Pb1-xCaxTiO3 solid solution (x=0.0, 0.25, 0.50, and 0.75): A theoretical and experimental approach

In this paper we report an experimental and theoretical study based on a periodic density functional investigation into selected compositions of Pb1-xCaxTiO3 (x=0.0, 0.25, 0.50, and 0.75). Based on our findings, we propose that the pseudocubic structure of these perovskites presents a long-range tendency for cubic symmetry, while the short-range displacements bring the solid solution to a tetragonal symmetry. The results are discussed in terms of x-ray diffraction, structural optimized parameters, Raman spectroscopy, band structure, density of states, Mulliken charge, and overlap population.

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The solid solution between platinum and palladium in nature

Chemical and structural data are reported for platinum-palladium intermediates from two nuggets found at Corrego Bom Sucesso, Minas Gerais, Brazil. Three grains with simple stoichiometries (i.e. PtxPd1 -x with x ∼0.67, ∼0.5 and ∼0.33, which correspond to Pt2Pd, PtPd and PtPd2, respectively) were characterized by single-crystal X-ray diffraction and electron-probe microanalysis. In the absence of single-crystal data it might be tempting to hypothesize that such simple stoichiometries represent distinct mineral species, however structural analyses show that all of the phases are cubic and crystallize in space group Fm3̄m. They are, therefore, natural intermediates in the palladium-platinum solid solution. Reflectance and micro-hardness values are reported for the samples and a comparison with the pure metallic elements made. On the basis of information gained from the chemical and structural characterization it can be concluded that there is a complete solid solution between Pt and Pd in nature. These findings corroborate results from experiments on synthetic compounds. © 2013 The Mineralogical Society.

Vanadium-doped TiO2 anatase nanostructures: the role of V in solid solution formation and its effect on the optical properties

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Partial oxidation of methane on NiO-MgO-ZrO2 catalysts

Catalysts containing mixtures of NiO, MgO and ZrO2 were synthesized by the polymerization method. They were characterized by X-ray diffraction (XRD), physisorption of N-2 (BET), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES), and then tested in the partial oxidation of methane (POM) in the presence of air (2CH(4):1O(2)) at 750 degrees C for 6 h. Among the ternary oxides, the catalyst with 40 mol% MgO showed the highest conversion rates in the catalytic processes, but also the highest carbon deposition values (48 mmol h (1)). The greater the amount of NiO-MgO solid solution formed, the higher was the conversion rate of reactants (CH4), peaking at 40 mol% of MgO. Catalysts with lower Ni content on the surface achieved a high rate of CH4 conversion into synthesis gas (H-2 + CO). The formation of more NiO-MgO solid solution seemed to inhibit the deactivation of Ni degrees during reaction. The values of the H-2/CO product ratio were generally found to be slightly lower than stoichiometric. (C) 2012 Elsevier Ltd. All rights reserved.

The effect of solid solution additions on the thermal conductivity of UO₂ /

"Contract No. AT-30-1 Gen-366."

Void formation and grain boundary sliding in aluminum-magnesium solid solution alloys

"Materials Central, Contract no. AF 33(616)-5926. Project no. 7351."

Tuning solid acid catalysts for glucose conversion to platform chemicals

Worldwide concern over dwindling fossil fuel reserves and impact of CO2 emissions on climate change means there is an urgent need to reduce our dependence on oil based sources of fuels and chemicals. The direct conversion of lignocellulosic derived glucose to 5-Hydroxymethylfurfural (5-HMF) is an attractive process for the production of chemicals and fuels but requires a bi-functional catalyst with acid-base or Lewis-Brönsted sites which can operate efficiently in the aqueous phase. While conventionally viewed as a superacid, the potential for tuning the acid strength in SO4/ZrO2 and potential for coupling bi-functional ZrO2-SO4/ZrO2 sites at low sulfate contents have been overlooked. Our previous work has shown effective tuning of the acid strength in SO4/ZrO2 can be used to direct selectivity in terpene isomerisation thus we rationalised control over HMF selectivity could achieved in a similar fashion. Here we report on a systematic study of the impact of acid properties of SO4/ZrO2 catalysts on the conversion of C6 sugars to 5-HMF in aqueous media and correlate the surface acid-base properties with glucose isomerisation and dehydration capabilities.

Bifunctional organorhodium solid acid catalysts for methanol carbonylation

Robust, bifunctional catalysts comprising Rh(CO)(Xantphos) exchanged phosphotungstic acids of general formulas [Rh(CO)(Xantphos)]+n[H3–nPW12O40]n− have been synthesized over silica supports which exhibit tunable activity and selectivity toward direct vapor phase methanol carbonylation. The optimal Rh:acid ratio = 0.5, with higher rhodium concentrations increasing the selectivity to methyl acetate over dimethyl ether at the expense of lower acidity and poor activity. On-stream deactivation above 200 °C reflects Rh decomplexation and reduction to Rh metal, in conjunction with catalyst dehydration and loss of solid acidity because of undesired methyl acetate hydrolysis, but can be alleviated by water addition and lower temperature operation.

Hierarchical nanoporous solid base catalysts for biofuels

Novel macroporous solid bases have been developed as alternative clean technologies to existing commercial homogeneous catalysts for the production of biodiesel from triglycerides; the latter suffer process disadvantages including complex separation and associated saponification and engine corrosion, and are unsuitable for continuous operation. To this end, tuneable macroporous MgAl hydrotalcites have been prepared by an alkali-free route and characterised by TGA, XRD, SEM and XPS. The macropore architecture improves diffusion of bulky triglyceride molecules to the active base sites, increasing activity. Lamellar and macroporous hydrotalcites will be compared for the transesterification of both model and plant oil feedstocks, and structure-reactivity relations identified.

New solid base catalysts for biodiesel synthesis

The application of heterogeneous catalysts for the manufacture of renewable biodiesel fuels offers an exciting, alternative clean chemical technology to current energy intensive processes employing soluble base catalysts. We recently synthesised tuneable MgO nanocrystals as efficent solid base catalysts for biodiesel synthesis, and have developed a simple X-ray spectroscopic method to quantitatively determine surface basicity, thereby providing a rapid screening tool for predicting the reactivity of new solid base catalysts. Promotion of these MgO nanocrystals through Cs doping dramatically enhances biodiesel production rates due to the formaion of a mixed Cs Mg(CO ) phase. These MgO derived nanocatalysts permit energy efficent, continuous processing of diverse, sustainable oil feedstocks in flow reactors.