Rh 3d Research Articles

Photoelectrochemical Performance Improving Mechanism: Hybridization Appearing at the Energy Band of BiVO4 Photoanode by Doped Quantum Layers Modification.

Surface passivation of the photoelectrode by wide bandgap semiconductor quantum layer is an important strategy to improve work stability and surface state inhibition. However, an inevitable energy barrier is generated during the quantum tunneling process of the photocarriers. To overcome this shortage, a tandem photo-generated hole transfer route is fabricated on BiVO4 photoanode by doped dual-quantum layers modification, Ni-ZnO (5nm) and Rh-SrTiO3 (≈10nm). Modulated photoelectrochemical (PEC), Scanning Kelvin Probe (SKP), and DFT calculation method results indicate that a tandem hole ohmic contact route is formed in the photoanode to reduce the quantum tunneling energy barrier, meanwhile, the photon absorption capacity of BiVO4 is improved after doped quantum layers modification. Both a phenomenal attribute to the energy band hybridization between Ni, Rh 3d orbits in quantum layers with BiVO4 photoanode. Then, the modified BiVO4 photoanode achieves the recoded photocurrent density of 6.47 and 5.18mAcm-2 (Na2 SO3 electrolyte, VRHE = 1.23V) under simulated sun light (100mWcm-2 AM 1.5G) by xenon lamp illumination without and with UV composition cutting down to ≈5%, respectively. Generally, this work will highlight a potential application in the fields of PEC water splitting and photovoltaic conversion for various semiconductor nanomaterials.

On the Real Nature of Rh Single‐Atom Catalysts Dispersed on the ZrO2 Surface

AbstractThe nature of a Rh single‐atom catalyst (SAC) stabilized on the surface of tetragonal zirconia, t‐ZrO2, is investigated here by performing extensive DFT calculations on various possible structural models and comparing the resulting spectral properties with existing data from the literature. The models considered include a Rh atom adsorbed on the clean surface, (Rh)ads, Rh atoms stabilized by the reaction with surface OH groups to form direct Rh−O bonds, (RhO)ads, and (RhO2)ads, the interaction of a Rh atom with an OH group, (RhOH)ads, and a Rh atom replacing Zr in the lattice, (Rh)subZr. Also a t‐ZrO2 supported Rh6 cluster has been considered for comparison with Rh single atoms. Surface heterogeneity has been taken into account by computing the various Rh species at terraces and at step sites of the zirconia surface. Based on the calculated adsorption energies, Rh 3d core level binding energies, and stretching frequencies of adsorbed CO and comparison with the experimental data we conclude that the potential candidates for Rh SAC on t‐ZrO2 are (RhO)ads and (RhOH)ads species.

Rhodium Catalyst–Ionic Liquids Interaction by X-ray Photoelectron Spectroscopy Data

We investigate the Schrock–Osborn catalyst, [Rh(COD)(PPh3)2][PF6], in a series of ionic liquids by XPS. The electronic environment of the rhodium centre is demonstrated. The subtle change of the electronic environment of the rhodium centre due to the catalyst-ionic liquids interaction is revealed based upon Rh 3d binding energy. It suggests that the anion of ionic liquids can have significant impact on the electronic environment of the rhodium centre.

Pt nanostructures with different Rh surface entities: Impact on NH3 electro-oxidation

Ammonia electro-oxidation activity is promoted at Pt nanostructured catalysts which combine high surface area values and a high proportion of (100) surface atoms. The latter is extensively known to be the most active surface arrangement of atoms for NH3 oxidation. In the present study, Pt(100) nanostructured thin films were prepared and subsequently modified by surface functionalization with rhodium through pulsed electrodeposition. Rh surface coverage was varied by modifying the number of applied electrodeposition pulses, and was found to modify the voltammetric Hupd features. When Rh surface content was assessed by Hupd deconvolution analyses, it was revealed that Rh nucleation first occurred at (100) Pt step sites in the form of Rh(100) sub-monolayers, and subsequently grew further to form Rh multilayer species. For minute amounts of rhodium, NH3 activity is increased slightly, provided that long range (100) Pt wide domains were not shortened. The lower onset potential for NH3 oxidation in the presence of Rh surface atoms, which is shifted negatively by more than 50mV as compared to Pt, is attributed to the NH3 oxidative dehydrogenation processes at lower potential values. For similar Rh coverage (around 20%), similar NH3 activity is obtained at pseudomorphic Rh(100) adlayers and Rh 3D islands, a finding which emphasizes the non-specific NH3 activity of Rh(100) atoms.

X-ray photoelectron spectroscopy as a probe of the interaction between rhodium acetate and ionic liquids

X-ray photoelectron spectroscopy (XPS) is used as a probe of the interaction between rhodium acetate ([Rh2(OAc)4]) and ionic liquids. Due to the impact of the anion of ionic liquids on the electronic environment of the rhodium centre, the measured Rh 3d binding energies of [Rh2(OAc)4] dissolved in a series of ionic liquids were found to decrease along with the increasing of the basicity of anions. The reduction of Rh(II) to Rh(0) in 1-octyl-3methylimidazolium acetate ([C8C1Im][OAc]) under UHV condition was monitored by XPS. The intensity of the new formed metallic Rh(0) peak was found increased along with time. The surface enrichment of the new formed Rh(0) species in the system was also concluded.

Synthesis and electrochemistry of p-substituted phenyl diphenylphosphinite rhodium(I) complexes

The electrochemical behaviour of a series of rhodium(I) complexes of the type [Rh(CH3COCHCOCH3)CO(Ph2POPh-p-R)], where R=H (1), CH3 (2), tBu(3) and Cl(4)] revealed an irreversible oxidation of Rh(I) to Rh(III), an irreversible oxidation of the phosphorus atom followed by the decomposition of the phosphinite ligand. An unexpected reaction occurred between the electrochemical internal standard, free ferrocene, in its ferricinium ion form and the radical cation of the oxidised diphenyl phosphinite, leading to uncharacteristic electrochemical behaviour. Electronic communication between different molecular fragment was confirmed by the linear relationships obtained between the Gordy group electronegativities of the R-groups on the phosphinites (χR) and the Epa of Rh and the phosphorus atoms as well as the binding energy (eV) (measured by XPS) of the Rh 3d and P 2p peak positions. V-shape correlations were found between the Hammett constants of the R-groups on the phosphinites (χR) and the oxidation potentials and binding energies. This shows the difference in stabilisation either resonance or inductive between the electrondonating and electronwithdrawing substituents.

X-ray photoelectron spectroscopy as a probe of rhodium-ligand interaction in ionic liquids

We use X-ray photoelectron spectroscopy (XPS) to identify the interaction between the rhodium atom and phosphine ligands in six 1-octyl-3-methylimidazolium-based ionic liquids ([C8C1Im][X]). The formation of a mono-phosphine rhodium complex based upon addition of triphenylphosphine (PPh3) is confirmed by XPS in all ionic liquids studied herein. Due to the electron donation effect of the ligand, the rhodium atom becomes more negatively charged and thus exhibits a lower measured binding energy. The influence of the anion basicity on the formation of different types of rhodium complexes is also investigated. By introducing a biphosphine ligand, a chelated diphosphine rhodium complex is formed in ionic liquids with more basic anions and verified by both XPS and Infrared Spectroscopy (IR). The measured Rh 3d binding energies are correlated to the reaction selectivity of a hydroformylation reaction which inspires a method to design a metal catalyst to control the chemical reaction towards desired products in the future.

The N2O activation by Rh5 clusters. A quantum chemistry study.

Nitrous oxide (N2O) is a by-product of exhaust pipe gases treatment produced by motor vehicles. Therefore, the N2O reduction to N2 is necessary to meet the actual environmental legislation. The N2O adsorption and dissociation assisted by the square-based pyramidal Rh5 cluster was investigated using the density functional theory and the zero-order regular approximation (ZORA). The Rh5 sextet ground state is the most active in N2O dissociation, though the quartet and octet states are also active because they are degenerate. The Rh5 cluster spontaneously activates the N2─O cleavage, and the reaction is highly exothermic ca. -75kcal mol(-1). The N2─O breaking is obtained for the geometrical arrangement that maximizes the overlap and electron transfers between the N2O and Rh5 frontier orbitals. The Rh5 high activity is due to the Rh 3d orbitals are located between the N2O HOMO and LUMO orbitals, which makes possible the interactions between them. In particular, the O 2p states strongly interact with Rh 3d orbitals, which finally weaken the N2─O bond. The electron transfer is from the Rh5 HOMO orbital to the N2O antibonding orbital.

Spiroketal‐Based Phosphorus Ligands for Highly Regioselective Hydroformylation of Terminal and Internal Olefins

A new class of bidentate phosphoramidite ligands, based on a spiroketal backbone, has been developed for the rhodium-catalyzed hydroformylation reactions. A range of short- and long-chain olefins, were found amenable to the protocol, affording high catalytic activity and excellent regioselectivity for the linear aldehydes. Under the optimized reaction conditions, a turnover number (TON) of up to 2.3×10(4) and linear to branched ratio (l/b) of up to 174.4 were obtained in the Rh(I)-catalyzed hydroformylation of terminal olefins. Remarkably, the catalysts were also found to be efficient in the isomerization-hydroformylation of some internal olefins, to regioselectively afford the linear aldehydes with TON values of up to 2.0×10(4) and l/b ratios in the range of 23.4-30.6. X-ray crystallographic analysis revealed the cis coordination of the ligand in the precatalyst [Rh(3d)(acac)], whereas NMR and IR studies on the catalytically active hydride complex [HRh(CO)(2)(3d)] suggested an eq-eq coordination of the ligand in the species.

Role of the nature of support on the structure of Au–Rh bimetallic nanoparticles

Au, Rh, and Au–Rh clusters were studied on Al2O3, TiO2 powders and titania nanowire by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and infrared spectroscopy (FTIR). On the XP spectra of the Au–Rh/TiO2 and Au–Rh/Al2O3 powders and wires the binding energy of the Au 4f emission was practically unaffected by the presence of Rh, the position of Rh 3d remained also constant on alumina, while it shifted to lower binding energy with gold admixture on titania. New emission for Rh 3d at 309.2 eV and for Au 4f at 85.6 eV developed on titania wire case. The bands due to Rho-CO and (Rho)2–CO were observed on IR spectra of titania supported bimetallic samples. The peak due to Rh+–(CO)2 was less intense on bimetallic nanowire. All three bands however are intense on Au–Rh/Al2O3. The results were interpreted by electron donation from titania through gold to rhodium. “Core-shell” bimetallic structures are supposed on Au–Rh/titania wire.

Fabrication of Rh Nanoparticle and Adsorption Reaction with DMS Studied by NEXAFS and XPS

We have studied the adsorption reaction of DMS on the Rh nanoparticle fabricated by the gas evaporation method by using AFM, XPS and NEXAFS techniques. The AFM result shows that we can fabricate the Rh nanoparticle which has a small diameter with a small distribution and high dispersion of it by the gas evaporation method with the Rh wire as an evaporation source. The Rh L3-edge NEXAFS spectra indicate that the surface and bulk of Rh nanoparticle is stable in the chemical state of Rh despite the exposure to air. The Rh 3d XPS and S K-edge NEXAFS results show the lower degree of oxidized Rh nanoparticle has the stronger bonding with atomic S than the more oxidized one.

Relativistic many-body XMCD theory including core degenerate effects

A many-body relativistic theory to analyze X-ray Magnetic Circular Dichroism (XMCD) spectra has been developed on the basis of relativistic quantum electrodynamic (QED) Keldysh Green's function approach. This theoretical framework enables us to handle relativistic many-body effects in terms of correlated nonrelativistic Green's function and relativistic correction operator Q, which naturally incorporates radiation field screening and other optical field effects in addition to electron-electron interactions. The former can describe the intensity ratio of L2/L3 which deviates from the statistical weight (branching ratio) 1/2.In addition to these effects, we consider the degenerate or nearly degenerate effects of core levels from which photoelectrons are excited. In XPS spectra, for example in Rh 3d sub level excitations, their peak shapes are quite different: This interesting behavior is explained by core-hole moving after the core excitation. We discuss similar problems in X-ray absorption spectra in particular excitation from deep 2p sub levels which are degenerate in each sub levels and nearly degenerate to each other in light elements: The hole left behind is not frozen there. We derive practical multiple scattering formulas which incorporate all those effects.

Localized magnetic moments in the Heusler alloy Rh2MnGe

X-ray magnetic circular dichroism (XMCD) of core-level absorption (x-ray absorption spectroscopy, XAS) spectra in the soft x-ray region has been measured for the ferromagnetic Heusler alloy Rh2MnGe at the Rh M3,2 and Mn L3,2 edges. The ratio of Rh and Mn spin moments amounts to 0.05 which is smaller than the ratio of 0.1 determined by a local density approximation electronic band structure calculation. We have found that the orbital moments of the Rh 4d and Mn 3d states are very small. The observed Rh 2p XAS spectrum can be understood on the basis of the Rh 3d partial density of unoccupied states as is typical for metals. The observed features of the Mn 2p XAS and XMCD spectra are dominated by final state multiplets as is typical for oxides. The comparison of experimental and ab initio calculated XAS/XMCD spectra reveals a strong narrowing of the Mn 3d bands, indicating strongly localized Mn moments. The magnetic moments are considerably more localized for Rh2MnGe in comparison with the isoelectronic compound Co2MnGe. In spite of the strong localization of the Mn moment, the temperature dependences of sublattice magnetization are equal for the Mn and Rh sublattices in contrast to the prediction by a Heisenberg model. This might be attributed to the remaining itinerant character of the Rh moment.

Probing the interactions of Pt, Rh and bimetallic Pt–Rh clusters with the TiO 2(1 1 0) support

Pt, Rh, and Pt–Rh clusters on TiO 2(1 1 0) have been investigated by scanning tunneling microscopy (STM), soft X-ray photoelectron spectroscopy (sXPS), and low energy ion scattering (LEIS). The surface compositions of Pt–Rh clusters are Pt-rich (66–80% Pt) for room temperature deposition of both 2 ML of Pt on 2 ML of Rh (Rh + Pt) and 2 ML of Rh on 2 ML of Pt (Pt + Rh). Pt and Rh atoms readily diffuse within the clusters at room temperature, and although diffusion is slower at 240 K, intermixing of Pt and Rh still occurs. The binding energies of surface and bulk states for Rh(3d 5/2) and Pt(4f 7/2) can be distinguished in sXPS studies, and an analysis of these spectra indicates that the surface compositions of the Pt + Rh and Rh + Pt clusters are similar at room temperature but not identical. In addition to sintering, the pure Pt, pure Rh and Pt–Rh clusters become completely encapsulated by titania upon heating to 700 K. sXPS investigations show that annealing the clusters to 850 K induces reduction of titania support to Ti +2 and Ti +3, with the extent of reduction being the greatest for Pt, the least for Rh and intermediate for Pt–Rh. We propose that TiO 2 is reduced at the metal–titania interface on top of the clusters, not at the base of the clusters. Furthermore, the extent of titania reduction is greater for metal clusters with weaker metal–oxygen bonds because oxygen atoms are less likely to migrate to the top of the clusters, and therefore the encapsulating titania is oxygen-deficient.

Surface alloy formation after deposition of Ce on Rh(1 1 0)

Vapour deposition of Ce onto a Rh(1 1 0) single crystal at room temperature is studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and low energy electron diffraction (LEED). The thicknesses of the deposited Ce layers are estimated to be between 2 and 9 Å. To study the changes in the Ce–Rh surface layer, the samples are annealed at temperatures between 500 and 1000 °C after Ce deposition. After heating, a c(2 × 2) LEED pattern appears for the sample with the thinnest deposited Ce layer (2.4 Å). For samples with thicker Ce-films, the LEED pattern co-exists of a c(2 × 2) structure and a more diffuse 6% contracted (2 × 1) structure. This appears at the same temperature as the Ce 3d and Rh 3d core levels exhibit sharp intensity changes and binding energy shifts. The intensity of the f 0, f 1 and f 2 multiplets in the Ce 3d core level spectra change when the annealing temperature is increased. The relative intensity of the Ce 3d f 0 and f 2 features compared to the Ce 3d f 1 features is largest after annealing to 500 °C. This is below the temperature at which the ordered surface alloy is formed. When the sample is heated above the formation temperature of the surface alloy, the relative intensity of the Ce 3d f 0 and f 2 features decrease.

Attention deficit/hyperactivity disorder (ADHD) symptoms and digit ratios in a college sample

Diagnosticians recognize three subtypes of attention deficit/hyperactivity disorder (ADHD) if there are developmentally inappropriate levels (six or more symptoms) of Hyperactive-Impulsive behavior, or Inattentive behavior, or both (Combined), respectively. ADHD may partly reflect androgen dysfunction, and an arguable proxy for prenatal androgen exposure is the 2D:4D finger ratio set at least as early as week 9 in the fetus; this is lower in men than in women. We examined the relationship between digit ratios and ADHD symptoms representing the three phenotypes: ADHD/Combined as measured by "summarized" (Rasched) scales, i.e., 1) the short version of the Wender Utah Rating Scale (WURS) and a total symptom list derived from the DSM IV, and the subdivided DSM IV into 2) ADHD/Inattentive and 3) ADHD/Hyperactive-Impulsive inventories, in a sample of European-descent college students (135 female, 52 male) not selected for ADHD. All digit ratios were calculated excluding the thumb. There were significant sex differences for the 2D:4D digit ratios of both hands (RH and LH), and between the RH 3D:4D and between the LH 2D:3D ratio. In females, the more masculine the LH 2D:4D ratio, the more the ADHD/Combined symptoms (both WURS and DSM) and the more the ADHD/Inattentive symptoms and ADHD/Hyperactive-Impulsive symptoms. More masculine ratios also correlated between the total WURS and RH 2D:3D, RH 2D:4D, and LH 2D:3D; and between the inattentive DSM symptoms and LH 2D:5D, and between the ADHD/Hyperactive and Impulsive symptoms and RH 3D:4D.

Relaxed core projector-augmented-wave method

We extend the full-potential projector-augmented-wave method beyond the frozen core approximation, i.e., include the self-consistent optimization of the core charge density, in such a manner that the valence wave functions remain orthogonal to the core. The method consists of an on-the-fly repseudization of the all-electron problem, solving for the self-consistent core charge density within a spherical approximation. The key ideas in our procedure are to keep the projector functions fixed throughout the electronic minimization and to derive the new pseudopartial waves from these original projector functions, at each step of the electronic minimization procedure. Results of relaxed core calculations for atomic interconfigurational energies, structural energy differences between bulk phases of Fe, atomization energies of a subset of Pople's G2-1 set, and the Rh 3d surface core level shifts for the (log3 x log3)-Rh(111) surface at 1/3 CO coverage are presented.

Construction of Metal Butterflies on a Metallacarborane Scaffold. 1. Synthesis and Structures of Bimetallic Precursors

Treatment of [N(PPh3)2][NEt4][1,1,1-(CO)3-2-Ph-closo-1,2-MCB9H9] (M = Mn (1a), Re (1b)) with sources of the cations {M‘(CO)2}+ (M‘ = Ir, Rh) affords the bimetallic species [N(PPh3)2][1,3,6-{M(CO)3}-3,6-(μ-H)2-1,1-(CO)2-2-Ph-closo-1,2-M‘CB9H7] (M = Re, M‘ = Ir (2a), Rh (2b); M = Mn, M‘ = Ir (2c), Rh (2d)). In these, the {M(CO)3} fragment, formerly a cluster vertex, has assumed an exo-polyhedral role, while the {M‘(CO)2} units now occupy a site within the cluster. Compounds 2 convert to [N(PPh3)2][1,3-{M(CO)4}-3-(μ-H)-1,1-(CO)2-2-Ph-closo-1,2-M‘CB9H8] (M = Re, M‘ = Ir (3a), Rh (3b); M = Mn, M‘ = Ir (3c), Rh (3d)) by deliberate CO addition or by CO scavenging. Reaction of 2b with PEt3 gives [N(PPh3)2][1,3-{Re(CO)3(PEt3)}-3-(μ-H)-1,1-(CO)2-2-Ph-closo-1,2-RhCB9H8] (4), which has a mirror-symmetric structure, whereas 2a with NH2C6H4Me-1,4 affords [N(PPh3)2][1,3-{Re(CO)3(NH2C6H4Me-1,4)}-3-(μ-H)-1,1-(CO)2-2-Ph-closo-1,2-IrCB9H8] (5), which is asymmetric. The structures of 2b, 3b, and 5 have been confirmed by X-ray diffraction studies.

XPS and TPD study of Rh/SnO 2 system – Reversible process of substrate oxidation and reduction

Rh films were deposited onto SnO 2 polycrystalline substrate prepared by spray pyrolysis method. Immediately after the Rh deposition, partial reduction of the substrate was observed, while almost no reduced Sn was found on the pure SnO 2 substrate. The peak of metallic Sn increased after annealing of Rh deposited sample at about 670 K. No substrate reduction was observed after heating it up to 670 K, when the surface had not been covered by Rh deposit. These results confirm an influence of Rh deposit to the SnO 2 reduction. After the Rh/SnO 2 sample was treated in O 2, the partial reduction of SnO 2 almost disappeared. The process of SnO 2 substrate reduction and oxidation was performed repeatedly. The shape of Rh 3d doublet did not change during all these procedures; it only shifted to lower binding energy when the substrate was reduced. Thermo programmed desorption spectra of CO were different on the oxidized and reduced SnO 2 substrate. We concluded that the substrate oxygen influences this behaviour of Rh/SnO 2 system. These effects can be important in heterogeneous catalysis and gas sensors technology.

Growth of Rh nanoclusters on TiO 2(1 1 0): XPS and LEIS studies

Rhodium clusters were prepared by evaporation on a nearly stoichiometric TiO 2(1 1 0) surface. The growth of metal nanoparticles, as a function of rhodium coverage, could be followed by monitoring the Rh 3d 5/2 XP peak position and by low energy ion scattering spectroscopy (LEIS). The substrate temperature in the 160–300 K regime during evaporation significantly influences the cluster size, leading to smaller crystallites at low temperature. Annealing the surface results in the agglomeration of rhodium, which commenced at lower temperature for smaller clusters. At high temperatures (∼900 K) encapsulation of rhodium also occurred.