Theoretical Investigation on H-Abstraction Reactions of Silanes with H and CH3 Attacking: A Comparative Study with Alkane Counterparts.

Silicon-based organic precursors are widely applied in the vapor-fed flame synthesis of monocrystalline silicon, silicon dioxide, and silicon nitride. Due to the lack of kinetic investigations on reactions of silicon-based organic precursors, rate constants were usually analogized to those of their hydrocarbon counterparts. Investigations on the similarities and differences between the two types of compounds become necessary. This work reports a comparative theoretical investigation on H-abstraction reactions with H and CH3 attacking for silanes and their alkane counterparts, including silane and methane, disilane, methylsilane and ethane, dimethylsilane and propane, trimethylsilane and iso-butane, and tetramethylsilane and neo-pentane at the domain-based local pair natural orbital coupled cluster with perturbative triple excitations (DLPNO-CCSD(T))/cc-pVTZ//M06-2X/cc-pVTZ level. The rate constants were calculated using the conventional transition-state theory coupled with the asymmetric Eckart tunneling corrections over 600-2000 K. The calculated results show that dramatic discrepancies exist between H-abstraction from silicon sites in silanes and equivalent carbon sites in their alkane counterparts with H and CH3 attacking. The H-abstraction reactions from the primary carbon sites in silanes have generally lower barrier energies than the similar reactions in their alkane counterparts, while those in methylsilane and dimethylsilane with H attacking are the only two with higher barrier energies. Electrostatic potential mapped molecular van der Waals surfaces were adopted to provide insight into the calculated trends in barrier energies. The H-abstraction reactions from silicon sites in silanes have much higher rate constants than those from equivalent carbon sites in their alkane counterparts, especially under low-temperature conditions, while the rate constants of H-abstraction reactions from primary carbon sites in silanes and their alkane counterparts show relatively strong analogy.

Investigation of low-temperature selective catalytic reduction of NOx with ammonia over Cr-promoted Fe/AC catalysts.

Fe/activated coke (AC) and Cr-Fe/AC catalysts with AC as a supporter and Cr and Fe as active components were prepared by an impregnation method for low-temperature selective catalytic reduction (SCR) of NO with NH3. The effects of Cr addition and its concentrations on the deNOx performance of Fe/AC catalysts were studied at low temperature. The Cr addition promotes the low-temperature SCR activity of the 8Fe/AC catalyst and the 8Fe6Cr/AC catalyst has the best low-temperature SCR deNOx performance, which the NOx conversions are greater than 90% at 160-240 °C. The 8Fe6Cr/AC catalyst has good water resistance. However, when 100 ppm SO2 was introduced into the reaction gas, its deNOx efficiency drops to 45% at 180 °C. To clarify the specific effects of Cr addition on the NOx conversions and sulfur poisoning, the Cr-Fe/AC catalysts were characterized by X-ray diffraction, BET, H2 temperature-programmed reduction, NH3 temperature-programmed desorption, X-ray photoelectron spectroscopy, and Fourier infrared spectroscopy. The addition of Cr into Fe/AC catalysts greatly increases the BET surface area and the number of weak and medium-strong acid sites on the catalyst surface and improves the ratio of Fe3+/Fe2+. These factors enhance the NOx conversion of 8Fe/AC catalyst. The formed sulfates and hydrogen sulfates cover the active sites on the catalyst surface, which lead to the sulfur poisoning of the 8Fe6Cr/AC catalyst. Graphical abstract.

Promotional effect of Mn modification on DeNOx performance of Fe/nickel foam catalyst at low temperature.

Manganese (Mn)-modified ferric oxide/nickel foam (Fe/Ni) catalysts were prepared using Ni as a carrier, Fe and Mn as active components to study NH3-SCR of NOx at low temperature. The effects of different Fe loads and Mn-modified Fe/Ni catalysts on the DeNOx activity were investigated. Results show that when the amount of Fe is 10%, Fe/Ni catalyst has the highest NOx conversion. For the Mn-modified Fe/Ni catalysts, the NOx conversions firstly increase and then decrease with the Mn loading amount increasing. 3MnFe/Ni catalyst shows high NOx conversions, which reach 98.4-100% at 120-240 °C. The characterization analyses reveal that Mn-modified Fe/Ni catalysts increase the FeOx dispersion on Ni surface, improve significantly the valence ratio of the Fe3+/Fe2+, the content of lattice oxygen which promotes the catalyst storage and exchange oxygen capacity at low temperature, and the number of Brønsted active acid sites on the catalyst surface, and enhance the low-temperature redox capacity. These factors remarkably increase the NOx conversions at low temperature. Especially, 3Mn10Fe/Ni catalyst not only has excellent DeNOx activity but also has better water resistance. However, the anti-SO2 poisoning performance needs to be improved. To further analyze the reason why different catalysts show different DeNOx performance, the reaction kinetics was also explored.

Hollow silica nanospheres coated with insoluble calcium salts for pH-responsive sustained release of anticancer drugs.

Hollow silica nanospheres coated with biocompatible and pH-sensitive inorganic insoluble calcium salts including calcium carbonate and hydroxyapatite have been successfully prepared. The results indicate that the nanospheres can efficiently load doxorubicin and release it in a pH-responsive and sustained manner, and improve the treatment efficacy significantly.

Facile one-pot preparation of calcite mesoporous carrier for sustained and targeted drug release for cancer cells.

Herein, mesoporous calcite/chondroitin sulfate hybrid microrods are prepared through a one-pot method. Biological assays indicate that the microrods might be used as good active targeted drug delivery carriers to treat tumor tissues with high specificity and low toxic side effects.