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The activity of CaNaY zeolites in selective oxidation of propane with increasing Ca(super 2+) content at room temperature was studied with infrared spectroscopy and ammonia temperature-programmed desorption. Increasing the Ca(super 2+) exchange level in CaNaY zeolites resulted in a variety of altered properties: the amount of Bronsted and Lewis acid sites increased, the adsorption of propane increased, the initial acetone formation rate increased, and the desorption of acetone retarded.

The adsorption of oxygen and d2-propane (CH3CD2CH3) is studied on a series of alkaline-earth-exchanged Y-zeolite at room temperature. The study demonstrates that O2 and propane can simultaneously attach to one active center [M(sub 2+)] to form a M(super 2+)(O2)(C3H8) species, which is proposed to be the precursor in thermal propane selective oxidation.

The relationship between the structure of yttrium-stabilized zirconia (YSZ) and ZrO2 catalysts and their ability to activate N2O and O2 is studied by determination of catalytic properties. N2O can be activated at structural defects and intrinsic oxygen vacancies [Zr'(sub Zr-)V(super ..)(sub O-)Zr'(sub Zr)] and forms two types of oxygen species (alpha-O and beta-O) on the surface, respectively.

Investigation on the temperature-programmed-desorption (TDP) of propane partial oxidation products using in situ FTIR and MS is presented. It is concluded that water clearly facilitates acetone desorption, most likely via shielding of the electrostatic field and creation of additional sites.

Abstract: The influence of water and surface hydroxyl groups on the catalytic performance of yittrium-stabilized ZrO2 (YSZ) in the partial oxidation of methane to synthesis gas was investigated using FT-IR as well as steady state kinetic experiments. Besides physically adsorbed water, terminal OH groups, bi-bridging and tri-bridging OH groups exist on the surface of YSZ. Oxidation of formaldehyde to formate occurs on the low index planes rather than at the structural defects, i.e. corners, edges, kinks and steps. Adsorbed formaldehyde is attacked by neighboring lattice oxygen ions in low index surface planes to form surface formate. Neighboring hydroxyl groups and hydrogen-bonded molecular water on the surface of YSZ suppress this nucleophilic attack. In short, the presence of water on the surface stabilizes adsorbed formaldehyde, decreasing the rate of oxidation to formate; this effect is responsible for the increase in selectivity to H2 and CO when water is added during CPO. [Copyright &y& Elsevier]

Abstract: Catalytic partial oxidation of methane to synthesis gas over ZrO2 and yttrium-stabilized zirconia (YSZ) is studied using O2 and N2O as oxidants. ZrO2 is much more active than YSZ in oxidation of methane with N2O. In contrast, YSZ is significantly more active than ZrO2 when O2 is used as an oxidant. The presence of O2 does not influence the rate of N2O decomposition over ZrO2 and YSZ, while the presence of H2O in the system decreases N2O conversion significantly. O2 and N2O are activated at different active sites. Y-induced oxygen vacancies are active for O2 activation, whereas oxygen co-ordinatively unsaturated Zr cations (Zr-CUS) located at corners, edges, steps and kinks are responsible for N2O activation. These sites are also capable of dissociating H2O, resulting in competition between H2O and N2O. As compared with N2O, molecular O2 is easier to be activated over YSZ and ZrO2. [Copyright &y& Elsevier]

Abstract: The isotopic exchange reaction on ZrO2 and yttrium-stabilized ZrO2 (YSZ) during catalytic partial oxidation of methane to synthesis gas (CPOM) was studied with transient pulse experiments. The results reveal, surprisingly, that CPOM over both oxides proceeds via a Mars–van Krevelen mechanism. Despite the presence of adsorbed oxygen species, as confirmed by isotopic exchange experiments under reaction conditions, methane is selectively oxidized by lattice oxygen ions on the surfaces of YSZ and ZrO2. At 900 °C, about 8 and 14% of lattice oxygen in the outermost surface layer of ZrO2 and YSZ, respectively, can be extracted by methane. Extraction of lattice oxygen results in the formation of surface oxygen vacancies. However, the routes for replenishing oxygen differ for the two oxides. For ZrO2, the extracted lattice oxygen ions are replenished by direct activation of molecular oxygen at the site of the surface vacancy. The presence of a high concentration of surface oxygen vacancies on YSZ, generated by doping of ZrO2 with Y2O3, permits fast activation of oxygen molecules and fast lattice diffusion of oxygen. The two effects together lead to a rapid replenishment of the surface lattice oxygen extracted by methane. The proposed mechanism explains both the comparatively high activity of YSZ in CPOM and the observation that, in contrast to ZrO2, lattice oxygen is found exclusively in oxidation products of methane over YSZ during pulse experiments. [Copyright &y& Elsevier]

Reports on the preparation of alumina and lantana-alumina samples through coprecipitation. Comparison of the surface areas; Ethanol washing to improve the textural stability of the samples; Effect of steam on the thermal stability of the sample.

A fundamental understanding of the interplay between ligand-removal kinetics and metal aggregation during the formation of platinum nanoparticles (NPs) in atomic layer deposition of Pt on TiO 2 nanopowder using trimethyl(methylcyclo-pentadienyl)platinum(IV) as the precursor and O 2 as the coreactant is presented. The growth follows a pathway from single atoms to NPs as a function of the oxygen exposure (P O2 × time). The growth kinetics is modeled by accounting for the autocatalytic combustion of the precursor ligands via a variant of the Finke-Watzky two-step model. Even at relatively high oxygen exposures (<120 mbar s) little to no Pt is deposited after the first cycle and most of the Pt is atomically dispersed. Increasing the oxygen exposure above 120 mbar s results in a rapid increase in the Pt loading, which saturates at exposures >> 120 mbar s. The deposition of more Pt leads to the formation of NPs that can be as large as 6 nm. Crucially, high P O2 (≥5 mbar) hinders metal aggregation, thus leading to narrow particle size distributions. The results show that ALD of Pt NPs is reproducible across small and large surface areas if the precursor ligands are removed at high P O2 ., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)