Porous Nanocrystalline Silicon Supported Bimetallic Pd-Au Catalysts: Preparation, Characterization, and Direct Hydrogen Peroxide Synthesis.

Bimetallic Pd-Au catalysts were prepared on the porous nanocrystalline silicon (PSi) for the first time. The catalysts were tested in the reaction of direct hydrogen peroxide synthesis and characterized by standard structural and chemical techniques. It was shown that the Pd-Au/PSi catalyst prepared from conventional H2[PdCl4] and H[AuCl4] precursors contains monometallic Pd and a range of different Pd-Au alloy nanoparticles over the oxidized PSi surface. The PdAu2/PSi catalyst prepared from the [Pd(NH3)4][AuCl4]2 double complex salt (DCS) single-source precursor predominantly contains bimetallic Pd-Au alloy nanoparticles. For both catalysts the surface of bimetallic nanoparticles is Pd-enriched and contains palladium in Pd0 and Pd2+ states. Among the catalysts studied, the PdAu2/PSi catalyst was the most active and selective in the direct H2O2 synthesis with H2O2 productivity of 0.5 [Formula: see text] at selectivity of 50% and H2O2 concentration of 0.023 M in 0.03 M H2SO4-methanol solution after 5 h on stream at -10°C and atmospheric pressure. This performance is due to high activity in the H2O2 synthesis reaction and low activities in the undesirable H2O2 decomposition and hydrogenation reactions. Good performance of the PdAu2/PSi catalyst was associated with the major part of Pd in the catalyst being in the form of the bimetallic Pd-Au nanoparticles. Porous silicon was concluded to be a promising catalytic support for direct hydrogen peroxide synthesis due to its inertness with respect to undesirable side reactions, high thermal stability, and conductivity, possibility of safe operation at high temperatures and pressures and a well-established manufacturing process

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

Peculiarities of structure and morphology of copper-cerium nanopowders produced by laser ablation

Copper-cerium nanopowders CuOx–CeO2 (mass ratio Cu:Ce = 6:100) are prepared by mixing the dispersions of the copper and cerium oxides produced by the method of pulse laser ablation (PLA) in liquid, followed by drying. The initial dispersions of copper oxides were prepared by the method of PLA of a metal copper target in distilled water or 1% hydrogen peroxide solution, and those of cerium oxide – by PLA of metal cerium in distilled water. It is shown that ablation of copper in water and water solution of peroxide is followed by the formation of copper oxide particles of different morphologies and compositions (structure). It is established that no crystal phases of copper oxides are formed in the copper-cerium nanopowders produced from separate dispersions. Given this approach to forming copper-cerium nanoparticles, the oxidized copper is distributed in the form of a thin layer on the CeO2 surface, which is demonstrated by the results of investigation of these particles by the methods of high-resolution transmission electron microscopy and X-ray diffraction. The formation of a Cu–O–Ce interface at the interphase boundary gives rise to the formation of defects on the CeO2 surface, which is confirmed by the Raman spectroscopy. An investigation of the composition and electronic structure of the surface of CuOx nanoparticles and CuOx–CeO2 nanopowders performed by the method of X-ray photoelectronic spectroscopy reveals the presence of copper in the form of a combination of Cu (I) and Cu (II) with the prevailing contribution from a single-valence state for CuOx–CeO2 nanopowders, which could have resulted from the interaction between CuOx and CeO2 particles

Porous Nanocrystalline Silicon Supported Bimetallic Pd-Au Catalysts: Preparation, Characterization, and Direct Hydrogen Peroxide Synthesis

Bimetallic Pd-Au catalysts were prepared on the porous nanocrystalline silicon (PSi) for the first time. The catalysts were tested in the reaction of direct hydrogen peroxide synthesis and characterized by standard structural and chemical techniques. It was shown that the Pd-Au/PSi catalyst prepared from conventional H2[PdCl4] and H[AuCl4] precursors contains monometallic Pd and a range of different Pd-Au alloy nanoparticles over the oxidized PSi surface. The PdAu2/PSi catalyst prepared from the [Pd(NH3)4][AuCl4]2 double complex salt (DCS) single-source precursor predominantly contains bimetallic Pd-Au alloy nanoparticles. For both catalysts the surface of bimetallic nanoparticles is Pd-enriched and contains palladium in Pd0 and Pd2+ states. Among the catalysts studied, the PdAu2/PSi catalyst was the most active and selective in the direct H2O2 synthesis with H2O2 productivity of 0.5 mol gPd-1 h-1 at selectivity of 50% and H2O2 concentration of 0.023 M in 0.03 M H2SO4-methanol solution after 5 h on stream at −10°C and atmospheric pressure. This performance is due to high activity in the H2O2 synthesis reaction and low activities in the undesirable H2O2 decomposition and hydrogenation reactions. Good performance of the PdAu2/PSi catalyst was associated with the major part of Pd in the catalyst being in the form of the bimetallic Pd-Au nanoparticles. Porous silicon was concluded to be a promising catalytic support for direct hydrogen peroxide synthesis due to its inertness with respect to undesirable side reactions, high thermal stability, and conductivity, possibility of safe operation at high temperatures and pressures and a well-established manufacturing process

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

Ceria–Zirconia-Supported Ruthenium Catalysts for Hydrogen Production by Ammonia Decomposition

Commercial cerium–zirconium oxide supports (Ce0.5Zr0.5O2, Ce0.75Zr0.25O2, and Ce0.4Zr0.5Y0.05La0.05O2) were used to prepare Ru/CeZrOx catalysts. According to the XRD and IR spectroscopy data, the supports consist of ceria-based substitutional solid solutions. The specific surface areas of supports and catalysts are similar and range from 71–89 m2/g. As shown by TEM and XRD methods, the size of support particles equals 6–11 nm. According to the TEM data, the size of ruthenium particles does not exceed 1.3 nm. The catalyst activity in the ammonia decomposition process was studied. The Ru/Ce0.75Zr0.25O2 catalyst at temperature 500 °C and GHSV 120,000 h−1 demonstrated the highest hydrogen productivity of 53.3 mmol H2/(gcat·min) and compares well with the best results reported in the literature. The kinetics of ammonia decomposition reaction were calculated using the Temkin–Pyzhov exponential expression. The developed mathematical model well described the experimental data. The studied catalysts demonstrated high activity for the ammonia decomposition reaction