Experimental and Theoretical Study of the Reactivity of Gold Nanoparticles Towards Benzimidazole‐2‐ylidene Ligands

The reactivity of benzimidazol‐2‐ylidenes with respect to gold nanoparticles (AuNPs) has been investigated using a combined experimental and computational approach. First, the grafting of benzimidazol‐2‐ylidenes bearing benzyl groups on the nitrogen atoms is described, and comparisons are made with structurally similar N‐heterocyclic carbenes (NHCs) bearing other N‐groups. Similar reactivity was observed for all NHCs, with 1) the erosion of the AuNPs under the effect of the NHC and 2) the formation of bis(NHC) gold complexes. DFT calculations were performed to investigate the modes of grafting of such ligands, to determine adsorption energies, and to rationalize the spectroscopic data. Two types of computational models were developed to describe the grafting onto large or small AuNPs, with either periodic or cluster‐type DFT calculations. Calculations of NMR parameters were performed on some of these models, and discussed in light of the experimental data.     

XPS study of the surface properties and Ni particle size determination of Ni‐supported catalysts

The surface properties of Ni/MgAl₂O₄ catalysts doped with Ce or Pr were analyzed by XPS after treatment in an inert and reductive atmosphere at 400 °C. The Ce‐promoted solids presented the Ce³⁺/Ce⁴⁺ couple on the surface even after treatment in a reductive atmosphere, H₂(5%)/Ar. The promotion effect of Ce on these solids could be associated with their participation on the carbon deposition‐removal mechanism. Pr‐doped catalysts showed a very high concentration of Pr³⁺ under a reductive atmosphere and the redox behavior associated with the carbon removal could be partially inhibited or become slower. The size of the Ni⁰ particles after both an inert and a reductive atmosphere was estimated by XPS intensity ratio using the model proposed by Davis. The results obtained from the Davis model showed that an important increase occurred in Ni particle size after treatment in H₂(5%)/Ar for the Pr‐promoted solids. The metal sintering under reductive atmosphere could be the reason for the higher loss of activity of the Pr‐doped solids under reforming conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and characterization of benzimidazolium‐functionalized polysulfones as anion‐exchange membranes

Anion‐exchange membranes containing pendant benzimidazolium groups were synthesized from polysulfone by chrolomethylation followed by nucleophilic substitution reaction with 1‐methylbenzimidazole. The structures of the polymers were characterized by ¹H‐NMR and FTIR analysis. The resulting membranes showed high thermal stability below 200 °C. The values of water uptake and swelling degree increased with the ion‐exchange capacity of the polymeric membrane. The ionic conductivity was measured by means of impedance spectroscopy in aqueous solution of potassium hydroxide (10^?4?10^?1 M). The results show not only a clear correlation between the membrane's electrochemical behavior with the electrolyte solution embedded in the membrane, but also with the degree of the polysulfone's chloromethylation.Thus, the ionic conductivity increased more than two orders of magnitude when the degree of chloromethylation increased from 40 to 140%. Benzimidazolium‐functionalized polysulfones exhibited better thermal, mechanical, and electrochemical properties than the widely used polymeric membranes containing quaternary ammonium groups. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2363–2373     

A theoretical NMR study of polymorphism in crystal structures of azoles and benzazoles

The NMR chemical shifts of two azoles and one benzazole whose crystal structures present polymorphism have been computed using the GIPAW approach. ¹⁵N and ¹³C nuclei have been studied. Statistical analysis of the computed ¹³C and ¹⁵N chemical shifts indicates that the GIPAW chemical shifts reproduce with a high degree of accuracy those experimentally reported. This methodology can be used to identify other polymorphic crystal structures.