The Structural Control And Performance Of Pt/CeO₂ Single-Atom Catalysts Interface For Carbon Dioxide Reforming Of Methane

Methane（CH₄）and carbon dioxide（CO₂）,two dominant greenhouse gases,are identified as well-stocked Carbon-One（C1）resource in nature.Carbon dioxide reforming of methane（dry reforming of methane,DRM）reaction promotes the progress of carbon peaking and carbon neutrality by converts greenhouse gases（CH₄/CO₂）into syngas（H₂/CO）,a valuable feedstock for the production of clean energy.DRM reaction suffers from high energy consumption,catalytic sintering and coking under hursh reaction condition.Among traditional metal catalysts,Pt shows higher catalytic activity than Ni,but high cost limits its application.The development of single-atom catalysts（SACs）with high atomic utilization and catalytic activity can reduce the cost and energy consumption.However,DRM reaction surfers from deactivation.In addition,the synthesis,characterization and structure-function relationship of SACs are challenging.The structure and properties of catalytic interface are the key factors of catalysis.This thesis focuses on the construction and interpretation of Pt₁/CeO₂ catalytic interface for DRM reaction to develop efficient and stable Pt SACs and reveal its structure-function relationship.The structure of SACs interface,mechanism of DRM reaction at the interface and catalytic behaviors such as sintering and coking have been hypothesized,demonstrated and summarized based on advanced techniques,including systematic structure characterization,in situ experiment and theoretical calculation.The perspectives,such as synergistic interface,Pt atom doping,N atom doping as well as defect engineering,make semse in theory and practice.The main research contents and conclusions are as follows:1.The effects of Pt atom doping,surface reconstruction,as well as synergy in structure-function at Pt₁/p-CeO₂ interface constructed by atom trapped and have been investigated by advance characterization and in situ experiment.For structure,Pt atoms are stabilized by defects of p-CeO₂and feeds back to p-CeO₂ surface for decoration promoting the stability of catalytic interface.For propertice,Pt single-atoms with tetracordinate Pt–O–Ce structure promote O-assisted CH₄ dissociation into CO and H*through the CH₃O*intermediate,which has no inclination towards carbon deposition.Oxygen vacancy（V_O）/lattice oxygen(O_lattice)structure promotes H-assisted CO₂dissociation to produce CO and O*.The two units are linked through the transfer of H*and O*,the formation and repair of V_O etc.,which contributes to the catalytic cycle.The CO₂ reaction rates of Pt₁/p-CeO₂ and Pt/p-CeO₂ are 10.2 and 2.3 mmol·g_Cat^-1·h^-1,respectively.Pt₁/p-CeO₂ is more conducive to the activation of CH₄ and CO₂ showing lower activation temperature,higher high-temperature stability,as well as anti-sintering and anti-coking properties.2.Morphology effects of CeO₂ on structure and properties of Pt SACs have been investigated based on the synergistic interface of Pt₁/p-CeO₂.The synergy,Pt doping effects and catalytic mechanism combined with the morphology effects have been investigated by in situ experiment and theoretical calculation.Morphology effects of CeO₂reflected by crystal planes effects.The formation energy（E_f）is depended on planes structure.The E_f is 1.30 e V for（110）planes,the lowest in series planes,and decreases to-0.57 e V after Pt doping,which induces surface reconstruction to generate more V_O,modify chemical structure and electronic properttices of Pt atoms,enhance covalent metal-support interaction and catalytic interface stability.The Pt atomic dispersion,oxidation state,defect concentration,metal-support interaction,and catalytic performance decreases in the order of Pt₁/r-CeO₂>Pt₁/p-CeO₂>Pt₁/c-CeO₂（r:rod,c:cube,p:particle）.Under the synergistic effects of Pt₁/r-CeO₂ interface,the formation of CO and H*form O-assisted CH₄ dissociation via CH₃O*intermediate has a low energy barrier and no inclination towards coking.The V_Oproduced by the consumption of O_lattice in CH₄oxidation is repaired by O*produced by H-assisted CO₂dissociation.The CO₂ reaction rates of Pt₁/r-CeO₂,Pt₁/p-CeO₂,and Pt₁/c-CeO₂ are 10.4 mmol·g_Cat^-1·h^-1,6.4 mmol·g_Cat^-1·h^-1,and 0.1mmol·g_Cat^-1·h^-1,respectively.3.The construction and application of stable catalytic interface doped with N atoms are based on particular Pt₁/r-CeO₂ interface.Catalytic structure-function of Pt₁/r-CeO₂-NH₃obtained by temperature programmed natridation have been investigated in detail.Pt–O–Ce single-atoms structure is in favour of N atoms doping.N atoms is introduced during the reduction of r-CeO₂ surface by NH₃ generating new V_O.A part of Pt atoms coordinates with N atoms improving strong metal-support electronic interaction,oxidation state of Pt atoms.Some Pt atoms aggregate into Pt nanoclusters after nitridation.Finally,the Pt₁/r-CeO₂-NH₃ shows coexistence of Pt nanoparticles and Pt clusters.The N atoms doping is not obvious on Pt/r-CeO₂-NH₃ with Pt nanoparticles obtained by direct nitrization of H₂Pt Cl₆/CeO₂.Serious catalytic deactivation due to sintering and coking occur on Pt/r-CeO₂-NH₃ after reaction.The Pt₁/r-CeO₂-NH₃ shows a special metal-support electron interaction,which promotes the equivalent chemisorption of CH₄ and CO₂.As a results,Pt₁/r-CeO₂-NH₃ shows an equivalent and high reaction rates of CH₄ and CO₂(361.7/371.4mmol·g_Cat^-1·h^-1),performing excellent thermostability with anti-sintering,anti-coking,and negligible side reaction preoperties.4.High performance DRM catalysts have been developed by bottom-up defect engineering based on the investegation of defective interface.Defective CeO₂-M have been synthesized by using Ce based Ui O-66（metal-organic frameworks,MOFs）as precursor.The concentration of CeO₂ defects is regulated by defect manufacturing of Ui O-66 frameworks using formic acid as conditioner to terminate The coordination between Ce⁴⁺and 2-aminoterephthalic acid linker.Thermal stable Pt₁/CeO₂-M50 have been constructed with higher defect concentration and stronger covalent metal-support interaction than the traditional hydrothermal synthesis Pt SACs supported by CeO₂synthesized by hydrothermal method.The efficient DRM catalysts have been developed.The structure-function relationship and reaction path have been described by systematic characterization.The reaction rates of CO₂/CH₄ at 800°C are 935.8/752.1 mmol·g_Cat^-1·h^-1on Pt₁/CeO₂-M50.