A fundamental analysis of enhanced cross-coupling catalytic activity for palladium clusters on graphene supports.

Combining the recyclability of heterogeneous catalysts with the high activity of ligated homogeneous catalysts for the production of complex organic molecules is a cardinal goal of catalyst development. We have investigated the activity of ultra-fine Pd clusters bound to vacancy defective sites in graphene and found that the defective graphene both serves as a support to stabilize the recyclable catalyst, and also functions as a ligand enhancing the catalytic activity. In this paper, we report computational and experimental results that provide insights into the nature of the interfacial interactions between metal nanoparticles and defect sites on the graphene surface. Theoretical investigations reveal that while the vacancy/void sites on the graphene surface strongly bind to the metal clusters providing enhanced stability against leaching, graphene also serves as a reservoir of electron density that effectively reduces the activation energy of specific steps within the catalytic cycle. Furthermore, multiple experimental methods were used to unambiguously demonstrate that these cross-coupling reactions are occurring at the Pd/G catalyst surface.

Gas phase analogs of stable sodium-tin Zintl ions: anion photoelectron spectroscopy and electronic structure.

Mass spectrometry and photoelectron spectroscopy together with first principles theoretical calculations have been used to study the electronic and geometric properties of the following sodium-tin, cluster anion/neutral cluster combinations, (Na(n)Sn(4))(-)/(Na(n)Sn(4)), n = 0-4 and (NaSn(m))(-)/(NaSn(m)), m = 4-7. These synergistic studies found that specific Zintl anions, which are known to occur in condensed Zintl phases, also exist as stable moieties within free clusters. In particular, the cluster anion, (Na(3)Sn(4))(-) is very stable and is characterized as (Na(+))(3)(Sn(4))(-4); its moiety, (Sn(4))(-4) is a classic example of a Zintl anion. In addition, the cluster anion, (NaSn(5))(-) was the most abundant species to be observed in our mass spectrum, and it is characterized as Na(+)(Sn(5))(2-). Its moiety, (Sn(5))(2-) is also known to be present as a Zintl anion in condensed phases.

Electron-atom superelastic scattering in magnesium at millielectron volt energies.

The energy dependence of superelastic scattering is measured for electrons on Mg(3(1)P) from threshold to 270 meV with a novel technique. The method uses photoelectrons produced by a narrow bandwidth laser as an approximately monoenergetic incident electron source to collide with excited atoms. Measurements are made at energies as low as 1.5 meV with a resolution of 1 meV near threshold. An efficient magnetic-bottle time-of-flight electron spectrometer allows for the simultaneous measurement of multiple scattering channels. Above-threshold ionization is also observed. The measured energy dependence for transitions from the 3(1)P state to both the 3(3)P and 3(1)S are found to be inversely proportional to the energy from 10 to 270 meV. Below 10 meV, the dependencies are different, with the 3(3)P transition having an E(-1/2) dependence and the 3(1)S channel retaining an E(-1) dependence.

Al4H7(-) is a resilient building block for aluminum hydrogen cluster materials.

The formation and oxygen etching of Al(n)H(m)(-) clusters are characterized in a flow reactor experiment with first-principles theoretical investigations to demonstrate the exceptional stability of Al(4)H(7)(-). The origin of the preponderance of Al(4)H(7)(-) in the mass spectra of hydrogenated aluminum anions and its resistance to O(2) etching are discussed. Al(4)H(7)(-) is shown to have the ability to bond with ionic partners to form stable hydrides through addition of an alkali atom [XAl(4)H(7) (X = Li-Cs)]. An intuitive model that can predict the existence of stable hydrogenated cluster species is proposed. The potential synthetic utility of the superatom assemblies built on these units is addressed.