The nature of the relative bonding chemistry in zeolites: An XPS study

A detailed analysis is provided of the chemical-bonding implications of a series of XPS studies of various zeolite systems. Both XPS core level and valence band results are analyzed. The study demonstrates that tetrahedral sodium aluminate is a relatively ionic oxide, whereas the SiO bonds in silica are much more covalent. The varying combinations of these two species found in different zeolites produce progressive shifting patterns in the XPS results that are indicative of related progressions in the relative covalency/ionicity in the zeolite bonding. The study is employed to track the Brönsted acidity of various HZ zeolite systems including dealuminated (ultra stabilized) Y zeolites. Interconnections are also demonstrated with changing patterns of features related to the Sanderson intermediate electronegativity. A key aspect of this study is that we suggest that it is necessary to consider that the oxygens in these zeolite (and related) systems are subject to extensive polarization.     

Photo-induced decomposition of platinum metalorganic films for electroless copper plating

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Electrodeposition of copper on Poly(o-aminophenol) modified platinum electrode

Potentiostatic transients of copper electrodeposition on polyorthoaminophenol-Pt modified electrodes were fitted to the three dimensional nucleation and growth model with diffusion control proposed by Scharifker et al. (B. Scharifker, G. Hills, Electrochimica Acta 28 (1983) 879). Non-dimensional plots showed a transition from instantaneous nucleation, at low overpotentials, to progressive nucleation at higher potentials. The formation of nuclei with approximately the same diameter at low potentials and the presence of a major dispersion in the size of the clusters at higher values of overpotential agrees with the fitting. However, discrepancies between the charge consumed during the formation of the copper deposit, at low potential, and that calculated by assuming hemispherical centres suggest that the nuclei are not hemispherically shaped but probably truncated spheres. Nuclei formed at large potential steps are not single centres but cluster of copper around a central site which produces an early overlapping of diffusion fields. The shape of the nucleation centres is explained in terms of electrochemical reduction forming conducting strands in a poorly conducting matrix. The distribution of clusters is fixed by the presence of these conducting chains in the polymer-solution interface.     

Removal of pyridine from liquid and gas phase by copper forms of natural and synthetic zeolites

Zeoadsorbents on the basis of copper forms of synthetic zeolite ZSM5 and natural zeolite of the clinoptilolite type (CT) have been studied taking into account their environmental application in removing harmful pyridine (py) from liquid and gas phase. Sorption of pyridine by copper forms of zeolites (Cu-ZSM5 and Cu-CT) has been studied by CHN, X-ray photoelectron spectroscopy, X-ray powder diffractometry, FTIR spectroscopy, thermal analysis (TG, DTA and DTG) and analysis of the surface areas and the pore volumes by low-temperature adsorption of nitrogen. The results of thermal analyses of Cu-ZSM5, Cu-(py)(x)ZSM5, Cu-CT and Cu-(py)(x)CT zeolitic products with different composition (x depends on the experimental conditions of sorption of pyridine) clearly confirmed their different thermal properties as well as the sorption of pyridine. In the zeolitic pyridine containing samples the main part of the pyridine release process occurs at considerably higher temperatures than is the boiling point of pyridine, which proves strong bond and irreversibility of py-zeolite interaction. FTIR spectra of Cu-(py)(x)zeolite samples showed well resolved bands of pyridine. The results of thermal analysis and FTIR spectroscopy are in a good agreement with the results of other used methods.     

The microwave heating of zeolites

The heating of zeolites caused by the microwave irradiation at 2450 MHz is examined. Zeolites in the H form absorb little energy, but some Na and K zeolites absorb sufficient energy to melt within a few minutes. The contribution of ions held at particular sites is discussed, but heating appears associated with the presence of cations in large cavities.     

The flexibility window in zeolites

Today synthetic zeolites are the most important catalysts in petrochemical refineries because of their high internal surface areas and molecular-sieving properties. There have been considerable efforts to synthesize new zeolites with specific pore geometries, to add to the 167 available at present. Millions of hypothetical structures have been generated on the basis of energy minimization, and there is an ongoing search for criteria capable of predicting new zeolite structures. Here we show, by geometric simulation, that all realizable zeolite framework structures show a flexibility window over a range of densities. We conjecture that this flexibility window is a necessary structural feature that enables zeolite synthesis, and therefore provides a valuable selection criterion when evaluating hypothetical zeolite framework structures as potential synthetic targets. We show that it is a general feature that experimental densities of silica zeolites lie at the low-density edge of this window--as the pores are driven to their maximum volume by Coulomb inflation. This is in contrast to most solids, which have the highest density consistent with the local chemical and geometrical constraints.     

Spectroscopic investigations on sorption and oxidation of carbon monoxide in transition metal ion-exchange zeolites A: Studies on cobalt,nickel and copper forms

Sorption and oxidation of carbon monoxide in Co-, Ni- and Cu-ion-exchanged zeolites A, have been studied applying ultraviolet-visible (u.v.-vis.) and infrared (i.r.) spectroscopy. Carbon monoxide sorption takes place in front of the cations, resulting in a change of the coordination sphere of the cation as can be observed in the u.v.-vis. spectra and an upscale frequency shift of the CO fundamental. The latter can be roughly correlated with the charge/radius ratio of the interacting cation. In contrast, carbon dioxide sorption in zeolites A also gives evidence for a location near cations, but results only in small unspecific frequency shifts. Room temperature oxidation of carbon monoxide to carbon dioxide was found in zeolite NiA. CoA requires at least 523 K and CuA is inactive even at higher temperatures, undergoing autoreduction upon pretreatment.     

The Fermi surface of platinum

We have made measurements of the extremal cross-sectional areas of the open hole surface of the Fermi surface of platinum for the previously unobserved, heavy mass orbits centered on and X with the magnetic field along the [100] and [110] directions, respectively. When combined with previous measurements, the necessary data associated with all classes of orbits on all three sheets of the surface are now available. Using a relativistic non-muffin-tin, Korringa-Kohn-Rostoker formalism, data were fitted using the scattering phase shifts associated with the appropriate irreducible relativistic cubic representations as disposable parameters (through l = 2) to an accuracy of 0.3%. The resulting radii of all sheets of the Fermi surface are reported. A volume integration yields the necessary charge neutrality for this even-valent metal to within 1%. Next, available cyclotron mass data were fitted using the energy derivatives of the scattering phase shifts as disposable parameters (many-body effects being absorbed in the parameter set) to an accuracy of 3.4% ; here the measured total electronic density of states was used as a constraint. The resulting Fermi velocities are also reported.Research supported by the Northwestern Materials Research Center, the National Science Foundation under Grant No. DMR-76-21370, and U.S. Energy Research and Development Agency.     

The conversion technology of fly ash into zeolites

This paper presents a sub-pilot scale process of synthesis of Na-P1 zeolite from the coal fly ash. After establishing the appropriate synthesis conditions (20 kg of fly ash, 12 kg of NaOH, 90 dm³ of water, the reaction temperature: 80 °C and reaction time: 36 h), the high-purity (81 wt%) Na-P1 zeolite product was obtained. Its chemical, mineralogical, and textural properties were determined (by means of XRD, XRF, SEM–EDS and ASAP 2020). The synthesized material has a specific BET surface area (88 m²/g) c.a. six times higher than the fly ash from which it has been derived (15 m²/g). The pore-size distribution indicates a mesoporous character of the obtained zeolite, with the following pores size contents: micropores (2.76 %), mesopores (61.81 %), and macropores (35.43 %). The presented technological/production line is fully automated and allows to regulate the conditions of the synthesis process, therefore different types of zeolite materials (including: Na-X, Linde-A, and Na-P1) can be obtained using the same equipment.     

The rheology of collapsing zeolites amorphized by temperature and pressure

Low-density zeolites collapse to the rigid amorphous state at temperatures that are well below the melting points of crystals of the same composition but of conventional density. Here we show, by using a range of experimental techniques, how the phenomenon of amorphization is time dependent, and how the dynamics of order-disorder transitions in zeolites under temperature and pressure are equivalent. As a result, thermobaric regions of instability can be charted, which are indicative of polyamorphism. Moreover, the boundaries of these zones depend on the rate at which temperature or pressure is ramped. By directly comparing the rheology of collapse with structural relaxation in equivalent melts, we conclude that zeolites amorphize like very strong liquids and, if compression occurs slowly, this is likely to lead to the synthesis of perfect glasses.     

The wetting of three component silicate glasses on platinum

Measurements of the contact angles of sessile drops of alkali silicate glasses, containing other oxide additions, on platinum have been used to study the role of the glass composition in the wetting processes. A model has been proposed which relates the degree of wetting to the competition between the substrate metal and cationic and anionic groups in the molten glass for the valency electron of non-bridging oxygen ions. An empirical relationship between equilibrium contact angle and the affinity for oxygen ions of cations in the glass supports this model.     

The wetting of carbon by copper and copper alloys

The effects of alloying additions on the wetting of two types of carbon, HX30 graphite and vitreous carbon, have been investigated, with a view to developing a system for metal impregnation of carbon fibre assemblies. Pure copper is inert and non-wetting but two additions caused the copper to wet: Cr on both substrates and V on the vitreous carbon only. Many of the additions formed a carbide reaction layer at the interface, and in the two wetting systems this was a thin, continuous, coherent layer. The data have been analysed in terms of the chemical and physical properties of the system and it was found that the wetting behaviour of copper alloys on HX30 graphite and vitreous carbon could be explained in terms of the behaviour of the reaction product carbides of the alloying addition when these existed.     

The chemical vapor deposition of copper and copper alloys

The chemical vapor deposition of copper and copper alloys for very large scale integrated interconnects is described using a series of Lewis base stabilized copper (I) 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato (hfac) complexes. When the Lewis base is dimethyl-1,5-cyclooctadiene, high-purity copper metal is deposited at substrate temperatures from 150 to 250 °C. The deposition rate becomes mass-transport limited at the higher substrate temperatures, but excellent filling of sub-micron vias (3:1 aspect ratio) was achieved. The deposition of copper-tin alloys can also be achieved when vinyl trialkyltin is used as the Lewis base. At 180 °C, a carbon-free copper film, containing 0.6 at.%Sn, is deposited. A very strong substrate temperature dependence towards film purity was observed and results from thermal decomposition of the tin-containing ligand. These preliminary results demonstrate the utility of using single-source, mixed-metal precursors for copper alloy formation.     

The effect of sodium poisoning on acid sites in ZSM-22 zeolites

Acidic properties of NaHZSM-22 zeolites of various exchange degrees were studied by infrared and N_1s X-ray photoelectron spectra of chemisorbed pyridine. Two kinds of Brönsted and one type of Lewis sites were detected in fully protonated ZSM-22 zeolite. The concentration of these two kinds of Brönsted acid sites and of Lewis acid sites were determined as a function of sodium content. For fully protonated ZSM-22 zeolite, it has been found that among the total acid sites about 30% are stronger Brönsted acid sites. Introduction of sodium ions into zeolites poisoned both weak and strong Brönsted acid sites simultaneously. Comparison of N_1s XPS data with i.r. results allowed us to conclude that at an early stage of sodium poisoning surface Brönsted sites are poisoned preferentially to those in the bulk and that the relative rate of poisoning was higher for stronger Brönsted acid sites than for weak Brönsted acid sites.