Synthesis and catalytic application in isobutane dehydrogenation of the mesoporous chromia/alumina catalysts based on a metal-organic framework

The mesoporous chromia/alumina (Cr2O3/Al2O3) catalysts were successfully synthesized using a porous metal-organic framework MIL-101 (Cr3F(H2O)(2)O(BDC)(3)center dot nH(2)O, BDC = 1,4-benzenedicarboxylate) as a molecular host and chromium precursor, inorganic aluminium salt as the aluminium precursor. The aluminium sources had the significant effects on the structure of the products. The formation of alpha-Cr2O3 phase was observed in the mesoporous catalyst (Cr2O3/Al2O3-C) prepared by AlCl3 center dot 6H(2)O, whereas additional chromia alumina solid solution CrxAl2-xO3 phase was produced in the catalyst (Cr2O3/Al2O3-N) using Al(NO3)(3)center dot 9H(2)O as the aluminium precursor. The surface Cr species existed in the Cr6+ and Cr3+ state over the mesoporous catalysts. The Cr species had a strong interaction with the alumina support. Preliminary catalytic studies showed that the Cr2O3/Al2O3-N catalyst exhibited much higher isobutene selectivity and higher stability than the reference catalyst in the isobutane dehydrogenation. The maintainable dehydrogenation activity during the five dehydrogenation-regeneration cycles indicated high regenerative ability of the catalyst Cr2O3/Al2O3-N. Consequently, this study represents a feasible way toward the facile synthesis of the mesoporous chromia/alumina catalyst. Moreover, this work proposes a novel application of metal-organic framework

One-pot synthesis of ordered mesoporous zirconium oxophosphate with high thermostability and acidic properties

A series of mesoporous zirconium oxophosphate (M-ZrPO) with different P/Zr molar ratios (0-1.25) has been prepared via a facile one-pot evaporation-induced self-assembly (EISA) strategy. After removing the structure-directing agents, the M-ZrPO with large specific surface area (160 m(2) g(-1)), big pore volume (0.26 cm(3) g(-1)) and narrow pore size distribution (5.64 nm) has been obtained. Small-angle X-ray diffraction (SXRD) and transmission electron microscopy (TEM) results showed that these materials had ordered mesoporous structure. With the increase of P/Zr, the textural properties of M-ZrPO could be improved. Moreover, the ordered mesostructure could be maintained even when treated at 800 degrees C, indicating the M-ZrPO had attractive thermal stability. NH3-TPD and pyridine-IR analyses showed the presence of abundant Bronsted and Lewis acid sites in the material. The M-ZrPO has been used successfully as solid acid catalyst and showed excellent performance in the ketalization reaction

Structure-thermal property correlation of aligned silicon dioxide nanorod arrays

Quantitative characterization of thermal properties of nanorod (NR) arrays appears to be challenging due to the complex combination of high volume of air voids, anisotropy, and structural non-uniformity. This work investigates the structure-thermal property correlation of arrays consisting of either vertically aligned or slanted silicon dioxide (SiO2) NRs, fabricated by the dynamic shadowing growth technique. We apply the frequency-dependent time-domain thermoreflectance method to quantify the thermal properties of SiO2 NR arrays that may possess inhomogeneity along the depth direction. The effective thermal conductivities of four SiO2 NR array films and one reference capping layer for the SiO2 NR array are obtained. The impact of the structure on the effective thermal conductivities of the SiO2 NR array is discussed. The lowest effective thermal conductivity among all samples in this work is found to be 0.13 W m(-1) K-1 for the slanted NR array. We attribute the reduction in the effective thermal conductivity of the NR array to the discontinuous nature of SiO2 NRs, which reduces the density of the thermal transport channels and thus prevents heat flux from propagating downwards along the through-plane direction. The results from this work facilitate the potential applications of NR-array-based thermal insulators for micro-thermal devices. Published by AIP Publishing