Performance And Mechanism Study Of Photothermocatalytic Water-gas Shift Reaction Over CeO₂/Cu_1.5Mn_1.5O₄ Catalyst

Water-gas shift（WGS）reaction provides a facile approach to convert the toxic carbon monoxide（CO）into carbon dioxide（CO₂）and meanwhile reduce water（H₂O）into clean hydrogen（H₂）fuel,which are widely applied in the hydrogen production from coal gasification and the hydrogen feedstock purification for the application of fuel cells.Up to now,a noble-metal-free catalyst working at low temperature to achieve the cost-efficient WGS process is still a great challenge.The hydrogen feedstock purification for the application of fuel cells especially requires such cost-efficient catalysis,since it aims to complete a purification procedure to remove low-concentration CO.Photothermocatalysis has drawn extensive attention since it attains a light-to-thermal conversion and subsequently drives a thermocatalytic process,which sharply reduces the energy cost of traditional thermocatalysis.A series of classic catalytic reactions,such as Sabatier reaction,Fischer-Tropsch synthesis,reverse water-gas shift reaction and so on,have been successfully executed via photothermocatalysis.However,most of the photothermocatalysis studied at present is thermal catalysis driven by the conversion of light into heat.The coupling of photocatalysis and photothermocatalysis can only be observed in few material systems.Due to the combined effect of photocatalysis and photothermocatalysis,the catalytic process delivers remarkably promoted catalytic efficiency and low energy consumption.Unfortunately,the investigation on the reaction mechanism of such reaction still lacks in-depth exploration.Herein,a series of Cu-based catalysts are applied on photothermocatalytic WGS reaction and the main conclusions are listed as follows:A series of Cu-based catalysts were synthesized and their catalytic performance was tested under light irradiation and H₂-rich condition.The experimental results show that the precipitation p H of 11.0,the calcination temperature of 550^oC and calcination time of 2 h were the optimal synthesis conditions for the preparation of Cu_1.5Mn_1.5O₄.Cu_1.5Mn_1.5O₄ with better photon absorption capacity and photothermal conversion efficiency delivered higher catalytic activity than Cu O_x/Al₂O₃ under H₂-rich condition.Furthermore,inspired by previous reference,CeO₂ which can transfer reactive oxygen species was loaded on Cu_1.5Mn_1.5O₄.It is found that Cu_1.5Mn_1.5O₄ with 5 wt.%of CeO₂ loading exhibited the highest activity.Notably,under the reaction temperature as low as 225^oC,the catalyst delivered a 96.6%of CO conversion in 30 min,and subsequently,the concentration of CO was decreased from 6.26 vol.%to less than 0.2 vol.%in the system,which matches the industrial standard（<1 vol.%）.The mechanism of photothermocatalytic WGS reaction over Cu_1.5Mn_1.5O₄ with5 wt.%of CeO₂ loading was explored in detail.The Cu_1.5Mn_1.5O₄ was the active phase;the Cu²⁺and Mn⁴⁺species on the surface were the active sites for CO oxidation and H₂O reduction,respectively.Additionally,the oxidation of CO was proved to be the rate-limited step.The loading of CeO₂ could prevent the spinel structure from destroying;besides,the photocarriers produced by CeO₂ were injected into active sites,which induced a 61%reduction of apparent activation energy to endow the present reaction a low-temperature feature.The results of in-situ FT-IR spectroscopy indicate that this photothermocatalysis can be specified as the mechanism that the photogenerated carriers activate the reactants and the thermal effect enhances the reaction rate.This thesis firstly reveals that the photocarriers can effectively activate the reactants of thermocatalysis,which attains a remarkable reduction of apparent activation energy.Therefore,a photothermocatalyst with semiconductor loading as a promoter can achieve an energy-efficient light-to-chemical conversion,which is a prosing alternative for assisting or substituting industrial thermocatalysis.