XPS and TPD study of NO interaction with Cu(111): Role of different oxygen species

Surface-like NOx Reduction at an Atomically-Precise Tricopper Cluster

The combustion of nitrogen-containing fuels and increasing use of nitrogen-rich fertilizers is accumulating NOx pollutants in the environment. Copper is an attractive catalyst material for reductive NOx remediation, yet ambiguity persists regarding the elementary bond-making and bond-breaking steps occurring at the catalyst interface. Starting from a molecular tricuprous μ3-oxo complex (1), an unusually reduced and highly reactive surface-like cluster (2) has been prepared. Characterization data and electronic structure calculations are consistent with 2 featuring σ-aromaticity that primes the tricopper core for two-electron chemistry. Cluster 2 mediates catalytic reductive coupling of NO to N2, proceeding through N2O, via sequential oxygen atom transfer steps. Stoichiometric reduction of NO3 - and NO2 - is also disclosed, mapping the complete denitrification cycle at an atomically-precise molecular cluster.

The need for robust model systems in the study of hybrid interfaces for photocatalysis and photoelectrocatalysis

Small molecule conversion to value-added products using renewable energy sources has emerged as a promising strategy to mitigate our reliance on fossil fuels. Hybrid materials that integrate the strengths of photoabsorbers and co-catalysts (electrocatalysts) are essential for maximizing the efficiency of photochemical (PC) and photoelectrochemical (PEC) systems. In this perspective, we will focus on the need for fundamental studies with a strong emphasis on the importance of beginning with well-defined hybrid interfaces. A particular focus is given to small molecule adsorption studies that correlate surface structure and chemistry to reactivity, highlighting its potential in characterizing complex interfaces. We also make the case for understanding how light and electrochemical environments influence surface structure, adsorption, and reactivity and should be considered in model hybrid system design. Finally, we provide a framework to connect the theory and experiment of model hybrid surfaces to provide a molecular understanding of PC and PEC at these interfaces and accelerate our integration of these materials into real systems capable of meeting our renewable energy needs.

Sulfur resistance of Ce-Mn/TiO2 catalysts for low-temperature NH3-SCR

Ce-Mn/TiO₂ catalyst prepared using a simple impregnation method demonstrated a better low-temperature selective catalytic reduction of NO with NH₃ (NH₃-SCR) activity in comparison with the sol-gel method. The Ce-Mn/TiO₂ catalyst loading with 20% Ce had the best low-temperature activity and achieved a NO conversion rate higher than 90% at 140-260°C with a 99.7% NO conversion rate at 180°C. The Ce-Mn/TiO₂ catalyst only had a 6% NO conversion rate decrease after 100 ppm of SO₂ was added to the stream. When SO₂ was removed from the stream, the catalyst was able to recover completely. The crystal structure, morphology, textural properties and valence state of the metals involving the novel catalysts were investigated using X-ray diffraction, N₂ adsorption and desorption analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy, respectively. The decrease of NH₃-SCR performance in the presence of 100 ppm SO₂ was due to the decrease of the surface area, change of the pore structure, the decrease of Ce⁴⁺ and Mn⁴⁺ concentration and the formation of the sulfur phase chemicals which blocked the active sites and changed the valence status of the elements.