Experimental Study On The Removal Of Elemental Mercury By Perovskite Photocatalytic Materials

Mercury is a very harmful pollutant.In the process of nonferrous metal smelting,a large amount of mercury containing waste gas will be emitted,among which zinc smelting flue gas is the most serious.After washing or dedusting,the mercury content in the flue gas of zinc smelting is still 1～30 mg/m³,of which Hg⁰ is mainly zero valent mercury（Hg⁰）.Hg⁰ is not only difficult to be removed by washing or dust removal process,but also has high mobility and volatility,which is the key control pollutant in flue gas.In recent years,with the development of environmental protection and clean photocatalytic technology,it has become a new project of mercury removal.For photocatalytic technology,catalyst is an important factor affecting the photocatalytic effect.Perovskite oxides have become a hot spot in recent years due to their excellent performance in the field of photocatalysis.In this paper,Ce/Cr double doped strontium titanate（Sr Ti O₃）type perovskite materials were synthesized by hydrothermal method,and then the photocatalytic oxidation of Hg⁰from zinc smelting flue gas was studied.Firstly,the effect of Ce/Cr doping on the photocatalytic performance of mercury removal was investigated under 254 nm UV irradiation and room temperature reaction conditions.The experimental results show that the performance of Ce/Cr double doped sample is better than that of single doped sample and undoped sample,and the best photocatalytic effect is 99%when the doping material is Sr_0.9Ce_0.1Ti_0.9Cr_0.1O₃.The net photocatalytic efficiency of Sr_0.9Ce_0.1Ti_0.9Cr_0.1O₃ is 10%higher than that of commercial nano-Ti O₂,and the catalytic efficiency is more stable than commercial nano-Ti O₂ in a long time,and the efficiency is still above 85%after five cycles of recycling.Then the effects of flue gas composition and temperature on the photocatalytic oxidation mercury removal efficiency of Sr_0.9Ce_0.1Ti_0.9Cr_0.1O₃ were studied.The results show that the increase of O₂ can promote the reaction when the oxygen content is 0～10%;the water vapor will inhibit the photocatalytic reaction under the experimental water vapor concentration gradient（0,4%,7%）;under the experimental SO₂ concentration（500-1500ppm）,SO₂ can promote the photocatalytic reaction;under the experimental no concentration（50-200 ppm）,the photocatalytic reaction can be promoted However,no inhibited the photocatalytic reaction.In addition,the longer the flue gas temperature,the lower the photocatalytic mercury removal efficiency.Finally,the catalyst was characterized and analyzed.Combined with the above experimental phenomena,the following conclusions are obtained:XRD results show that the position of Sr in Sr Ti O₃ replaced by Ce and the position of Ti substituted by Cr enter into the lattice uniformly;XPS results show that Ce keeps Cr in a low valence state through electron transfer;FE-SEM results show that uniform granular samples are prepared,and the maximum particle size of Sr_0.9Ce_0.1Ti_0.9Cr_0.1O₃ is 4 times of Sr Ti O₃,and the increase of particle size is mainly Because of Ce doping,BET specific surface area of different samples is 10 m²/g,the difference of photocatalytic effect is not related to specific surface area;UV Vis DRS,ESR,PL and other characterization show that Sr_0.9Ce_0.1Ti_0.9Cr_0.1O₃ has obvious advantages in photoresponse activity,surface free radical intensity and utilization rate of photogenerated electron hole.According to the characterization and experiment,the photocatalytic mechanism including surface reaction and internal electron transfer was proposed.