Predicting NO_<i>x</i> Catalysis by Quantifying Ce³⁺ from Surface and Lattice Oxygen

Our work introduces a novel technique based on the magnetic response of Ce³⁺ and molecular oxygen adsorbed on the surface of nanoceria and ceria-based catalysts that quantifies the number and type of defects and demonstrates that this information is the missing link that finally enables predictive design of NO_<i>x</i> catalysis in ceria-based systems. The new insights into ceria catalysis are enabled by quantifying the above for different ceria nanoparticle shapes (i.e., surface terminations) and O₂ partial pressure. We used ceria nanorods, cubes, and spheres and evaluated them for catalytic reduction of NO by CO. We then demonstrated the quantitative prediction of the reactivity of nanomaterials via their magnetism in different atmospheric environments. We find that the observed enhancement of reactivity for ceria nanocubes and nanorods is not directly due to improved reactivity on those surface terminations but rather due to the increased ease of generating lattice defects in these materials. Finally, we demonstrate that the method is equally applicable to highly topical and industrially relevant ceria mixed oxides, using nanoscale alumina-supported ceria as a representative case–a most ill-defined catalyst. Because the total oxide surface is a mixture of active ceria and inactive support and ceria is not likely present as crystallographically well-defined phases, reactivity does not easily scale with surface area or a surface termination. The key parameter to design efficient NO reduction in ceria-based catalysts is knowing and controlling the surface localized excess Ce³⁺ ion areal density

Acceptorless Dehydrogenative Coupling of Neat Alcohols Using Group VI Sulfide Catalysts

Group VI sulfides were synthesized via coprecipitation of elemental sulfur and metal hexacarbonyl and characterized with XRD, XPS, and TEM. These materials were then demonstrated as active catalysts for the acceptorless dehydrogenative coupling of neat ethanol to ethyl acetate, rapidly reaching equilibrium conversion and up to 90% selectivity. Other primary alcohols form the corresponding esters, while diols formed the corresponding cyclic ethers and oligomers

Isolated Fe^II on Silica As a Selective Propane Dehydrogenation Catalyst

We report a comparative study of isolated Fe^II, iron oxide particles, and metallic nanoparticles on silica for non-oxidative propane dehydrogenation. It was found that the most selective catalyst was an isolated Fe^II species on silica prepared by grafting the open cyclopentadienide iron complex, bis­(2,4-dimethyl-1,3-pentadienide) iron­(II) or Fe­(<i>o</i>Cp)₂. The grafting and evolution of the surface species was elucidated by ¹H NMR, diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption spectroscopies. The oxidation state and local structure of surface Fe were characterized by X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure. The initial grafting of iron proceeds by one surface hydroxyl Si–OH reacting with Fe­(<i>o</i>Cp)₂ to release one diene ligand (<i>o</i>CpH), generating a SiO₂-bound Fe^II(<i>o</i>Cp) species, <b>1-Fe</b><i><b>o</b></i><b>Cp</b>. Subsequent treatment with H₂ at 400 °C leads to loss of the remaining diene ligand and formation of nanosized iron oxide clusters, <b>1-C</b>. Dispersion of these Fe oxide clusters occurs at 650 °C, forming an isolated, ligand-free Fe^II on silica, <b>1-Fe</b>^<b>II</b>, which is catalytically active and highly selective (∼99%) for propane dehydrogenation to propene. Under reaction conditions, there is no evidence of metallic Fe by in situ XANES. For comparison, metallic Fe nanoparticles, <b>2-NP-Fe</b>^<b>0</b>, were independently prepared by grafting Fe­[N­(SiMe₃)₂]₂ onto silica, <b>2-FeN*</b>, and reducing it at 650 °C in H₂. The Fe NPs were highly active for propane conversion but showed poor selectivity (∼14%) to propene. Independently prepared Fe oxide clusters on silica display a low activity. The sum of these results suggests that selective propane dehydrogenation occurs at isolated Fe^II sites