Controlled Synthesis Of Pt/Pd-based Nanocatalysts And Catalytic Performances For Alcohols Oxidation

Among the many noble metal nanomaterials,Pt and Pd have attracted attention because of their excellent catalytic performance in alcohol(electro-)oxidation reactions.However,due to their scarce reserves and high prices,the effective utilization of Pt and Pd is always research hotspots in the field of catalysis.At present,the design and optimization of Pt-based and Pd-based catalysts are mainly focused on the following three aspects:(i)components control,introducing a cheap 3d transition metal(M,such as Cu,Fe,Ni,etc.)to form Pt-M and Pd-M catalysts not only reduces the usage of Pt and Pd,but also enhances the catalytic property as compared to that of pure Pt and Pd;(ii)structure design,synthesizing a specific morphology/structure that is beneficial to catalysis,which Pt and Pd atoms are exposed on the surface of the catalyst,in order to increase the atomic utilization ratio of Pt and Pd atoms and maximize economic benefits;(iii)support effect,changing the interface charge transfer and the metal structure through the strong interaction between metal and support,so as to achieve the purpose of improving the catalytic property of the active components.This thesis takes Pt-and Pd-based nanocrystals as the research object,and aims at designing high-performance catalysts and clarifying the structure-activity relationship.Research on the microstructure,growth mechanism and formation factors of the nanomaterial,and explore the catalytic performance in alcohol(electro-)oxidation reactions.The main works are summarized as follows:(1)Hollow PtCu nanorings with high performance for the methanol oxidation reaction and their enhanced durability by using trace Ir.We develop an efficient one-pot hydrothermal strategy to prepare unique PtCu alloy nanorings(NRs)with a highly open hollow structure.The galvanic replacement reaction between Pt²⁺and Cu is the key to the formation of NR structure.The influence of reaction time,precursor ratio,reducing agent,structure directing agent and other factors on the morphology or structure are systematically investigated.The synthesized hollow PtCu NRs are used as catalysts in methanol oxidation reaction(MOR).Among them,hollow Pt_0.75Cu NRs with an input Pt/Cu molar ratio of 0.75/1 exhibites superior MOR performance,with a mass activity of 2.175 A mg _Pt^-1and a specific activity of 52.26 A m^-2,which are 4.5-and 6.6-fold enhancements relative to those of commercial Pt Ru/C-JM,respectively.Doping with trace Ir can significantly improve the catalytic stability of the Pt_0.75Cu NRs.The stability test results show that the mass activity loss of trace Ir-doped Pt_0.75Cu NRs is only 7.44%after 10000 CV cycles,which is much smaller than those of Pt_0.75Cu NRs(37.76%)and Pt Ru/C-JM(50.27%).This work opens up a new avenue for designing advanced electrocatalysts with a low cost and a high catalytic performance for fuel cell applications.(2)When Pd meets graphene-like monoclinic titanium dioxide nanosheets:Synergic boosting of catalytic performance in benzyl alcohol selective oxidation into benzaldehyde.We develop a low-temperature hydrothermal method to synthesize graphene-like monoclinic titanium dioxide nanosheets(TiO₂-B NSs),which are used as a support for the Pd catalyst to catalyze benzyl alcohol selective oxidation into benzaldehyde.Using tetrabutyl titanate as the titanium source and F127 as the template agent,the TiO₂-B NSs with a thickness of only 0.93 nm can be obtained by a hydrothermal method at 150°C,and the specific surface area is 350.05 m²g^-1,which is about 6 times enhancement relative to commercial P25(59.28 m²g^-1).The Pd/TiO₂-B catalyst with Pd mass fraction of 0.62 wt%is synthesized via impregnation reduction method and the particle size of the Pd nanocrystal is only about 3 nm.Using the obtained Pd/TiO₂-B catalyst for selective oxidation of benzyl alcohol,the benzyl alcohol conversion of 85%,benzaldehyde selectivity of 97%and benzaldehyde yield of 82%are achieved when reaction temperature and time are 120?and 6 h,respectively.In addition,the Pd/TiO₂-B also exhibits excellent catalytic stability with no significantly weakened in activity after six cycles.Cycling experiments also demonstrate that Pd⁰is the active center for benzyl alcohol selective oxidation into benzaldehyde.