Search

Abstract: A reduced mesoporous 5% Pd-YSZ precatalyst was observed to be very active for the Heck reaction providing up to 770,000 TON. Three-phase tests have experimentally confirmed that a leached [...]

The infrared spectroscopy (IR) is utilized to study the interaction of CO molecules with a model catalyst system formed by alumina-supported vanadia particles. Low -energy electrons that are supplied either by an electron gun or by exposing the sample to X-rays could induce an oxidation reaction.

A model system of alumina-supported vanadia particles, representing catalysts of the type oxide1/oxide2, is prepared under ultrahigh vacuum (UHV) conditions. The results show that the particles interact strongly with the alumina support.

Kinetic studies of the influence of aqueous dimethyl sulfoxide (DMSO) on the cleavage of m- and p-nitrophenyl alkanoates (mNPAlk and pNPAlk) by alpha- and beta-cyclodextrin (CD) reveal that the rate of cleavage is increased by the addition upto 60% (v/v) of DMSO, while DMSO exerts little influence on transition state binding and substrate binding. Aryl group inclusion occurs in the cleavage of mNPAlk, while pNPAlk cleavage proceeds through acyl group inclusion. Change of solvent from water to DMSO induces more weakening in the substrate binding compared to transition state binding, leading to an increase in the cleavage rate of m-tert-butylphenylacetate.

Total ammonia nitrogen (TAN) uptake by sodium functionalized graphene oxide as an efficient adsorbent was evaluated and optimized using response surface methodology (RSM). Batch adsorption tests were carried out based on a central composite design experimental plan at 3 pH levels (6, 7, and 8) and 3 temperature levels (5, 25, and 45°C). The equilibrium condition was reached within 5 min. Quadratic models for percent TAN removal (R%) and solid phase TAN concentration (qe) as response were obtained and evaluated by statistical analysis to predict the experimental data. The models were reduced by eliminating insignificant terms. The final reduced models were significant (p <.0001) with R2 values.96 for R% and.97 for qe, respectively. The optimum pH and temperature to reach the maximum values for R% (58.23%) and qe (27.45 mg/g) were predicted by the RSM. The laboratory experiments were in very good agreement with the predicted optimized values for R% and qe by RMS as the error was 1.2 and 0.3%, respectively. [ABSTRACT FROM AUTHOR]

A sub-monolayer of atomic sodium was deposited on a LiF(001) surface at 40 K. The adsorbed sodium exists at the surface as single atoms and clusters. The surface was dosed with 1 L of HF, to form adsorbed (HF)2...Nan (n=1,2,3,...) complexes, which were then irradiated by 640 nm laser light, to induce charge-transfer reaction. The reaction-product atomic H(g) was observed leaving the surface by two-color Rydberg-atom time-of-flight (TOF) spectroscopy. The TOF spectrum of the desorbed H atoms contained two components; a “fast” component with a maximum at ≈0.85 eV, and a “slow” component with a maximum at 0.45 eV. These two components were attributed to photoreaction on adsorbed single atoms and clusters of sodium, respectively. The fast component exhibited a structure (48±17 meV spacing) near the high-energy end of spectrum. This structure was attributed to vibration of NaFHF photoproduct residing on the surface. The cross section of the harpooning event in the Na...(HF)2 adsorbed complex was determined as (9.1±2.0)×10-19 cm2. To interpret the experimental vibrational structure and the relative energies of the fast and slow components of the TOF spectrum, high-level ab initio calculations were performed for reactants Nan...(HF)m (n,m=1,2) and reaction products NanFmHm-1. The calculated NaF–HF and Na–Na(HF)2 bond dissociation energies indicated that photoexcitation of the precursor complexes led not only to ejection of H atoms, but also to dissociation of the Nan...(HF)2 (n=1,2) species through cleavage of the NaF–HF and Na–Na(HF)2 bonds. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photolysis of H[sub 2]S adsorbed on LiF(001) was studied by means of hydrogen Rydberg-atom time-of-flight spectroscopy. The H-atom translational energy distributions using 193.3 nm radiation showed three main features: a high energy channel attributed to H atoms escaping the surface without collisions (DIR); a vibrational progression from v=0 to v=5 [EL(v=0) and INEL(v>0)]; and a low energy channel attributed to multiple inelastic collisions [INEL(2)]. The vibrational progression can be attributed to two concurrent processes: the primary production of vibrationally excited SH in the dissociative event, and a secondary T→V energy transfer between the outgoing translationally hot H atom and a neighboring H[sub 2]S(ad) molecule. The coverage dependence and angular distribution of the DIR, EL, and the INEL(v>0) channels has been used to define a minimum set of required H[sub 2]S(ad) geometries. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photodissociation of chlorine adsorbed on a LiF(001) surface at 25-70 K has been investigated by means of angularly resolved resonantly enhanced multiphoton ionization spectroscopy (REMPI). The translational-energy distributions and angular distributions for forming Cl(g) photofragments were determined. Photolysis was performed employing 351 nm radiation, with laser pulse energies of 0.3-1.2 mJ/cm2. A peak in the translational energy of Cl(g) at about 0.4 eV was identified as being due to the direct photodissociation of the Cl[sub 2](ad) molecule by 3.5 eV photons. Particular interest attached to the observation of a further channel (termed "A") for photodissociation leading to Cl(g) with translational energy peaking at ∼1 eV and extending to 1.5 eV. The available photon energy renders it highly unlikely that this "high-energy" Cl(g) originates in Cl[sub 2](ad). Channel A had the same linear dependence of Cl-atom flux on laser pulse-energy as did the lower energy (0.4 eV) channel, termed "B," but differed from it in exhibiting a slow approach to steady state. It appears that channel A requires the prior build-up of Cl(ad) concentration due to the photodissociation of Cl[sub 2]. It is proposed that this leads to the formation of a steady-state concentration of Cl[sub 2]...Cl which when photolyzed yields high-energy Cl(g) via channel A. Channel A exhibits a distinctive angular distribution at low coverage and a characteristic Cl[sup *]/Cl ratio, as compared with channel B. The suggested mechanism for channel A is Cl[sub 2]...Cl+hν→Cl[sub 3][sup *]→Cl[sub 2]•Cl→Cl[sub 2]+Cl (where* is an electronically excited state and • represents repulsion in the lower electronic state to which Cl[sub 3][sup *] reverts). This mechanism is interpreted in terms of an extensive diatomics-in-molecules (DIM) model for the trichlorine radical, shown to be in agreement with high level ab initio multireference internally contracted configuration int... [ABSTRACT FROM AUTHOR]

Under ultrahigh vacuum (UHV) conditions, alumina-supported vanadium particles were prepared and characterized with respect to their structural and CO adsorption properties. As a result, a charge-frequency relationship is set up which allows to quantify the extent of charge transfer from vanadium to alumina.

Studies the photolysis of HCl adsorbed on LiF(001) by Rydberg-atom time-of-flight spectroscopy. Results of the experiments performed in an ultrahigh vacuum chamber; Modification in the behavior of energy distributions; Photorecoiling of hydrogen.

Discusses the use of hydrogen Rydberg-atom time-of-flight spectroscopy to study the photolysis of HX, where X maybe chlorine, bromine or iodine, adsorbed on lithium fluoride. Adsorption characteristics; Inability of HI to wet the surface under equilibrium conditions; Corresponding translational energies of H-atoms as calculated from the bond energies.