| Nowadays,fossil fuels are the main energy source for human production and life.Fossil fuel combustion produce a large amount of carbon dioxide(CO2)and discharge into the air.Excessive CO2 not only cause the greenhouse effect,but also break the carbon balance.Photothermal reduction of CO2 is an effective way to release the greenhouse effect.In this thesis,we studied the performance and mechanism of Bi photothermal reduction carbon dioxide.Then the performance of Bi for photothermal catalytic reduction CO2 were improved by compounding Pd and doping Co.In addition,a series of means were taken to characterize the morphology,surface valence states and photoelectron utilization efficiency of those catalysts.The research contents were summarized as the following three points:(1)Bi photothermal synergistic carbon dioxide reductionBismuth(Bi)photothermal catalysts were prepared by hydrothermal and electrodeposition methods,which named H-Bi and E-Bi,respectively.Scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and other methods were used to characterize the morphology and structure of Bi.The results showed that the diameter of H-Bi nanospheres were about 200 nm.E-Bi nanorods had a length of 80?200 nm.Photothermal carbon dioxide reduction reactions(CO2RR)were carried out at different temperatures by H-Bi and E-Bi,respectively.The experimental results showed that the production of carbon monoxide(CO)had a linear dependence with temperature.The CO generation rate of H-Bi and E-Bi can reach to 24.2?mol·h-1·g-1 and 19.8 ?mol·h-1·g-1,respectively.Fourier infrared(FTIR)test revealed that*COOH was the key intermediate at CO2RR.*COOH reacted with activated hydrogen and electrons,which can form CO and H2O.(2)Bi-Pd photothermal synergistic carbon dioxide reductionBi compounding different amount Pd catalysts were fabricated by two-step reduction method,and mass ratio of Pd in Bi-Pd bimetals were 5?20%.TEM image showed that Bi-Pd bimetals were composed of nanoblock below 50 nm.The results of photothermal catalytic reduction of CO2 shows that bimetallic Bi-Pd catalysts exhibits the highest activity when the mass ratio of Pd reach to 15%.At 190? and 420 nm LED light irradiation,the CO generation rate of BiPd-15%reached to 97.6 ?mol·h-1g-1.This is mainly due to the fact that BiPd-15%had the highest charge separation efficiency and the smallest charge transfer resistance among the four Bi-Pd bimetals.Moreover,with compounded of Pd,CO was easily desorbed from Bi-Pd catalyst.So,it could suppress catalyst poisoning and increase stability.The stability of Bi-Pd can attain 15 h.(3)Bi-Co photothermal synergistic carbon dioxide reductionBi-Co catalysts with different molar ratios were prepared by one-step hydrothermal method,and those Bi-Co bimetals were named as BiCo0.15,BiCo0.25 and BiCo0.5,respectively.TEM images showed that Bi-Co catalysts were nanospheres with a diameter between 350?500 nm.Energy dispersive X-ray spectroscopy(EDS)liner scan showed that Bi and Co elements almost completely overlaped,which proved that Bi-Co alloy formed.The results of CO2RR showed that BiCo0.25 had the most active catalyst.This was mainly due to the higher photo-generated charge separation efficiency of the BiCo0.25 catalyst among the three prepared catalysts.At 180? and 420 nm LED as light source,the CO and CH4 evolution rate can reach to 109.8 ?mol·h-1·g-1 and 51?mol·h-1·g-1,respectively.At this time,the selectivities of CO and CH4 were 32%and 68%,respectively.The synergistic effect between Bi and Co can facilitate the activation of H2 and CO2.In addition,from the FTIR results,a reasonable mechanism of CO2 reduction reaction can be deduced.CO2 molecules were activated at the Bi site to form*COOH intermediates,and*COOH was deoxygenated to form CO and H2O.CO2 at the Co site could break the carbon-oxygen bonds in CO2,hydrogen atoms were transferred from Bi to Co via the hydrogen spillover mechanism could react with the intermediate and form CH4. |
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