Molecular N2 chemisorption—specific adsorption on step defect sites on Pt surfaces

Adsorption and solar light activity of noble metal adatoms (Au and Zn) on Fe(111) surface: a first-principles study

Noble metals such as gold (Au), zinc (Zn), and iron (Fe) are highly significant in both fundamental and technological contexts owing to their applications in optoelectronics, optical coatings, transparent coatings, photodetectors, light-emitting devices, photovoltaics, nanotechnology, batteries, and thermal barrier coatings. This study presents a comprehensive investigation of the optoelectronic properties of Fe(111) and Au, Zn/Fe(111) materials using density functional theory (DFT) first-principles method with a focus on both materials' spin orientations. The optoelectronic properties were obtained employing the generalized gradient approximation (GGA) and the full-potential linearized augmented plane wave (FP-LAPW) approach, integrating the exchange-correlation function with the Hubbard potential U for improved accuracy. The arrangement of Fe(111) and Au, Zn/Fe(111) materials was found to lack an energy gap, indicating a metallic behavior in both the spin-up state and the spin-down state. The optical properties of Fe(111) and Au, Zn/Fe(111) materials, including their absorption coefficient, reflectivity, energy-loss function, refractive index, extinction coefficient, and optical conductivity, were thoroughly examined for both spin channels in the spectral region from 0.0 eV to 14 eV. The calculations revealed significant spin-dependent effects in the optical properties of the materials. Furthermore, this study explored the properties of the electronic bonding between several species in Fe(111) and Au, Zn/Fe(111) materials by examining the density distribution mapping of charge within the crystal symmetries.

A Platinum Nanowire Sensor for Ethylene in Air

A single platinum nanowire (PtNW) chemiresistive sensor for ethylene gas is reported. In this application, the PtNW performs three functions: (1) Joule self-heating to a specified temperature, (2) in situ resistance-based temperature measurement, and (3) detection of ethylene in air as a resistance change. Ethylene gas in air is detected as a reduction in nanowire resistance by up to 4.5% for concentrations ranging from 1 to 30 ppm in an optimum NW temperature range from 630 to 660 K. This response is rapid (30-100 s), reversible, and reproducible for repetitive ethylene pulses. A threefold increase in signal amplitude is observed as the NW thickness is reduced from 60 to 20 nm, commensurate with a signal transduction mechanism involving surface electron scattering.

Quantum state and surface-site-resolved studies of methane chemisorption by vibrational spectroscopies

Infrared spectroscopic methods enable quantum-state-specific and surface-site-selective studies of methane chemisorption on stepped platinum surfaces.

Mechanism and kinetics for both thermal and electrochemical reduction of N2 catalysed by Ru(0001) based on quantum mechanics

QM calculations were used to predict the free energy surfaces for N₂ thermal and electrochemical reduction (N₂TR and N₂ER) on Ru(0001), to find the detailed atomistic mechanism and kinetics, and provide the basis for improving the efficiency of N₂ER.

The atomic simulation environment-a Python library for working with atoms

The atomic simulation environment (ASE) is a software package written in the Python programming language with the aim of setting up, steering, and analyzing atomistic simulations. In ASE, tasks are fully scripted in Python. The powerful syntax of Python combined with the NumPy array library make it possible to perform very complex simulation tasks. For example, a sequence of calculations may be performed with the use of a simple 'for-loop' construction. Calculations of energy, forces, stresses and other quantities are performed through interfaces to many external electronic structure codes or force fields using a uniform interface. On top of this calculator interface, ASE provides modules for performing many standard simulation tasks such as structure optimization, molecular dynamics, handling of constraints and performing nudged elastic band calculations.

Probing the effect of the Pt-Ni-Pt(111) bimetallic surface electronic structures on the ammonia decomposition reaction

We report a detailed investigation of elementary catalytic decomposition of ammonia on the Pt-Ni-Pt(111) bimetallic surface using in situ near ambient pressure X-ray photoelectron spectroscopy. Under the near ambient pressure (0.6 mbar) reaction conditions, a different dehydrogenation pathway with a reduced activation energy barrier for recombinative nitrogen desorption on the Pt-Ni-Pt(111) bimetallic surface is observed. The unique surface catalytic activity is correlated with the downward shift of the Pt 5d band states induced by the Ni subsurface atoms via charge redistribution of the topmost Pt layer. Our results provide a practical understanding of the unique chemistry of bimetallic catalysts for facile ammonia decomposition under realistic reaction conditions.

Density functional theory in surface chemistry and catalysis

Recent advances in the understanding of reactivity trends for chemistry at transition-metal surfaces have enabled in silico design of heterogeneous catalysts in a few cases. The current status of the field is discussed with an emphasis on the role of coupling theory and experiment and future challenges.

Weak molecular chemisorption of N(2)/Pt(111)

The ordering in a higher-order-commensurate monolayer solid of Pt(111)- (3 × 3)-4  N(2), which has coexisting physisorbed and weakly chemisorbed N(2) species, is analyzed with model calculations. Density functional theory calculations are also used to evaluate properties of chemisorbed N(2) in a (2 × 2) unit cell on Pt(111). The relation of these results to the orientational ordering of N(2) on other metal surfaces is discussed.

Phenomenological study of monomer adsorption on fcc (335) surfaces with application to CO, O, and N(2) adsorption on Pt(335)

We extend our recent study of adsorption on fcc (112) to fcc (335) surfaces, still considering only first- and second-neighbor interactions with repulsive first-neighbors. We consider the adsorbate-substrate interaction on the step sites of one of the two edges of the infinitely long terraces to be different from that on the remaining sites. The adsorption features on fcc (335) surfaces are richer than those on fcc (112), which can be attributed to the fact that the equilateral triangular terraces are now four-atoms wide rather than three. Our approach is independent of the chemical composition of the substrate and adsorbates and consequently may be applied to a variety of adsorption systems on fcc (335) surfaces which satisfy the limitations of our model. The basic question that our phenomenological approach intends to answer is: what are the constraints that can be obtained on the interaction energies from the experimental observation of one or more phases? This question is answered in the cases of CO, O, and N(2) adsorbed on Pt(335).

Adsorption and dissociation of NO on stepped Pt (533)

We present an experimental and theoretical investigation of the adsorption, desorption, and dissociation of NO on the stepped Pt (533) surface. By combining temperature programmed desorption and reflection absorption infrared spectroscopy, information about the adsorption sites at different temperatures is obtained. Surprisingly, metastable adsorption structures of NO can be produced through variation of the dosing temperature. We also show that part of the NO molecules adsorbed on the step sites dissociates around 450 K. After dissociation the N atoms can desorb either by combining with an O fragment, or with another N atom, resulting in NO and N(2). The N(2) production can be enhanced by coadsorbing CO on the surface: CO scavenges the oxygen atom, thereby suppressing associative recombinative desorption of N and O atoms. Density functional theory calculations are used to reveal the adsorption energies and vibrational frequencies of adsorbed NO as well as barriers for dissociation of NO and for diffusion of N atoms. The combined experimental results and theoretical calculations reveal that dissociation of NO is the rate limiting step in the formation of N(2).

Reflection absorption infrared spectroscopy and the structure of molecular adsorbates on metal surfaces

Infrared (IR) spectroscopy is widely used to identify molecular adsorbates that form on metals in the course of surface chemical reactions. Because IR spectroscopy is one of the few surface-sensitive probes that provide molecule-specific information without perturbing the chemisorbed state, there is great interest in extracting as much structural information from the spectra as possible. The various ways IR spectroscopy is used to determine the structure of molecular adsorbates, from strictly qualitative interpretations based on symmetry selection rules to the use of ab initio electronic structure calculations to predict the IR spectrum of a chemisorbed molecule, are reviewed.