Origin of Efficient Catalytic Combustion of Methane over Co₃O₄(110): Active Low-Coordination Lattice Oxygen and Cooperation of Multiple Active Sites

A complete catalytic cycle for methane combustion on the Co₃O₄(110) surface was investigated and compared with that on the Co₃O₄(100) surface on the basis of first-principles calculations. It is found that the 2-fold coordinated lattice oxygen (O_2c) would be of vital importance for methane combustion over Co₃O₄ surfaces, especially for the first two C–H bond activations and the C–O bond coupling. It could explain the reason the Co₃O₄(110) surface significantly outperforms the Co₃O₄(100) surface without exposed O_2c for methane combustion. More importantly, it is found that the cooperation of homogeneous multiple sites for multiple elementary steps would be indispensable. It not only facilitates the hydrogen transfer between different sites for the swift formation of H₂O to effectively avoid the passivation of the active low-coordinated O_2c site but also stabilizes surface intermediates during the methane oxidation, optimizing the reaction channel. An understanding of this cooperation of multiple active sites not only might be beneficial in developing improved catalysts for methane combustion but also might shed light on one advantage of heterogeneous catalysts with multiple sites in comparison to single-site catalysts for catalytic activity

Highly Selective Detection of Carbon Monoxide in Living Cells by Palladacycle Carbonylation-Based Surface Enhanced Raman Spectroscopy Nanosensors

A novel nanosensor was explored for the highly selective detection of intracellular carbon monoxide (CO) by surface enhanced Raman spectroscopy (SERS) on the basis of palladacycle carbonylation. By assembling new synthesized palladacycles (PC) on the surface of gold nanoparticles (AuNPs), SERS nanosensors (AuNP/PC) were prepared with good SERS activity and reactivity with CO. When the AuNP/PC nanosensors were incubated with a CO-containing system, carbonylation of the PC assembled on AuNPs was initiated, and the corresponding SERS spectra of AuNP/PC changed significantly, which allowed the carbonylation reaction to be directly observed <i>in situ</i>. Upon SERS observation of CO-dependent carbonylation, this SERS nanosensor was used for the detection of CO under physiological conditions. Moreover, benefiting from the specificity of the reaction coupled with the fingerprinting feature of SERS, the developed nanosensor demonstrated high selectivity over other biologically relevant species. <i>In vivo</i> studies further indicated that CO in normal human liver cells and HeLa cells at concentrations as low as 0.5 μM were successfully detected with the proposed SERS strategy, demonstrating its great promise for the analytical requirements in studies of physiopathological events involved with CO

Origin of low CO2 selectivity on platinum in the direct ethanol fuel cell

Calculated answer: First-principles calculations have been applied to calculate the energy barrier for the key step in CO formation on a Pt surface (see picture; Pt blue, Pt atoms on step edge yellow) to understand the low CO 2 selectivity in the direct ethanol fuel cell. The presence of surface oxidant species such as O (brown bar) and OH (red bar) led to an increase of the energy barrier and thus an inhibition of the key step

Visible-Light-Driven Valorization of Biomass Intermediates Integrated with H₂ Production Catalyzed by Ultrathin Ni/CdS Nanosheets

Photocatalytic upgrading of crucial biomass-derived intermediate chemicals (i.e., furfural alcohol, 5-hydroxy­methyl­furfural (HMF)) to value-added products (aldehydes and acids) was carried out on ultrathin CdS nanosheets (thickness ∼1 nm) decorated with nickel (Ni/CdS). More importantly, simultaneous H₂ production was realized upon visible light irradiation under ambient conditions utilizing these biomass intermediates as proton sources. The remarkable difference in the rates of transformation of furfural alcohol and HMF to their corresponding aldehydes in neutral water was observed and investigated. Aided by theoretical computation, it was rationalized that the slightly stronger binding affinity of the aldehyde group in HMF to Ni/CdS resulted in the lower transformation of HMF to 2,5-diformyl­furan compared to that of furfural alcohol to furfural. Nevertheless, photo­catalytic oxidation of furfural alcohol and HMF under alkaline conditions led to complete transformation to the respective carboxylates with concomitant production of H₂

Evidence To Challenge the Universality of the Horiuti–Polanyi Mechanism for Hydrogenation in Heterogeneous Catalysis: Origin and Trend of the Preference of a Non-Horiuti–Polanyi Mechanism

The Horiuti–Polanyi mechanism has been considered to be universal for explaining the mechanisms of hydrogenation reactions in heterogeneous catalysis for several decades. In this work, we examine this mechanism for the hydrogenation of acrolein, the simplest α,β-unsaturated aldehyde, in gold-based systems as well as some other metals using extensive first-principles calculations. It is found that a non-Horiuti–Polanyi mechanism is favored in some cases. Furthermore, the physical origin and trend of this mechanism are revealed and discussed regarding the geometrical and electronic effects, which will have a significant influence on current understandings on heterogeneous catalytic hydrogenation reactions and the future catalyst design for these reactions

Engineering Fractal MTW Zeolite Mesocrystal: Particle-Based Dendritic Growth via Twinning-Plane Induced Crystallization

Constructing superstructured crystalline materials by crystal engineering is an attractive objective for miscellaneous fields of researchers spanning biomimetics to catalytic materials. Zeolite is a kind of important crystalline catalyst, and superstructured zeolite has great potential for widespread applications. However, the ambiguous crystallization mechanisms hamper the effective and scientific fabrication of superstructured zeolite with exceptional properties. Herein, a fractal superstructured MTW zeolite with mesocrystal side branches is prepared via a nanoparticle-based nonclassical pathway with twinning-plane induced crystallization, which is distinct from the formation of general mesocrystal via crystal–crystal oriented attachment. Deformed atomic connection at a specific crystallographic plane contributes to the production of side branches. Moreover, this intriguing morphology could be regulated merely via adjusting the crystallization kinetics based on the unequivocal nonclassical crystallization mechanism. It will open a new avenue for design and synthesis of targeted crystals with superstructure and extraordinary properties

Low-Temperature Methane Combustion over Pd/H-ZSM-5: Active Pd Sites with Specific Electronic Properties Modulated by Acidic Sites of H‑ZSM‑5

Pd/H-ZSM-5 catalysts could completely catalyze CH₄ to CO₂ at as low as 320 °C, while there is no detectable catalytic activity for pure H-ZSM-5 at 320 °C and only a conversion of 40% could be obtained at 500 °C over pure H-ZSM-5. Both the theoretical and experimental results prove that surface acidic sites could facilitate the formation of active metal species as the anchoring sites, which could further modify the electronic and coordination structure of metal species. PdO_<i>x</i> interacting with the surface Brönsted acid sites of H-ZSM-5 could exhibit Lewis acidity and lower oxidation states, as proven by the XPS, XPS valence band, CO-DRIFTS, pyridine FT-IR, and NH₃-TPD data. Density functional theory calculations suggest PdO_<i>x</i> groups to be the active sites for methane combustion, in the form of [AlO₂]­Pd­(OH)-ZSM-5. The stronger Lewis acidity of coordinatively unsaturated Pd and the stronger basicity of oxygen from anchored PdO_<i>x</i> species are two key characteristics of the active sites ([AlO₂]­Pd­(OH)-ZSM-5) for methane combustion. As a result, the PdO_<i>x</i> species anchored by Brønsted acid sites of H-ZSM-5 exhibit high performance for catalytic combustion of CH₄ over Pd/H-ZSM-5 catalysts