CC Bond Breaking Research Articles

Density functional theory studies on combustion oxidative decomposition mechanism of 3,3,3-trifluoropropene

The environmentally friendly refrigerant 3,3,3-trifluoropropene (HFO-1243zf) suitable for refrigeration and heat pump systems has flammability. Based on density functional theory, the oxidation decomposition mechanism of 3,3,3-trifluoropropene was studied, including the main initial oxidation decomposition and subsequent reactions. The results indicate that among the initial thermal decomposition reactions, the reaction with the lowest energy barrier is simultaneous elimination of HF, followed by CC bond breaking to form ∙CF3. In the H abstraction reaction, the reaction energy barrier of H atom capture by ∙F is the lowest. In F abstraction reaction, the ∙H is the most active. In the addition reaction, the reaction energy barrier of ∙F is the lowest. The energy barriers of reactions involving different free radicals, from high to low, are: thermal decomposition, F abstraction, H abstraction and addition reaction. The subsequent reactions mainly involve the generation pathways of ∙CF3 and the formation of stable products.

Vanadium (IV)oxo catalyzed One-Pot transformation of cinnamate to aromatic ester and its mechanistic aspects

Metal-catalyzed oxidative cleavage of unsaturated carbon–carbon bond is among the utmost valuable chemical transformations in synthetic organic chemistry. However, the direct transformation of cinnamate to benzoate remains an unsolved task in the series. Herein, we have developed an unprecedented one-pot strategy for the direct transformation of cinnamate esters to aromatic ester using V-catalyst [(L2)VIVO](ClO4) and green oxidant H2O2 in alcohol-reflux condition. The reaction on cinnamate proceeded via CC bond breaking to generate aldehyde intermediate, followed by oxidative esterification to yield two carbon less aromatic esters in 52–95% yields. Further, experimental and DFT studies confirmed the mechanism and in-situ aldehyde formation which consequently supported to the developed protocol.

Experimental and computational study on xylan pyrolysis: The pyrolysis mechanism of main branched monosaccharides

The high percentage of branched units with different structures leads to the complex pyrolysis chemistry and product distribution of hemicellulose. In this study, four main branched monosaccharides, i.e., arabinose (Ara), galactose (Gal), galacturonic acid (GacA), and glucuronic acid (GlcA) were employed as typical xylan-based hemicellulose model compounds. The pyrolysis behaviors and mechanisms of these monosaccharides were deeply explored by the combination of pyrolysis experiments and density functional theory (DFT) calculations. Particularly, the roles of structural differences of these monosaccharides were carefully analyzed. Due to the uronic acid group, GacA and GlcA were easier to decompose, having two weightloss peaks with close intensity, and the release of CO2 had greater intensity than Ara and Gal pyrolysis at low temperatures. GlcA with the equatorial hydroxyl group can undergo a special CC bond breaking reaction to depart the C6 uronic acid group to release HCOOH. The fast pyrolysis of these monosaccharides obtained similar product species but distinct relative contents. The structure of an uncertain hydromethyl-furnaose product was identified as 5-(hydroxymethyl)furan-3(2H)-one (5-HMFO) by combined DFT calculations and experimental results. The findings of this work are beneficial to gain a deep understanding of the pyrolysis chemistry of hemicellulose, especially the role of different branches.

The mechanism of photothermal catalytic reforming of biomass tar: An exploratory study based on density functional theory

Tar removal is a hot topic in the biomass gasification field. Photothermal catalytic reforming (PCR) is an emerging approach that shows high efficiency, but the mechanism and tar cracking reaction pathway under PCR are still not clear. In this paper, as a widely recognized catalyst that has both thermal and photo-catalysis effects, Ni/TiO2 was investigated and the model was calculated by density functional theory (DFT). Toluene was selected as the model tar compound, and the cracking performances were analyzed in both PCR and conventional heating conditions. It was found that H2O and toluene can be stably adsorbed on the catalyst surface but the adsorption sites are different, which provides support for the comparisons of toluene cracking pathways. The energy barriers of CC bond breaking reactions were calculated and the toluene cracking pathway showed significant changes under PCR, due to the formation of oxygen vacancy and hydroxyl radical. Toluene mainly occurs in the dissociation reaction of methyl group under conventional conditions, but toluene tends to open aromatic ring to form chain hydrocarbons under PCR conditions. It indicates that PCR shows greater activation on the aromatic ring which is crucial for tar cracking. This study confirms the change of the toluene cracking pathway under photothermal conditions by the DFT calculation method and also provides guidance for the optimization of the tar removal process and photothermal catalyst preparation.

Pyrolysis mechanism of R601a/R245fa mixture: A ReaxFF-MD and DFT study

R601a/R245fa mixture is one kind of promising working fluid in ORC. In this study, the thermal decomposition mechanism of R601a/R245fa mixture was studied by reactive molecular dynamic simulation (ReaxFF-MD) and density function theory (DFT). In the R601a/R245fa mixed working fluid system, pyrolysis begins with the CC bond breaking of R601a, generating a large number of CH3 radicals, which further decompose to produce a certain amount of H radicals. Due to the presence of R245fa, the hydrogen extraction reactions between CH3, H radicals and R601a, which have low energy barriers were inhabited to a certain extent. The addition of R245fa reduces the generation of small molecule flammable gases such as H2 and CH4, however, it increases the risk of HF generation. When the molar ratio of R245fa exceeds 0.5, pyrolysis will cause more serious HF corrosion problems than pure R245fa.

Effect of CO2/propane ratio and trimetallic oxide catalysts on maximizing dry reforming of propane

This study aimed at increasing the dry reforming reaction of propane with CO2 by using trimetallic oxide catalyst based on the reactive support of ZrO2/TiO2. Multiple basic (Mg, Be and Ba) and transition metal oxide (Cu, Fe) and Al were impregnated separately into 5%ZrO2/TiO2 catalyst support and characterized by XRD, BET, CO2-TPD and NH3-TPD. The catalysts showed an increase in the number of basic surface sites, with the trimetallic catalysts exhibiting more than 2.2–9.7 times the original number of basic sites of the Zr/Ti oxide support. In order to maximize greenhouse gas conversion, selected ratios of CO2/propane were correlated to increase syngas (CO and H2) product and promote more CO2 reactions via surface intermediates from CC bond dissociation of propane. Utilizing trimetallic catalysts enabled a three folds increase of CO yield compared to the reactive support used in the study. Although the selectivity towards H2 and CO increase with trimetallic catalysts, 2%Fe/5%ZrO2/TiO2 and 2%Be/5%ZrO2/TiO2 exhibited the highest propane dry reforming conversions (84–97%) with yields of H2 (35–51%) and CO (60–68%), respectively. The study demonstrated that each trimetallic oxide catalyst consumed CO2 differently, promoting distinct CC bond breaking patterns of propane over the catalyst surface.

Fragmentation dynamics of acetylene in collision with highly charged ions: Concerted and sequential breakage of CH and CC bonds

The three-body fragmentation of ${\mathrm{C}}_{2}\mathrm{H}{{}_{2}}^{3+}$ to ${\mathrm{H}}^{+}+{\mathrm{C}}^{+}+{\mathrm{CH}}^{+}$ as a consequence of one CH and one CC bond breaking is investigated by 50-keV/u ${\mathrm{Ne}}^{8+}$ impact. All three fragments are detected in coincidence with a scattered projectile (either ${\mathrm{Ne}}^{7+}$ or ${\mathrm{Ne}}^{6+}$) employing a reaction microscope, and their momentum vectors as well as the kinetic energies were obtained. Four distinguished structures are observed in the energy correlation spectra, indicating that abundant fragmentation mechanisms contribute to the ${\mathrm{H}}^{+}+{\mathrm{C}}^{+}+{\mathrm{CH}}^{+}$ channel. The Newton diagrams and Dalitz plots are employed to trace fragmentation mechanisms. We found that both the concerted fragmentation and the sequential pathway with CH bond breaking prior to CC contribute to this channel. The possible electronic states of the ${\mathrm{C}}_{2}\mathrm{H}{{}_{2}}^{3+}$ precursor that may contribute to the identified fragmentation mechanisms are analyzed with the help of quantum chemical calculations. Furthermore, the influence of the collision dynamics between the projectile and the target to the dissociation mechanisms is discussed by comparing the contributions from the reaction channel with transferring one electron while ionizing the other two, i.e., T1I2, and the reversed channel T2I1. The T2I1 channel is observed to be more efficient to initiate fragmentation mechanisms leading to higher kinetic-energy release.

Two- and three-body dissociations of C3H6 isomer dications investigated by 4 keV/u Ar8+ impact.

The fragmentation dynamics of two isomers of C3H6, cyclopropane and propene, induced by 4 keV/u Ar8+ are investigated employing a reaction microscope. Four two-body and two three-body dissociation channels of C3H6 2+ dications are identified for each isomer, among which the channels involving CC bond breaking are found to be much more favored than H3 + and H2 + formation channels. The observation of the CH3 + or H3 + formation channels from cyclopropane are direct evidence of the proton migration within the carbon skeleton before dissociation. Obvious isomer effects are revealed by comparing the relative branching ratios of different channels of the two isomers. Moreover, it was shown that a sequential dissociation mechanism with H elimination prior to CC bond cleavage may be dominant for the two three-body dissociation channels for both isomers.

Online investigation on catalytic co-pyrolysis of cellulose and polyethylene over magnesium oxide by advanced mass spectrometry

Due to rapid deactivation of catalysts, the effective conversion of biomass with oxygen-rich and hydrogen-deficient characteristics to transportation fuels and high-valued chemicals via catalytic pyrolysis remains a challenge for commercialization. Hydrogen-rich plastic is used as feedstock co-fed with biomass to improve the catalytic pyrolysis process. The present work aims to investigate the co-pyrolysis process of cellulose and polyethylene (PE) over MgO by TG combined with photoionization time-of-flight mass spectrometry (PI-TOF-MS), which features on-line detection of catalytic pyrolysis products in real time. The MgO catalyst could improve the pyrolysis of cellulose and enhance the CC bond breaking of PE, respectively. During catalytic co-pyrolysis, the yields from olefins and furan as well as its derivatives can be enhanced obviously. Further, the formation of additional aromatics can be observed due to the Diels-Alder reaction. This work shows TG coupled to PI-TOF-MS is a powerful setup to study and optimize catalytic co-pyrolysis process.

Improved carbon dioxide selectivity during ethanol electrooxidation in acid media by Pb@Pt/C and Pb@PtSn/C electrocatalysts

One key challenge for the fuel cell technology commercialization is the development of low Pt charge electrocatalysts with high fuel oxidation efficiency. Here, we evaluate the electrocatalytic performance of Pb1@Pt3/C and Pb1@Pt3Sn1/C core–shell and Pt3Sn1/C alloy nanocatalysts towards ethanol oxidation, evidencing the contributions provided when a PtSn alloy is present in the shell of these materials. Physical characterizations confirm the presence of Pb, Pt, and/or Sn in the catalytic composites, and the interaction between them from displacements in lattice parameters of core–shell materials. TEM results indicated the presence of small particles supported on carbon with some agglomeration. The 4f region profiles of Pt and Pb obtained from the XPS measurements suggest the formation of core-shell structure for the Pb1@Pt3/C and Pb1@Pt3Sn1/C electrocatalysts, which is in good agreement with their voltammetric profile, considering the inhibition of the hydrogen adsorption process caused by the presence of Sn on the surface of Pb1@Pt3Sn1/C. The core–shell electrocatalysts display the best electrocatalytic activities. The bimetallic Pb1@Pt3/C catalyst achieves the lowest onset oxidation potentials and the highest current density thus shows the positive changes provided by core–shell morphology from its electronic and geometric effects. Besides, in situ Fourier transform infrared spectroscopy measurements show that Pb1@Pt3/C and mainly Pb1@Pt3Sn1/C yields the highest CO2 production. Therefore, the presence of Sn makes the Pb1@Pt3Sn1/C electrocatalyst much more selective to CC bond breaking and CO2 production than the Pb1@Pt3/C. These outcomes can result from the combination of the electronic and geometric effects (core–shell) and the presence of Sn in the shell that promotes the bifunctional mechanism.

New mechanistic insights into the reversible aldol reaction catalysed by Rhamnulose-1-phosphate aldolase from Escherichia coli

Stereoselective CC bond formation is one of the most exciting challenges of synthetic organic chemistry. Biocatalysts have emerged as promising tools, with aldolases being among the most employed. Unfortunately, the features of their active sites that modulate the mechanistic details have been poorly assessed. Here, the electronic and structural factors associated with the substrates binding and catalytic mechanism of rhamnulose-1-phosphate aldolase (RhuA) from E. coli are computationally analysed. The results allowed us to furnish a holistic view of the RhuA’s entire turnover cycle. The active site bears three pockets that anchor different moieties of the substrates: l-rhamnulose-1-phosphate (R1P), dihydroxyacetone phosphate (DHAP) and (S)-lactaldehyde (LLA). The results predict a 5-step catalytic mechanism, being the CC bond breaking (Ea =24.2 kcal mol−1) and the DHAP deprotonation (Ea =22.0 kcal mol−1) the rate-determining steps for the retro- and aldolic reactions, respectively. The residues E117, E171′, G31 and N29, and the Zn2+ cofactor, play a major role in stabilizing the correct substrates’ orientation, securing the stereocontrol at C4. Our findings suggest the presence of two acid/base catalytic residues, E117 and E171′, the latter of which being also involved in assisting the CC bond formation through a concerted protonation of the transition state.

Highly active Pt3Rh/C nanoparticles towards ethanol electrooxidation. Influence of the catalyst structure

The electrochemical oxidation of ethanol results in the formation of strongly adsorbed intermediates. Pt–Rh catalysts are proposed as alternatives since they easy the CC bond breaking. However, the effect of the Pt–Rh structure on the catalytic activity and selectivity to CO2 is not well understood. Here, we synthesised Pt/C and two different Pt–Rh/C catalyst architectures, an alloy (Pt3Rh/C) and a bimetallic mixture (Pt3–Rh/C) to study the effect of catalyst structure on its catalytic activity and on the products formed during the ethanol oxidation in acid media. The nanoparticles were prepared by a modified polyol reduction method using ethylene glycol as a co-reducing agent and Pb as a material of sacrifice, to obtain very small and well-dispersed nanoparticles on the carbon support. Fourier transform infrared spectroscopy and derivative voltammetry was used to give insights about the ethanol oxidation mechanism occurring at the developed catalysts. The samples characterised by X-ray diffraction analysis showed distortions in the Pt lattice parameters for the Pt-Rh alloy structure due to the presence of Rh in the catalyst’s composition. Transmission electron microscopy analyses indicate that nanoparticles were well-dispersed on a carbon support, with spherical shapes and small particle sizes (2–3 nm). in situ X-ray absorption spectroscopy data evidence that Pt–Rh interactions produce changes in the Pt 5d band vacancy. The electronic effect is maximized when Pt forms an alloy with Rh, resulting in the highest d-band vacancy of the Pt3Rh/C. The Pt3Rh/C catalyst showed the highest activity towards ethanol oxidation, presenting current densities in a quasi-steady-state condition (measured at 600 mV) around 5.2 times higher than the commercial Pt/C (Alfa Aesar). Moreover, the onset potential for ethanol oxidation shifts to more negative potentials (110 mV lower taken at 1 mA cm–2) was also observed. In situ FTIR data revealed that Pt/C catalyst favours the formation of acetic acid. The synergistic effect between Rh and the alloy structure results in an easier CC bond breaking for Pt3Rh/C, in comparison to Pt3–Rh mixture, thus favouring CO2 formation at lower potentials.

Two-body dissociation of C3H4 isomers investigated by 50 keV/u Ne8+ impact.

The fragmentation of two isomers of C3H4, propyne (CH3CCH) and allene (CH2CCH2), is investigated by 50 keV/u Ne8+ impact. Obvious isomer effects are observed by comparing the time-of-flight spectra generated from the two isomers. Six two-body fragmentation channels of C3H4 2+ dications are identified for each isomer. CH2 + + C2H2 + is found to be the most favored CC bond breaking channel for both isomers, indicating that CH3CCH2+ intends to rearrange to the structure containing the CH2 group before fragmentation. For CH bond breaking channels, it is found that the CH3CCH which contains a CH3 group is more efficient for H2 + and H3 + ejection. In addition, two-body dissociation channels of C3H4 3+ trications are identified. While the H+ + C3H3 2+ channel is observed in the fragmentation of both isomers, the H2 + + C3H2 2+ channel only occurs in the fragmentation of CH3CCH3+. For CH2CCH2 3+, the peak and shoulder structures in the kinetic energy release spectrum of the H+ + C3H3 2+ channel are attributed to different geometries of the C3H3 2+ product.

Surface properties enhanced MnxAlO oxide catalysts derived from MnxAl layered double hydroxides for acetone catalytic oxidation at low temperature

MnxAlO mixed oxide catalysts derived from MnxAl-LDHs were prepared and tested for acetone catalytic oxidation. Detailed results indicated that the surface intrinsic and formed oxygen vacancies can induce the Mn-O bond of structural unit [MnO6] weakened. Subsequently, it can improve the redox properties of catalysts, and enhance the capacity of gaseous oxygen species dissociation and adsorption. Among them, Mn3AlO catalyst displayed the best catalytic performance for acetone oxidation (T90 = 164 °C) with the production of low amount of byproduct (<5 ppm) and high CO2 yield (>99%) producted. Additionally, the Mn3AlO catalyst can proceed consecutively for 12 h reaction without notable deactivation. Furthermore, in situ DRIFT and theoretical calculations methods was adopted to explore the reaction mechanism. And η1(O)(ads) (adsorption mode of acetone), CH2=C(CH3)=O(ads), O*, CH3CHO*, CH2O* and COO(ads) were considered as the main intermediate species and/or transient state during the reaction process. It was revealed that the acetone and oxygen molecules were activated by the dehydrogenation (α-H abstraction) and dissociation process over Mn3AlO catalyst, respectively, and then the intermediate specie, CH2C(CH3)O and O*, were produced, which was followed by the breaking of CC bonds to produce the CH3CHO* and CH2O* species. Finally, these species were attacked by dissociated oxygen (O*) and therefore further dehydrogenation occurred, form H2O and CO2 via the COO adsorbed species. Particularly, CC bond breaking was the main rate determining step for acetone oxidation.

The mechanism of ethanol steam reforming on the Co0 and Co2+ sites: A DFT study

It is well known that Co catalysts are efficient for ethanol steam reforming (ESR) reactions, but whether the active site is Co0, Co2+, or Co0–Co2+ is still debated. In the present work, density functional theory calculations are performed to study the reaction mechanisms of ESR over Co0, Co2+, and Co0–Co2+ sites. The mechanism of ESR on Co0 sites is CH3CH2OH → CH3CH2O → CH3CHO → CH3CO → CH3 + CO, and H2 is formed by the combination of adsorbed H species with a relatively high barrier (1.37 eV). On the CoO(1 0 0) surface, the main product CH3CHO is produced through the consecutive dehydrogenation of ethanol, but the CoO surface lacks the C–C bond activation that ESR requires. On Co catalysts with a combination of Co0 and Co2+ (Co10/CoO(1 0 0) model), a strong synergetic effect was found: On interface, it occurs through the path CH3CH2OH → CH3CH2O → CH3CHO → CH3CO, the resulting CH3CO on interface will spread to Co10 cluster and bind to OH on the interface which results from H2O dissociation on the CoO surface: CH3CO → CH3COOH (interface), and the resulting acetic acid (CH3COOH) will spread to the Co10 cluster and go on CC scission with the path CH3COOH → CH3 + trans-COOH → CH3 + CO2 + H to form CO2. On CoO parts (Co2+ sites), H2O dissociation is more facile than that on Co0 sites, and the formed OH (or O) migrates to the interface easily and reacts with CHx species to release carbon deposition. On the interface between Co0 and Co2+, some key coupling reactions related to ESR are favored, such as H2 formation, the formation of CH3COOH, and the oxidation of CHx species to release coke formation, thus leading to high activity for ESR. Possible reasons for the result that CC bond breaking can take place on Co0 sites instead of Co2+ sites have been analyzed, and it was found that Co0 sites with a large ensemble size of Co favor dissociation reactions such as CC scission. Based on the present work, it is expected that a proper catalyst for ESR reactions should have metallic sites with large ensemble size to break CC bonds and oxidized metal sites with small ensemble size to favor water dissociation as well as acetate species formation.

Effects and mechanism on Kapton film under ozone exposure in a ground near space simulator

The effect on aircraft materials in the near space environment is a key part of air-and-space integration research. Ozone and aerodynamic fluids are important organizational factors in the near space environment and both have significant influences on the performance of aircraft materials. In the present paper a simulated ozone environment was used to test polyimide material that was rotated at the approximate velocity of 150–250 m/s to form an aerodynamic fluid field. The goal was to evaluate the performance evolution of materials under a comprehensive environment of ozone molecular corrosion and aerodynamic fluids. The research results show that corrosion and sputtering by ozone molecules results in Kapton films exhibiting a rugged “carpet-like” morphology exhibits an increase in surface roughness. The morphology after ozone exposure led to higher surface roughness and an increase in surface optical diffuse reflection, which is expressed by the lower optical transmittance and the gradual transition from light orange to brown. The mass loss test, XPS, and FTIR analysis show that the molecular chains on the surface of the Kapton film are destroyed resulting in CC bond breaking to form small volatile molecules such as CO2 or CO, which are responsible for a linear increase in mass loss per unit area. The CN and CO structures exhibit weakening tendency under ozone exposure. The present paper explores the evaluation method for Kapton’s adaptability under the ozone exposure test in the near space environment, and elucidates the corrosion mechanism and damage mode of the polyimide material under the combined action of ozone corrosion and the aerodynamic fluid. This work provides a methodology for studying materials in the near-space environment.

Influence of ∗OH adsorbates on the potentiodynamics of the CO2 generation during the electro-oxidation of ethanol

Direct ethanol fuel cells (DEFCs) are a promising technology for the generation of electricity via the direct conversion of ethanol into CO2, showing higher thermodynamic efficiency and volumetric energy density than hydrogen fuel cells. However, implementation of DEFCs is hampered by the low CO2 selectivity during the ethanol oxidation reaction (EOR). Comprehensive understanding of the electro-kinetics and reaction pathways of CO2 generation via CC bond-breaking is not only a fundamental question for electro-catalysis, but also a key technological challenge since practical implementation of DEFC technology is contingent on its ability to selectively oxidize ethanol into CO2 to achieve exceptional energy density through 12-electron transfer reaction. Here, we present comprehensive in situ potentiodynamics studies of CO2 generation during the EOR on Pt, Pt/SnO2 and Pt/Rh/SnO2 catalysts using a house-made electrochemical cell equipped with a CO2 microelectrode. Highly sensitive CO2 measurements enable the real time detection of the partial pressure of CO2 during linear sweep voltammetry measurements, through which electro-kinetics details of CO2 generation can be obtained. In situ CO2 measurements provide the mechanistic understanding of potentiodynamics of the EOR, particularly the influence of ∗OH adsorbates on CO2 generation rate and selectivity. Density functional theory (DFT) simulations of Pt, Pt/SnO2, and Pt/Rh/SnO2 surfaces clarify reaction details over these catalysts. Our results show that at low potentials, inadequate ∗OH adsorbates impair the removal of reaction intermediates, and thus Pt/Rh/SnO2 exhibited the best performance toward CO2 generation, while at high potentials, Rh sites were overwhelmingly occupied (poisoned) by ∗OH adsorbates, and thus Pt/SnO2 exhibited the best performance toward CO2 generation.

Insight into carbon formation from acetic acid decomposition over Pd(100) via density functional theory calculations

The mechanism of carbon deposition in acetic acid/palladium system is of great research significance in the catalytic field. In order to illustrate the plausible carbon formation routes, a systematic survey on the stepwise decomposition from adsorbed acetic acid to atomic carbon on Pd(100) was conducted via density functional theory calculations. A complex reaction network including OH bond scission reaction and various CH and CC bond scission reactions was built and the relevant structural and energetic properties were calculated. The results show that OH bond breaking is very possible for CH3COOH, that CC bond breaking is always more favorable than CH bond breaking for CHxCOO (x = 1–3), and the dehydrogenation of CHx (x = 1–3) is more likely to proceed than most of other reactions. The most possible pathway for the formation of carbon monomer was proposed based on the analysis of the reaction network and it features the decarbonation of CH3COO to CH3 as the rate-limiting step.

Probing ethanol oxidation mechanism with in-situ FTIR spectroscopy via photodeposited Pt nanoparticles onto titania

Hybrid Pt/TiO2-C catalysts were synthesized via photodeposition in this study in order to increase the kinetics and the carbonate yield of the Ethanol Oxidation Reaction. Photodeposition was chosen because it was believed that the Pt nanoparticles would deposit predominately on top of the oxide sites, which would change the reactivity of the Pt nanoparticles. First, TiO2-C composites with varying TiO2 mass percentages were synthesized by sol gel using Vulcan Carbon XC-72R and titanium isopropoxide as precursors. The composites were dispersed in isopropanol and mixed with Chloroplatinic Acid such that the final Pt concentration was 20% by weight. This mixture was illuminated with UV light for 3h and the Pt/TiO2-C catalysts were recovered. Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) analysis showed that the Pt photodeposition was almost quantitative and XRD patterns showed that the average particle size ranged from 4 to 5nm. XPS Spectra showed that the Pt nanoparticles shifted to lower binding energies as TiO2 concentration increased, whereas Ti binding energies shifted to higher values with higher TiO2 concentrations. The synthesized catalysts showed increased current density in Linear Sweep Voltammetry when compared to a commercial Pt/C catalyst experiments which was attributed to increased nucleophilicity on the Pt which allowed for kinetically easier nucleophilic attacks. In-situ FTIR studies showed that the bands attributed to carbonate vibrations were more intense on the synthesized catalysts. All of these experiments allowed us to conclude that the increased electron density facilitates nucleophilic attacks and CC bond breaking.

Hydrogen-plasma patterning of multilayer graphene: Mechanisms and modeling

We study the atomic-scale etching mechanisms of multilayer graphene, and the subsequent formation of nanopores, when exposed to downstream hydrogen plasma. Our molecular dynamics simulations based on reactive force-field potential reveal precise energy regimes for the transport of ions through, and selective etching of, individual graphene layers within the multilayer structure. Etching initiates with hydrogenation of the graphene basal plane, followed by localized CC bond breaking which leads to the formation of CH2, and subsequently, unstable CH3 bond configurations. We establish the basal plane and edge etching rates of the individual graphene layers as a function of ion energy, and introduce a micromechanics model to predict the 3D-patterned pore structure at experimental length- and time-scales. Our results demonstrate the development of columnar holes in multilayered graphene, which transition to stepped-edge holes at higher fluence due to cumulative effects of basal-plane etching. The contributions of thermal radicals and dehydrogenation effects on the hole growth process are discussed.