Study On The Physical And Chemical Properties And Modification Mechanism Of ?-Fe₂O₃-VOSO₄/AC

As an efficient and cheap catalyst carrier,activated carbon has the advantages of large specific surface area,rich pore structure,stable chemical properties and good adsorption performance,as well as high strength and easy to be regenerated many times.?-Fe₂O₃ has the advantages of inverse spinel structure,wide activity temperature window,good catalytic activity,water resistance;The highly dispersed;VOSO₄ can improve the number of active sites and weak acid sites on the surface of activated carbon,and change the pore structure at the same time.Starting from the activation of activated carbon with nitric acid and the modification of activated carbon with load,the subject takes coconut shell activated carbon as raw material and the optimized activated carbon with nitric acid as precursor;through the impregnation of modified activated carbon with FeSO₄,Fe?NO₃?₃ and VOSO₄,a new preparation method of?-Fe₂O₃-VOSO₄/AC composite catalyst is developed,which improves the sulfur resistance and water resistance of the catalyst to a certain extent and optimizes its low-temperature activity.The specific surface area,pore structure distribution and active components of the catalyst were systematically studied by changing the experimental conditions and material characterization methods.Meanwhile,the mechanism of the modified catalyst under different conditions was deduced and evolved.The main results are as follows:?1?The response surface method was used to optimize the experimental design,and a mathematical model was established,with the nitric acid concentration,activation time,and activation temperature as independent variables,and the specific surface area as the response value.According to the analysis of variance?ANOVA?,the largest influencing factors for each experimental design response were determined.The best combination of specific surface area is:activation temperature 74.5?,activation time 8h,nitric acid concentration 3.7mol/L,theoretical specific surface area is 749.97m²/g,and the actual specific surface area after optimization under this condition is 742.01m²/g,It agrees well with the experimental values and has a small error.For each group of experiments,the iodine adsorption value is further verified.It is found that the experimental results are consistent with the expected results.The specific surface area of activated carbon and the iodine adsorption value are basically positively related.Furthermore,the interaction between nitric acid concentration and activation time and the interaction between nitric acid concentration and activation temperature has a significant effect on the surface area,and there is a relationship between activation temperature>nitric acid concentration>activation time.?2?Among the three Fe/AC catalysts prepared by FeSO₄ over impregnation,the Fe/AC-2 catalyst mainly exists in the form of micropores,and the content of?-Fe₂O₃is more.At the same time,under the condition of increasing temperature,a small amount of uncontrollable transformation of?-Fe₂O₃ occurs,?-Fe₂O₃ appears;among the three Fe/AC catalysts prepared by Fe?NO₃?₃ over impregnation,the iron nitrate in Fe/AC-4 fails to decompose in time,covering part of the pore structure;As the temperature of Fe/AC-5 increases,the decomposition amount of iron nitrate increases,the crystal distribution of iron oxide is relatively uniform,and the dispersion degree is high.At the same time,a new pore structure is formed on the surface of iron oxide under the impact of NO₂ and O₂.The relationship between the number of micropores of six kinds of activated carbon modified by different conditions:Fe/AC-4>Fe/AC-5>Fe/AC-2>NAC>Fe/AC-1>Fe/AC-6>Fe/AC-3.?3?Vanadium species can be highly dispersed on the surface of activated carbon or in the pores.It is easy to form micropores in low concentration VOSO₄ solution,and Lewis acid sites on the surface are obviously increased,V=O The functional groups play a major role in the catalytic process,the active components are highly dispersed,and the catalyst can provide more active sites;with the increase of the loading amount of VOSO₄ solution,the active components form a agglomeration phenomenon.In addition to blocking the pore,a large number of VOSO₄ in the micropores are easy to react with oxygen in the modification process to form the intermediate product V₂O₃?SO₄?₂,which will further reduce the micropores,so that The reduction of the specific surface area of the catalyst results in the decrease of the active sites on the surface of the catalyst.In the process of modification,the intermediate products are not easy to react with sulfur oxides,and the sulfur resistance is improved to some extent.?4?The introduction of vanadium into the new composite catalyst forms complex on the surface.The synergistic effect of iron oxide crystal and vanadium species further increases the number of active oxygen and Lewis acid sites in the catalyst,leaves a large number of oxygen vacancies after the consumption of active oxygen,thus improving the catalytic activity.Moreover,the synergistic effect between the ligand and vanadium reduces the activation energy of the catalytic reaction and widens the operating temperature window.The number of micropores of the new composite catalyst has the following relationship:Fe V/AC-2>Fe V/AC-3>Fe V/AC-1.The Fe V/AC-3 catalyst contains a lot of?-Fe₂O₃ and vanadium active component V₂O₃?SO₄?₂.It has a certain sulfur resistance and water resistance,and its specific surface area,pore structure and other properties have been improved.