CN108816225B

CN108816225B - In-situ synthesis Pt/MnO for VOCs catalytic combustion2@Mn3O4Catalyst, preparation method and application thereof

Info

Publication number: CN108816225B
Application number: CN201810705844.4A
Authority: CN
Inventors: 曲振平; 段潇潇
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2018-07-02
Filing date: 2018-07-02
Publication date: 2019-12-13
Anticipated expiration: 2038-07-02
Also published as: CN108816225A

Abstract

The invention belongs to the technical field of environmental catalytic purification, and provides in-situ synthesized Pt/MnO for VOCs catalytic combustion₂@Mn₃O₄Catalyst, preparation method and application thereof. MnO is prepared by using potassium permanganate and oxalic acid as raw materials and adopting a hydrothermal method₂(ii) a Then with the MnO₂As initial carrier, sodium borohydride as reducer, and through liquid phase reduction of H at normal temperature₂PtCl₆While for MnO₂The carrier is subjected to structure regulation and control, and one-step reduction to obtain in-situ synthesized mixed-phase MnO₂@Mn₃O₄A supported Pt-based catalyst wherein the Pt content is 0.2 to 0.5 wt%. The preparation process is simple, and the dispersed loading of the active components and the optimization of the carrier structure can be simultaneously realized in one step. The catalyst is applied to catalytic combustion of VOCs (volatile organic compounds) such as toluene and xylene, and has good low-temperature activity and stability, and no other waste gas is generated.

Description

in-situ synthesis Pt/MnO for VOCs catalytic combustion2@Mn3O4Catalyst, preparation method and application thereof

Technical Field

The invention belongs to the technical field of environmental catalytic purification, and particularly provides in-situ synthesized Pt/MnO applied to VOCs catalytic combustion₂@Mn₃O₄A catalyst and a preparation method thereof.

Background

With the development of modern industry and economy, the environmental problems become more serious, and the phenomenon of air pollution is prominent. The volatile organic compounds are one of the main pollutants in the air, and the main sources of the volatile organic compounds comprise industrial waste gas discharged in the chemical industry, automobile tail gas, materials used for indoor decoration and the like. The release of volatile organic compounds can form PM2.5 and photochemical smog, destroy ecological health, and damage the respiratory system and immune system of human body, wherein benzene series (such as toluene, xylene, etc.) even have teratogenic hazard, so the removal of VOCs in the air is not slow. The catalytic combustion method can realize the conversion of VOCs at a lower temperature, and the application of the high-efficiency and stable catalyst becomes a research focus and has important significance.

the catalyst applied to VOCs catalytic combustion at present mainly comprises transition metal oxide and supported noble metalA metal catalyst. Compared with the former, the supported noble metal catalyst has better low-temperature activity, high catalytic efficiency and low ignition temperature, and the Pt-based catalyst is considered as an ideal VOCs catalytic combustion material. Chen et al, which uses TEOS (tetraethyl orthosilicate) as a raw material, obtains a carrier ZSM-5 by a hydrothermal method, prepares a Pt/ZSM-5 catalyst with a Pt content of 1 wt% by impregnation, calcination, reduction, and the like, and can completely catalyze and oxidize toluene at 160 ℃ (chem. Zhang et al prepared layered porous zeolite by hydrothermal reaction and acid and alkali treatment, and obtained 1 wt% Pt supported catalyst by impregnation method with alumina as carrier, and reached 90% toluene conversion at 190 ℃ and 210 ℃ respectively (chem. Pt-based catalysts using inert components such as molecular sieves as carriers usually require the use of high molecular polymers, are complex in preparation process, and are susceptible to poisoning. Using transition metal oxides (CeO)₂、TiO₂、MnO_xEtc.) can simplify the preparation process of the carrier by loading Pt, has better stability, and can adjust the chemical valence state of Pt species by the synergistic action between the carrier and Pt and activate the lattice oxygen on the surface of the oxide, thereby improving the performance of the catalyst. Therefore, the loading of Pt on such an oxide as a carrier has been studied in a large amount. CeO is obtained by adopting a microwave hydrothermal method in Chinese patent CN 103386312A₂And then the catalyst Pt/CuO-CeO with 1 wt% Pt loading capacity is prepared by an impregnation method₂It was applied to toluene catalytic combustion to 100% toluene removal at 250 ℃. Zhou et al supported Pt on different MnO by liquid phase reduction₂Thus, Pt/alpha-MnO was obtained₂、Pt/L-MnO₂(layered MnO)₂) And Pt/alpha-MnO₂@ L-MnO₂When the Pt content was 1 wt%, analysis revealed Pt/α -MnO₂@L-MnO₂Middle Pt⁰At most, the presence of a miscible carrier may promote O₂The removal of formaldehyde by reaction for one hour at room temperature can reach 92.1 percent, which is higher than 81.3 percent and 75.9 percent of the former two (appl.Catal. B-environ, 2017.207,233-243). Preparation of cubic and mesoporous CeO by Mao et al₂Then, the mixture is immersed by stirring,Grinding and reducing to obtain Pt/CeO₂The results show that the difference of the carriers can influence the activity and reducibility of lattice oxygen on the surface of the catalyst and the concentration of surface oxygen vacancies, wherein the mesoporous CeO₂The performance of loading 1 wt% of Pt is more excellent, and benzene can be completely catalyzed and oxidized at 175 ℃ (ACS Catal.,2016.6,418-427). Although there have been many studies on supporting Pt by using transition metal oxide, the catalyst preparation usually requires multiple steps and is complicated, and since Pt is a noble metal (the unit price of Pt is about 180 yuan/g), the catalyst is expensive, the loading amount of 1 wt% is still high, which results in increased application cost, and catalytic activity and stability need to be further improved.

Aiming at the problems, the invention synthesizes Pt/MnO in situ by a liquid phase reduction method₂@Mn₃O₄The catalyst, the load of Pt active species and the optimization of the carrier structure are simultaneously completed in one step, the later-stage calcination is not needed, the preparation process is simple and quick, the content of Pt active components can be effectively controlled to be below 0.5 wt%, the application cost is greatly reduced, and when the catalyst is applied to the catalytic combustion of VOCs, the complete conversion of VOCs at a lower temperature can be realized.

Disclosure of Invention

The invention aims to provide in-situ synthesis of Pt/MnO₂@Mn₃O₄The catalyst and a specific preparation method thereof are used for catalytic combustion of VOCs. The catalyst has the characteristics of simple preparation method, low Pt loading capacity, high activity, good stability and the like, the carrier material has wide sources and relatively low price, the repeatability of the catalyst is high, and the catalyst shows good low-temperature activity in the catalytic combustion of VOCs.

The technical scheme of the invention is as follows:

In-situ synthesis Pt/MnO for VOCs catalytic combustion₂@Mn₃O₄The catalyst is supported by mixed-phase MnO₂@Mn₃O₄And the content of Pt is 0.2-0.5 wt%.

In-situ synthesis Pt/MnO for VOCs catalytic combustion₂@Mn₃O₄the preparation method of the catalyst comprises the following steps:

(1) Dissolving potassium permanganate in deionized water, and magnetically stirring for 20-30min at 60 deg.C in water bath; dissolving oxalic acid in deionized water to obtain an oxalic acid solution; controlling the molar ratio of potassium permanganate to oxalic acid to be 1:1-2, wherein the volumes of the potassium permanganate solution and the oxalic acid solution are the same; dropwise adding the obtained oxalic acid solution into the potassium permanganate solution, and mixing and stirring for 20-50min at the temperature of 60 ℃; then pouring the mixed solution into a reaction kettle, placing the reaction kettle into an oven, and carrying out hydrothermal reaction for 12 hours at 180 ℃;

(2) After the temperature of the reaction kettle is reduced to room temperature, centrifugally washing the obtained precipitate by using deionized water and absolute ethyl alcohol, and drying the precipitate in an oven at the temperature of 60-100 ℃ for 10-24 hours; then calcining the mixture for 5 to 8 hours at the temperature of between 300 and 500 ℃ to obtain MnO₂；

(3) MnO obtained in the step (2)₂Dispersing the powder in deionized water, adding appropriate amount of H₂PtCl₆Stirring the solution vigorously for 30-60min to obtain suspension; then NaBH with the concentration of 0.01mol/L-0.05mol/L is prepared₄Quickly adding the solution into the suspension, and continuously stirring for 60-90 min; MnO in Mixed solution₂:Pt⁴⁺:NaBH₄The molar ratio of (1) is 6.55-6.95:0.01-0.03: 0.001-0.005;

(4) Washing the precipitate obtained in the step (3) with deionized water and absolute ethyl alcohol, and drying in a drying oven at the temperature of 60-100 ℃ for 10-15h to obtain in-situ synthesized Pt/MnO₂@Mn₃O₄Catalyst, wherein the content of Pt is 0.2-0.5 wt%.

Pt/MnO of the present invention₂@Mn₃O₄The catalyst is applied to VOCs catalytic combustion, the reaction gas is 100-1000ppm volatile organic gas, and the equilibrium gas is Ar and O₂In which O is₂The volume fraction is 20 percent, and the airspeed of the mixed reaction gas is 20000h^-1-60000h^-1The activity test was carried out continuously on a microreaction device. The catalyst can realize the removal of VOCs at 30-180 ℃.

Pt/MnO of the present invention₂@Mn₃O₄The catalyst can realize complete catalytic combustion of VOCs at a lower temperature and has better stability. Meanwhile, the catalyst can also be applied to selective catalytic oxidation of ammonia gas and removal of nitrogen oxides.

The invention has the beneficial effects that: in-situ synthesis of Pt/MnO by combining hydrothermal method and liquid phase reduction method₂@Mn₃O₄A catalyst. Pt is loaded by the mixed-phase manganese oxide, and the oxygen activating capacity of the catalyst can be improved by the synergistic effect of the carrier and the noble metal, so that the catalyst has good low-temperature activity and stability for the catalytic combustion reaction of benzene series (such as toluene, xylene and the like) in VOCs. The preparation method is simple, the Pt loading capacity is low (less than or equal to 0.5 wt%), the carrier material is wide in source and relatively low in price, the catalyst is good in repeatability, the application cost is low, VOCs can be completely removed through catalytic combustion at a relatively low temperature, and the catalyst has good industrial application potential.

drawings

FIG. 1 shows XRD patterns of catalysts A, B, C and D prepared in example 1 and comparative examples 1 to 3.

FIG. 2 is a graph showing the catalytic combustion activity of toluene in catalysts A, B, C, and D prepared in example 1 and comparative examples 1 to 3.

FIG. 3 is a graph of the reaction stability activity of catalyst A prepared in example 1.

Detailed Description

The following further describes a specific embodiment of the present invention with reference to the drawings and technical solutions.

example 1

In-situ synthesis of Pt/MnO₂@Mn₃O₄Preparation of the catalyst:

(1) Dissolving 0.02mol of potassium permanganate in 35mL of deionized water, and placing the mixture under the condition of 60 ℃ water bath to be vigorously stirred; dissolving 0.036mol of oxalic acid in 35mL of deionized water to obtain an oxalic acid solution; while stirring, dropwise adding the oxalic acid solution into the potassium permanganate solution, mixing, and stirring for 30min at 60 ℃; then the mixed solution is transferred into a reaction kettle and reacts for 12 hours at 180 ℃. Centrifugally washing the reacted precipitate by deionized water and absolute ethyl alcohol, drying in a drying oven at 80 ℃ for 12h, and calcining in a muffle furnace at 400 ℃ for 5h to obtain MnO₂；

(2) 0.6g of prepared MnO was taken₂Dispersing in 8mL deionized water, adding 0.8mL H with concentration of 0.0193mol/L₂PtCl₆Solution, stirring at ambient temperature 60min; preparing 0.005mol/L NaBH₄0.95mL of the solution was added to the mixture, and the mixture was further stirred for 60 min. Centrifugally washing the obtained substance, and drying in an oven at 80 ℃ for 12h to obtain in-situ synthesized Pt/MnO₂@Mn₃O₄Denoted as catalyst A, with a Pt mass content of 0.3 wt%.

Comparative example 1

Pt/MnO₂Preparation of the catalyst: 0.034g PVP (polyvinylpyrrolidone) and 0.09g sodium citrate were weighed into 50mL deionized water, stirred in an oil bath and heated to 80 ℃; take 0.8mL of H₂PtCl₆Dropwise adding the solution into the mixed solution, and stirring for 5 min; dissolving 0.054g of ascorbic acid in 5mL of water, dropwise adding the ascorbic acid into the mixed solution, and stirring for 60min at 80 ℃; 0.6g of MnO prepared in example 1 was taken₂The mixture was dispersed by sonication in 50mL of deionized water, the colloidal solution was added and stirring was continued at 80 ℃ for 4 h. Centrifugally washing the reacted solid, and drying in an oven at 80 ℃ for 12h to obtain Pt/MnO₂Denoted as catalyst B, in which the mass content of Pt is 0.3 wt%.

Comparative example 2

Pt/Mn₃O₄Preparation of the catalyst: 0.6g of Mn purchased was weighed₃O₄Dispersed in 10mL deionized water, 0.8mL H was added₂PtCl₆Mixing and stirring the solution for 10 min; appropriate amounts of sodium borohydride, sodium hydroxide and sodium citrate were dissolved in deionized water to make the concentrations 0.572mol/L, 0.250mol/L and 0.001mol/L, respectively, 5mL of this mixed solution was added rapidly to the above liquid at 60 deg.C, vigorously stirred for 60 min. Centrifugally washing the obtained substance, and drying in an oven at 80 ℃ for 12h to obtain Pt/Mn₃O₄Denoted as catalyst C, with a Pt mass content of 0.3 wt%.

Comparative example 3

Step-by-step synthesis of Pt/MnO₂@Mn₃O₄Preparation of the catalyst:

(1) 1g of MnO prepared in example 1 was taken₂100mL of NaBH with a concentration of 0.15mol/L was added₄In the solution, stirring vigorously for 1 h; the solid obtained is washed centrifugally and dried in an oven at 80 DEG CDrying for 12h, and roasting the dried sample at 200 ℃ for 5h to obtain the required carrier;

(2) Pt was supported in the same manner as in comparative example 1 except that the carrier used was obtained in step (1) to give Pt/MnO synthesized stepwise₂@Mn₃O₄Denoted as catalyst D, where the mass content of Pt is 0.3 wt%.

Example 2

The catalysts a, B, C, D prepared in example 1 and comparative examples 1-3 were subjected to X-ray diffraction measurements to obtain corresponding XRD patterns, the results of which are shown in fig. 1. No diffraction peak for Pt occurred in all catalysts. The catalysts of example 1 and comparative example 3 showed MnO₂And Mn₃O₄Of the mixed phase of comparative examples 1 and 2, respectively, having only MnO₂And Mn₃O₄The corresponding diffraction peak.

Example 3

The catalysts obtained in example 1 and comparative examples 1 to 3 were subjected to a toluene catalytic combustion activity test using a self-made fixed bed continuous microreactor and quantitative analysis of the toluene concentration before and after the oxidation reaction was carried out by gas chromatography GC 7900 equipped with an FID detector. Specific conditions of the test include: the initial concentration of toluene is 500ppm, argon is used as balance gas, and the space velocity of reaction gas is 24000h^-1(ii) a The chromatographic column is a special column for benzene series, the temperature of the column is 80 ℃ during detection, and the temperature of the detector is 200 ℃. The reactivity of each catalyst is shown in FIG. 2, wherein the activity of catalyst A is the best, and the toluene removal rate at 150 ℃ is 97%.

Example 4

The catalyst A prepared in example 1 was used in a xylene catalytic combustion reaction, the initial concentration of xylene was 500ppm, the column temperature of the column at the time of detection was 100 ℃, and the other conditions were the same as in example 3. The test results are shown in table 1.

Table 1 results of activity test

Example 5

The catalyst a prepared in example 1 was subjected to the stability test under the same reaction conditions as in example 3, and the results are shown in fig. 3. The catalyst is continuously tested for 48 hours at 160 ℃, and the toluene conversion rate is always kept above 99%, which shows that the catalyst has better stability.

example 6

The catalyst A obtained in example 1 was subjected to an activity test while adjusting the gas flow rate so as to increase the toluene concentration to 1000ppm and keeping the other conditions the same as in example 3. The measurement result shows that the catalyst can reach 97 percent of toluene conversion rate at 160 ℃, and the specific result is shown in table 2.

Table 2 results of activity test

Claims

1. In-situ synthesis Pt/MnO for VOCs catalytic combustion₂@Mn₃O₄Catalyst, characterized in that said in situ synthesis of Pt/MnO₂@Mn₃O₄The carrier of the catalyst is mixed-phase MnO₂@Mn₃O₄The content of Pt is 0.2-0.5 wt%; in-situ synthesis Pt/MnO for VOCs catalytic combustion₂@Mn₃O₄The catalyst is prepared by the following steps:

(3) Will be step (2)The obtained MnO₂Dispersing the powder in deionized water, adding appropriate amount of H₂PtCl₆Stirring the solution vigorously for 30-60min to obtain suspension; then NaBH with the concentration of 0.01mol/L-0.05mol/L is prepared₄Quickly adding the solution into the suspension, and continuously stirring for 60-90 min; MnO in Mixed solution₂:Pt⁴⁺:NaBH₄The molar ratio of (1) is 6.55-6.95:0.01-0.03: 0.001-0.005;

2. The in situ synthesized Pt/MnO of claim 1₂@Mn₃O₄The application of the catalyst in catalytic combustion of VOCs is characterized in that reaction gas is 100-1000ppm volatile organic gas, and balance gas is Ar and O₂In which O is₂The volume fraction is 20 percent, and the airspeed of the mixed reaction gas is 20000h^-1-60000h^-1The reaction temperature is 30-180 ℃, and the activity test is carried out on a micro-reaction device by continuous operation.