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Atomically defined MnO(001) thin films were grown on an Au(111) substrate, and their interaction with water (D2O) was investigated by infrared reflection absorption spectroscopy (IRAS) and thermal desorption spectroscopy (TDS). Carbon monoxide adsorption experiments were performed to probe surface atoms and defects on oxide films. Next, water interaction was investigated from which an associative binding pathway and a dissociative binding pathway were revealed, where the water molecules adsorb at terraces and water dissociation takes place at oxygen vacancies mediated by nearby Mn2+ sites. The IRAS data are supported by TDS experiments, which also manifest the importance of defects in the adsorption characteristics of MnO. [ABSTRACT FROM AUTHOR]

Although clean energy generation utilizing the Oxygen Reduction Reaction (ORR) can be considered a promising strategy, this approach remains challenging by the dependence on high loadings of noble metals, mainly Platinum (Pt). Therefore, efforts have been directed to develop new and efficient electrocatalysts that could decrease the Pt content (e.g., by nanotechnology tools or alloying) or replace them completely in these systems. The present investigation shows that high catalytic activity can be reached towards the ORR by employing 1.8 ± 0.7 nm Ir nanoparticles (NPs) deposited onto MnO2 nanowires surface under low Ir loadings (1.2 wt.%). Interestingly, we observed that the MnO2-Ir nanohybrid presented high catalytic activity for the ORR close to commercial Pt/C (20.0 wt.% of Pt), indicating that it could obtain efficient performance using a simple synthetic procedure. The MnO2-Ir electrocatalyst also showed improved stability relative to commercial Pt/C, in which only a slight activity loss was observed after 50 reaction cycles. Considering our findings, the superior performance delivered by the MnO2-Ir nanohybrid may be related to (i) the significant concentration of reduced Mn3+ species, leading to increased concentration of oxygen vacancies at its surface; (ii) the presence of strong metal-support interactions (SMSI), in which the electronic effect between MnOx and Ir may enhance the ORR process; and (iii) the unique structure comprised by Ir ultrasmall sizes at the nanowire surface that enable the exposure of high energy surface/facets, high surface-to-volume ratios, and their uniform dispersion. [ABSTRACT FROM AUTHOR]

We present the preparation and investigation of a fluorine‐free surface‐active bis‐N‐heterocyclic carbene (NHC) platinum(II) complex — trans‐[Pt(mPEG3C8Im)2Cl2] — for interface‐enhanced supported ionic liquid phase (SILP) catalysis within a group of (mPEGn)‐substituted ionic liquids (ILs) ([(mPEGn)2Im][A] ILs). The complex was characterized by means of single‐crystal X‐ray diffraction (scXRD) analysis and multinuclear (1H, 13C, 195Pt) NMR spectroscopy, indicating the presence of two almost equimolar syn–anti‐rotamers of the square‐planar complex in solution. Angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) revealed pronounced interface‐accumulation of trans‐[Pt(mPEG3C8Im)2Cl2] in IL solutions of [(mPEG2)2Im][A] (A−=I− and PF6−). [ABSTRACT FROM AUTHOR]

Renewable ethylene can be obtained by dehydration of bio‐ethanol and used for production of vinyl acetate (VAM) through reaction with acetic acid (AcOH), using Pd−Cu catalysts. In the present manuscript, structural characterizations of Pd−Cu/ZrO2 catalysts show that these systems present cubic structure with different spatial distributions. Particularly, it is shown that combustion of ethylene and acetic acid can be inhibited below 180 °C, maximizing the rates of VAM formation, when the catalysts are modified with Ti+4. The effects of AcOH concentration on rates of VAM formation show that higher AcOH concentrations favor the formation of undesired byproducts, while lower AcOH concentrations favor effects related to O2 mobility, which can lead to surface decomposition. VAM formation is favored, with selectivities ranging from 0.8 to 1.0. XPS results indicate the existence of metallic Pd, CuO species and Zr species, in agreement with IR results. DRIFTS results also show that different Pd‐acetate intermediates can be present, depending on the electronic effects associated to Pd−Cu and Zr species. Order in the court: PdCu alloys over ZrO2 based catalysts were studied for Vinyl acetate synthesis. Interesting results were found, showing a structure feasible for acetoxidation process. Ligand effects were achieved at ZrO2 interphase with PdCu particles, promoting VAM desorption, due to the H spillover and surface hydroxyl recovery; However, the orientation of alloys suggest that ordered PdCu over ZrO2−Ti+4, enables efficiently the dehydrogenation step. [ABSTRACT FROM AUTHOR]

We present the preparation and investigation of a fluorine-free surface-active bis-N-heterocyclic carbene (NHC) platinum(II) complex - trans-[Pt(mPEG 3 C 8 Im) 2 Cl 2 ] - for interface-enhanced supported ionic liquid phase (SILP) catalysis within a group of (mPEG n )-substituted ionic liquids (ILs) ([(mPEG n ) 2 Im][A] ILs). The complex was characterized by means of single-crystal X-ray diffraction (scXRD) analysis and multinuclear ( 1 H, 13 C, 195 Pt) NMR spectroscopy, indicating the presence of two almost equimolar syn-anti-rotamers of the square-planar complex in solution. Angle-resolved X-ray photoelectron spectroscopy (ARXPS) revealed pronounced interface-accumulation of trans-[Pt(mPEG 3 C 8 Im) 2 Cl 2 ] in IL solutions of [(mPEG 2 ) 2 Im][A] (A - =I - and PF 6 - )., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

We studied the adsorption and thermal behavior of the nitrile-functionalized ionic liquid (IL) [C 3 CNC 1 Im][Tf 2 N] on Au(111) and Pt(111) between 150 and 600 K. Ultrathin films were prepared at 150 K by physical vapor deposition (PVD) and were characterized by angle resolved X-ray photoelectron spectroscopy (ARXPS). At 150 K, the IL adsorbs intact with a similar orientation on both surfaces: In the first layer, the so-called wetting layer, the cation lies flat on the surface and the anion is bound in cis -configuration with the SO 2 groups toward the surface and the CF 3 groups away from the surface. On Au(111), subsequent deposition of IL in the multilayer regime at 150 K shows 2D growth up until ∼0.75 ML and a transition to moderate 3D at higher coverages. Temperature-programmed XPS indicates a change in surface morphology toward more pronounced 3D islands for the multilayers on top of the wetting layer between 220 and 290 K. From 350 to 440 K, desorption of multilayers occurs, with IL decomposition starting at 375-400 K. On the more reactive Pt(111) surface, decomposition starts already above 280 K. Notably, this temperature is ∼80 K higher than the onset for decomposition of related nonfunctionalized imidazolium-based ILs, that is, [C 2 C 1 Im][OTf], [C 1 C 1 Im][Tf 2 N], and [C 8 C 1 Im][Tf 2 N] on Pt(111). This difference is attributed to the nitrile functionality. Our findings demonstrate that functionalizing ILs significantly modifies their thermal properties, which is of high relevance for SCILL (solid catalyst with an ionic liquid layer) systems.

In this work, we performed a detailed analysis of the x-ray photoemission spectroscopy (XPS) of the Mn 2 p peak for Mn 3 O 4 (001) thin films. This is a challenging task since Mn 3 O 4 is composed of two different cations, Mn 2+ at tetrahedral and Mn 3+ at octahedral sites, which both contribute to the XPS spectra. The oxide spectra consist of many multiplets arising from the angular momentum coupling of the open Mn 2 p and 3 d shells, thus increasing the spectrums' complexity. Moreover, the energy spacing and intensities of the different multiplets also reflect the covalent mixing between Mn 3 d and O 2 p shells. However, we show that a detailed analysis, which provides relevant information about the cations in the oxide structure, is possible. We prepared experimentally different Mn 3 O 4 films on Au(111), and their structure was monitored with the diffraction pattern obtained with low-energy electron diffraction. The Mn 2 p spectra were fit, guided by cluster model theoretical predictions, and checked for films prepared at different oxygen partial pressures. Therefore, we could observe the Mn 2+ and Mn 3+ cations' relative concentration in the Mn 2 p mains peaks., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

The concept of a solid catalyst with an ionic liquid layer (SCILL) is a promising approach to improve the selectivity of noble metal catalysts in heterogeneous reactions. In order to understand the origins of this selectivity control, we investigated the growth and thermal stability of ultrathin 1-ethyl-3-methylimidazolium trifluormethanesulfonate [C 2 C 1 Im][OTf] films on Pt(111) by infrared reflection absorption spectroscopy (IRAS) and X-ray photoelectron spectroscopy (XPS) in time-resolved and temperature-programmed experiments. We combined these spectroscopy experiments with scanning tunneling microscopy (STM) to obtain detailed insights into the orientation and adsorption geometry of the ions in the first IL layer. Furthermore, we propose a mechanism for the thermal evolution of [C 2 C 1 Im][OTf] on Pt(111). We observe an intact IL layer on the surface at temperatures below 200 K. Adsorbed [C 2 C 1 Im][OTf] forms islands, which are evenly distributed over the surface. The [OTf] - anion adsorbs via the SO 3 group, with the molecular axis perpendicular to the surface. Anions and cations are arranged next to each other, alternating on the Pt(111) surface. Upon heating to 250 K, we observe changes in geometry and structural distribution. Whereas at low temperature, the ions are arranged alternately for electrostatic reasons, this driving force is no longer decisive at 250 K. Here, a phase separation of two different species is discernible in STM. We propose that this effect is due to a surface reaction, which changes the charge of the adsorbates. We assume that the IL starts to decompose at around 250 K, and thus, pristine IL and decomposition products coexist on the surface. Also, IRAS and XPS show indication of IL decomposition. Further heating leads to increased IL decomposition. The reaction products associated with the anions are volatile and leave the surface. In contrast, the cation fragments remain on the surface up to temperatures above 420 K.