The Effect Of CeO₂ Modification And Facet-tuned On Photo-oxidation Of Elemental Mercury

Elemental mercury?Hg⁰?is one of the most harmful environmental pollutants.It is another difficult problem in the field of air pollution control for how to efficiently control its emissions.Due to the high-efficiency and low-temperature catalytic performance,TiO₂ is used for Hg⁰ removal.While its photocatalytic oxidation efficiency is significantly suppressed when the reaction temperature is too high?>100°C?.However,the catalytic efficiency can be effectively improved by changing the chemical composition of the catalyst surface and adjusting the crystal structure.Therefore,cerium dioxide?CeO₂?with a narrow band gap width,high reactivity and excellent oxygen storage capacity was selected as a modifier.And CeO₂/TiO₂ were prepared by the sol-gel method,then explore the effects of energy band structure,types and number of surface free radicals,and their photocatalytic performance for mercury removal,clarify the mechanism of CeO₂ modification to promote the photocatalytic oxidation of Hg⁰ by TiO₂.Subsequently,the effect of facet-tuned TiO₂ and CeO₂modification on the photocatalytic performance of mercury removal was studied,and the synergistic effects of crystal plane effect and CeO₂ modification on energy level structure,generation of strong oxidizing free radicals,and photocatalytic activity were studied.And clarify the photocatalytic reaction path.The main conclusions of this study are as follows:?1?Preparation of CeO₂ modified TiO₂ catalyst and its mercury removal performance.CeO₂/TiO₂ catalyst is granular,and the average particle diameter is 20-30 nm;TiO₂ is an anatase type,and CeO₂ with an amorphous structure,exists in the gap of the TiO₂ lattice structure.?2?The reaction mechanism of CeO₂/TiO₂ catalyst in removing Hg⁰.The doping of CeO₂ can reduce the band gap of TiO₂,reduce the inherent ohmic resistance of TiO₂and inhibit the recombination of electron-hole pairs and thereby improve the photocatalytic activity.In addition,4%CeO₂/TiO₂ has the best photocatalytic activity due to the the potential difference between its conduction band potential and O₂/·O₂^-standard redox potential and its low inherent resistance.This is consistent with the characteristics of its band structure.The CeO₂/TiO₂ catalysts contribute to the formation of·O₂^-rather than·OH,which affects the photo-oxidation mechanism of Hg⁰.?3?Preparation of CeO₂-TiO₂ catalyst with different exposed crystal planes and Hg⁰ removal performance.TiO₂{001}has a nano-plate morphology and an octahedral structure with a particle size of 50-200 nm.All five unsaturated coordination bonds on the crystal surface increase the adsorption sites.TiO₂{101}and TiO₂{001-101}are granular,with a particle size between 20-50 nm.The TiO₂{101}crystal plane is a double-pyramid structure,and all of them have 6 saturated coordination bonds,and there are fewer adsorption sites.CeO₂ supported by the dipping method is mainly dispersed on the surface of CeO₂-TiO₂{101},and does not change the morphology and structure of TiO₂.?4?Study on the synergy effect of crystal plane effect and CeO₂ loading.Due to the formation of new Ti-O-Ce bonds,new Ce 4f energy levels are introduced into the valence and conduction bands of TiO₂,and CeO₂ can reduce the band gap and reduce the electrochemical impedance of CeO₂-TiO₂ and promotes charge transfer.In addition,7%CeO₂-TiO₂{001}has the highest photocatalytic activity at 50-150? due to the formation of more surface Ti³⁺and superoxide radicals on its crystal plane;However,the surface Ti³⁺and superoxide free radicals are suppressed by high temperature.CeO₂has high temperature stability and deposits most on{101}surface,which is helpful for photocatalytic oxidation to remove Hg⁰.Thus 7%CeTi{101}has the highest photocatalytic activity at 200-250?.