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Low-temperature CO adsorption on NiNaY leads to formation of Ni2+–CO species (IR band at 2195 cm-1). In line with this, mainly mononitrosyls (1892 cm-1) are produced after NO adsorption on the sample. These results show the existence of one coordinative vacancy of the Ni2+ ions in NiNaY. The results are compared with those of Ni-H-ZSM-5. In the latter case formation of dicarbonyls, dinitrosyls and mixed carbonyl–nitrosyl complexes of Ni2+ have been established. It was found that Ni-H-ZSM-5 is active in the selective catalytic reduction (SCR) of nitrogen oxides with methane, whereas the activity of NiNaY is rather poor. The stable species formed after coadsorption of NO and O2 on both samples are surface nitrates and/or nitrites. However, whereas the monodentate nitrates on Ni-H-ZSM-5 are highly reactive towards methane, the reactivity of the nitrates/nitrites on NiNaY is significantly lower. The mechanism of SCR with methane is discussed. In particular, it is proposed that the high coordinative unsaturation of the Ni2+ cations in Ni-H-ZSM-5 is very important for the proceeding of SCR with methane. [Copyright &y& Elsevier]

Ceria and ceria-zirconia nanomaterials of different origin were studied in order to elucidate the role of their structural and textural characteristics in controlling the performance towards CO 2 capture. Two commercial cerias and two home-prepared samples, CeO 2 and CeO 2 -ZrO 2 (75% CeO 2 ) mixed oxide, were investigated. The samples were characterized by a number of analytical techniques including XRD, TEM, N 2 -adsorption, XPS, H 2 -TPR, Raman and FTIR spectroscopy. Static and dynamic CO 2 adsorption experiments were applied to assess the CO 2 capture performance. The type of surface species formed and their thermal stability were evaluated by in situ FTIR spectroscopy and CO 2 -TPD analysis. The two commercial ceria samples possessed similar structural and textural characteristics, formed the same types of carbonate-like surface species upon CO 2 adsorption and, consequently, demonstrated almost identical CO 2 capture performance under both static and dynamic conditions. The thermal stability of the adsorbed species increased in the order bidentate (B) carbonates, hydrogen carbonates (HC) and tridentate carbonates (T-III, T-II, T-I). Reduction of CeO 2 increased the relative amount of the most strongly bonded T-I tridentate carbonates. Preadsorbed water led to hydroxylation and enhanced formation of hydrogen carbonates. Although the synthesized CeO 2 sample had a higher surface area (by 30%) it showed a disadvantageous long mass transfer zone in the CO 2 -adsorption breakthrough curves. Because of its complex pore structure, this sample probably experiences severe intraparticle CO 2 diffusion resistance. Having the same surface area as the synthesized CeO 2 , the mixed CeO 2 -ZrO 2 oxide exhibited the highest CO 2 capture capacity of 136 μmol g -1 under dynamic conditions. This was related to the highest concentration of CO 2 adsorption sites (including defects) on this sample. The CeO 2 -ZrO 2 system showed the lowest sensitivity to the presence of water vapor in the gas stream due to the lack of dissociative water adsorption on this material.

The UV photoproduction of a hydrophilic TiO(2)(110)(1x1) surface has been investigated in a pressurized ultrahigh vacuum apparatus under controlled conditions of hydrocarbon concentration in oxygen gas at 1 atm pressure. Water droplet contact angles have been measured continuously as the droplet is exposed to UV irradiation, yielding the first observations of a sudden wetting process during irradiation. Using hexane as a model hydrocarbon, it is found that when low partial pressures of hexane are present, the sudden onset of surface wetting occurs during UV irradiation after an induction period under photooxidation conditions. The induction period to reach the critical condition for sudden wetting increases when the partial pressure (and equilibrium surface coverage) of hexane is increased. These results indicate that the removal of adsorbed hydrocarbons by photooxidation is the critical factor leading to the UV-induced hydrophilicity phenomenon on TiO(2). The phenomenon does not occur in the absence of O(2) gas. A concept concerned with kinetic screening of the TiO(2)-H(2)O interface from O(2) by water droplets is presented to explain the observation of sudden wetting in our experiments, compared to gradual wetting which is observed following UV irradiation in all other experiments reported in the literature. Complementary infrared spectroscopy measurements of the effect of UV irradiation in an O(2) atmosphere on adsorbed Ti-OH groups and on adsorbed H(2)O on the surface of a high-area TiO(2) powder show that no spectroscopic changes occur. This indicates that UV-induced changes in the -OH coverage or the nature of -OH bonding to TiO(2), as suggested by others, cannot be used to explain the photoinduced hydrophilicity effect.

Results are presented on Omega production in central Pb+Pb collisions at 40 and 158A GeV beam energy. For the first time in heavy ion reactions, rapidity distributions and total yields were measured for the sum Omega(-) + Omega(+) at 40A GeV and for Omega(-) and Omega(+) separately at 158A GeV. The yields are strongly underpredicted by the string-hadronic UrQMD model but agree better with predictions from hadron gas models.

Emission of pi+/-, K+/-, phi, and Lambda was measured in near-central C+C and Si+Si collisions at 158 AGeV beam energy. Together with earlier data for p+p, S+S, and Pb+Pb, the system-size dependence of relative strangeness production in nucleus-nucleus collisions is obtained. Its fast rise and the saturation observed at about 60 participating nucleons can be understood as the onset of the formation of coherent systems of increasing size.

Production of Lambda and Antilambda hyperons was measured in central Pb-Pb collisions at 40, 80, and 158A GeV beam energy on a fixed target. Transverse mass spectra and rapidity distributions are given for all three energies. The Lambda/pi ratio at midrapidity and in full phase space shows a pronounced maximum between the highest BNL Alternating Gradient Synchrotron and 40A GeV CERN Super Proton Synchrotron energies, whereas the Lambda/pi ratio exhibits a monotonic increase.

The photooxidation of 2-chloroethyl ethyl sulfide (2-CEES), a simulant for mustard gas, was studied using transmission IR spectroscopy on a mixed-oxide TiO2-SiO2 photocatalyst. Ultraviolet irradiation in the photon energy range from 2.1 to 5 eV was employed at a catalyst temperature of 200 K. Rapid photooxidation was observed by the loss of infrared intensity in the v(CHx) stretching region, and concomitant infrared features of adsorbed oxidation products were observed to develop. The oxidation products, captured on the photocatalyst at 200 K, were found to block 2-CEES readsorption. Upon heating the poisoned photocatalyst to about 300 K, infrared measurements indicate that the adsorbed CO2 oxidation product was desorbed. The capability for full readsorption of 2-CEES was achieved upon heating the poisoned photocatalyst to 397 K, and continued rapid photooxidation of the 2-CEES was then possible at about 1/3 the rate found for the fresh catalyst. Thus thermal treatment at 397 K of oxidation-product-poisoned TiO2-SiO2 material is able to partially restore the TiO2-SiO2 photooxidation activity.

Results of resonance searches in the Xi(-)pi(-), Xi(-)pi(+), Xi;(+)pi(-), and Xi;(+)pi(+) invariant mass spectra in proton-proton collisions at sqrt[s]=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi(-)pi(-) baryon resonance with mass of 1.862+/-0.002 GeV/c(2) and width below the detector resolution of about 0.018 GeV/c(2). The significance is estimated to be above 4.2sigma. This state is a candidate for the hypothetical exotic Xi(--)(3/2) baryon with S=-2, I=3 / 2, and a quark content of (dsdsū). At the same mass, a peak is observed in the Xi(-)pi(+) spectrum which is a candidate for the Xi(0)(3/2) member of this isospin quartet with a quark content of (dsus[-]d). The corresponding antibaryon spectra also show enhancements at the same invariant mass.