Synthesis, Structure and Thermophysical Properties of Phosphates MNi0.5Zr1.5(PO4)3 (M = Mg, Ca, Sr)

New phosphates MNi0.5Zr1.5(PO4)3 (M = Mg, Ca, Sr) were prepared by the precipitating method. Phosphates were characterized using X-ray powder diffraction, IR-spectroscopy and electron microprobe analyses. The crystal structure of phosphates was refined by the Rietveld method. Phosphates CaNi0.5Zr1.5(PO4)3 and SrNi0.5Zr1.5(PO4)3 are shown to have been crystallized in the NaZr2(PO4)3-type structure and the phosphate MgNi0.5Zr1.5(PO4)3 was obtained as a single-phase with Sc2(WO4)3-type structure. Heat capacity of phosphate CaNi0.5Zr1.5(PO4)3 was measured in the range 7 – 650 K and increased monotonically over the entire temperature range studied. Thermal expansion of phosphate CaNi0.5Zr1.5(PO4)3 was studied in the interval 295-1073 K by the high temperature X-ray diffraction. This phosphate is similar to the best low-expansion ceramics, such as zircon, cordierite and silica glass in thermal expansion behavior

Conversion of sugars to ethylene glycol with nickel tungsten carbide in a fed-batch reactor: high productivity and reaction network elucidation

Bifunctional nickel tungsten carbide catalysis was used for the conversion of aqueous sugar solutions into short-chain polyols such as ethylene glycol. It is shown that very concentrated sugar solutions, viz, up to 0.2 kg L-1, can be converted without toss of ethylene glycol selectivity by gradually feeding the sugar solution. Detailed investigation of the reaction network shows that, under the applied reaction conditions, glucose is converted via a retro-aldol reaction into glycol aldehyde, which is further transformed into ethylene glycol by hydrogenation. The main byproducts are sorbitol, erythritol, glycerol and 1,2-propanediol. They are formed through a series of unwanted side reactions including hydrogenation, isomerisation, hydrogenolysis and dehydration. Hydrogenolysis of sorbitol is only a minor source of ethylene glycol. To assess the relevance of the fed-batch system in biomass conversions, both the influence of the catalyst composition and the reactor setup parameters like temperature, pressure and glucose addition rate were optimized, culminating in ethylene glycol yields up to 66% and separately, volume productivities of nearly 300 gEG L-1 h-1

NH 2-MIL-53(Al): A high-contrast reversible solid-state nonlinear optical switch

The metal-organic framework NH 2-MIL-53(Al) is the first solid-state material displaying nonlinear optical switching due to a conformational change upon breathing. A switching contrast of at least 38 was observed. This transition originates in the restrained linker mobility in the very narrow pore configuration. © 2012 American Chemical Society

Molecular shape-selectivity of MFI zeolite nanosheets in n-decane isomerization and hydrocracking

MFI zeolite nanosheets with thickness of 2 and 8 nm were synthesized, transformed into bifunctional catalysts by loading with platinum and tested in n-decane isomerization and hydrocracking. Detailed analysis of skeletal isomers and hydrocracked products revealed that the MFI nanosheets display transition-state shape-selectivity similar to bulk MFI zeolite crystals. The suppressed formation of bulky skeletal isomers and C cracking products are observed both in the nanosheets and the bulk crystals grown in three dimensions. This is typical for restricted transition-state shape-selectivity, characteristic for the MFI type pores. It is a first clear example of transition-state shape-selectivity inside a zeolitic nanosheet. Owing to the short diffusion path across the sheets, expression of diffusion-based discrimination of reaction products in the MFI nanosheets was limited. The 2-methylnonane formation among monobranched C isomers and 2,7-dimethyloctane among dibranched C isomers, which in MFI zeolite are favored by product diffusion, was much less favored on the nanosheets compared to the reference bulk ZSM-5 material