyphenyl)ethyl)malonate in 95% isolated yield and 96% ee. This work marks the first time that a Werner-type complex has been applied as a catalyst for organic transformations with high enantioselectivities. The unique stereochemistry of the Werner complex, which features a chiral metal center, is primarily responsible for the stereoselectivity of the catalyzed reactions.Item Theoretical studies of transition metal surfaces as electrocatalysts for oxygen electroreduction(Texas A&M University, 2007-09-17) Lamas, Eduardo J.In the last few years the quest towards a hydrogen based economy has intensified interest for effective and less expensive catalysts for fuel cell applications. Due to its slow kinetics, alternative catalysts for the oxygen electroreduction reaction are actively researched. Platinum alloys with different transition metals (for example: Ni, Co and Fe) have shown improved activity over pure Pt. The design of a Pt-free catalysts is also highly desirable, and different alternatives including metalloporphyrins and Pd-based catalysts are being researched. Pd-based catalysts constitute an attractive alternative to Pt alloys in some fuel cell applications, not only because of lower costs but also because of the lower reactivity of Pt alloys towards methanol, which is important for improved methanol crossover tolerance on direct methanol fuel cells. In this work we apply density functional theory (DFT) to the study of four catalysts for oxygen electroreduction. The electronic structure of these surfaces is characterized together with their surface reconstruction properties and their interactions with oxygen electroreduction intermediates both in presence and absence of water. The energetics obtained for the intermediates is combined with entropy data from thermodynamic tables to generate free energy profiles for two representative reaction mechanisms where the cell potential is included as a variable. The study of the barriers in these profiles points to the elementary steps in the reaction mechanisms that are likely to be rate-determining. The highest barrier in the series pathway is located at the first proton and charge transfer on all four catalytic surfaces. This is in good agreement with observed rate laws for this reaction. The instability of hydrogen peroxide on all surfaces, especially compared with the relatively higher stability of other intermediates, strongly points at this intermediate as the most likely point where the oxygen bond is broken during oxygen reduction. This adds to the argument that this path might be active during oxygen electroreduction. A better understanding behind the reaction mechanism and reactivities on these representative surfaces will help to find systematic ways of improvement of currently used catalysts in the oxygen electroreduction reaction.