Small Catalyst Particles Research Articles

The facilitating effect of sulfide treatment coupled sol-gel method on NH3-SCR activity of Fe–Mn/TiO2 catalysts

The 5Fe–3Mn–S/TiO2-SG catalysts were synthesized by sulfide treatment coupled sol-gel method to develop new NH3-SCR catalysts with wide temperature window, good low-temperature activity and environment-friendly. The evolution of catalyst surface chemical state, morphology, structure, acidity and interaction forces were systematically investigated by XPS, BET, XRD, SEM, H2-TPR, NH3-TPD, UV, IR and steady-state kinetic tests. The influence of sulfide treatment coupled sol-gel method on NO conversion was explored. XRD, BET and SEM characterization revealed that sulfide treatment resulted in smaller catalyst particles and higher dispersion, which increased the specific surface area. XPS, NH3-TPD and steady-state kinetic tests results demonstrated that the sulfide treatment catalysts had a higher surface adsorbed oxygen (Oα) content, which could produce more oxygen vacancies on the catalyst surface, thus increasing the number of acid sites. H2-TPR and UV results demonstrated that the 5Fe–3Mn–S/TiO2-SG catalysts exhibited the strongest contact between the carrier and the active component. The 5Fe–3Mn–S/TiO2-SG catalyst obtained more than 80% NO conversion in the operational temperature range of 220–420 °C, according to the NH3-SCR reaction data. The temperature window was expanded by 120 °C compared to conventional Fe–Mn/TiO2 catalysts, and 98% conversion was achieved at 300 °C. Meanwhile, DFT calculations of the SO42--MnFe2O4(311) crystalline surface of the 5Fe–3Mn–S/TiO2-SG catalysts revealed that it could form stronger chemisorption for both NH3 and NO, which promoted the NH3-SCR reaction more effectively. The DFT calculation results and the experimental findings agreed well.

The Behavior of Carbon Dots in Catalytic Reactions

Since their discovery in 2004, carbon dots (CDs), with particle sizes < 10 nm, have found use in various applications, mainly based on the material’s fluorescent properties. However, other potential uses of CDs remain relatively unexplored when compared to other carbon-based nanomaterials. In particular, the use of CDs as catalysts and as supports for use in catalytic reactions, is still in its infancy. Many studies have indicated the advantages of using CDs in catalysis, but there are difficulties associated with their stability, separation, and aggregation due to their small size. This small size does however allow for studying the interaction of small catalyst particles with small dimensional supports, including the inverse support interaction. However, recent studies have indicated that CDs are not stable under high temperature conditions (especially >250 °C; with and without a catalyst) suggesting that the CDs may agglomerate and transform under some reaction conditions. The agglomeration of the metal in a CD/metal catalyst, especially because of the CDs agglomeration and transformation at high temperature, is not always considered in studies using CDs as catalysts, as post-reaction analysis of a catalyst is not always undertaken. Further, it appears that under modest thermal reaction conditions, CDs can react with some metal ions to change their morphology, a reaction that relates to the metal reducibility. This review has thus been undertaken to indicate the advantages, as well as the limitations, of using CDs in catalytic studies. The various techniques that have been used to evaluate these issues is given, and some examples from the literature that highlight the use of CDs in catalysis are described.

Critical dehydrogenation steps of perhydro-[formula omitted]-ethylcarbazole on Ru(0001) surface

Understanding of the critical atomistic steps during the dehydrogenation process of liquid organic hydrogen carriers (LOHCs) is important to the design of cost-efficient, high-performance LOHC catalysts. Based on the density functional theory (DFT) we studied the thermodynamics and kinetics of the complete dehydrogenation path of perhydro-N-ethylcarbazole (12H-NEC) on Ru(0001) surface, involving the adsorption of 12H-NEC, the discharge of H ions onto Ru surface, and the desorption of H2 and hydrogen-lean NEC. It was found that the bonding of nH-NEC is significantly strengthened for n≤4 because of the flat aromatic ring. Although the whole dehydrogenation process is endothermic, the release of H from nH-NEC, with H adsorbed onto the Ru surface, was found to be exothermic. The desorption of flat, hydrogen-lean NEC, which costs ∼255 kJ/mol, was identified as the most energy demanding step. In addition, the effect of surface morphology on adsorption was studied based on an amorphous surface model. Overall, the results imply more efficient dehydrogenation could be achieved from relatively weak bonding of NEC to catalysts, either through engineering catalyst surface (such as surface defects or smaller catalyst particles) or different catalyst materials. Our calculations also revealed possible dealkylation at elevated temperatures.

Dynamic modelling of trickle bed reactor: Case study of arabinose oxidation

Trickle beds are among the most used reactors in different sectors of chemical industries. In this work the aim was to develop a general heterogeneous multiscale model for continuous trickle bed reactors, which enables the calculation of instantaneous concentration and temperature changes as well as the stationary behaviour of the reactor. The model development was based on solving simultaneously both the energy and mass balances for the continuous gas and liquid phases and for the stagnant catalyst particles. Mass transfer coefficients and pressure drop equations from well-established correlations were used. The developed model is aimed to be as general as possible in order to be used as a framework for other kind of bed reactors and arbitrary reaction schemes.The model can be simplified taking into consideration only one or two phases, and in this case it was applied to catalytic sugar oxidation to sugar acid and the effect of catalyst shape and size was investigated. Simulation results revealed that complete sugar conversion was achieved only for small catalyst particles, also the length of the reactor affects the conversion of arabinose more than the residence time or the bed radius: in fact for much bigger particles the conversion can also be achieved for longer reactor beds.

(Invited) Tuning Ag Nanoparticle Size for Selective Electrocatalytic Reduction of CO2 to CO

Coinage metals (Au, Ag and Cu) have shown propensity to reduce CO2 under electrochemical condition. For Au and Cu, nanoparticle size has been used as a lever to tune their activity and selectivity and it was found that the competing hydrogen evolution reaction (HER) becomes an issue for small catalyst particles. For the Ag case, which has been shown to produce CO, the effect of the particle size remains a subject of ongoing discussion because of the lack of thorough benchmark studies. In this presentation, we highlight our detailed investigation of electrochemical CO2 reduction on Ag to ascertain whether size variation can be used to tune the reactivity of the catalyst material. Our combined density functional theory, microkinetic modeling, and experiment demonstrate a strong size-dependence for pristine Ag particles in the sub-10 nm range. The modeling reveals that the enhanced activity can be correlated to the population of a moderately high index facet. Experimental results validated these predictions and we identified an optimal particle diameter that balanced selectivity and activity. The availability of synthetic method to make Ag nanoparticle with different sizes and predictive computational methods that factor in the kinetic aspects could potentially enhance future outlook for material design.

Effect of Co-Doping on Cu/CaO Catalysts for Selective Furfural Hydrogenation into Furfuryl Alcohol.

Cu/CaO catalysts with fine-tuned Co-doping for excellent catalytic performance of furfural (FAL) hydrogenation to furfuryl alcohol (FOL) were synthesized by a facile wetness impregnation method. The optimal Co1.40Cu1/CaO catalyst, with a Co to Cu mole ratio of 1.40:1, exhibited a 100% FAL conversion with a FOL yield of 98.9% at 100 °C and 20 bar H2 pressure after 4 h. As gained from catalyst characterizations, Co addition could facilitate the reducibility of the CoCu system. Metallic Cu, Co-Cu alloys, and oxide species with CaO, acting as the major active components for the reaction, were formed after reduction at 500 °C. Additionally, this combination of Co and Cu elements could result in an improvement of catalyst textures when compared with the bare CaO. Smaller catalyst particles were formed after the addition of Co into Cu species. It was found that the addition of Co to Cu on the CaO support could fine-tune the appropriate acidic and basic sites to boost the FOL yield and selectivity with suppression of undesired products. These observations could confirm that the high efficiency and selectivity are mainly attributed to the synergistic effect between the catalytically active Co-Cu species and the CaO basic sites. Additionally, the FAL conversion and FOL yield insignificantly changed throughout the third consecutive run, confirming a high stability of the developed Co1.40Cu1/CaO catalyst.

Under-coordinated AlF3 clusters confined in carbon matrix with robust sintering resistance for dehydrofluorination of hydrofluorocarbons

The development of catalysts for the resource utilization of potent greenhouse gases, hydrofluorocarbons (HFCs) by catalytic pyrolysis is of great significance to alleviate the greenhouse effect. Fabricating small catalyst particles with high specific surface area leading to more Lewis acid sites is the effective strategies to achieve highly functional catalysts. However, catalysts tend to sinter at elevated temperatures. Herein, we synthesized carbon matrix confined Al2O3 clusters via the calcination of MIL-53-Al under N2 atmosphere. Then the Al2O3 clusters were in situ fluorinated and turned into AlF3 clusters accordingly. The derived carbon confined AlF3 clusters exhibited outstanding sintering resistance even following thermal treatment at 600 °C. Moreover, the carbon confined AlF3 clusters presented superior catalytic performance for 1,1-difluoroethane (HFC-152a) conversion with near 40% higher than that of AlF3 prepared by traditional precipitation. The excellent catalytic activity and stability were mainly ascribed to the abundant under-coordinated Al species with strong interaction with carbon matrix and high specific surface area. Thus, in this paper, we developed new practicable method to synthesize highly efficient Lewis acid catalysts with strong sintering resistance and abundant acid sites.

Search for the Microwave Nonthermal Effect in Microwave Chemistry: Synthesis of the Heptyl Butanoate Ester with Microwave Selective Heating of a Sulfonated Activated Carbon Catalyst

The heptyl butanoate ester was synthesized from butanoic acid and heptanol in a heterogeneous medium in the presence of sulfonated activated carbon (AC-SO3H) catalyst particles subjected to microwave irradiation, which led to higher conversion yields (greater product yields) than conventional heating with an oil bath. The advantage of the microwaves appeared only when the moisture content in the butanoic acid batch(es) was high, suggesting that, unlike conventional heating, the reverse reaction caused by the moisture content and/or by the byproduct water was suppressed by the microwaves. This contrasted with the results that were found when carrying out the reaction in a homogeneous medium in the presence of the 2,4,6-trimethylpyridinium-p-toluene sulfonate (TMP-PTS) catalyst, as product yields were not improved by microwave heating relative to conventional heating. The removal of moisture/water content in the reaction solution was more pronounced when the reactor was cooled, as the reaction yields were enhanced via selective heating of the heterogeneous catalyst. A coupled electromagnetic field/heat transfer analysis gave credence to the selective heating of the AC-SO3H catalyst, which was further enhanced by cooling the reactor. It was deduced that unforeseen impurities and local high-temperature fields generated on the surface of small fine catalyst particles may have had an effect on the microwave chemistry such that the associated phenomena could be mistaken as originating from a nonthermal effect of the microwaves. Accordingly, it is highly recommended that impurities and selective heating be taken into consideration when examining and concluding the occurrence of a microwave nonthermal effect.

Hydrogenolysis of N-Benzylcyclohexylamine: A Support Specific ‘Nano Effect’

The hydrogenolysis of N-benzylcyclohexylamine (NBCA) was carried out at low temperature and pressure using series of Pd/SiO2 catalysts having Pd contents between 0.5 and 10%. Three different silica supports were used, two of them having pore diameters of 60A and 40A and one an amorphous material. In the hydrogenolysis of NBCA over the Pd/SiO2 (60A) series of catalysts there was a slight increase in the reaction rate on gong from the 10% Pd to the 2% Pd catalysts. This was followed by significant rate increases using the 1% Pd, 0.75% Pd and 0.5% Pd catalysts. It is proposed that this unexpectedly large rate increase observed using the catalysts having the smallest Pd particles was the result of a true ‘nano effect’. The rates of debenzylations run over the Pd/SiO2 (40A) series of catalysts steadily increased with the use of the 10% Pd to the 2% Pd catalysts, a trend observed for some Structure Sensitive reactions, though, in this case, there was also a rate decrease using the 1% Pd catalyst even though the Pd particles in this catalyst were smaller than the others. No relationship was observed between reaction rate and Pd composition of the amorphous silica supported catalysts. It is commonly accepted that the nano effect is the result of an interaction between the small catalyst particles and the support so the electronic character of the support could have an influence on the surface electrons of the catalyst and, thus, modify its reaction capabilities.

Packed Periodic Open Cellular Structures – an Option for the Intensification of Non-Adiabatic Catalytic Processes

Conductive structured catalysts offer significant potential for the intensification of gas-solid catalytic processes owing to their enhanced heat transfer properties. A major drawback is the limited catalyst inventory. Recently, packed foams were proposed to overcome the catalyst inventory limitation. The effectiveness of this concept was proven at lab-scale for intensified reactors filled with small catalyst particles. When adopting commercial foams and industrial-scale catalyst pellets, however, poor packing efficiencies are expected, limiting the potential of this concept.Similarly to foams, Periodic Open Cellular Structures (POCS) grant high heat transfer rates thanks to substantial heat conduction in their solid matrix. Additively manufactured POCS additionally offer great design flexibility. This allows for using a wider range of pellet sizes. In this work, particle packed POCS are introduced and packing efficiencies are systematically studied. Pressure drop in packed POCS is also analyzed and a suitable correlation is proposed. The heat transfer associated with this innovative reactor solution is investigated by performing non-reactive heat transfer experiments. Based on these experiments, a predictive heat transfer model is established and successfully validated with experimental data. The enormous potential of packed POCS for process intensification is illustrated by a case study of a Sabatier pilot reactor.

Facile catalyst deposition using mists for fluidized-bed production of sub-millimeter-long carbon nanotubes

We developed a facile mist deposition method that yields nanometer-thick catalyst films on ceramic beads using aqueous solution of metal nitrates as a low cost catalyst precursor through two different strategies: (a) using a monolayer of a mixture of Fe(NO3)3 and Al(NO3)3 (Fe + Al) and (b) using a bilayer of Fe(NO3)3 on top of the mixture of Fe(NO3)3 and Al(NO3)3 (Fe/(Fe + Al)). In the fluidized bed, the catalyst precursor films were converted into Fe nanoparticles on an AlOx layer by thermal annealing and CNTs were synthesized by chemical vapor deposition. The yield and specific surface area of the resulting CNTs were strongly influenced by the deposition methods. The bilayer deposition strategy showed an improved controllability in acquiring small catalyst particles at a high density, which obtained high yields of CNTs with large specific surface area. As a result, CNTs of 7.5 nm in diameter, triple-wall on average, and 0.6 mm in length were synthesized by employing the fluidized bed chemical vaper deposition technique, suggesting a new way for the high-yield production of long few-wall CNTs at reasonable cost.

Interface of Hydrated Perfluorosulfonic Acid Electrolyte with a Platinum Catalyst: Structural Analyses with Dissipative Particle Dynamics Simulations

Dissipative particle dynamics (DPD) simulations were performed to study structures of hydrated perfluorosufuonic acids (PFSA) in contact with platinum surfaces. Two types of interfacial systems were simulated, where PFSA molecules interact with a cube and a slab of platinum, respectively representing a small catalyst particle used in regular fuel cells and a platinum substrate popularly used in model system experiments. The calculated results suggest that the two systems form a shell structure and a layer structure, respectively, of PFSA components near the platinum surfaces. The water component covers the platinum surfaces popularly in both systems, of which the coverage depends on the hydration levels of PFSA. Detailed analyses revealed that the water component networks are quite different in the two systems, which are three-dimensionally connected in the systems with a platinum cube, while disrupted by hydrophobic components in the systems with a platinum slab.

Influence of the formation of short-chain olefins by manganese/cobalt-catalyzed Fischer–Tropsch synthesis on the selectivity and effective reaction rate

For cobalt catalysts with manganese as promoter, a high selectivity to olefins is found in low-temperature FTS over small catalyst particles. With industrial scale particles severe changes in selectivity and an increase of reaction rate is found.

High production circulating fluidized bed polymerization reactors

This paper is an extension of the Gidaspow invention relating to fluidized bed polymerization reactors, such as the UNIPOL reactor or the later reactors containing cooling tubes. It shows that the polymer production rate can be increased by two or more orders of magnitude over that obtained in the UNIPOL reactor due to the orders of magnitude decreased adiabatic temperature rise. The CFD design of several size polyethylene reactors is described. In all cases the small catalyst particle concentrations are high at the walls showing that electrostatics is not the only mechanism for sheet formation.

Particle Size and Morphology of Carbon Dioxide Reduction Electrocatalysts Fabricated By Pulse/Pulse-Reverse Electrodeposition

A variety of techniques for management of carbon dioxide emissions from power generation facilities and other industrial sites have been under active investigation for decades, in an effort to mitigate the environmental impacts of these releases. Once such approach is electrochemical reduction, which treats the waste CO2 as a source material for the production of value-added materials. Currently, the most promising form factor for this electrocatalytic application appears to be a stack-based system, where catalyst is immobilized on porous media that is interfaced with a liquid or solid electrolyte, and the reactant carbon dioxide is delivered to the active region by gaseous diffusion, which is orders of magnitude faster that diffusion though aqueous media. Various carbonaceous reduction products can be created depending on the composition, size, and microstructure of the catalyst particles, including formic acid/formate, carbon monoxide, alcohols, and hydrocarbons. In general, smaller catalyst particles, ideally in the nanoparticulate (« 1 μm) range, tend to yield superior catalytic performance, due to a combination of factors such as a higher density of exposed grain boundaries and a higher fraction of exposed crystalline facets that are uncommon in particles of micron size or larger. This talk will survey recent work illustrating the ability of pulse/pulse-reverse electrodeposition processes to tune the size of particles applied to gas-diffusion electrode substrates, with a primary focus on two single-metal catalyst materials relevant to carbon dioxide electroreduction: tin and copper. The former is a catalyst primarily for formic acid production, while the latter is unique among single-metal catalysts as the only element known to date to produce significant amounts of hydrocarbons and/or alcohols. Particle morphology and representative particle size will be discussed as a function of pulsed electrodeposition waveform parameters, with the goal of highlighting overarching trends across the waveform space.

Investigation of Pt-Nb-NbOx Loaded on TiN As Cost-Effective Electrocatalyst for Polymer Electrolyte Membranes Fuel Cell

Proton Exchange Membrane Fuel Cells (PEMFC) play a key hole for sustainable energy, due its low temperature operation and high potential for automotive and stationary-application. Although, catalyst degradation remains one of the main challenges for PEMFC commercialization. The commercial available electrocatalyst based on Pt/C is susceptible to Pt dissolution and carbon supports corrosion [1]. In this context, we have defined an alternative electrocatalyst for PEM Fuel Cells based on Pt/Nb-NbOx loaded on TiN nanoparticles. Alloying Pt to Nb-NbOx is expected to reduce materials costs by lowering Pt amount [2], while the use of TiN nanoparticles as catalyst support is expected to increase support stability and durability [3]. The Pt/Nb-NbOx loaded on TiN electrocatalyst was successfully synthesized in a one-step process using Reactive Spray Deposition Technology (RSDT). RSDT is breakthrough process for deposition of small catalyst particles with significantly lower production costs while maintaining maximum efficiency [4]. A homogeneous nanostructured electrocatalyst layer of ca. 5 μm thickness was grown on nafion membrane (Figure 1 a). A Pt/Nb-NbOx catalyst content of 7.6 wt.% and 15 wt.% with 0.045 mg∙cm-2 and 0.90 mg∙cm-2 Pt loading respectively were achieved. The catalyst composition was measured by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and double-checked by X-ray Energy Dispersive Spectroscopy (EDS). The electrocatalyst activity was evaluated by Rotating Disk Electrode toward Oxygen Reduction Reaction (ORR). RDE results (Figure 1 b) show that an half-wave potential of 78 mV and 89 mV was achieved for 7.6 wt.% and 15 wt.% Pt/Nb-NbOx catalyst, respectively. Preliminary results suggest that Pt/Nb-NbOx loaded on TiN nanoparticles have electrochemical performance comparable to the state of art Pt/C electrocatalyst [5] and may be a suitable catalyst for PEMFC. Further evaluation regarding Pt-Nb-Ti metal and metal oxide interactions as well as electrochemical performance and durability are in the way and will be discussed.

Investigation of disorder in carbon encapsulated core-shell Fe/Fe3C nanoparticles synthesized by one-step pyrolysis

Fe/Fe3C (core) - graphite (shell) nanoparticles embedded in micron sized amorphous carbon globules were synthesized by pyrolysis route in a closed reactor. A large number of such nanoparticles were observed to be distributed in the inner section of each globule covered by amorphous carbon in the outer regions. The distribution of nanoparticles varies according to the reaction-temperature-profile of the furnace during the synthesis process. These particles catalyze the formation of the graphitic coating on their surface, due to metastable nature of Fe3C. The globules which contain smaller catalyst particles were found to contain defective- and less amount of graphitic carbon and large amount of amorphous carbon. We observed that for low synthesis temperature conditions the globules contain a thicker shell of amorphous carbon (without any catalyst particle). Furthermore, the amount of disorder in the graphitic layer is determined by the number and size of the (Fe/Fe3C) catalyst particles and reaction-temperature. The disorder in the graphitic layer on the particles can be potentially important for the catalytic behaviour of these particles.

Development and Evaluation of Ir Based Anode Electrocatalysts for Water Electrolysis

Introduction Hydrogen production through PEM type water electrolysis followed by hydrogen storage and use has been focused on as one of the efficient uses of renewable energy. Although PEM type water electrolyzer has an advantage on reduced ohmic resistance between two electrodes, it has also a disadvantage that common carbon supports cannot be used in order to disperse small catalyst particles under the high potential condition over 1.5 V at the anode. That leads to low active surface area of anode electrocatalysts, resulting in high cost. Therefore, the purpose of this study is to develop carbon-free porous anode electrocatalysts with high active surface area. So far, our group has been working on mesoporous carbon materials for PEFC studies1, and we have found that such a porous structure is kept even after being built into the device and can improve the mass transfer within catalyst layers. Then, basic concepts of mesoporous carbon are applied to this study. We propose development of carbon-free porous metal catalysts to enhance the performance of water electrolyzer. Experimental method Ir(acac)3 and Pluronic F127 were used as a metal precursor and a template to form a porous structure, respectively. A mixture of the metal precursor, solvent, and surfactant was heated up by step-by-step treatments in N2 or Air atmosphere to make the porous structure. After the fundamental material characterizations of the resulting Ir material, electrochemical measurements were performed using a common half-cell setup in the acidic solution. Oxygen evolution reaction (OER) activity was evaluated as anode electrocatalysts. Also, membrane electrode assembles (MEAs) were developed, and then a single cell performance was evaluated. Results and discussion Based on nitrogen sorption measurements and a SEM image as shown in Figure 1, the porous structure consisted by aggregation of particles was confirmed for the obtained Ir material. The resulting pore diameter was mostly smaller than 70 nm. When OER activity of porous Ir material was measured and compared with commercial IrO2 electrocatalyst (Figure 2), initial OER activity was lower than IrO2. This was due to fact that porous Ir material is mainly composed by Ir metal, which was confirmed by XRD. Then, the surface of porous Ir was activated via electrochemical oxidation. As a result, activated porous Ir/IrOx showed equivalent OER activity to commercial IrO2 as seen in Figure 2. Even though OER activity was just equivalent to commercial IrO2 as powder, the difference was seen when electrocatalysts were built into MEAs. The details of IV characteristics will be discussed. Furthermore, we have also worked on durability analyses against potential fluctuation derived by renewal energy, which will be also discussed. Reference (1) Hayashi, et al., Electrochim. Acta, 53, 6117-6125 (2008). Figure 1

Interface of Hydrated Perfluorosulfonic Acid Electrolyte and Platinum Catalyst: Dissipative Particle Dynamics Simulation Model

Polymer electrolyte fuel cells (PEFC) are expected to be used widely in the future as a non-polluting power source in various applications. PEFC applications are only limited currently however, as PEFCs are still not competitive with existing power sources in energy efficiency and cost. One of the most popular forms of PEFC are composed of an electrolyte of hydrated perfluorosulfonic acid (PFSA), and carbon based electrodes that support small catalyst particles (typically Pt) on the surface. The global performance of PEFC of this type is governed by the rate of red-ox reactions on the catalyst surface, which are affected by molecular level dynamics of fuel, oxidants, and protons in the electrolyte near the catalyst surface. We need deeper understanding on this interfacial structures for new insights into the mechanisms that control the electrochemical surface processes. Several structure models have been proposed for the bulk electrolyte, while only little is understood as to its structure near the catalyst surface so far. In this study, to investigate the interfacial system of hydrated PFSA and platinum surface, we constructed models of this system for dissipative particle dynamics (DPD) simulations. DPD simulation is a kind of coarse-grained simulation which is used to study mesoscopic systems, typically consisting of macromolecules like polymers and biomolecules. We coarse grained the simulation system with DPD particles corresponding to PFSA segments A-C (see Fig.1), those grouping four water molecules (denoted as W), and those grouping ~8 platinum atoms (Pt). The catalyst surface was represented by a fixed slab of the Pt particles forming a simple lattice. We used soft potentials constructed via quantum chemical calculations by Okuwaki et al. [1] for interactions of DPD particles A-C and W; while we newly constructed soft potentials for the interactions of Pt with other DPD particles by analyzing their affinities via all-atom classical MD simulations for some small systems. For these all-atom MD simulations, we derived some intermolecular potential functions by first principles calculations. Details of our DPD simulations as well as the interaction model constructions will be presented in the conference session (a snapshot is displayed in Fig. 2). A portion of this research was supported by MEXT within the priority issue 6 of the FLAGSHIP2020 project (Project ID: hp160226, hp170253,hp180187). [1] K. Okuwaki et al., JSAP spring meeting (2016) 20a-W323-6. Figure 1

Mesoporous Metal Electrocatalysts for the Oxygen Evolution Reaction

Introduction Development of anode electrocatalys for the PEM type water electrolyzer is challenging since carbon supports cannot be used in order to disperse small catalyst particles under the high potential condition over 1.5 V. Without carbon supports, electrocatalysts result in relatively low active surface area and low activity. Our group has been working on mesoporous materials for PEFC and has found that mesoporous materials can keep their porous structure even after being built into the device. Based on the similar idea used in our PEFC studies, we propose development of carbon-free mesoporous metal electrocatalysts with high active surface area to increase the efficiency of water electrolyzer cells. In this study, mesoporous platinum and iridium materials were particularly developed, and their oxygen evolution reaction (OER) activity was evaluated. Experimental method Mesoporous platinum and mesoporous iridium materials were synthesized using Pt(acac)2 or Ir(acac)3 as a metal precursor and Pluronic F127 as a surfactant. After mixing the surfactant and metal precursor, the resulting mixture was heated up under N2 or Air atmosphere to decompose Pluronic F127 and make the mesoporous structure. Their electrochemical measurements were performed using a common half-cell setup in the solution, in order to evaluate OER activity. The durability against high potential like 1.8 V was also analyzed. Results and discussion The resulting platinum and iridium materials were confirmed to have the randomly oriented porous structure constructed by aggregation of Pt and Ir/IrOx nanoparticles, respectively. The pore diameter was found mostly smaller than 100 nm. With these porous metal materials, OER activity was evaluated. Regarding platinum based materials, the initial activity resulted in the same as a standard Pt/KB electrocatalyst, TEC10E50E, even though ECSA was six times higher for Pt/KB. However, for their durability, as expected, Pt/KB lost most of OER activity owing to carbon corrosion. Consequently, carbon-free porous Pt electrocatalyst with high activity and durability was successfully prepared. Similarly, a porous iridium electrocatalyst has been prepared, and its OER activity will be discussed.