Rare Earth Doping Modified Hydrothermal Synthesis Of Nano V₂o₅ And Application In Vanadium Catalyst Of Sulfuric Acid

Vanadium catalyst is the core of modern contact sulfuric acid production process.Its performance determines the production cost and environmental protection.At present,the traditional vanadium catalysts in China have some disadvantages,such as low activity at low temperature and low total conversion of SO₂.This is mainly due to the fact that the traditional vanadium catalysts are prepared by mixing and milling method,which results in larger grain size of active components,higher melting phase transition temperature of active components,lower V⁵⁺which plays a key role in catalysis and lower proportion of surface chemisorbed oxygen,and pore size.Small capacity,etc.Based on this,the effect of rare earth doping modification on the performance of vanadium catalysts was investigated by increasing the ratio of V⁵⁺and oxygen chemisorbed on the surface of vanadium catalysts,doping rare earth elements La,Ce and Pr into vanadium catalysts;starting from reducing the crystal size of active component V₂O₅ in vanadium catalysts,the micro-size of active component V₂O₅ was pre-prepared by hydrothermal method before preparing vanadium catalysts.The effect of hydrothermal modification on the performance of vanadium catalysts was investigated.The effect of hydrothermal modification and rare earth doping on the performance of vanadium catalysts was investigated by increasing the ratio of V⁵⁺and surface chemisorbed oxygen in vanadium catalysts and reducing the crystal size of active component V₂O₅.The vanadium catalysts were characterized by XPS,XRD,SEM,DSC,physical adsorption of N₂ at low temperature and MIP.The conversion of Sulfur Dioxide Catalyzed by vanadium catalysts was determined by fixed bed reactor.The results indicated these:1.The effect of rare earth doping modification on the performance of vanadium catalyst was studied.Rare earth elements La,Ce and Pr doped vanadium catalysts were prepared.The results show that the doping of La,Ce and PR improves the ratio of V⁵⁺and surface chemisorbed oxygen in vanadium catalysts,and improves the conversion of Sulfur Dioxide Catalyzed by vanadium catalysts.Among them,V⁵⁺and surface chemisorbed oxygen are the largest in Pr-doped vanadium catalysts.The conversion of Sulfur Dioxide Catalyzed by La,Ce and Pr is higher,and the conversion of sulfur dioxide is 58.73%（16h、410℃,the same as below）.The conversion of Sulfur Dioxide Catalyzed by vanadium catalyst was 17.30%higher than that of the original vanadium catalyst.With the increase of Pr doping from 1.7wt%to 6.5wt%,the proportion of V⁵⁺and chemisorbed oxygen on the surface of vanadium catalyst increases gradually,but the pore volume of vanadium catalyst decreases gradually.The conversion of sulfur dioxide for catalytic oxidation of vanadium catalyst increases first and then decreases with the increase of Pr doping.The conversion of sulfur dioxide for catalytic oxidation of vanadium catalyst prepared by 3.3wt%Pr doping is better,and the conversion of sulfur dioxide reaches 62.32%.When Pr doping is 3.3wt%,the conversion of sulfur dioxide for catalytic oxidation of vanadium catalyst prepared by step impregnation method is higher than that of one-step impregnation method.It is about 3.52%.2.The effect of hydrothermal modification on the performance of vanadium catalyst was studied.Nano-vanadium catalysts were prepared by hydrothermal method,and the specific valence of nano-vanadium catalysts prepared by water quenching method and hydrogen peroxide method was used.The results showed that compared with the original vanadium catalyst,the grain size and melting temperature of the active components in the vanadium catalyst decreased after modification by water quenching,hydrogen peroxide and hydrothermal method,and the conversion rate of Sulfur Dioxide Catalyzed by vanadium catalyst increased.Among them,the grain size of the active components in the hydrothermal modified vanadium catalyst was the smallest,and the melting phase of the active components occurred.The conversion rate of Sulfur Dioxide Catalyzed by vanadium catalyst is higher than that of original vanadium catalyst.The conversion rate of Sulfur Dioxide Catalyzed by vanadium catalyst is 50.68%,which is 9.32%higher than that of original vanadium catalyst.Three kinds of vanadium precursors were synthesized by using C₂H₂O₄,H₂SO₄and H₂O₂ as solvents and V₂O₅ as vanadium source.V/SiO₂（SRC）,V/SiO₂（SRL）and V/SiO₂（SRG）catalysts were prepared by hydrothermal method.The results show that the grain size and melting phase transition temperature of the active component in V/SiO₂（SRG）are lower,and the conversion rate of catalytic oxidation of sulfur dioxide is higher,and the conversion rate of sulfur dioxide reaches 53.24%.On this basis,the effects of adding dispersants PVP,SDBS and CTAB on hydrothermal synthesis of vanadium catalysts are studied.The results show that the grain size and melting phase transition temperature of the active component in the vanadium catalyst prepared by hydrothermal method with dispersant CTAB are lower,and the conversion rate of SO₂ is higher.The conversion rate of SO₂ is 58.45%,which is about 4.63%higher than that of the vanadium catalyst prepared by hydrothermal method without dispersant.3.The effect of rare earth doping/hydrothermal modification on the performance of vanadium catalyst was studied.Compared with rare earth doped modified vanadium catalysts and hydrothermal modified vanadium catalysts,the conversion of Sulfur Dioxide Catalyzed by composite modified vanadium catalysts increased significantly.The conversion rate of Sulfur Dioxide Catalyzed by rare earth doped modified vanadium catalysts reached 67.84%,which was 2.20%and 9.37%higher than that of rare earth doped modified vanadium catalysts and hydrothermal modified vanadium catalysts,respectively.With the increase of calcination temperature and the extension of calcination time,the grain size and melting phase transition temperature of the active components of the composite modified vanadium catalyst first decrease and then increase,and the conversion rate of sulfur dioxide first increases and then decreases.At the calcination temperature and time of 550℃and 3h,respectively,the crystalline size of the active component of the catalyst is the smallest,and the temperature at which the active component melts is the lowest.The conversion rate of sulfur dioxide by catalytic oxidation is higher,and the conversion rate of sulfur dioxide is 73.88%.4.Compared with imported vanadium catalyst VK38,the composite modified vanadium catalyst with optimized preparation conditions has smaller grain size,lower melting temperature of active component,higher ratio of V⁵⁺and chemisorbed oxygen on the surface,and larger pore volume,which makes the conversion of sulfur dioxide higher.The conversion rate of Sulfur Dioxide Catalyzed by composite modified vanadium catalyst reached 92.09%at 8h and 485℃,which was 4.85%higher than that catalyzed by VK38.At 16h and 410℃,the conversion rate of Sulfur Dioxide Catalyzed by composite modified vanadium catalyst reached 73.88%,which was about 9.27%higher than that catalyzed by VK38.