Fine Control Of Active Sites Of Cobased Catalyst Materials For Enhanced CO_x Photothermal Reduction Application

The photothermocatalytic strategy has been developed to become one of the most promising technologies which can solve energy and environmental problems by coupling the photochemistry and thermochemistry effects.The key to the application of this technology is the development of high-performance catalytic materials.Regarding the problems of difficult target activation of reactant molecules,low activity and product selectivity in the photothermocatalytic COx（CO₂ and CO）reduction process,the design of a multi-component synergistic-catalytic system is expected to provide new idea for solar conversion.In this thesis,based on the rational control of the active sites of the catalytic material,multi-component microstructure of Co-based catalytic materials was constructed and applied to the COx photothermocatalytic reduction.The structure of catalysts and catalytic performance were investigated systematically;the reasonable reaction mechanism was proposed.The main work was as follows:（1）The interfacial structure consisting of atomically dispersed Co-N species anchored carbon layers with embedded Co nanoparticles（entitled as Co@Co N&C）was developed,which regulates catalytic properties in thermodynamic and kinetic processes to achieve efficient and highly product yield in CO₂ photothermal reduction.Optimal Co@Co N&C-1 delivered the maximum yield rate of 132 mmol g^-1 h^-1 and the remarkable CO selectivity（91.1%）,while the undesirable methanation activity,compared to typical of Co nanoparticles（43.3%）,was suppressed.Mechanism study suggested that the co-interaction over graphitic-carbon and Co could enhance the light-to-heat conversion efficiency and thus induced the high work temperature,which was thermodynamically beneficial for CO₂ conversion.Furthermore,the carbon layers improved the adsorption of CO₂ and the surface atomically dispersed Co-N species weakened hydrogenation capability,which kinetically controlled the reaction pathway and therefore attained the high selectivity for CO.（2）The synthesized Co nanoparticles were loaded on Sr Ti O₃ catalyst（Co/Sr Ti O₃）to construct an active interface for photocarriers-assisted photothermocatalysis to promote FTS,and the reaction mechanism was studied.The light-driven FTS on the optimized2Co/Sr Ti O₃ catalyst achieved a CO conversion rate of 14%after 2 hours,while the selectivity of C2-C4 hydrocarbons was as high as 37.2%,which was 3.9 times and 5times that of 2Co/Si O₂,respectively.The photocarriers-assisted photothermocatalysis delivered high catalytic efficiency,which could be ascribed to the combined effect of photocatalysis and photothermocatalysis.The photogenerated holes could enhance the CO hydrogenation capacity,and photogenerated electrons could assist in C-C coupling on the Co sites,which were beneficial to produce C2-C4 hydrocarbons.（3）Constructing an adjacent Co and Cu nanoparticles co-loading on Sr Ti O₃（abbreviated as Cu-Co/Sr Ti O₃）interface structure could enhance the photo-and thermal-synergistic catalysis.The optimized 1.5Cu-2Co/Sr Ti O₃ catalyst had a total organic carbon rate of 1.36 mmol g^-1 h^-1 to C2-C4 hydrocarbons.Compared with2Co/Sr Ti O₃ and 1.5Cu/Sr Ti O₃,the selectivity of C2-C4 reached 53.4%,which was nearly 1.5-fold and 17-fold,respectively,clearly indicating the synergistic effect among Co,Cu,and Sr Ti O₃.Under irradiation of concentrated solar light,the Sr Ti O₃ support was excited by UV light to induce photocatalytic effect to generate photocarriers;meanwhile,the LSPR-active Cu nanoparticles mainly absorbed the visible-IR light to produce hot electrons which were either quenched to generate heat or transported to active site;finally,photogenerated holes could enhance the CO hydrogenation capacity;the active-phase Co nanoparticles accumulated the electrons and heat to drive CO hydrogenation towards the high selectivity of C2-C4 hydrocarbons.（4）For the first time,the active components of the alkali metal K modified oxide Co Fe₂O₄（KCFO）and carbide(Fe_1-xCo_x)₅C₂ were controlled by the solar light field,and RWGS and FTS tandem reaction were successfully realized,thereby realizing light drive CO₂ hydrogenation to produce high selectivity of light olefins（C₂H₄,C₃H₆ and C₄H₈）.In a flow reactor,the conversion of CO₂ was 27%and selectivity of C_2-4⁼ was up to 46.4%（O/P=10.4）.The regional temperature-difference of the solar field induced the central part of KCFO oxide transformation into(Fe_1-xCo_x)₅C₂ carbide.Mechanism studies showed that KCFO was the active phase of RWGS while(Fe_1-xCo_x)₅C₂ was the active phase of FTS,which achieved targeted-activation of CO₂ and CO,respectively.In addition,the bifunctional catalysts had excellent stability and demonstrated continuous and stable activity within 72-hours in flow reactor,which has a good prospect of industrial application.