Mesoporous silicon sulfonic acid as a highly efficient and stable catalyst for the selective hydroamination of cyclohexene with cyclohexylamine to dicyclohexylamine in the vapor phase

In this work,a new mesoporous silicon sulfonic acid catalyst derived from silicic acid has been successfully prepared by the chemical bonding method.The physicochemical properties of mesoporous silicon sulfonic acid catalysts have been systematically characterized using various techniques.The results demonstrate that sulfonic acid groups have been grafted on silicic acid by forming a new chemical bond(Si-O-S).The mesoporous silicon sulfonic acid exhibits excellent catalytic performance and stability in the vapor phase hydroamination reaction of cyclohexene with cyclohexylamine.Cyclohexene conversion of 61% and 97% selectivity to dicyclohexylamine was maintained after running the reaction for over 350 h at 280℃.The developed mesoporous silicon sulfonic acid catalyst shows advantages of low cost,superior acid site accessibility,and long term reactivity stability.Moreover,a possible catalytic hydroamination reaction mechanism over silicon sulfonic acid was suggested.It has been demonstrated that the sulfonic acid groups of the catalyst play an important role in the hydroamination.The present work provides a simple,efficient,and environmentally friendly method for the hydroamination of cyclohexene to valuable dicyclohexylamine,which also shows important industrial application prospects.

Incorporation of europium (Ⅱ) nanostructures into the channels of mesoporous silicon oxy-nitride for enhanced photoluminescence

Divalent europium（Ⅱ）-doped mesoporous silicon oxy-nitride materials, as a novel type of nanoscopic photoluminescent material, are studied in which the optically active luminescent centers are isolated within the pores. Colorless and transparent blue emitting luminous Eu2＋-doped mesoporous silicon oxy-nitride materials were prepared from mesoporous silica via impregnation, nanocasting and nitrogen-assisted carbothermal reduction and nitridation method. The morphology and porosity of the silica remain unchanged during the synthesis process as revealed by SEM images and by nitrogen sorption studies. Photoluminescence studies reveal a strong blue emission band for Eu2＋ centered at 425 nm with a quantum efficiency of 47%. The luminescent intensity is greatly influenced by the amount of co-dopant, AI3＋ ions.

Characterization and modeling of the temperature-dependent thermal conductivity in sintered porous silicon-aluminum nanomaterials

Nanostructured silicon and silicon-aluminum compounds are synthesized by a novel synthesis strategy based on spark plasma sintering(SPS)of silicon nanopowder,mesoporous silicon(pSi),and aluminum nanopowder.The interplay of metal-assisted crystallization and inherent porosity is exploited to largely suppress thermal conductivity.Morphology and temperaturedependent thermal conductivity studies allow us to elucidate the impact of porosity and nanostructure on the macroscopic heat transport.Analytic electron microscopy along with quantitative image analysis is applied to characterize the sample morphology in terms of domain size and interpore distance distributions.We demonstrate that nanostructured domains and high porosity can be maintained in densified mesoporous silicon samples.In contrast,strong grain growth is observed for sintered nanopowders under similar sintering conditions.We observe that aluminum agglomerations induce local grain growth,while aluminum diffusion is observed in porous silicon and dispersed nanoparticles.A detailed analysis of the measured thermal conductivity between 300 and 773 K allows us to distinguish the effect of reduced thermal conductivity caused by porosity from the reduction induced by phonon scattering at nanosized domains.With a modified Landauer/Lundstrom approach the relative thermal conductivity and the scattering length are extracted.The relative thermal conductivity confirms the applicability of Kirkpatrick’s effective medium theory.The extracted scattering lengths are in excellent agreement with the harmonic mean of log-normal distributed domain sizes and the interpore distances combined by Matthiessen’s rule.