In situ probing of Pt/TiO2_{2} activity in low-temperature ammonia oxidation

The improvement of the low-temperature activity of the supported platinum catalysts in selective ammonia oxidation to nitrogen is still a challenging task. The recent developments in in situ/operando characterization techniques allows to bring new insight into the properties of the systems in correlation with their catalytic activity. In this work, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and operando X-ray absorption spectroscopy (XAS) techniques were applied to study Pt/TiO$_{2}$ catalysts in ammonia oxidation (NH$_{3}$ + O$_{2}$ reaction). Several synthesis methods were used to obtain samples with different size of Pt particles, oxidation state of Pt, and morphology of the support. Metal platinum particles on titania prepared by pulsed laser ablation in liquids exhibited the highest activity at lower temperatures with the temperature of 50% conversion of NH$_{3}$ being 150 °C. The low-temperature activity of the catalysts synthesized by impregnation can be improved by the reductive pretreatment. NAP-XPS and operando XANES data do not show formation of PtO$_{x}$ surface layers or PtO/PtO$_{2}$ oxides during NH$_{3}$ + O$_{2}$ reaction. Despite the differences in the oxidation state of platinum in the as-prepared catalysts, their treatment in the reaction mixture results in the formation of metallic platinum particles, which can serve as centers for stabilization of the adsorbed oxygen species. Stabilization of the bulk platinum oxide structures in the Pt/TiO$_{2}$ catalysts seems to be less favorable due to the metal–support interaction

Society, State, Nation and the People in the Democratic South Africa: Two Decades of Illusions in The Practice of Public Administration, Development Planning and Management

The purpose of this article is to provide a conceptual argument in that as South Africa transcended beyond its democratic dispensation, an opportunity was missed in the process leading to transition to define a society, state, nation and the people for sustaining the democratic founding for purposes of public administration practice, development planning and management. That is done by critically portraying South Africa as a society, state, nation and locating the people for governance purposes within a democratic founding. It is argued that attempts are made to rewrite the history of the country with a view of bolstering its societal status, nation, state and the people without a profound context. South Africa has become what it is today due to its history that remains its defining factor if it has to locate its society, state, nation and the people. Having lost that opportunity during transition, governance has become so unwieldy in that those assigned with authority in the governance landscape, tend to confuse the roles of society, nation, state and the people and that eventually strain the fragile democracy by distorting the facts and the role of constitutional apparatus that are instrumental to the country’s democratic founding. The conclusion is rather pessimistic in that as long as these issues are not properly located within the governance landscape; the democratic dispensation remains vulnerable for demise just like other democracies within the African continent with the potential of the middle class hijacking it from the vulnerable poor majority being the people that public administration practice has to serve. DOI: 10.5901/mjss.2015.v6n2s1p61

Контроль электропроводности пленок однослойных углеродных нанотрубок в процессе синтеза

We investigated electrical conductance of single-walled carbon nanotubes (SWCNTs) films during the time of synthesis. The time dependence of conductance have been described in terms of the Shklovsky - de Gennes percolation model. Measurements of electrical conductance during the synthesis allow to control the repeatability and take samples from the desired values of electrical conductanc

A study of Pt/al2O3 nanocomposites obtained by pulsed laser ablation to be used as catalysts of oxidation reactions

Pulsed laser ablation (PLA) in liquids is an effective high-energy method for the synthesis of functional nanomaterials. In the present work, a nanocomposite catalyst Pt/Al2O3(PLA) is prepared by mixing solutions of platinum and aluminium nanodispersions obtained by the PLA method in alcohol and water, respectively. After being dried out, the obtained nanocomposite is thermally treated in air at 400 °C and 550 °C. It is shown by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction that platinum in the composition of the calcined samples stabilizes on the Al2O3 surface in the form of metal nanoparticles. The main crystal structure of η-Al2O3 is determined and impurity phases of Al(OH)3 hydroxide and metallic aluminium are revealed using X-ray powder diffraction (XRPD). The Pt/Al2O3 nanocomposite samples obtained by the PLA method are found to be highly prospective for the use in reactions of catalytic oxidation of CO and NH3. The Pt/Al2O3(PLA) nanocomposites are compared with the Pt/Al2O3 (IMP) catalyst synthesized by the method of solution chemistry. The Pt/Al2O3(IMP) sample containing highly dispersed platinum nanoparticles (1–2 nm) on the γ-Al2O3 surface has a lower T50 value (188 °C) in the reaction of CO oxidation that the PLA catalyst (T50 = 198 °C). At the same time, in the reaction of NH3 oxidation, the PLA catalyst is more active (T50 = 167 °C) than the IMP sample (T50 = 180 °C). The observed regularities are discussed in terms of the dispersion and the oxidation depth of platinum particles in the composition of Pt/Al2O3 catalysts

Temperature Dependences of Conductivity and Magnetoconductivity of Multiwall Carbon Nanotubes Annealed at Different Temperatures

Представлены температурные зависимости проводимости (в диапазоне 4.2-300 K) и магнето- проводимость (в полях до 10 кГ при 4.2 K) многослойных углеродных нанотрубок со средним внешним диаметром 8-10 и 20-22 нм, отожженных при различных температурах (1600, 2200, 2600, 2800◦C). Показано, что зависимость проводимости для нанотрубок со средним диаметром 20-22 нм характерна для квантовых поправок к проводимости взаимодействующих электронов в двумерных проводниках с локальным беспорядком. Для нанотрубок со средним диаметром 8- 10 нм имеет место одномерная прыжковая проводимость с переменной длиной прыжка. Показано, что при температурной обработке многослойных углеродных нанотрубок изменяется вклад квантовых поправок в проводимость, а также параметры прыжковой проводимости, что отжиг образцов влияет на магнетопроводимость. Многослойные углеродные нанотрубки со средним диаметром 20-22 нм имеют положительную магнетопроводимость.Temperature (in range 4.2-300 K) and magnetic field (in fields up to 10 kG at 4.2 K) dependences of the conductivity of two sets of multiwall carbon nanotubes with different average diameters (8-10 nm and 20-22 nm) heated at various temperatures (1600, 2200, 2600, 2800◦C) were investigated. Temperature dependences for nanotubes with average diameter 20-22 nm is typical for quantum corrections to conduc- tivity of the systems with interaction electrons in two dimensional conductors with local disorder. For nanotubes with average diameter 8-10 nm temperature dependences corresponds to one-dimensional variable range hopping conductivity (VRHC). The variation of annealing temperature of MWNTs influence on the contribution of corrections to conductivity and parameters of VRHC. The magnetoconductivity of MWNTs also depends on the annealing temperature and is less than that of highly oriented pyrographite. Annealed MWNTs with average diameter 20-22 nm has a positive magnetoconductivity