Research On The Key Issue And Applications Of Natural Photothermal Catalysis

Extensive amounts of fossil fuels are consumed by industrial catalysis reactions,which produce a large amount of carbon dioxide and lead to the problem of air pollution.Using sunlight as energy source to drive industrial catalytic reactions can avoid problems of fossil fuel consumption.Among them,photothermal catalysis has the potential for industrial application due to its property of the whole solar spectrum absorption ability,high energy conversion effciency and scalability.However,the temperature of photothermal materials under low-density natural sunlight is generally too low（less than 100℃）to drive photothermal catalysis.Until now,photothermal catalysis requires extra heating or increasing the intensity of light irradiation（at least 10 times of the standard solar irradiance density）to increase the temperature of catalysts to drive photothermal catalytic reactions.However,both methods result in tremendous cost and energy consumption,making it difficult for practical applications.Therefore,this dissertation investigates photothermal catalysis from two aspects.On one hand,to solve the low temperature issue faced by photothermal materials under natural sunlight,introducing the principle of selective spectral absorption into the field of photothermal catalysis,also constructing photothermal devices via a heterogeneous structure strategy,which greatly increases the natural sunlight temperature of photothermal materials and provides driving-energy for photothermal catalysis.On the other hand,synthesizing efficient catalysts and tuning the thermal catalytic reaction process in photothermal catalysis.Finally,combing the photothermal device and catalysts,a series of high-efficiency photothermal catalytic reactions were realized under weak light irradiation.The main research contents of this thesis are as follows:（1）Construction of efficient photothermal devices:By analyzing material thermal dissipation,it was found that infrared radiation is the essential reason for the low temperature of photothermal materials under low natural light radiation.Therefore,the principle of spectral selective absorption was introduced into photothermal material design,and an Al N_x/Al selective absorption film was used to construct the photothermal device,which can realize efficient light absorption and low infrared radiation synergy.As a result,the temperature of catalysts was increased from 78℃ to 288℃ under one standard solar irradiation(1 k W m^-2).Furthermore,an heterostructure photothermal material strategy was proposed by using a narrow-bandgap semiconductor and an infrared-blocking material Cu to form an heterostructure.This strategy successfully increased the temperature of Bi₂Te₃,Ti₂O₃,Cu₂Se,and Cu₂S from below 100℃ to around 300℃ under one standard solar irradiation.（2）Photothermal catalytic reduction of carbon dioxide:Taking reverse water gas shift reaction（RWGS）as an example,the advantages of photothermal devices in photothermal catalysis were verified.In this thesis,a single-atom Bi catalyst（Bi O_x/Ce O₂）was synthesized by a polyvinylpyrrolidone templated method.At 400℃,the RWGS performance of Bi O_x/Ce O₂reached 34.88 mmol g^-1 h^-1,with a TOF value of 26.83 min^-1 and 100%selectivity towards CO.Characterization of the Bi O_x/Ce O₂ catalyst before and after the RWGS reactions showed that the structure substitution of Bi for Ce enabled Bi atoms to maintain their oxidized state throughout the test.Combining Bi O_x/Ce O₂ catalysts with the Ti₂O₃-based photothermal device,CO generation rates of 1.01 and 31.00 mmol g^-1 h^-1 were achieved through CO₂ reduction under1 and 3 kW m^-2 light irradiation,respectively,which is much higher than the performance of photothermal catalytic RWGS reported before.（3）Photothermal catalytic methanol dehydrogenation for syngas production:Catalytic hydrogen production driven by light can reduce fossil energy consumption in industrial.Based on photothermal devices,high loaded Pt single-atom catalysts（Pt_s-Ce O₂）were synthesized via a bimetallic deposition method with oxidized graphene as the template.The catalyst showed excellent methanol dehydrogenation activity at 300℃and maintained catalytic stability for500 hours.With the assistance of the photothermal device,the temperature of Pt_s-Ce O₂ reached299℃under 1 k W m^-2 light irradiation,and the hydrogen production rate from methanol decomposition reached 481.1 mol g^-1 h^-1,with a solar-to-hydrogen conversion efficiency of32.9%,and exhibited catalytic stability for more than one month.（4）Photothermal catalytic methanol reforming for hydrogen production:The hydrogen production from methanol dehydrogenation contains a large amount of CO,and the separation process between H₂ and CO is complex and costly.Methanol steam reforming reaction（MSR）produce H₂ and CO₂,which can be separated easily by pressure or low temperature.Industrial copper-zinc-aluminum（Cu Zn Al）catalysts are efficient for MSR,but their catalytic performance needs to be improved.Therefore,Cu Zn Al nanosheets（Cu Zn Al NS）catalysts were synthesized in large-scale by using a polyvinylpyrrolidone-assisted method.Under 1 k W m^-2solar irradiation,the temperature of Cu Zn Al NS in the Bi₂Te₃/Cu-based photothermal device reached 305℃,and the photothermal-catalytic MSR performance reached 310 mol g^-1 h^-1 with a solar-to-hydrogen conversion efficiency of 30.1%and 20 days of catalytic stability.Under outdoor conditions with a solar area of 6 m²,Cu Zn Al NS catalysts can produce 23.27 m³ of hydrogen through MSR in one day.（5）Photothermal catalytic decomposition of formic acid for hydrogen production:The hydrogen produced by MSR contains a small amount of CO,which can cause irreversible damage to the Pt electrode of the hydrogen fuel cell.However,the decomposition of formic acid can produce H₂ without CO.Therefore,a magnetron sputtering method was applied to synthesize Mo S₂ catalysts（Ni/G/Mo S₂）.Theoretical calculation showed that S in high-quality Mo S₂ as active sites could avoid the CO generation pathway during formic acid decomposition.At 100℃,the hydrogen production rate of Ni/G/Mo S₂ from formic acid decomposition was176.73 mmol g^-1 h^-1,and products only contain CO₂ and H₂.Combining Ni/G/Mo S₂ catalysts with a Cu₂Se-based photothermal device,a hydrogen production rate of 982 mmol g^-1 h^-1 was achieved under 0.6 kW m^-2 light irradiation from formic acid decomposition.