Structure Regulation And Performance Study Of Pt-based Nanocatalyst

The supported Pt catalyst is invaluable in many important industrial processes such as propane dehydrogenation,CO oxidation and NO_x reduction.The catalytic performance of Pt nanocatalysts is closely related to the size of Pt particles and support materials.However,Pt NPs tend to aggregate to reduce surface energy.This seriously affects the application prospect of Pt nanocatalysts.Furthermore,TiO₂-SiO₂system shows various unique features,such as high stability and large specific surface area,and has been widely used in Pt based nanocatalysts.Fabricating novel Pt based nanocatalysts by regulating the morphology and content of TiO₂-SiO₂ materials could further extend the applications of Pt based nanocatalysts.Thus,in this work,novel double-shelled TiO₂ hollow sphere,hierarchical TiO₂@Pt@mSiO₂ hollow nanocatalyst,low Pt content Sn²⁺-doped double-shelled Pt/TiO₂ hollow nanocatalyst,high-quality mesoporous or hollow ZnS@g-C₃N₄/TiO₂ nanospheres and hierarchical silica-Pt nanotubes were synthesized successfully.Moreover,the structural characteristics,catalytic performance and thermal stability were characterized and studied by TEM、SEM、XRD、BET、XPS and TGA systematically.（1）High-quality double-shelled TiO₂ hollow sphere（DHS-Ti）assembled with TiO₂ nanosheets was synthesized successfully via a simple solvothermal treatment.The double-shelled structure shows a high BET surface area up to 417.6 m²g^-1.Anatase DHS-Ti of high crystallinity can be obtained without collapse by calcination treatment.Besides,the effects of CTAB concentration,pH and hydrothermal temperature have also been investigated with a series of contrast experiments.A formation mechanism involving in-situ growth of amorphous TiO₂ nanosheets followed by the redeposition of silica species is proposed.Lastly the DHS-Ti forming strategy can be extended as a general strategy to fabricate various morphological hollow nanostructures and double-shelled Pt nanocatalysts by rationally selecting different SiO₂ nanoparticles as core materials.（2）A novel hierarchical TiO₂@Pt@mSiO₂ hollow nanocatalyst with enhanced thermal stability has been synthesized successfully.The formation procedure involves a facile synthesis of SiO₂@TiO₂@Pt nanospheres and a subsequent solvothermal process.During the hydrothermal process,original TiO₂ layer was transformed into nanoplatelet structure and,meanwhile,etch-released silica species redeposited on the surface of in-situ grown TiO₂ nanoplatelets.In the catalytic system,the in-situ grown TiO₂ nanoplatelets were buried in redeposited mSiO₂ layers and the Pt NPs dispersed uniformly between TiO₂ nanoplatelets and mSiO₂ layers.Importantly,the redeposited mSiO₂ layer provides a physical barrier to prevent Pt NPs from sintering and the hierarchical TiO₂ nanostructure shows an obvious co-catalysis effect in the reduction of 4-NP.Besides,in the high temperature reaction of propane dehydrogenation,HHN exhibits a lower deactivation parameter,indicating the excellent thermal stability.（3）A facile strategy is proposed for the synthesis of low Pt content Sn²⁺-doped double-shelled Pt/TiO₂ hollow nanocatalyst(DHS-PtSn²⁺)with excellent solar H₂production properties.After calcination in N₂,DHS-PtSn²⁺shows highest photocatalytic H₂ production rate of 28502μmol h^-1 g^-1,nearly three-fold higher than Sn⁴⁺-doped counterpart,thereby demonstrating better synergistic effect of Sn²⁺than Sn⁴⁺in H₂ evolution.The influences of calcination atmosphere,Sn²⁺content and Sn/Pt atomic ratio on H₂ production have been investigated with a series of contrast experiments.Besides,the proposed Sn²⁺doping strategy could also be applied in many other light-sensitive materials（e.g.home-made TiO₂ NPs,commercial P25 and g-C₃N₄）,suggesting its extensive applications in H₂ production.Finally,based on the excellent synergistic effect of Sn²⁺in H₂ production,a possible photocatalytic mechanism is tentatively proposed.（4）High-quality mesoporous or hollow ZnS@g-C₃N₄/TiO₂ nanospheres were fabricated successfully via structure regulation strategy for efficient photocatalytic H₂production under visible-light irradiation.The entire process was started with the construction of solid g-C₃N₄/TiO₂（S-g-C₃N₄/TiO₂）nanospheres.Then,with TiO₂nanosheets（NSs）in situ grown or Ostwald ripening treatment,S-g-C₃N₄/TiO₂ could be converted into mesoporous or hollow ZnS@g-C₃N₄/TiO₂ nanospheres automatically.The obtained porous ZnS@g-C₃N₄/TiO₂ nanospheres were featured of regular shape,high porosity,large specific surface area and adjustable g-C₃N₄ content.In mesoporous ZnS@g-C₃N₄/TiO₂（M-ZnS-g-C₃N₄/TiO₂）nanospheres,the specially constructed mesoporous served as channels for the access of reactants in heterogeneous catalysis.Besides,the doped ZnS NPs in M-ZnS-g-C₃N₄/TiO₂ can extend visible light response region and act as electron-sink function to improve visible-light H₂ production significantly.（5）A simple sol-gel method for the fabrication of hierarchical silica-Pt nanotubes was proposed.Initial Pt NPs can be obtained via the reduction of K₂PtCl₆ with trisodium citrate as reductant.The self-assembled SiO₂@Pt@SiO₂ spheres were stuck together and etched through the"surface-protected etching"strategy.Lots of vertically aligned silica branches in-situ grown from inlaid SiO₂@Pt@SiO₂ spheres,fabricating the hierarchical silica-Pt nanotubes automatically.TEM and SEM were conducted to monitor morphological evolution.The effects of PVP concentration and molar ratios of NH₄OH to TEOS have also been investigated with a series of contrast experiments.Besides,the hierarchical silica-Pt nanotubes exhibited a high thermal stability and excellent catalytic performance in the reaction of propane dehydrogenation,suggesting their potential application in various high temperature reactions.