贵金属基双金属纳米催化剂的合成及其性能研究

【作者】 李富民；

【导师】 胡满成；

【作者基本信息】 陕西师范大学 ， 无机化学， 2020， 博士

【摘要】 贵金属基双金属纳米催化剂以其独特、高效的催化性能引起了全球科研工作者的研究兴趣。如何实现它们的组分优选、结构设计及性能提升已经成为贵金属基催化剂应用领域中具有重大意义的热点课题。本论文以Pt/Pd基双金属纳米催化剂为研究对象,以提升氧气还原反应、过氧化氢(H2O2)直接合成和甲酸氧化反应效率为研究目标,在设计合成催化剂和揭示构效关系上进行了有益的探索。(一)开发了聚胺(PAH/PAA)辅助水热热解法,合成出功能化的Pd-Pt双金属核壳纳米枝晶。由于Pd与Pt之间的配体效应和几何效应、纳米枝晶结构和表面聚胺功能化,Pd-Pt双金属纳米催化剂对氧气还原反应表现出了增强的催化活性、稳定性和耐醇性。为高效氧气还原电催化剂的设计合成提供了新的思路。(二)实现了Au@PAA@Pd三明治纳米结构的设计和成功合成。利用中间层PAA携带的-NH2基团大幅地调控了Pd壳的电子结构并保持其外表面清洁,这促使Au@PAA@Pd对甲酸电氧化表现出超高的催化活性。揭示了一种高效调控催化剂电子结构的策略。(三)合成了组分可调的一系列Pd-Sn双金属合金纳米催化剂,并成功应用于H2O2直接合成。通过调节催化剂的组成和催化条件,可以完全抑制H2O2在催化剂上的降解,并实现高的H2选择性和催化活性。性能的提升被归因于Pd的氧化、集团效应以及界面协同效应,为催化剂构效关系的构建提供了多重角度。(四)合成并使用金属间的Pd3Sn2纳米网络作为甲酸电氧化材料。一方面,金属间化合物的结构导致的Pd-Sn强相互作用抑制了 Pd对甲酸的化学分解。另外,Pd-Sn协同效应和三维/金属间化合物结构,提升了催化中心Pd对甲酸电氧化的活性和稳定性。展示了同一催化材料在电催化和化学催化中不同的构效关系。(五)发展了从Pt-on-Au纳米结构到PtAu-on-Au纳米结构原子扩散合成的新方法,即异质结构的合金化。由于PtAu合金结构的形成,PtAu-on-Au纳米结构显著增强了甲酸电氧化的直接氧化途径,为双金属合金纳米催化剂的制备提供了新的思路。(六)进一步合成了组分可调的PtAu合金和Rh掺杂的PtAu合金纳米线作为甲酸电氧化材料。基于组分优化、集团效应和界面协同效应,催化中心Pt的质量/本征活性均被大幅提高,证明了PtAu双金属合金纳米催化剂在甲酸电氧化领域更大的提升空间。更多还原

【Abstract】 Precious metal-based bimetallic nanocatalysts have attracted the interest of researchers due to their unique and efficient catalytic performance.How to realize their component optimization,structural design and performance improvement has become a hot topic of great significance in the application of precious metal-based nanocatalyst.In this thesis,Pt/Pd-based bimetallic nanocatalysts are selected as the research object;the purpose is to improve the efficiency of oxygen reduction reaction(ORR),H2O2 direct synthesis and formic acid oxidation reaction(FOR),and to explore the design and synthesis of catalysts and the interpretation of structure-activity relationship.(1)A polyamine(PAA)-assisted thermal decomposition method are developed to synthesize functionalized Pd-Pt bimetallic core/shell nanodendrites.Due to the ligand effect and geometric effect between Pd and Pt,the nanodendritic structure and the adsorbed polyamine molecule,Pd-Pt bimetallic nanocatalysts exhibit enhanced catalytic activity,stability and selectivity for ORR,providing a new idea for the design and synthesis of highly effective ORR electrocatalysts.(2)Sandwich-structured Au@PAA@Pd nanostructures are designed and synthesized successfully.The electronic structure of Pd shell with clean surface is greatly regulated by the amino group of PAA in the middle layer,which motivates Au@PAA@Pd nanostructures to exhibit ultra-high catalytic activity for FOR.An effective strategy for regulating the electronic structure of catalysts is revealed.(3)A series of Pd-Sn alloy bimetallic nanocatalysts with adjustable composition are synthesized and successfully applied to H2O2 direct synthesis.By controlling the composition and catalytic conditions,H2O2 degradation on the catalyst is completely inhibited,and high H2 selectivity and catalytic activity are achieved simultaneously.The improvement in catalytic performance is attributed to the oxidation of Pd,ensemble effects and interfacial synergistic effects,which provide multiple perspectives for the construction of structure-activity relationship.(4)The intermetallic Pd3Sn2 nanonetworks are synthesized and developed as electrocatalysts for FOR.On the one hand,the strong Pd-Sn interaction caused by the intermetallic structure inhibits the chemical decomposition of formic acid on Pd.On the other hand,the synergistic effect between Pd and Sn and the three-dimensional intermetallic structure improve FOR activity and stability of Pd active sites.Different structure-activity relationships of the same nanocatalyst for electrocatalysis and heterogeneous catalysis are well demonstrated.(5)A novel atomic diffusion synthesis method,from Pt-on-Au nanostructures to PtAu-on-Au nanostructures,is developed,that is,alloying of heterostructures.Due to the formation of the PtAu alloy,PtAu-on-Au nanostructures significantly enhance the direct oxidation pathway of FOR,providing new insights into the preparation of bimetallic alloy nanocatalysts.(6)PtAu alloy and Rh-doped PtAu alloy nanowires with adjustable composition are synthesized as FOR electrocatalysts.Based on component optimization,ensemble effects,and interfacial synergistic effects,the mass/intrinsic activities of Pt active sites are greatly improved,proving that PtAu alloy bimetallic nanocatalysts have more room for performance improvement in the field of FOR.更多还原