J. Camra

XPS studies of nitrogen-containing conjugated polymers–palladium systems

Polyaniline (PANI) and polypyrrole doped with chloride ions (PPyCl) have been treated with PdCl 2 solutions in HCl of various concentrations. Basing on the results of XPS studies it is shown that the differences in the redox and basic properties of both polymers lead to different mechanisms of their interactions with palladium ions present in the PdCl 2 solutions studied. Thus, in the PdCl 2 solutions of low acidity in which [PdCl 2 (H 2 O) 2 ] predominates, both polymers are oxidized with simultaneous reduction of a part of Pd 2+ to Pd 0 . In the PdCl 2 solutions of high acidity in which [PdCl 4 ] 2 is the major complex, reduction of Pd 2 does not occur. Owing to stronger basic properties of PANI than those of PPyCl, palladium is incorporated into the former polymer as anionic chlorocomplexes via protonation reaction. In the case of PPyCl the situation is more complex. Detailed analysis of the possible surface reactions taking place in the PPyCl Pd systems studied is given in the paper.

Evolution of the surface species of the V2O5–WO3 catalysts

Abstract Vanadia-related species formed as a result of vanadium segregation at the surface of V–W oxide bronze crystallites were investigated. The structures of these species and their transformations induced by oxygen removal and oxygen adsorption were monitored using photoelectron spectroscopy and the FT Raman technique. Assignments of the MeO vibrational bands, based on the results of DFT calculations for model clusters, have been proposed. Two kinds of surface species are dominant depending on the tungsten content: V 4+ –O–W 6+ at low tungsten content and V 5+ –O–W 5+ at higher tungsten concentration.

Three-dimensional information on the phase domain structure of thin films of polymer blends revealed by secondary ion mass spectrometry

We describe the technique of dynamic secondary ion mass spectrometry developed to determine three-dimensional phase domain structures of films of polymer blends. The polymers are composed of light elements or are labeled with deuterium or heavy elements. The applicability of this method to various polymer blends forming thin and ultrathin films with flat and undulated air/film interface is discussed.

Polypyrrole-palladium systems prepared in PdCl2 aqueous solutions

Abstract In the work, reactions of a partially deprotonated polypyrrole doped with hydroxide ions (PPyOH) in various PdCl2 aqueous solutions which differed in acidity were studied. Using X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy it was established that in the PdCl2 solutions of lower acidity PPyOH was oxidatively doped and Pd0 and Pd2+ were incorporated into the polymer matrix. Pd2+ formed palladium(II) hydroxy-and/or aquochlorocomplex dopant anions and/or was coordinated by nitrogen atoms of the polymer (Pd–N bond). Additionally, deprotonation of PPyOH occurred in the PdCl2 solutions of lower acidity. It was proposed that deprotonation of PPyOH was caused by nucleophilic attack of [PdCl3(H2O)]− on the positively charged, doped polymer chain. By comparison of the PPyOH and chloride-doped polypyrrole (PPyCl)–palladium systems prepared in similar PdCl2 solutions of lower acidity it was shown that the type of the counterion in the starting polymer has a decisive effect on the deprotonation process. PPyOH was less reactive towards palladium species in the PdCl2 solutions of higher acidity where [PdCl4]2− was the dominant complex. PPy–palladium systems containing exclusively Pd2+ were obtained in this case. It was proposed that incorporation of palladium species in these conditions proceeded via an acid–base reaction or coordination of palladium ions by the polymer chain (Pd–N bond formation). Results of the studies may serve as the basis for the preparation of a variety of polypyrrole-supported palladium catalysts.

Structural studies of V2O5–WO3 and WO3–V2O5 solid solutions

Powder X-ray diffraction, Fourier transform Raman spectroscopy, solid-state NMR and X-ray photoelectron spectroscopy were used to determine the composition and structure of a mixed oxide containing 10 mol% V2O5 and 90 mol% WO3. The parent sample consists of hybrid crystallites of a tungsta-bronze isostructural with tetragonal WO3 but containing atomic vanadium in the bulk of the crystals and V(III) in the surface region, and of small crystals of strongly reduced vanadia-like surface species (V2O5–x with x=0.42). Further thermal treatment causes progressive surface segregation of vanadium from the V2O5–WO3 solid solution, accompanied by the formation of a WO3–V2O5 solid solution and partial tetragonal–monoclinic structural transformation of the bronze.

Evolution of Ti–Sn-rutile-supported V2O5–WO3 catalyst during its use in nitric oxide reduction by ammonia

This paper concerns the relation between surface structure of crystalline vanadia-like active species on vanadia–tungsta catalyst and their activity in the selective reduction of NO by ammonia to nitrogen. The investigations were performed for Ti–Sn-rutile-supported isopropoxy-derived catalyst. The SCR activity and surface species structure were determined for the freshly prepared catalyst, for the catalyst previously used in NO reduction by ammonia (320 ppm NO, 335 ppm NH3 and 2.35 vol% O2) at 573 K as well as for the catalyst previously annealed at 573 K in helium stream containing 2.35 vol% O2. The crystalline islands, exposing main V2O5 surface, with some tungsten atoms substituted for V-ones, were found, with XPS and FT Raman spectroscopy, to be present at the surface of the freshly prepared catalyst. A profound evolution of the active species during the catalyst use at 573 K was observed. Dissociative water adsorption on V5+OW6+ sites is discussed as mainly responsible for the catalyst activity at 473 K and that on both V5+OW6+ and V4+OW6+ sites as determining the activity at 523 K.

Evolution of 3D structures in a phase-separating polymer blend film confined by symmetric flat walls

Abstract.The recently extended imaging mode of dynamic Secondary Ion Mass Spectroscopy as well as its depth profiling variant were used to study three-dimensional structures in a phase-separating polymer blend film. Formation of layered morphology and its further reorganisation into columns were observed in a system confined by symmetric flat surfaces. The integral-geometry-based morphological image analysis provided a quantitative description of the evolution of the phase morphology.