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Pt x Pd 1-x (x ) 1, 0.7, or 0.5) nanoparticles submitted to hydrogen reduction and posterior H 2 S sulfidation at 150 or 300 °C were characterized by in situ X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The in situ XAS measurements allowed monitoring of short-range order changes around the Pt atoms induced by the thermal processes. The surface sensitivity and atom specific characteristics of XPS provided additional information about the chemical state of the atoms present in the outermost layers of the nanoparticles. Our experiments also indicate a Pd migration toward the surface of the nanoparticles driven by the thermal processes. We observed that the reduction process is necessary prior to the occurrence of any sulfur reaction and that the number of chemisorbed sulfur atoms is directly proportional to the quantity of Pd atoms.

Here, we report the Pt nanoparticle mediated reduction (oxidation) and lattice expansion (contraction) of mesoporous CeO 2 under H 2 (O 2 ) atmospheres and in the temperature range of 50−350 °C. We found that CeO 2 in the Pt/CeO 2 catalyst was partially reduced in H 2 (and fully oxidized back in O 2 ) as demonstrated by several in situ techniques: APXPS spectra (4d core levels) for the topmost surface, NEXAFS total electron yield spectra (at the M 5,4 edges) in the near surface regions, and (N)EXAFS fluorescence spectra (at the L 3 edge) in the bulk. Moreover, XRD and EXAFS showed the reversible expansion and contraction of the CeO 2 unit cell in H 2 and O 2 environments, respectively. The expansion of the CeO 2 cell was mainly associated with the formation of oxygen vacancies as a result of the Pt-mediated reduction of Ce 4+ to Ce 3+ . We also found that pure mesoporous CeO 2 can not be reduced in H 2 under identical conditions but can be partially reduced at above 450 °C as revealed by APXPS. The role of Pt in H 2 was identified as a catalytic one that reduces the activation barrier for the reduction of CeO 2 via hydrogen spillover.

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Ceria (CeO2) is being increasingly used as support of metallic nanoparticles in catalysis due to its unique redox properties. Shedding light into the nature of the strong metal support interaction (SMSI) effect in CeO2-containing catalysts is important since it has a strong influence on the catalytic properties of the system. In this work, Cu/CeO2 and Ni/CeO2 nanoparticles are characterized when submitted to a reduction treatment at 500 °C in H2 atmosphere with a combination of in situ (XAS – X-ray absorption spectroscopy and time-resolved XAS) and ex situ (TEM – transmission electron microscopy and XPS - X-ray photoelectron spectroscopy) techniques. The existence of a capping layer decorating the Ni/CeO2 nanoparticles after the reduction treatment is shown, representing evidence for the SMSI effect. The kinetics of the SMSI occurrence is elucidated. It is proposed that the electronic factor of the SMSI effect has a strong influence on the reduction properties of the Ni nanoparticles supported on CeO2, decreasing its reduction temperature if compared to nonsupported Ni nanoparticles. The same phenomenon is not observed for Cu/CeO2 nanoparticles, where there is no evidence for the SMSI effect, and no changes on the reduction properties between supported and nonsupported Cu nanoparticles are observed.

The strong metal–support interaction (SMSI) effect plays a central role in catalysis by decreasing the catalytic activity or even improving it in some specific cases. In spite of the intense research, a detailed description of the SMSI effect in CeO2-based catalysts is still missing. In this work, Cu x Ni1–x /CeO2 (0 < x < 1) nanoparticles were exposed to a reduction treatment in a H2 atmosphere followed by an oxidation treatment in a CO2 atmosphere, both at 500 °C, and studied by using state-of-the-art techniques (in situ time-resolved X-ray absorption near edge structure (XANES) and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS)). It was observed the migration of Cu (Ni) atoms toward the surface of Cu–Ni bimetallic nanoparticles during reduction (oxidation) treatments. The core–shell-like structure is dependent on the Cu/Ni ratio. It was observed the existence of a capping layer from the support (CeO2–x ) surrounding the metallic nanoparticles after reduction treatment (characteristic of the SMSI effect) in some specific cases, depending on the Cu/Ni ratio as well. The surface of the nanoparticles presenting the SMSI effect is recovered to the initial state after exposure to the CO2 atmosphere. Moreover, the nature of the SMSI effect was elucidated. The capping layer interacts with the Cu and Ni atoms via Ce 3d10 O 2p6 Ce 4f0 and Ce 3d10 O 2p6 Ce 4f1 initial states, depending on the case studied. As a consequence of the SMSI effect, the Cu atoms of the nanoparticles reduce at lower temperature than similar nanoparticles that do not present the SMSI effect. Therefore, the decrease in reduction temperature is directly related to the interaction between the CeO2–x capping layer and Cu and Ni atoms.

We have been able to “tune” the electrocatalytic activity of iron phthalocyanine (FePc) and iron hexadodecachlorophthalocyanine (16­(Cl)­FePc) for the oxygen reduction reaction (ORR) by manipulating the “pull effect” of pyridinium molecules axially bounded to the phthalocyanine complexes (FePcs). These axial ligands play both the role of molecular anchors and also of molecular wires. The axial ligands also affect the reactivity of the Fe metal center in the phthalocyanine. The “pull effect” originates from the positive charge located on the pyridinium core. We have explored the influence of the core positions (Up or Down), in two structural pyridiniums isomers on the activity of FePc and 16­(Cl)­FePc for the ORR. Of all self-assembled catalysts tested, the highest catalytic activity was exhibited by the Au(111)/Up/FePc system. XPS measurements and DFT calculations showed that it is possible to tailor the FePc–N­(pyridiniums) Fe–O2 binding energies, by changing the core positions and affecting the “pull effect” of pyridiniums. This affects directly the catalytic activity of FePcs. The plot of activity as (log I)E versus the calculated Fe–O2 binding energies gives an activity volcano correlation, indicating that an optimum binding energy of O2 with the Fe center provides the highest activity.

Ionic liquid (IL)-hybrid organosilicas based on 1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic and hydrophobic anions decorated with well dispersed and similar sized (1.8-2.1 nm) Pd nanoparticles (PdNPs) are amongst the most active and selective catalysts for the partial hydrogenation of conjugated dienes to monoenes. The location of the sputter-imprinted Pd-NPs on different supports, as determined by RBS and HS-LEIS analysis, is modulated by the strength of the contact ion pair formed between the imidazolium cation and the anion, rather than the IL-hybrid organosilica pore size and surface area. In contrast, the pore diameter and surface area of the hybrid supports display a direct correlation with the anion hydrophobicity. XPS analysis showed that the Pd(0) surface component decreases with increasing ionic bond strength between the imidazolium cation and the anions (contact ion pair). The finding is corroborated by changes in the coordination number associated with the Pd-Pd scattering in EXAFS measurements. Hence, the interaction of the IL with the metal surface is found to occur via IL contact pairs (or aggregates). The observed selectivities of ≥99% to monoenes at full diene conversion indicate that the selectivity is intrinsic to the electron deficient Pd-metallic surfaces in this "restricted" ionic environment. This suggests that ILhybrid organosilica/Pd-NPs under multiphase conditions ("dynamic asymmetric mixture") operate akin to catalytically active membranes, i.e. far from the thermodynamic equilibrium. Detailed kinetic investigations show that the reaction rate is zero-order with respect to hydrogen and dependent on the fraction of catalyst surfaces covered by either the substrate and/or the product. The reaction proceeds via rapid inclusion and sorption of the diene to the IL/Pd metal surface saturated with H species. This is followed by reversible hydride migration to generate a π-allyl intermediate. The reductive elimination of this intermediate, the formal ratedetermining step (RDS), generates the alkene that is rapidly expelled from the IL phase to the organic phase.