Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
In view of the fact that the catalytic activity of the red mud based on nitric acid modified red mud is difficult to further improve due to the high content of Fe2O3 in the Bayer process red mud, the invention provides a nitric acid modified red mud-based VOCs catalyst, and a preparation method and application thereof.
According to a typical implementation mode of the invention, a preparation method of a nitric acid modified red mud-based VOCs catalyst is provided, bayer process red mud is modified by adopting 2.5-3.5 mol/L nitric acid, modified red mud and manganese salt are uniformly mixed in a solution to obtain a precursor of modified red mud and manganese composite, and the precursor is calcined at 500-600 ℃ to obtain the catalyst.
In some embodiments, the concentration of nitric acid is 2.8-3.2 mol/L.
In some embodiments, the bayer process red mud is dried and then treated with nitric acid. Specifically, the nitric acid is added in an amount of at least enabling the nitric acid to permeate the red mud, preferably the mass ratio of the red mud to the nitric acid solution is 1:5-15, preferably 1:8-12. Specifically, the treatment time is 0.5-1.5 h.
In some embodiments, the modified red mud is washed to neutral pH after modification treatment, and then the modified red mud is mixed with manganese salt in solution uniformly.
The manganese salt is a compound of which the cations are manganese ions, such as manganese sulfate, manganese nitrate and the like.
The method for compounding the modified red mud and the manganese must be carried out in a solution, if the modified red mud and the manganese are mixed in a solid phase, such as grinding, the manganese and the modified red mud are not easy to be uniformly mixed, the method can be impregnation or adding a precipitant (such as ammonia water) to precipitate after the mixing, in some embodiments, the modified red mud and the manganese salt are uniformly mixed in the solution, and the solvent is removed by evaporation to obtain the precursor for compounding the modified red mud and the manganese. Namely, the use of chemical reagents can be reduced by adopting an impregnation method, and the production cost is reduced.
In some embodiments, the catalytic oxidation of toluene has excellent catalytic effect when the mass of manganese is 5-15% of the mass of the catalyst, and the catalytic effect is better when the mass of manganese is 14-15% of the mass of the catalyst.
In some embodiments, the precursor is dried and then calcined. Specifically, the drying temperature is 100-110 ℃.
In some embodiments, the calcination time is 4-6 hours.
The invention also provides a nitric acid modified red mud-based VOCs catalyst, which is obtained by the preparation method.
In a third aspect, the application of the nitric acid modified red mud-based VOCs catalyst in removing VOCs is provided.
Specifically, the removal of VOCs includes the catalytic oxidation of toluene. More specifically, the catalytic oxidation temperature is 250-320 ℃.
In order to enable those skilled in the art to more clearly understand the technical scheme of the present invention, the technical scheme of the present invention will be described in detail below with reference to specific examples and comparative examples.
The red mud used in the examples below was bayer process red mud, commercially available from the aluminum shandong company, inc.
Example 1
The preparation method of the nitric acid modified red mud-based VOCs catalyst comprises the following steps:
(1) Preparation of nitric acid modified red mud (ARM):
The red mud feedstock was ground to 200 mesh and then dried overnight in a dry box at 80 ℃. The obtained dry red mud is named RM. Subsequently, RM was treated with nitric acid (3 mol/L) for 1 hour (the mass ratio of red mud to nitric acid solution is 1:10). And then filtering and washing the mixed solution of nitric acid and RM by deionized water until the pH value of the washed solution is 7. And drying the RM in a water bath at 80 ℃ until the moisture is completely evaporated, and obtaining nitric acid modified red mud which is marked as ARM.
(2) Preparation of nitric acid modified red mud-based VOCs catalyst (Mn/ARM):
ARM was ground to 200 mesh and then mixed with deionized water at a solid to liquid mass ratio of 1:3, and the solution was stirred in an 80 ℃ water bath for 20 minutes. Then Mn (NO3)2 solution, 3g red mud and 1.042g 50% Mn (NO3)2 solution) are added in a mass percent of 5% in the final catalyst, and stirred in a water bath at 80 ℃ until the water is completely evaporated, then the sample is dried overnight in a drying oven at 105 ℃, the sample is taken out and calcined in a muffle furnace at 550 ℃ air for 5 hours, the muffle furnace is heated to 550 ℃ from room temperature at a speed of 5 ℃ per minute, and finally the calcined material is naturally cooled to room temperature, namely the red mud-based VOCs catalyst, which is marked as 5Mn/ARM.
Example 2
The preparation method of the nitric acid modified red mud-based VOCs catalyst comprises the following steps:
(1) Preparation of nitric acid modified red mud (ARM):
The red mud feedstock was ground to 200 mesh and then dried overnight in a dry box at 80 ℃. The obtained dry red mud is named RM. Subsequently, RM was treated with nitric acid (3 mol/L) for 1 hour (the mass ratio of red mud to nitric acid solution is 1:10). And then filtering and washing the mixed solution of nitric acid and RM by deionized water until the pH value of the washed solution is 7. And drying the RM in a water bath at 80 ℃ until the moisture is completely evaporated, and obtaining nitric acid modified red mud which is marked as ARM.
(2) Preparation of nitric acid modified red mud-based VOCs catalyst (Mn/ARM):
ARM was ground to 200 mesh and then mixed with deionized water at a solid to liquid mass ratio of 1:3, and the solution was stirred in an 80 ℃ water bath for 20 minutes. Then Mn (NO3)2 solution, 10% Mn in mass percent in the final catalyst prepared, i.e. 3g red mud and 2.174g 50% Mn (NO3)2 solution are mixed) is added at a concentration of 50% and stirred in a water bath at 80 ℃ until the water is completely evaporated, then the sample is dried overnight in a drying oven at 105 ℃, the sample in the drying oven is taken out and calcined in a muffle furnace at 550 ℃ air for 5 hours, the muffle furnace is heated to 550 ℃ from room temperature at a speed of 5 ℃ per minute, and finally the calcined material is naturally cooled to room temperature, namely the red mud-based VOCs catalyst, which is marked as 10Mn/ARM.
Example 3
The preparation method of the nitric acid modified red mud-based VOCs catalyst comprises the following steps:
(1) Preparation of nitric acid modified red mud (ARM):
The red mud feedstock was ground to 200 mesh and then dried overnight in a dry box at 80 ℃. The obtained dry red mud is named RM. Subsequently, RM was treated with nitric acid (3 mol/L) for 1 hour (the mass ratio of red mud to nitric acid solution is 1:10). And then filtering and washing the mixed solution of nitric acid and RM by deionized water until the pH value of the washed solution is 7. And drying the RM in a water bath at 80 ℃ until the moisture is completely evaporated, and obtaining nitric acid modified red mud which is marked as ARM.
(2) Preparation of nitric acid modified red mud-based VOCs catalyst (Mn/ARM):
ARM was ground to 200 mesh and then mixed with deionized water at a solid to liquid mass ratio of 1:3, and the solution was stirred in an 80 ℃ water bath for 20 minutes. Then Mn (NO3)2 solution, 15% Mn in mass percent in the final catalyst prepared, i.e. 3g red mud and 3.460g 50% Mn (NO3)2 solution are mixed) is added, and the mixture is stirred in a water bath at 80 ℃ until the water is completely evaporated, then the sample is dried overnight in a drying oven at 105 ℃, the sample in the drying oven is taken out and calcined in a muffle furnace at 550 ℃ air for 5 hours, the muffle furnace is heated to 550 ℃ from room temperature at a speed of 5 ℃ per minute, and finally the calcined material is naturally cooled to room temperature, namely the red mud-based VOCs catalyst, which is marked as 15Mn/ARM.
Comparative example 1
The preparation method of the nitric acid modified red mud-based VOCs catalyst comprises the following steps:
(1) Preparation of nitric acid modified red mud (ARM):
The red mud feedstock was ground to 200 mesh and then dried overnight in a dry box at 80 ℃. The obtained dry red mud is named RM. Subsequently, RM was treated with hydrochloric acid (3 mol/L) for 1 hour (the mass ratio of red mud to hydrochloric acid solution is 1:10). And then filtering and washing the mixed solution of nitric acid and RM by deionized water until the pH value of the washed solution is 7. And then drying the RM in a water bath at 80 ℃ until the moisture is completely evaporated, and obtaining nitric acid modified red mud which is marked as ARM-HCl.
Comparative example 2
The preparation method of the nitric acid modified red mud-based VOCs catalyst comprises the following steps:
(1) Preparation of nitric acid modified red mud (ARM):
The red mud feedstock was ground to 200 mesh and then dried overnight in a dry box at 80 ℃. The obtained dry red mud is named RM. Subsequently, RM was treated with nitric acid (3 mol/L) for 1 hour (the mass ratio of red mud to nitric acid solution is 1:10). And then filtering and washing the mixed solution of nitric acid and RM by deionized water until the pH value of the washed solution is 7. And drying the RM in a water bath at 80 ℃ until the moisture is completely evaporated, and obtaining nitric acid modified red mud which is marked as ARM.
(2) Preparation of nitric acid modified red mud-based VOCs catalyst (Ce/ARM):
ARM was ground to 200 mesh and then mixed with deionized water at a solid to liquid mass ratio of 1:3, and the solution was stirred in an 80 ℃ water bath for 20 minutes. Then Ce (NO3)3·6H2 O (added according to the mass percent of Ce in the final prepared catalyst: 3g red mud and 0.489g Ce (NO3)3·6H2 O) are mixed) is added, and the mixture is stirred in a water bath at 80 ℃ until the water is completely evaporated, then the sample is dried overnight in a drying oven at 105 ℃, the sample in the drying oven is taken out and calcined in a muffle furnace at 550 ℃ air environment for 5 hours, the muffle furnace is heated to 550 ℃ from room temperature at a speed of 5 ℃ per minute, and finally the calcined material is naturally cooled to room temperature, namely the red mud-based VOCs catalyst, which is marked as 5Ce/ARM.
Comparative example 3
The preparation method of the nitric acid modified red mud-based VOCs catalyst comprises the following steps:
(1) Preparation of nitric acid modified red mud (ARM):
The red mud feedstock was ground to 200 mesh and then dried overnight in a dry box at 80 ℃. The obtained dry red mud is named RM. Subsequently, RM was treated with nitric acid (3 mol/L) for 1 hour (the mass ratio of red mud to nitric acid solution is 1:10). And then filtering and washing the mixed solution of nitric acid and RM by deionized water until the pH value of the washed solution is 7. And drying the RM in a water bath at 80 ℃ until the moisture is completely evaporated, and obtaining nitric acid modified red mud which is marked as ARM.
(2) Preparation of nitric acid modified red mud-based VOCs catalyst (Co/ARM):
ARM was ground to 200 mesh and then mixed with deionized water at a solid to liquid mass ratio of 1:3, and the solution was stirred in an 80 ℃ water bath for 20 minutes. Then Co (NO3)2·6H2 O (added according to the mass percentage of Co in the final prepared catalyst: 3g red mud and 0.790g Co (NO3)2·6H2 O) are mixed) is added, and the mixture is stirred in a water bath at 80 ℃ until the water is completely evaporated, then the sample is dried overnight in a drying oven at 105 ℃, the sample in the drying oven is taken out and calcined in a muffle furnace at 550 ℃ air environment for 5 hours, and the muffle furnace is heated to 550 ℃ from room temperature at a speed of 5 ℃ per minute, finally, the calcined material is naturally cooled to room temperature, namely the red mud-based VOCs catalyst, which is marked as 5Co/ARM.
Comparative example 4
The preparation method of the nitric acid modified red mud-based VOCs catalyst comprises the following steps:
(1) Preparation of nitric acid modified red mud (ARM):
The red mud feedstock was ground to 200 mesh and then dried overnight in a dry box at 80 ℃. The obtained dry red mud is named RM. Subsequently, RM was treated with nitric acid (3 mol/L) for 1 hour (the mass ratio of red mud to nitric acid solution is 1:10). And then filtering and washing the mixed solution of nitric acid and RM by deionized water until the pH value of the washed solution is 7. And drying the RM in a water bath at 80 ℃ until the moisture is completely evaporated, and obtaining nitric acid modified red mud which is marked as ARM.
(2) Preparation of nitric acid modified red mud-based VOCs catalyst (Cr/ARM):
ARM was ground to 200 mesh and then mixed with deionized water at a solid to liquid mass ratio of 1:3, and the solution was stirred in an 80 ℃ water bath for 20 minutes. Then Cr (NO3)3·9H2 O (added according to the mass percentage of Cr in the final prepared catalyst is 5%), namely 3g red mud and 1.246g Cr (NO3)3·9H2 O are mixed) are continuously stirred in a water bath at 80 ℃ until water is completely evaporated, then the sample is dried overnight in a drying oven at 105 ℃, the sample in the drying oven is taken out and calcined in a muffle furnace for 5 hours under the air environment at 550 ℃, the temperature of the muffle furnace is raised to the speed of 5 ℃ per minute from room temperature, and finally, the calcined material is naturally cooled to the room temperature, namely the red mud-based VOCs catalyst, which is marked as 5Cr/ARM.
Comparative example 5
The preparation method of the nitric acid modified red mud-based VOCs catalyst comprises the following steps:
(1) Preparation of nitric acid modified red mud (ARM):
The red mud feedstock was ground to 200 mesh and then dried overnight in a dry box at 80 ℃. The obtained dry red mud is named RM. Subsequently, RM was treated with nitric acid (3 mol/L) for 1 hour (the mass ratio of red mud to nitric acid solution is 1:10). And then filtering and washing the mixed solution of nitric acid and RM by deionized water until the pH value of the washed solution is 7. And drying the RM in a water bath at 80 ℃ until the moisture is completely evaporated, and obtaining nitric acid modified red mud which is marked as ARM.
(2) Preparation of nitric acid modified red mud-based VOCs catalyst (Mn-Ce/ARM):
ARM was ground to 200 mesh and then mixed with deionized water at a solid to liquid mass ratio of 1:3, and the solution was stirred in an 80 ℃ water bath for 20 minutes. Mn (NO3)2 solution and Ce (NO3)3·6H2 O (2.5% by mass of Mn and Ce in the final catalyst prepared, respectively, 2.5% by mass, 3g red mud and 0.514g 50% by mass of Mn (NO3)2 solution and 0.245g Ce (NO3)3·6H2 O) were mixed) were then added in a water bath at 80 ℃ C.) until the water was completely evaporated, then the sample was dried overnight in a 105 ℃ C. Drying oven, the sample was taken out and calcined in a muffle furnace at 550 ℃ C. Air for 5 hours, the muffle furnace was warmed up from room temperature to 550 ℃ C. At a rate of 5 ℃ C/min, finally, the calcined material was naturally cooled to room temperature, namely, the red mud-based VOCs catalyst, denoted as 2.5Mn-2.5Ce/ARM.
Comparative example 6
Commercially available Al2O3 was ground to 200 mesh and then mixed with deionized water at a solid to liquid mass ratio of 1:3, and the solution was stirred in a water bath at 80℃for 20 minutes. Then Mn (NO3)2 solution, 15% by mass of Mn in the final catalyst prepared, 3g Al2O3 and 3.460g 50% Mn (NO3)2 solution) were added and stirred in a 80 ℃ water bath until the water evaporated completely, then the sample was dried overnight in a 105 ℃ oven, the sample was taken out of the oven and calcined in a 550 ℃ air atmosphere for 5 hours in a muffle furnace, the muffle furnace was warmed up to 550 ℃ at a rate of 5 ℃ per minute, and finally the calcined material was naturally cooled to room temperature, namely the red mud-based VOCs catalyst, denoted 15Mn/Al.
Comparative example 7
Commercially available TiO2 was ground to 200 mesh and then mixed with deionized water at a solid to liquid mass ratio of 1:3 and the solution was stirred in a water bath at 80℃for 20 minutes. Then Mn (NO3)2 solution, 15% by mass of Mn in the final catalyst prepared, 3g TiO2 and 3.460g 50% Mn (NO3)2 solution) were added and stirred in a 80 ℃ water bath until the water evaporated completely, then the sample was dried overnight in a 105 ℃ oven, the sample was taken out of the oven and calcined in a 550 ℃ air atmosphere for 5 hours in a muffle furnace, the muffle furnace was warmed up to 550 ℃ at a rate of 5 ℃ per minute, finally the calcined material was naturally cooled to room temperature, namely the red mud-based VOCs catalyst, denoted 15Mn/Ti.
The RM, ARM and 15Mn/ARM ingredient contents, physical structures of the RM, ARM and 15Mn/ARM ingredients prepared in example 3 are shown in tables 1 and 2 and FIG. 1.
TABLE 1 ingredient content of RM and ARM prepared in example 3
TABLE 2 physical Structure of RM, ARM and 15Mn/ARM prepared in example 3
Table 1 and FIG. 1 show that the red mud before and after the acid treatment contains Fe2O3, and the proportion of Fe in the red mud can be effectively improved by the nitric acid treatment, which is beneficial to the catalytic oxidation of toluene.
Table 2 shows that the specific surface area of ARM after the nitric acid treatment is increased from 23.5m2/g to 45.7m2/g, and further 15Mn/ARM is increased to 58.2m2/g, and the larger specific surface area shows that the catalyst has more active sites for adsorbing toluene in the reaction process. Meanwhile, the pore volume is increased from 0.12m3/g of ARM to 0.15m3/g of ARM and 15Mn/ARM, and the larger pore volume shows that the catalyst has stronger toluene containing capacity and is beneficial to the catalytic oxidation of toluene.
The catalysts prepared in each example and comparative example were subjected to activity detection, the detection apparatus is shown in fig. 2, and the detection process is as follows:
The simulated flue gas flow is 100mL/min, wherein the toluene concentration is 1000ppm, the percentage content of O2 is 21%, N2 is used as balance gas, and the mass airspeed is 60000 mL/(g.h). The temperature interval of the catalytic test is 200-350 ℃. The results are shown in FIGS. 3 to 6.
Fig. 3 shows that the catalytic effect of hydrochloric acid on modification of red mud is weaker than that of nitric acid.
Fig. 4 shows that the catalyst p-toluene catalytic effect can be improved to a certain extent by loading various metals, but the improvement is most obvious by loading Mn on the red mud ARM.
Fig. 5 shows that when the mass ratio of Mn is increased to 15%, T90 of the 15Mn/ARM catalyst (temperature at which toluene conversion reaches 90%) is increased over T90 of the ARM catalyst by more than 100 ℃, exhibiting good advantages.
Commercially available Al2O3、TiO2 is used as a catalyst carrier, a 15Mn/Al catalyst and a 15Mn/Ti catalyst are prepared in the same synthesis mode, and the temperature of T90 of the 15Mn/ARM catalyst is improved by 37 ℃ and 26 ℃ respectively compared with that of the 15Mn/Al catalyst and the 15Mn/Ti catalyst, so that the red mud can effectively improve the activity for toluene catalytic oxidation by adopting the method, and the effect is better than that of other catalysts, as shown in figure 6.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.