Preparation Of Silicon/Carbon Nanotute Supported Metal Catalysts And Their Catalytic Performance

Heterogeneous catalysts have attracted great interest because of their extensive applications in diverse catalytic fields,including organic synthesis,environment treatment,energy conversion,fuel cells,and bio-/gas sensors.The catalytic performance of supported heterogeneous catalysts is mainly dependent on their constitutive components including active species and supports.Therefore,the morphologies of supported metal Nanoparticles（NPs）and properties of the support have important influences on catalytic performance.However,developing reliable protocols to prepare well micro/nano-structured support materials and immobilize catalytically active metal NPs on them are still challengeable.In line with this,extensive research efforts have been focused on strategies for enhancing the catalytic performance,such as（1）Preparation of support materials with particular morphology and high accessible surface area;（2）increase the surface-to-volume ratio of metal NPs by reducing their size,and improved exposure of active NPs,atomic efficiency and a lower cost can be achieved;（3）strengthen the interaction between metal NPs and support so that an enhanced stability as well as recyclability can be realized.Therefore,the design and development of highly effective catalysts with low loading amount,high activity,stability and recyclability are of great significance.Herein,we fabricated three high-performance catalysts by depositing well-dispersed ultrafine metal or alloy NPs onto functionalized tubular supports and explore their application in organocatalysis.Furthermore,the micro/nano morphology of supports,size of NPs,interaction between NPs and support were also investigated.The methods and detailed results are described as follows:（1）A facile in situ reduction approach to prepare amine-functionalized silica nanotubes（ASNTs）-supported Pd（ASNTs@Pd）composite catalyst is demonstrated in this work.Benefiting from the intrinsic physical and chemical properties of the ASNT support and deposited Pd nanoparticles（NPs）,the as-prepared ASNTs@Pd catalyst exhibits superior catalytic activity,stability,and reusability toward 4-nitrophenol（4-NP）reduction reaction.The turnover frequency（TOF）is as high as 313.5 min^-1,which is much higher than that of commercial Pd/C（5.0 wt.%）and many noble-metal based catalysts reported in the last 5 years.In addition,a high TOF of 57.4 min^-1was alsorealized by ASNTs@Pd catalyst for Suzuki coupling reaction.（2）A rational strategy is presented to fabricate SNTs@NC/Pd-Fe catalyst by using SNTs as template,polydopamine-derived nitrogen doped carbon（NC）as outer layer and achoring Pd-Fe alloy NPs at the SNTs@NC surface.The permeable mesoporous SNTs@NC support combined with ultrafine Pd-Fe alloy NPs synergistically enhance the catalytic activity in organocatalysis.The resultant SNTs@NC/Pd-Fe tubular catalyst shows remarkably high activity toward the reduction of 4-NP,Congo red and methyl orange.The TOF is as high as 402.53 min^-11 for 4-NP reduction reaction.Furthermore,the catalyst maintain 87%of its initial catalytic activity even after 7 runs recyclability.（3）A facile strategy to prepare sintering-and leaching-resistant double–shelled nanocatalysts is reported in this section.Pd decorated multi-walled carbon nanotube（MWCNT）are coated with N doped carbon shell derived from polydopamine coating layer.Pd NPs are encapsulated in the confined interface,which prevent NPs from sintering at high temperature（500°C for 3 h）and leaching in the catalytic process.Due to the synergy effect of unique support structure and anchored ultrafine Pd NPs,the resultant MWCNTs@Pd@NC nanocatalyst exhibits excellent catalytic activity and recyclability for the reduction reactions of 4-NP,Congo red and methyl orange.After 6 repeated catalytic cycles,MWCNTs@Pd@NC showed a slight decrease of Pd amount compared to the freshly prepared sample,demonstrating an excellent stability.