On the nature of the active site in catalysis: the reactivity of surface oxygen on Cu(110)

Recent progress in single-atom alloys: Synthesis, properties, and applications in environmental catalysis

Heterogeneous catalysts have made outstanding advancements in pollutants elimination as well as energy and materials production over the past decades. Single-atom alloys (SAAs) are novel environmental catalysts prepared by dispersing single metal atoms on other metals. Integrating the advantages of single atom and alloys, SAAs can maximize atom utilization, reduce the use of noble metals and enhance catalytic performances. The synergistic, electronic and geometric effects of SAAs are effective to modulate the activation energy and adsorption strength, consequently breaking linear scaling relationship as well as offering an excellent catalytic activity and selectivity. Moreover, SAAs possess clear atomic structure, active sites and reaction mechanisms, providing an opportunity to tailor catalytic properties and develop effective environmental catalysts. In this review, we provide the recent progress on synthetic strategies, catalytic properties and catalyst design of SAAs. Furthermore, the applications of SAAs in environmental catalysis are introduced towards catalytic conversion and elimination of different air pollutants in many important reactions including (electrochemical) oxidation of volatile organic compounds (VOCs), dehydrogenation of VOCs, CO₂ conversion, NO_x reduction, CO oxidation, SO₃ decomposition, etc. Finally, challenges and opportunities of SAAs in a broad environmental field are proposed.

One-Pot Ethyl Acetate Production from Ethanol Photooxidation on Rutile TiO2(110): Strong Photon Energy Dependence

Ethyl acetate (EA) production from sequential ethanol (EtOH) photooxidation on a rutile(R)-TiO₂(110) surface has been investigated by the temperature-programmed desorption (TPD) method at 355 and 266 nm. Significant EA product is detected under 266 nm irradiation, which is most likely to be formed via cross-coupling of primary dissociation products, aldehyde (CH₃CHO) and ethoxy groups. On the contrary, EA formation at 355 nm is negligible. In addition, the initial rate of EA formation from EtOH at 266 nm is nearly 2 orders of magnitude faster than that at 355 nm. Quantitative analysis suggests that EA formation from sequential EtOH photooxidation on R-TiO₂(110) is strongly dependent on photon energy or the energy of hot holes. This experimental result raises doubt about the traditional photocatalysis model on TiO₂ where charge carriers relax to their respective band edges prior to charge transfer to adsorbates during the photocatalytic process, leading to no dependence on photon energy in TiO₂ photocatalysis.

Molecular-scale perspective of water-catalyzed methanol dehydrogenation to formaldehyde

Methanol steam reforming is a promising reaction for on-demand hydrogen production. Copper catalysts have excellent activity and selectivity for methanol conversion to hydrogen and carbon dioxide. This product balance is dictated by the formation and weak binding of formaldehyde, the key reaction intermediate. It is widely accepted that oxygen adatoms or oxidized copper are required to activate methanol. However, we show herein by studying a well-defined metallic copper surface that water alone is capable of catalyzing the conversion of methanol to formaldehyde. Our results indicate that six or more water molecules act in concert to deprotonate methanol to methoxy. Isolated palladium atoms in the copper surface further promote this reaction. This work reveals an unexpected role of water, which is typically considered a bystander in this key chemical transformation.