Identification of general linear relationships between activation energies and enthalpy changes for dissociation reactions at surfaces

Seeds and Potentials Mediated Synthesis of High-Index Faceted Gold Nanocrystals with Enhanced Electrocatalytic Activities

Because high-index facets (HIFs) possess high surface energy, the metal nanoparticles enclosed with HIFs are eliminated during their growth in a conventional shape-controlled synthesis due to the thermodynamics that drives the particles minimizing their total surface energy. This study develops a double-step potential method to prepare an unprecedentedly stellated Au nanocrystals (NCs) bounded by high-index {711} and {331} facets in deep eutectic solvent (DES) medium. The formation of Au NCs bounded by HIFs was systematically studied. It has demonstrated that the shapes of Au NCs are strongly dependent on the size of seeds and the growth potentials as well as the urea adsorbates in the DES. By adjusting the size of seeds and the growth potentials, the stellated Au NCs can be transformed into concave hexoctahedra (HOH) with high-index {421} facets and concave trisoctahedra (TOH) with high-index {991} facets. The electrocatalytic activities of the as-prepared Au NCs are evaluated by glucose oxidation. Thanks to HIFs having high density of atomic steps and kinks, the stellated, TOH, and HOH Au NCs exhibit higher electrocatalytic activity than that of the polycrystalline Au electrode, demonstrating that the steps and kinks serve as the active sites and play an important role in glucose electro-oxidation.

Confined catalysis under two-dimensional materials

Confined microenvironments formed in heterogeneous catalysts have recently been recognized as equally important as catalytically active sites. Understanding the fundamentals of confined catalysis has become an important topic in heterogeneous catalysis. Well-defined 2D space between a catalyst surface and a 2D material overlayer provides an ideal microenvironment to explore the confined catalysis experimentally and theoretically. Using density functional theory calculations, we reveal that adsorption of atoms and molecules on a Pt(111) surface always has been weakened under monolayer graphene, which is attributed to the geometric constraint and confinement field in the 2D space between the graphene overlayer and the Pt(111) surface. A similar result has been found on Pt(110) and Pt(100) surfaces covered with graphene. The microenvironment created by coating a catalyst surface with 2D material overlayer can be used to modulate surface reactivity, which has been illustrated by optimizing oxygen reduction reaction activity on Pt(111) covered by various 2D materials. We demonstrate a concept of confined catalysis under 2D cover based on a weak van der Waals interaction between 2D material overlayers and underlying catalyst surfaces.

An insight into methanol oxidation mechanisms on RuO2(100) under an aqueous environment by DFT calculations

In this work, we have studied methanol oxidation mechanisms on RuO₂(100) by using density functional theory (DFT) calculations and ab initio molecular dynamics (MD) simulations with some explicit interfacial water molecules. The overall mechanisms are identified as: CH₃OH* → CH₃O* → HCHO* → HCH(OH)₂* → HCHOOH* → HCOOH* → mono-HCOO* → CO₂*, without CO formation. This study provides a theoretical insight into C1 molecule oxidation mechanisms at atomic levels on metal oxide surfaces under an aqueous environment.

Identification of activity trends for CO oxidation on supported transition-metal single-atom catalysts

Identification of activity trends for CO oxidation on transition-metal single-atom catalysts by using E_ad(CO) and E_ad(O₂) as descriptors.

Surface restructuring of Cu-based single-atom alloy catalysts under reaction conditions: the essential role of adsorbates

The stabilities and catalytic performances of single-atom alloy (SAA) structures under the reaction conditions of acetylene hydrogenation are thoroughly examined utilizing density functional theory (DFT) calculations.

Thermodynamic assessment of the oxygen reduction activity in aqueous solutions

The hydrogen bonding of hydrophilic oxygen reduction intermediates to water has large effects on scaling relations and volcano plots.

Effect of alkyl branches on the thermal stability of quaternary ammonium cations in organic electrolytes for electrochemical double layer capacitors

The collective effect of the intrinsic properties of small quaternary ammoniums on their thermal stability is systematically investigated.

Insights into the mechanism of electrochemical ozone production via water splitting on the Ni and Sb doped SnO2 catalyst

The water-splitting mechanism for forming O₃ was studied using density functional theory.

Theoretical understanding on the selectivity of acrolein hydrogenation over silver surfaces: the non-Horiuti–Polanyi mechanism is the key

The significance of the non-Horiuti–Polanyi mechanism in understanding heterogeneous catalytic hydrogenation reactions is highlighted.

Selective hydrogenation of acetylene over Cu(211), Ag(211) and Au(211): Horiuti–Polanyi mechanism vs. non-Horiuti–Polanyi mechanism

The Horiuti–Polanyi and non-Horiuti–Polanyi mechanisms are thoroughly examined and compared for the hydrogenation of C₂ hydrocarbons using DFT calculations.

Significant enhancement of the selectivity of propylene epoxidation for propylene oxide: a molecular oxygen mechanism

As an attractive and environmentally friendly process for propylene oxide (PO) production, direct epoxidation of propylene (DEP) with molecular oxygen catalyzed by metal-based catalysts such as Ag and Cu has drawn much attention, but remains one of the biggest challenges in chemistry.

Size-dependence of carbon nanotube confinement in catalysis

An increasing number of studies have demonstrated that confinement within carbon nanotubes (CNTs) provides an effective approach for the modulation of catalysis. It was generally predicted that confinement became stronger with a decreasing diameter of CNTs. However, our present study here overturns the previous expectation: the influence on catalysis is not monotonic. Instead, it exhibits a volcano relationship with CNT diameter. Taking Pt catalyzing O2 conversion and Re catalyzing N2 conversion as probes using density functional theory, we show that only within tubes with an i.d. of ∼1 nm can the activity of metal clusters be enhanced to its maximum. Furthermore, confinement only enhances the catalytic activity of metals with strong intrinsic binding with reactants, whereas it is suppressed for those with weak binding. These findings shed further light on the fundamental effects of confinement on catalysis, and could guide more rational design of confined catalysts.

Reaction of CO, H2O, H2 and CO2 on the clean as well as O, OH and H precovered Fe(100) and Fe(111) surfaces

The adsorption and activation of CO, H₂O, CO₂ and H₂ on the clean as well as O, OH and H precovered Fe(100) surface at 0.25 ML coverage and Fe(111) surface at 0.33 ML coverage were computed (GGA-PBE) to investigate the catalytic activity of metallic iron.

ORR viability of alumina-supported platinum nanocluster: exploring oxidation behaviour by DFT

Despite abundant use of alumina-supported platinum nanoclusters as catalyst for various chemical reactions, their potential as an ORR catalyst is yet to be explored. Therefore, the present study aimed to assess the viability of alumina supported platinum clusters as ORR catalysts.

Establishing and Understanding Adsorption-Energy Scaling Relations with Negative Slopes

Adsorption-energy scaling relations are widely used for the design of catalytic materials. To date, only linear scaling relations are known in which the slopes are positive. Considering the adsorption energies of F, O, N, C, and B on transition metals, we show here that scaling relations with negative slopes also exist between certain adsorbates. The origin of such unconventional scaling relations is analyzed in terms of common descriptors such as d-band center, work function, number of outer electrons, electronic charge on the adsorbates, integrated crystal orbital overlap populations, and crystal orbital Hamilton populations. Conventional scaling relations are formed between adsorbates such as F, O, N, and C, which create ionic-like bonds with surfaces. Conversely, anomalous scaling relations are established between those and covalently bound adsorbates such as B. This widens the theory of adsorption-energy scaling relations and opens new avenues in physical chemistry and catalysis, for instance, in direct borohydride fuel cells.

PbTiO3(001) Capped with ZnO(112̅0): An ab Initio Study of Effect of Substrate Polarization on Interface Composition and CO2 Dissociation

Catalytic conversion of CO2 into useful chemicals is an attractive alternative to expensive physical carbon sequestration methods. However, this approach is challenging because current chemical conversion methods employ high temperatures or pressures, thereby increasing cost and potentially leading to net carbon positive processes. In this paper, we examine the interface properties of ZnO(112̅0)/PbTiO3 and its surface interaction with CO2, CO and O. We show that the stoichiometry of the stable interface is dependent on the substrate polarization and can be controlled by changing the growth conditions. Using a model reaction, we demonstrate that a dynamically tuned catalysis scheme could enable significantly lower-energy approaches for CO2 conversion.

Direct hydrodeoxygenation of raw woody biomass into liquid alkanes

Being the only sustainable source of organic carbon, biomass is playing an ever-increasingly important role in our energy landscape. The conversion of renewable lignocellulosic biomass into liquid fuels is particularly attractive but extremely challenging due to the inertness and complexity of lignocellulose. Here we describe the direct hydrodeoxygenation of raw woods into liquid alkanes with mass yields up to 28.1 wt% over a multifunctional Pt/NbOPO4 catalyst in cyclohexane. The superior performance of this catalyst allows simultaneous conversion of cellulose, hemicellulose and, more significantly, lignin fractions in the wood sawdust into hexane, pentane and alkylcyclohexanes, respectively. Investigation on the molecular mechanism reveals that a synergistic effect between Pt, NbOx species and acidic sites promotes this highly efficient hydrodeoxygenation of bulk lignocellulose. No chemical pretreatment of the raw woody biomass or separation is required for this one-pot process, which opens a general and energy-efficient route for converting raw lignocellulose into valuable alkanes.

Surface passivation of semiconducting oxides by self-assembled nanoparticles

Physiochemical interactions which occur at the surfaces of oxide materials can significantly impair their performance in many device applications. As a result, surface passivation of oxide materials has been attempted via several deposition methods and with a number of different inert materials. Here, we demonstrate a novel approach to passivate the surface of a versatile semiconducting oxide, zinc oxide (ZnO), evoking a self-assembly methodology. This is achieved via thermodynamic phase transformation, to passivate the surface of ZnO thin films with BeO nanoparticles. Our unique approach involves the use of Be_xZn_1-xO (BZO) alloy as a starting material that ultimately yields the required coverage of secondary phase BeO nanoparticles, and prevents thermally-induced lattice dissociation and defect-mediated chemisorption, which are undesirable features observed at the surface of undoped ZnO. This approach to surface passivation will allow the use of semiconducting oxides in a variety of different electronic applications, while maintaining the inherent properties of the materials.

Insights into the synergistic role of metal–lattice oxygen site pairs in four-centered C–H bond activation of methane: the case of CuO

Of the three mechanisms for activation of methane on copper and copper oxide surfaces, the under-coordinated Cu–O site pair mediated mechanism on CuO surfaces has the lowest activation energy barriers.

A systematic study on Pt based, subnanometer-sized alloy cluster catalysts for alkane dehydrogenation: effects of intermetallic interaction

The dehydrogenation of propane over platinum-based bimetallic nanoparticles is analyzed by the application of density functional theory to a series of tetrahedral Pt₃X cluster models.

Towards more accurate prediction of activation energies for polyalcohol dehydrogenation on transition metal catalysts in water

Polyols may be associated to a large catalytic reaction network. Brønsted–Evans–Polanyi (B.E.P.) relationships aim to easily predict activation barriers from reaction energies. Acting as a filter, such methods enable to quickly screen all the potential reaction intermediates and products.

Theoretical insights into the promotion effect of subsurface boron for the selective hydrogenation of CO to methanol over Pd catalysts

CO hydrogenation to methanol and methane on both Pd(211) and subsurface boron-modified Pd(211) are studied based on density functional theory calculations.

Effect of doping β-NiOOH with Co on the catalytic oxidation of water: DFT+U calculations

Electrocatalytic water splitting using energy from sunlight represents a promising strategy for clean, low-cost, and environmentally friendly production of H₂.

How molecular is the chemisorptive bond?

Scaling rules differ for early and late transition metals. Their electronic structure and topological bond analysis are shown.

Insights into the effect of Pt doping of Cu(110)/H2O for methanol decomposition: a density functional theory study

Density functional theory calculations with the periodic slab model were performed to investigate the methanol decomposition mechanism with different ratios of Pt doped into Cu(110)/H₂O surfaces.

A computational study of the competing reaction mechanisms of the photo-catalytic reduction of CO2 on anatase(101)

Three reaction pathways for the photocatalytic reduction of carbon dioxide to methane are investigated with density functional theory calculations.

Inferring Transition Rates of Networks from Populations in Continuous-Time Markov Processes

We are interested inferring rate processes on networks. In particular, given a network's topology, the stationary populations on its nodes, and a few global dynamical observables, can we infer all the transition rates between nodes? We draw inferences using the principle of maximum caliber (maximum path entropy). We have previously derived results for discrete-time Markov processes. Here, we treat continuous-time processes, such as dynamics among metastable states of proteins. The present work leads to a particularly important analytical result: namely, that when the network is constrained only by a mean jump rate, the rate matrix is given by a square-root dependence of the rate, kab ∝ (πb/πa)(1/2), on πa and πb, the stationary-state populations at nodes a and b. This leads to a fast way to estimate all of the microscopic rates in the system. As an illustration, we show that the method accurately predicts the nonequilibrium transition rates in an in silico gene expression network and transition probabilities among the metastable states of a small peptide at equilibrium. We note also that the method makes sensible predictions for so-called extra-thermodynamic relationships, such as those of Bronsted, Hammond, and others.