In this work, the geometric and electronic structure of N species in N-doped carbon nanotubes (NCNTs) is derived by X-ray photoemission (XPS) and absorption spectroscopy (NEXAFS) of the N 1s core excitation. Substitutional N species in pyridine-like configuration and another form of N with higher thermal stability are found in NCNTs. The structural configuration of the high thermally stable N species, in the literature often referred to as graphitic N, is assessed in this work by a combined theoretical and experimental study as a 3-fold substitutional N species in an NCNT basic structural unit (BSU). Furthermore, the nature of the interaction of those N species with a Pd metal center immobilized onto NCNTs is of σ-type donation from the filled π-orbital of the N atom to the empty d-orbital of the Pd atom and a π back-donation from the filled Pd atomic d-orbital to the π* antibonding orbital of the N atom. We have found that the interaction of pyridine N with Pd is characterized by a charge transfer typical of a covalent chemical bond with partial ionic character, consistent with the chemical shift observed in the Pd 3d core level of divalent Pd. Graphitic N sites interact with Pd by a covalent bond without any charge redistribution. In this case, the electronic state of the Pd corresponds to metallic Pd nanoparticles electronically modified by the interaction with the support. The catalytic reactivity of these samples in hydrogenation, CO oxidation, and oxygen reduction reaction (ORR) allowed clarifying some aspects of the metal carbon support interaction in catalysis.

Highly dispersed molybdenum oxide supported on mesoporous silica SBA-15 has been prepared by anion exchange resulting in a series of catalysts with changing Mo densities (0.2-2.5 Mo atoms nm(-2) ). X-ray absorption, UV/Vis, Raman, and IR spectroscopy indicate that doubly anchored tetrahedral dioxo MoO4 units are the major surface species at all loadings. Higher reducibility at loadings close to the monolayer measured by temperature-programmed reduction and a steep increase in the catalytic activity observed in metathesis of propene and oxidative dehydrogenation of propane at 8 % of Mo loading are attributed to frustration of Mo oxide surface species and lateral interactions. Based on DFT calculations, NEXAFS spectra at the O-K-edge at high Mo loadings are explained by distorted MoO4 complexes. Limited availability of anchor silanol groups at high loadings forces the MoO4 groups to form more strained configurations. The occurrence of strain is linked to the increase in reactivity.

We first report AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs) grown on nano-patterned sapphire substrates (NPSS) prepared through a nanosphere lithography technique. The AlN coalescence thickness on NPSS is only 3 μm due to AlN's nano-scaled lateral growth, which also leads to low dislocation densities in AlN and epi-layers above. On NPSS, the light-output power of a 282-nm UV-LED reaches 3.03 mW at 20 mA with external quantum efficiency of 3.45%, exhibiting 98% better performance than that on flat sapphire. Temperature-dependent photoluminescence reveals this significant enhancement to be a combination of higher internal quantum efficiency and higher light extraction efficiency.

Graphene/polyaniline (PANI) nanocomposites were prepared by reducing graphene oxide with hydrazine in the presence of different amounts of polyaniline nanoparticles. In situ cryo-transmission electron microscope (TEM) images of a graphene oxide (GO)/PANI solution revealed that the PANI nanoparticles were anchored on the surface of the GO sheets. During the reduction, the as-adsorbed PANI nanoparticles were sandwiched between layers of graphene sheets. These PANI nanoparticles acted as spacers to create gaps between neighboring graphene sheets, resulting in a higher surface area compared to pure graphene. Graphene/PANI nanocomposites exhibited the high specific surface area of 891 m2/g. Utilizing this composite material, a supercapacitor with a specific capacitance of 257 F/g at a current density of 0.1 A/g has been achieved.

Catalyst deactivation by coking is one major problem for propane dehydrogenation (PDH). To develop catalysts with high resistance to coke, the analysis of coke becomes essential. In this work, an analysis procedure is proposed and validated to acquire the detailed locations and compositions of the coke formed on an as-synthesized Pt–Sn/Al2O3 catalyst. This procedure combines high-resolution transmission electron microscopy (HRTEM), FT-IR, Raman, thermogravimetric analysis (TG), and pyrolysis GC-MS; with this procedure, the systematic and quantitative analysis of coke can be achieved. The results show that the coke is located on the metal, in the vicinity of the metal, and on the support. Besides, aliphatics, aromatics, and pregraphite cokes are identified, and they account for 69.0, 4.4, and 26.6 wt %, respectively. Finally, an in situ DRIFT study is performed, and the results show that the aliphatic coke can be transformed into the aromatic coke and this transformation is related to the deep dehydrogenation reactions.