Reducing the Cost and Preserving the Reactivity in Noble-Metal-Based Catalysts: Oxidation of CO by Pt and Al-Pt Alloy Clusters Supported on Graphene

CO oxidation reactions on 3-d single metal atom catalysts/MgO(100)

The present work deals with a comprehensive computational theoretical study of the molecular CO and O2 adsorption on 3d single atoms (M/MgO(100)). The study is based on the chemical elements of the 3d row, as they represent an economic advantage compared with the so-called noble metals. The present study has been performed employing density functional theory calculations. Through the representation of the metastable states, we perform a synergetic analysis of the CO oxidation reaction to find trends that suggest the possible use of new candidates such as Ni/MgO(100) or Cu/MgO(100) single-atom catalysts, for this type of redox reaction. We found that Ni and Cu produce energetically viable CO to CO2 reactions. Ni and Cu atoms show the greatest diffusion barrier and are the best candidates due to their low sintering capability. The energetic and electronic properties of the single Cu and Ni atoms on MgO (100) give them the best characteristics to help in the CO oxidation process.

Total Structure of Bimetallic Core-Shell [Au42 Cd40 (SR)52 ]2- Nanocluster and Its Implications

Bimetallic core-shell nanostructures hold great promise in elucidating the bimetallic synergism. However, it remains a challenge to construct atomically precise core-shell with high-valence active metals on the gold surface. In this work, we report the total structure of a [Au₄₂ Cd₄₀ (SR)₅₂ ]^2- core-shell nanocluster and multiple implications. Single crystal X-ray diffraction (SCXRD) reveals that the structure possesses a two-shelled Au₆ @Au₃₆ core and a closed cadmium shell of Cd₄₀ , and the core-shell structure is then protected by 52 thiolate (-SR) ligands. The composition of the nanocluster is further confirmed by electrospray ionization mass spectrometry (ESI-MS). A catalytic test for styrene oxidation and a comparison with relevant nanoclusters reveal the surface effect on the catalytic activity and selectivity.

Understanding CO oxidation on the Pt(111) surface based on a reaction route network

Kinetic analysis by the rate constant matrix contraction on the reaction route network of CO oxidation on the Pt(111) surface obtained by the artificial force induced reaction reveals the impact of entropic contributions arising from a variety of local minima and transition states.

Towards operando computational modeling in heterogeneous catalysis

An increased synergy between experimental and theoretical investigations in heterogeneous catalysis has become apparent during the last decade. Experimental work has extended from ultra-high vacuum and low temperature towards operando conditions. These developments have motivated the computational community to move from standard descriptive computational models, based on inspection of the potential energy surface at 0 K and low reactant concentrations (0 K/UHV model), to more realistic conditions. The transition from 0 K/UHV to operando models has been backed by significant developments in computer hardware and software over the past few decades. New methodological developments, designed to overcome part of the gap between 0 K/UHV and operando conditions, include (i) global optimization techniques, (ii) ab initio constrained thermodynamics, (iii) biased molecular dynamics, (iv) microkinetic models of reaction networks and (v) machine learning approaches. The importance of the transition is highlighted by discussing how the molecular level picture of catalytic sites and the associated reaction mechanisms changes when the chemical environment, pressure and temperature effects are correctly accounted for in molecular simulations. It is the purpose of this review to discuss each method on an equal footing, and to draw connections between methods, particularly where they may be applied in combination.

How seaweeds release the excess energy from sunlight to surrounding sea water

We report an atomistic insight into the mechanism regulating the energy released by a porphyra-334 molecule, the ubiquitous photosensitive component of marine algae, in a liquid water environment upon an electron excitation. To quantify this rapidly occurring process, we resort to the Fourier analysis of the mass-weighted auto-correlation function, providing evidence for a remarkable dynamic change in the number of hydrogen bonds among water molecules and between the porphyra-334 and its surrounding hydrating water. Hydrogen bonds between the porphyra-334 and close by water molecules can act directly and rather easily to promote an efficient transfer of the excess kinetic energies of the porphyra-334 to the surrounding solvating water molecules via an activation of the collective modes identified as hydrogen-bond stretching modes in liquid water which eventually results in a disruption of the hydrogen bond network. Since porphyra-334 is present in seaweeds, aquatic cyanobacteria (blue-green algae) and red algae, our findings allow addressing the question how algae in oceans or lakes, upon sunlight absorption, can release large amounts of energy into surrounding water without destabilizing neither their own nor the H₂O molecular structure.

Baize-like CeO2 and NiO/CeO2 nanorod catalysts prepared by dealloying for CO oxidation

Baize-like monolithic CeO₂ and NiO/CeO₂ nanorod catalysts were prepared by combined dealloying and calcination and the catalytic activities were evaluated using CO catalytic oxidation. The CeO₂ catalysts were composed of nanorods and exhibited a three-dimensional supporting structure with pores. After introduction of NiO, dispersed NiO nanosheets and nanoparticles were supported on the surface of CeO₂ nanorods and they were not well-crystallined due to CeO₂ inhibiting the NiO crystallization. The Raman and x-ray photoelectron spectroscopy analyses revealed that the introduction of NiO species into CeO₂ generated more coordinate unsaturated Ni atoms, oxygen vacancies, defects and active sites for CO catalytic reactions. The reaction activation energy of NiO/CeO₂ nanorod catalyst prepared from the Al₈₃Ce₁₀Ni₇ precursor alloy was just 31.2 kJ mol^-1 and the CO conversion can reach up to 97% at 240 °C, which was superior to that of pure CeO₂ and nanoporous NiO. The enhanced catalytic activity of baize-like NiO/CeO₂ nanorods can be attributed to the strong synergistic effects between finely dispersed NiO species and surface oxygen vacancies in CeO₂ nanorods.