Temperature-programmed X-ray Photoelectron Spectroscopy Research Articles

Bromination of 2D materials

The adsorption, reaction and thermal stability of bromine on Rh(111)-supported hexagonal boron nitride (h-BN) and graphene were investigated. Synchrotron radiation-based high-resolution x-ray photoelectron spectroscopy (XPS) and temperature-programmed XPS allowed us to follow the adsorption process and the thermal evolution in situ on the molecular scale. On h-BN/Rh(111), bromine adsorbs exclusively in the pores of the nanomesh while we observe no such selectivity for graphene/Rh(111). Upon heating, bromine undergoes an on-surface reaction on h-BN to form polybromides (170–240 K), which subsequently decompose to bromide (240–640 K). The high thermal stability of Br/h-BN/Rh(111) suggests strong/covalent bonding. Bromine on graphene/Rh(111), on the other hand, reveals no distinct reactivity except for intercalation of small amounts of bromine underneath the 2D layer at high temperatures. In both cases, adsorption is reversible upon heating. Our experiments are supported by a comprehensive theoretical study. DFT calculations were used to describe the nature of the h-BN nanomesh and the graphene moiré in detail and to study the adsorption energetics and substrate interaction of bromine. In addition, the adsorption of bromine on h-BN/Rh(111) was simulated by molecular dynamics using a machine-learning force field.

Cu modified VOx/Silicalite-1 catalysts for propane dehydrogenation in CO2 atmosphere

Propane dehydrogenation in CO2 atmosphere (PDH-CO2) is of interest with a potential to raise propane conversion. Here the catalytic performance of Cu modified 10VOx/Silicalite-1(S-1) for PDH-CO2 is presented for the first time. The initial propane conversion of 68.8% on 0.5Cu-10VOx/S-1 was reached from 59.3% on 10VOx/S-1, along with the CO2 conversion of 44.5% from 32.4%. The role of S-1 support and Cu modification were elucidated by means of X-ray diffraction (XRD), ultraviolet–visible diffuse reflection (UV–Vis), NH3/CO2 temperature-programmed desorption (NH3/CO2-TPD), H2 temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) characterization. While dispersing VOx, non-acidic S-1 minimized the side reactions usually occurring on the strong acidic sites. Cu modification promoted the dispersion of VOx and enabled 10VOx/S-1 exposing more weak acidic sites and basic sites, boosting respectively the adsorption of propane and CO2, for concurrently accelerating the reverse water gas shift (RWGS). Moreover, the highly dispersed V5+ was formed on the surface whereas the percentage of inactive V3+ decreased.

Mechanistic and Kinetic Measurements of Elementary Surface Reactions Using Temperature-Programmed X-ray Photoelectron Spectroscopy.

This paper describes a method by which surface-reaction kinetics can be measured by slowly and precisely ramping up the surface temperature at a constant rate while simultaneously collecting X-ray photoelectron spectra (XPS). This approach results in the collection of a large amount of data over relatively small temperature steps to produce quasi-continuous kinetic data. The method is illustrated for the desorption and reaction of diethyl disulfide (DEDS) on a Au(111) substrate in ultrahigh vacuum, where the results can be compared with previous conventional temperature-programmed desorption (TPD) data from Au(111). Experiments were carried out using a double-pass cylindrical-mirror analyzer with a channeltron detector to demonstrate how this approach can be implemented in a routine, multitechnique vacuum chamber. The approach will be even more effective in a more modern, specialized XPS apparatus with high-transmission hemispherical analyzers with multichannel array detectors, which will enable the spectra of several elements to be measured simultaneously. The results yielded an activation energy for multilayer desorption of DEDS of 41 ± 1 kJ/mol, with a pre-exponential factor of 8 ± 7 × 1012 s-1, an activation energy of 53 ± 6 kJ/mol and pre-exponential factor of 9 ± 8 × 1013 s-1 for monolayer desorption and an activation energy of 90 ± 6 kJ/mol with a prefactor of 1.0 ± 0.3 × 1015 s-1 for the reaction of adsorbed ethyl thiolate species to adsorbed DEDS. While these results were collected for a system for which the kinetic data could have been obtained using conventional TPD, this method can be more usefully applied to those surface reaction processes that do not rely on the formation of desorption products. This system, having been previously studied by TPD, facilitates a comparison with results obtained by conventional methods.

Mechanistic insights into on-surface reactions from isothermal temperature-programmed X-ray photoelectron spectroscopy.

On-surface synthesis often proceeds under kinetic control due to the irreversibility of key reaction steps, rendering kinetic studies pivotal. The accurate quantification of reaction rates also bears potential for unveiling reaction mechanisms. Temperature-Programmed X-ray Photoelectron Spectroscopy (TP-XPS) has emerged as an analytical tool for kinetic studies with splendid chemical and sufficient temporal resolution. Here, we demonstrate that the common linear temperature ramps lead to fitting ambiguities. Moreover, pinpointing the reaction order remains intricate, although this key parameter entails information on atomistic mechanisms. Yet, TP-XPS experiments with a stepped temperature profile comprised of isothermal segments facilitate the direct quantification of rate constants from fitting time courses. Thereby, rate constants are obtained for a series of temperatures, which allows independent extraction of both activation energies and pre-exponentials from Arrhenius plots. By using two analogous doubly versus triply brominated aromatic model compounds, we found that their debromination on Ag(111) is best modeled by second-order kinetics and thus proceeds via the involvement of a second, non-obvious reactant. Accordingly, we propose that debromination is activated by surface supplied Ag adatoms. This hypothesis is supported by Density Functional Theory (DFT) calculations. We foresee auspicious prospects for this TP-XPS variant for further exploring the kinetics and mechanisms of on-surface reactions.

Sheet-Like Morphology CuO/Co3O4 Nanocomposites for Enhanced Catalysis in Hydrogenation of CO2 to Methanol.

The selective hydrogenation of CO2 into high-value chemicals is an effective approach to address environmental issues. Cobalt-based catalysts have significant potential in CO2 hydrogenation reaction systems; however, there is a need to control their selectivity better. In this study, copper is introduced onto Co3O4 nanosheets using the ion exchange reverse loading method. The unique interaction of these materials significantly alters the selectivity of the cobalt-based catalyst. Results from scanning transmission electron microscopy and scanning electron microscopy indicate that this catalyst enables a more even dispersion of copper species in the Co3O4 nanosheets. Temperature-programmed reduction and X-ray photoelectron spectroscopy reveal that the catalyst facilitates the metal-metal interaction between Co and Cu. Temperature-programmed desorption experiments for CO2 and H2 demonstrate that the close interaction between Co and Cu modifies CO2 adsorption, leading to differences in catalytic activity. Moreover, the catalyst effectively suppresses CO2 methanation and promotes methanol formation by altering the alkalinity of the catalyst surface and weakening the hydrogen dissociation ability.

Bromine Adsorption and Thermal Stability on Rh(111): A Combined XPS, LEED and DFT Study.

This study addresses a fundamental question in surface science: the adsorption of halogens on metal surfaces. Using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (XPS), temperature-programmed XPS, low-energy electron diffraction (LEED) and density functional theory (DFT) calculations, we investigated the adsorption and thermal stability of bromine on Rh(111) in detail. The adsorption of elemental bromine on Rh(111) at 170 K was followed in situ by XPS in the Br 3d region, revealing two individual, coverage-dependent species, which we assign to fcc hollow- and bridge-bound atomic bromine. In addition, we find a significant shift in binding energy upon increasing coverage due to adsorbate-adsorbate interactions. Subsequent heating shows a high thermal stability of bromine on Rh(111) up to above 1000 K, indicating strong covalent bonding. To complement the XPS data, LEED was used to study the long-range order of bromine on Rh(111): we observe a (√3×√3)R30° structure for low coverages (≤0.33 ML) and a star-shaped compression structure for higher coverages (0.33-0.43 ML). Combining LEED and DFT calculations, we were able to visualize bromine adsorption on Rh(111) in real space for varying coverages.

Pt-Doped Lanthanum Ferrites as Versatile Electrode Material for Solid Oxide Cells

La0.6Sr0.4Fe0.8Co0.2O3-δ (LSCF) alone or mixed with doped ceria represents the reference air electrode material for IT-SOFC/SOEC, thanks to its intrinsic MIEC nature and unrivaled catalytic activity towards oxygen exchange reactions. Nevertheless, a steep growth in cobalt demand for automotive (EVs) and storage applications is expected in the next decades, and ethical issues related to cobalt mining in politically unstable countries endanger cobalt supply chain [1]. Noble metal doping to a low extent ( ≤ 5% mol) has drawn attention as a valid strategy to provide the parent oxide structure with high catalytic activity [2][3]. Such amounts of platinum-group-metals (PGM) could be profitably harvested from secondary sources, such as spent automotive three-way catalysts (TWCs) [4], rendering their supply less dependent from localized low-grade ores. In particular, due to the tendency of PGM to be easily reduced to the metallic state, PGM-doped perovskites have found application mainly as fuel electrode materials. Noble metal exsolution endows the parent perovskite with finely dispersed nanoparticles firmly anchored to the oxide substrate, that display high catalytic activity and stability [5].Here, platinum-doping on strontium-substituted lanthanum ferrites is explored as an innovative strategy to enhance the parent perovskite catalytic activity both in reducing and oxidizing environment. The ultimate goal is the design of a multi-functional electrode for Reversible Solid Oxide Cells (r-SOCs). La0.6Sr0.4Fe1-xPtxO3-δ, X = 0.005, 0.01, 0.05 (LSFPtX) stoichiometries were successfully synthesized and characterized by means of X-ray Powder Diffraction (XPRD) (Fig. 1), thermogravimetric analysis (TG), oxygen temperature-programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). LSFPtX were tested in symmetric cells to evaluate their activity as air electrode materials in terms of polarization resistance vs. temperature and vs. pO2. The rate-limiting steps of oxygen exchange reactions were investigated by means of electrochemical impedance spectroscopy (EIS) fitting experimental data with equivalent circuit (EC) modelling and distribution of relaxation times (DRT). Results were compared both to the undoped (LSF) and to a commercially available state-of-art 20 mol% Co-substituted LSCF. LSFPtX structural evolution is evaluated at different pO2 and in several SOCs operational environments (5%H2/Ar, 100% CO2 and 50% CO2 : 50% CO). B-site exsolution was studied by means of temperature-programmed reduction (H2-TPR) and scanning electron microscopy (FE-SEM) to assess their applicability as fuel electrode materials as well. Finally, LSGM-based symmetric cells were tested as SOFC and CO2-SOEC, evaluating the operational reversibility and the long-term stability.[1] IEA, Total Cobalt Demand by Sector and Scenario, October 2022, pp. 2020–2040.[2] Marcucci, A., Zurlo, F., Sora, I. N., Placidi, E., Casciardi, S., Licoccia, S., & Di Bartolomeo, E. (2019). A redox stable Pd-doped perovskite for SOFC applications. Journal of Materials Chemistry A, 7(10), 5344-5352.[3] Marasi, M., Duranti, L., Luisetto, I., Fabbri, E., Licoccia, S., & Di Bartolomeo, E. (2023). Ru-doped lanthanum ferrite as a stable and versatile electrode for reversible symmetric solid oxide cells (r-SSOCs). Journal of Power Sources, 555, 232399.[4] Karim, S., & Ting, Y. P. (2021). Recycling pathways for platinum group metals from spent automotive catalyst: A review on conventional approaches and bio-processes. Resources, Conservation and Recycling, 170, 105588.[5] Kothari, M., Jeon, Y., Miller, D. N., Pascui, A. E., Kilmartin, J., Wails, D., ... & Irvine, J. T. (2021). Platinum incorporation into titanate perovskites to deliver emergent active and stable platinum nanoparticles. Nature Chemistry, 13(7), 677-682. Figure 1

Chemisorption of CO2 on Nitrogen-Doped Graphitic Carbons.

The adsorption of CO2 on nitrogen-doped graphitic carbon materials, such as graphene nanosheet (GNS) powder and highly oriented pyrolytic graphite (HOPG), was comparatively studied using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Desorption of CO2 was observed at approximately 380 K for both pyridinic-nitrogen (pyri-N)-doped GNS and pyri-N-doped HOPG samples in the TPD experiments, whereas no CO2 desorption was observed for graphitic nitrogen-doped HOPG. This indicated that only pyri-N species create identical CO2 adsorption sites on any graphitic carbon surface. The adsorption energies of CO2 on pyri-N-doped carbons were estimated between 101 and 108 kJ mol-1, indicating that chemisorption, rather than physisorption, took place. The CO2 adsorption/desorption process was reproducible in repeated measurements, and no CO2 dissociation occurred during the process, suggesting that it is a promising CO2 capturing material. The O 1s peak of the adsorbed CO2 clearly appeared at 531.5-532 eV in the XPS measurements. The N 1s peak of pyri-N did not change with CO2 adsorption, indicating that CO2 is not directly bound to pyri-N but is adsorbed on a carbon atom near the pyridinic nitrogen via the nonbonding pz orbital of the carbon atom.

PtPd nanoparticles on LaCoO3 with ruthenium in the interfaces for CO oxidation

In this work, trimetallic Pt-Pd-Ru nanoparticles (NPs) loaded on LaCoO3 perovskite were prepared by using LaCo0.9PtxPdyRu0.1-x-yO3 as precursor through citrate complexing sol-gol method and characterized by N2 adsorption/desorption, XRD, H2 Temperature-programmed reduction, XPS, CO-TPD, ICP-OES and TEM techniques. The special structure of the trimetallic catalyst and its catalytic performance for CO oxidation were investigated. The results demonstrated that Pt, Ru and Pd ions were successfully incorporated into the lattice of LaCoO3 to form with perovskite structure. After the reduction treatment, the catalyst Pt-Pd-Ru/LaCoO3 was obtained, which exhibited special structure of Pt surface, Pd sub-surface and Ru interface. The trimetallic Pt-Pd-Ru/LaCoO3 displayed the highest activity and best stability for CO oxidation as compared with corresponding bimetallic and monometallic catalysts. The significant improvement on the catalytic activity was ascribed to the combination of the oxygen vacancies on the surface of LaCoO3 and the highly dispersed NPs. The excellent stability was owing to the special metal-support interaction, that is the Pt-Pd in the NPs are connected and adhered to the support of LaCoO3 by the Ru species in the interface.

Surface Chemistry of the Molecular Solar Thermal Energy Storage System 2,3-Dicyano-Norbornadiene/Quadricyclane on Ni(111).

The front cover artwork is provided by the group of Prof. Dr. Christian Papp at Physical Chemistry II of FAU Erlangen-Nürnberg and FU Berlin. The image shows the isomerization reaction of the molecule pair 2,3-dicyano-norbornadiene/quadricyclane as potential molecular solar thermal (MOST) energy storage system. Read the full text of the Research Article at 10.1002/cphc.202200199.

Cu/ACF adsorbent modified by non-thermal plasma for simultaneous adsorption–oxidation of H2S and PH3

Non-thermal plasma (NTP) surface modification technology is a new method to control the surface properties of materials, which has been widely used in the field of environmental protection because of its short action time, simple process and no pollution. In this study, Cu/ACF (activated carbon fiber loaded with copper) adsorbent was modified with NTP to remove H2S and PH3 simultaneously under low temperature and micro-oxygen condition. Meanwhile, the effects of different modified atmosphere (air, N2 and NH3), specific energy input (0–13 J/mL) and modification time (0–30 min) on the removal of H2S and PH3 were investigated. Performance test results indicated that under the same reaction conditions, the adsorbent modified by NH3 plasma with 5 J/mL for 10 min had the best removal effect on H2S and PH3. CO2 temperature-programmed desorption and X-ray photoelectron spectroscopy (XPS) analyzes showed that NH3 plasma modification could introduce amino functional groups on the surface of the adsorbent, and increase the types and number of alkaline sites on the surface. Brunauer-Emmett-Teller and scanning electron microscopy showed that NH3 plasma modification did not significantly change the pore size structure of the adsorbent, but more active components were evenly exposed to the surface, thus improving the adsorption performance. In addition, X-ray diffraction and XPS analysis indicated that the consumption of active components (Cu and Cu2O) and the accumulation of sulfate and phosphate on the surface and inner pores of the adsorbent are the main reasons for the deactivation of the adsorbent.

Contribution of Na/K Doping to the Activity and Mechanism of Low-Temperature COS Hydrolysis over TiO2-Al2O3 Based Catalyst in Blast Furnace Gas

As an organic sulfur pollutant generated in blast furnace gas, carbonyl sulfide (COS) has attracted more attention due to its negative effects on the environment and economy. The TiO2-Al2O3 composite metal oxide (Ti0.5Al) with uniformly dispersed particles was prepared by the co-precipitation method. And on this basis, a series of Na/K-doped catalysts were prepared separately. The activity evaluation results showed that the introduction of Na/K significantly improved the low-temperature COS hydrolysis activity, which exhibited a COS conversion of 98% and H2S yield of 95% at 75 °C with 24,000 h–1. And K showed a better promoting effect than Na. Brunauer–Emmett–Teller (BET) results revealed the increased mesopore proportion of Na/K-modified catalysts. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that Na and K formed prismatic and nanorod-like structures, respectively. More weakly basic sites with enhanced intensity and decreased Oads/Olat content contributed to the excellent catalytic activity, as certified by the results of CO2 temperature-programmed desorption (CO2-TPD) and X-ray photoelectron spectroscopy (XPS). It was also proposed that the decrease of weakly basic sites ultimately deactivated catalyst activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that the introduction of Na/K enhanced the dissociation of H2O, and the generated abundant hydroxyl groups promoted the adsorption of COS and formed surface transition species, such as HSCO2– and HCO3–.

On-surface Synthesis: What Happens Behind the Scenes?

On-surface synthesis has become a powerful approach to produce low-dimensional carbon-based nanostructures with atomistic precision. A large variety of analytical tools and methods are available to provide efficient monitoring of on-surface reactions, among which, scanning probe microscopy (SPM) has proven to be particularly efficient to characterize reaction intermediates and products down to the atomic scale. Nevertheless, due to limited temporal resolution, difficulties to explore the full temperature range, and lack of identifying the chemical environment of all elements involved in on-surface processes, SPM is ideally complemented with temperature programmed X-ray photoelectron spectroscopy (TP-XPS). In this short review, we aim to unveil some of the capabilities of synchrotron based TP-XPS reporting on our own research on Ullmann-type on-surface coupling reactions.

A high-resolution X-ray photoelectron spectroscopy study on the adsorption and reaction of ethylene on Rh(1 1 1)

The adsorption and thermal evolution of ethylene on Rh(111) were investigated by state-of-the-art surface science techniques. Synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (XPS) and temperature-programmed XPS allowed for the examination of the adsorption process and the reaction pathway of ethylene on Rh(111). At 140 K, ethylene adsorbs molecularly in a symmetrical geometry. The reaction intermediates formed upon heating were identified by the vibrational fine structure of XPS. At approximately 200 K, ethylidyne emerges, as expected from literature. Above 350 K, we observe the evolution of methylidyne. Simultaneously, decomposition to carbides sets in, which is completed at ∼ 460 K.

Asymmetric Elimination Reaction on Chiral Metal Surfaces.

The production of enantiopure materials and molecules is of uttermost relevance in research and industry in numerous contexts, ranging from nonlinear optics to asymmetric synthesis. In the context of the latter, dehalogenation, which is an essential reaction step for a broad class of chemical reactions, is investigated; specifically, dehalogenation of prochiral 5-bromo-7-methylbenz(a)anthracene (BMA) on prototypical, chiral, intermetallic PdGa{111} surfaces under ultrahigh vacuum conditions. Asymmetric halogen elimination is demonstrated by combining temperature-programmed X-ray photoelectron spectroscopy, scanning probe microscopy, and density functional theory. On the PdGa{111} surfaces, the difference in debromination temperatures for the two BMA surface enantiomers amounts up to an unprecedented 46 K. The significant dependence of the dehalogenation temperature of the BMA surface enantiomers on the atomic termination of the PdGa{111} surfaces implies that the ensemble effect is pronounced in this reaction step. These findings evidence enantiospecific control and hence promote intrinsically chiral crystals for asymmetric on-surface synthesis.

Effects of Treatment Conditions on Pd Speciation in CHA and Beta Zeolites for Passive NO x Adsorption.

The structure and evolution of Pd species in Pd-exchanged zeolite materials intended for use as passive NOx adsorbers were examined under various pretreatment conditions. Using in situ CO-diffuse reflectance infrared spectroscopy, Pd structures were characterized after 500 °C pretreatments in inert (Ar), water (1–2% H2O in Ar), oxidizing (air), and reducing (H2, CO) atmospheres. Two zeolites of similar Si/Al ratios but different framework topologies (Beta, CHA) were found to show different distributions of Pd species, depending on the reducing agent used. Reduction in H2 (500 °C; 10% H2 in Ar) followed by re-oxidation (500 °C; air) led to higher amounts of single-site Pd ions on Pd-CHA than Pd-Beta, whereas high-temperature reduction in CO (500 °C; 1000 ppm CO in Ar) followed by re-oxidation (500 °C; air) led to significant loss of ionic Pd on both Pd-CHA and Pd-Beta, albeit H2 temperature-programmed reduction and XPS experiments suggest that this phenomena may be limited to surface Pd. High-temperature treatments with water (500 °C; 1–2% H2O in Ar) are shown to form either Pd metal or PdO particles, with Pd-Beta being more susceptible to these effects than Pd-CHA. This work suggests that the effects of CO are especially problematic with respect to the durability of these materials in passive NOx adsorption applications, especially in the case of Beta zeolite.

X-ray-Induced CO2 Formation via CO Reaction with TiO2 at Cryogenic Temperature.

Cosmic rays, γ-rays, and X-ray-driven reactions on interstellar grains have been the main focus in understanding the extraterrestrial synthesis of complex organic molecules. Herein, using temperature-programmed desorption and X-ray photoelectron spectroscopy, we report for the first time X-ray-induced CO2 production from a CO-covered rutile TiO2(110) surface at 110 K, in addition to X-ray-induced CO desorption. The X-ray-induced CO2 production was found to follow a Mars and van Krevelen (MvK) mechanism via the reaction between adsorbed CO and surface lattice oxygen of TiO2. Defects of TiO2 suppress the X-ray-induced CO2 production but promote the X-ray-induced CO desorption. These findings suggest a novel X-ray-induced CO-to-CO2 reaction on oxide surfaces at cryogenic temperature likely occurring in the interstellar medium and also warn us to keep in mind the possibility of X-rays inducing chemical reactions during structural characterizations of oxides with X-ray-involved techniques.

Identification of Topotactic Surface-Confined Ullmann-Polymerization.

On-surface Ullmann coupling is an established method for the synthesis of 1D and 2D organic structures. A key limitation to obtaining ordered polymers is the uncertainty in the final structure for coupling via random diffusion of reactants over the substrate, which leads to polymorphism and defects. Here, a topotactic polymerization on Cu(110) in a series of differently-halogenated para-phenylenes is identified, where the self-assembled organometallic (OM) reactants of diiodobenzene couple directly into a single, deterministic product, whereas the other precursors follow a diffusion driven reaction. The topotactic mechanism is the result of the structure of the iodine on Cu(110), which controls the orientation of the OM reactants and intermediates to be the same as the final polymer chains. Temperature-programmed X-ray photoelectron spectroscopy and kinetic modeling reflect the differences in the polymerization regimes, and the effects of the OM chain alignments and halogens are disentangled by Nudged Elastic Band calculations. It is found that the repulsion or attraction between chains and halogens drive the polymerization to be either diffusive or topotactic. These results provide detailed insights into on-surface reaction mechanisms and prove the possibility of harnessing topotactic reactions in surface-confined Ullmann polymerization.

Selective Oxygen and Hydrogen Functionalization of the h-BN/Rh(111) Nanomesh.

We present detailed studies on the covalent adsorption of molecular oxygen and atomic hydrogen on the hexagonal boron nitride (h-BN) nanomesh on Rh(111). The functionalization of this two-dimensional (2D) material was investigated under ultra-high vacuum conditions using synchrotron radiation-based in situ high-resolution X-ray photoelectron spectroscopy, temperature-programmed X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. We are able to provide a deep insight into the adsorption behavior and thermal stability of oxygen and hydrogen on h-BN/Rh(111). Oxygen functionalization was achieved via a supersonic molecular beam while hydrogen functionalization was realized using an atomic hydrogen source. Adsorption of the respective species was observed to occur selectively in the pores of h-BN leading to spatially defined modification of the 2D layer. The adsorption of the observed molecular oxygen species was found to be an activated process that requires high-energy oxygen molecules. Upon heating to 700 K, oxygen functionalization was observed to be almost reversible except for small amounts of boron oxides evolving due to the reaction of oxygen with the 2D material. Hydrogen functionalization of h-BN/Rh(111) was fully reversed upon heating to about 640 K.

Cinnamaldehyde adsorption and thermal decomposition on copper surfaces

The uptake and thermal chemistry of cinnamaldehyde on Cu(110) single-crystal surfaces were characterized by temperature-programmed desorption and x-ray photoelectron spectroscopy (XPS). Adsorption at 85 K appears to be initiated by low-temperature decomposition to form styrene, which desorbs at 190 K, followed by the sequential buildup of a molecular monolayer and then a condensed molecular film. Molecular desorption from the monolayer occurs at 410 K, corresponding to a desorption energy of approximately 98 kJ/mol, and further decomposition to produce styrene (again) and other fragmentation products is seen at 550 K. The molecular nature and the quantitation of the low-temperature uptake were corroborated by the XPS data, which also provided hints about the adsorption geometry adopted by the unsaturated aldehyde on the surface. Density functional theory calculations, used to estimate adsorption energies as a function of coverage and coordination mode, pointed to possible η1-O binding, at least at high coverages, and to a stabilizing effect on the surface by the aromatic ring of cinnamaldehyde. Finally, coadsorption of oxygen on the surface was found to weaken the binding of cinnamaldehyde to the Cu substrate at high coverages without enhancing its uptake, but to not modify the decomposition mechanism or energetics in any significant way.