Abstract Despite progress in the understanding of how nanostructuring affects activity of heterogeneous catalysts, there are still fundamental questions to be answered. Do nanoparticle edges have the same catalytic properties as steps on single-crystal surfaces? How much does the increased structural flexibility of nanoparticles contribute to their activity? How do reaction barriers depend on the nanoparticle size? Herein we address these questions regarding an exemplary reaction sequence of complete methane dehydrogenation. Using density functional theory methods we calculate energy profiles of this reaction on edges of 1.2 nm large Pd 79 and 1.6 nm large Pd 140 particles as well as on Pd(1 1 1) and steps on Pd(2 1 1) single-crystal surfaces. The barriers of the two slowest reaction steps, CH 4 → CH 3 + H and CH → C + H, notably decrease in the following series of substrates: Pd(1 1 1) ≳ Pd(2 1 1) > Pd 140 > Pd 79 . Importantly, these barriers differ by ⩾20 kJ/mol on Pd 140 and Pd(2 1 1), whereas the differences between the barriers on Pd(1 1 1) and Pd(2 1 1) are only ⩽11 kJ/mol. Also, the structural flexibility contributes to higher reactivity several times stronger for Pd 79 than for Pd(1 1 1). All calculated elementary steps follow Bronsted–Evans–Polanyi relationships. This study advances the understanding of heterogeneous catalysis by shedding light on several fundamental questions concerning structure–property relationships in nanostructured catalysts.
In this paper, we study the dynamics of cylindrical armoured bubbles excited by mechanical vibrations. A step by step transition from cylindrical to spherical shape is reported as the intensity of the vibration is increased, leading to a reduction of the bubble surface and a dissemination of the excess particles. We demonstrate through energy balance that nonspherical armoured bubbles constitute a metastable state. The vibration instills the activation energy necessary for the bubble to return t...
To screen heterogeneous catalysts in silico, the linear energy relationships derived from the Bronsted–Evans–Polanyi principle are extremely useful. They connect the reaction energy of a given elementary step to its activation energy, hence providing data that can be fed to kinetics models at a minimal cost. However, to ensure reasonable predictions, it is essential to control the statistical error intrinsic to this approach. We derived several types of linear energy relations for a series of CH...
#2Farzad Behafarid(UCF: University of Central Florida)H-Index: 23
Abstract In recent years, the field of catalysis has experienced an astonishing transformation, driven in part by more demanding environmental standards and critical societal and industrial needs such as the search for alternative energy sources. Thanks to the advent of nanotechnology, major steps have been made towards the rational design of novel catalysts. Striking new catalytic properties, including greatly enhanced reactivities and selectivities, have been reported for nanoparticle (NP) cat...
Last. Francesc Illas(University of Barcelona)H-Index: 85
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Rational design of improved transition metal based materials mostly relies on their electronic structure descriptors, typically estimated by density functional theory and so unduly affected by self-interaction or static correlation errors. Here we show for all 30 transition metals that original or width-corrected d-band centers, and Hilbert transform highest peak descriptors are unaffected by self-interaction, while poor treatment of static correlation by hybrid functionals leads to an unbalance...
Absorbed hydrogen can dramatically increase hydrogenation activity of Pd nanoparticles and was predicted to do so also for Pt. This calls for investigations of the energetic stability of absorbed H in Pd and Pt using nanoparticle models as realistic as possible, i.e., (i) sufficiently large, (ii) supported, and (iii) precovered by hydrogen. Herein, hydrogen absorption is studied in MgO(100)-supported 1.6 nm large Pd and Pt nanoparticles with surfaces saturated by hydrogen. The effect of surface ...
Diffusion of adsorbates on transition metal nanoparticles is a precursor process for heterogeneously catalyzed reactions, and as a result, an atomistic understanding of the diffusion mechanism is very important. We systematically studied adsorption and diffusion of atomic and diatomic species (H, C, N, O, CO, and NO) on nanometer-sized Pt and Cu nanoparticles with different sizes and shapes using density functional theory calculations. We show that nanoparticles bind adsorbates more strongly tha...
Heterogeneous catalysis is commonly governed by surface active sites. Yet, areas just below the surface can also influence catalytic activity, for instance, when fragmentation products of catalytic feeds penetrate into catalysts. In particular, H absorbed below the surface is required for certain hydrogenation reactions on metals. Herein, we show that a sufficient concentration of subsurface hydrogen, Hsub, may either significantly increase or decrease the bond energy and the reactivity of the a...
Density functional theory calculations are performed to investigate oxygen dissociation on 116-atom truncated octahedron platinum particles. This work builds on results presented previously [Jennings et al., Nanoscale, 2014, 6, 1153], where it was shown that shell flexibility played an important role in facilitating fast oxygen dissociation. In this study, through investigation of the larger particle size, it is shown that oxygen dissociation on the (111) facet of pure platinum species is still ...
Platinum nanoparticle catalysts are used in a myriad of gas-phase, liquid-phase, and electrochemical reactions. Although a high catalytic activity is paramount, stability must also be guaranteed, especially when the nanoparticles are in contact with strongly bound adsorbates. Therefore, it is crucial to be able to accurately calculate adsorption-energy trends on Pt nanoparticles of multiple sizes and morphologies using ab initio methods at affordable computational expenses. Here, through an ener...
Platinum is a prominent catalyst for a multiplicity of reactions because of its high activity and stability. As Pt nanoparticles are normally used to maximize catalyst utilization and to minimize catalyst loading, it is important to rationalize and predict catalytic activity trends in nanoparticles in simple terms, while being able to compare these trends with those of extended surfaces. The trends in the adsorption energies of small oxygen- and hydrogen-containing adsorbates on Pt nanoparticles...
Reducing the temperature for methane activation is an important objective that would benefit many technological applications. In this work, we explore the possibility to achieve this goal using sin...
Last. L.P. Teh(UKM: National University of Malaysia)H-Index: 12
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The production of hydrogen to be used as an alternative renewable energy has been widely explored. Among various methods for producing hydrogen from hydrocarbons, methane decomposition is suitable for generating hydrogen with zero greenhouse gas emissions. The use of high temperatures as a result of strong carbon and hydrogen (C–H) bonds may be reduced by utilizing a suitable catalyst with appropriate catalyst support. Catalysts based on transition metals are preferable in terms of their activen...
Abstract Hydrogen produced by thermocatalytic decomposition of methane is a promising approach to reduce the greenhouse gas effects on environment. A series of experiments were carried out to study the intrinsic kinetic reaction rate, reaction mechanism and catalyst deactivation in methane decomposition using electroless nickel plating on SBA-15 as the catalyst in a fixed bed reactor. The experiments were conducted under atmospheric pressure at a temperature range of 525-600 °C and different met...
Last. De Chen(NTNU: Norwegian University of Science and Technology)H-Index: 71
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Abstract CO2 reforming of methane (DRM) is a promising reaction for the carbon cycle in nature. Ni was found to be active in this process. However, single component Ni catalysts cannot meet the stability, activity and selectivity demands simultaneously. This paper presents a systematical density functional theory study to investigate the catalytic performance of Ni@Pt(1 1 1) core-shell surface compared with Ni(1 1 1) and Pt(1 1 1) in methane dry reforming. Two ways of O* and OH* assisted CH4 deh...
Abstract Because of their high theoretical specific capacities, transition metal phosphides have been interested as promising anode candidates for lithium-ion batteries. However, high irreversible capacity reduction and pulverization of the transition metal phosphide structure caused by volumetric expansion during cycling obstruct the commercialization of transition metal phosphides as an anode for lithium-ion batteries. In this study, we fabricated a nanostructured electrode consisting of nano-...
Last. Qiang Song(NPU: Northwestern Polytechnical University)H-Index: 26
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A density functional theory (DFT) study was employed to explore the mechanism of the conversion of methane to benzene in chemical vapor infiltration (CVI) based on the concluded reaction pathways from C1-species to C6-species. The geometry optimization and vibrational frequency analysis of all the chemical species and transition states (TS) were performed with B3LYP along with a basis set of 6–311 +G(d, p), and Gaussian 09 software was used to perform the study. The rate constants were calculate...
Advances in heterogeneous catalysis are being enabled by ever-growing control over the structure of surfaces at the atomic scale. In order to propose new defected catalytic surfaces, there is a need to systematically search through a combinatorial number of possible atom arrangements. Mathematical optimization is well-suited to search this design space with algorithms that provide guarantees of optimality that are not possible with sampling algorithms. In this work, we develop several formulatio...
#2Henrik Grönbeck(Chalmers University of Technology)H-Index: 50
Understanding reaction kinetics over metal-nanoparticles is central in technical catalyst design. In this Perspective, we compare computational methods to analyze and model reaction kinetics on metal nanoparticles. We discuss energy-barrier and Sabatier analysis, mean-field microkinetic modeling, and kinetic Monte Carlo simulations. By explicit simulations, we show that reactions on metal-nanoparticles are characterized by long-range kinetic couplings, which requires methods that consider couple...
