CN115318286A - A kind of platinum catalyst for propane catalytic combustion and its preparation method and application - Google Patents

Abstract

The present invention is a platinum catalyst for propane catalytic combustion, a preparation method and application thereof. The catalyst uses Nb ₂ O ₅ as a carrier, Pt as an active component, W as an auxiliary agent, and the loading amount of Pt is 0.5% of the mass of the carrier. ‑2%, and the loading of W is 1% to 15% of the mass of the carrier. The Nb ₂ O ₅ carrier was synthesized by the sol-gel method, and then a certain content of Pt, W precursor was supported on the surface of the carrier by the equal volume co-impregnation method, and then Pt-xW/Nb ₂ O was obtained by standing, drying, and calcining in high temperature air. ₅ catalysts. Compared with the prior art, the catalyst of the present invention has the advantages of high activity, high thermal stability, strong resistance to water and _CO2 , and the like, and the preparation method is simple, high in repeatability, and environmentally safe.

Description

A kind of platinum catalyst for propane catalytic combustion and its preparation method and application

technical field

The invention belongs to the field of air pollution control, and in particular relates to a platinum catalyst for catalytic combustion of propane, a preparation method and application thereof.

Background technique

Exhaust gas emissions from the coal chemical industry, petroleum refining and other chemical industries and a large number of vehicle exhaust emissions that use liquefied petroleum gas and liquefied natural gas as fuel have led to an increasing emission of low-carbon alkanes such as methane, propane and butane. These low-carbon alkanes are the main precursors for the formation of near-ground ozone and pose a serious threat to human health and the natural environment. Therefore, how to control and eliminate low-carbon alkanes emissions has become one of the hotspots in the field of environmental research. The catalytic combustion method has the advantages of high purification efficiency, wide concentration of exhaust gas, no secondary pollution, and low economic cost. It is one of the most effective methods to control and eliminate low-carbon alkane emissions. Its core is to design and prepare high-performance catalysts .

Propane is a typical low-carbon alkane. Due to its relatively inert chemical properties and strong CH bonds, compared with aromatic hydrocarbons, aldehydes, acids, chlorinated compounds and other pollution, propane molecules are more difficult to catalyze and eliminate. The current high-performance catalysts for propane catalytic combustion can be mainly divided into Pt, Pd and Ru supported noble metal catalysts and Co-based and Mn-based transition metals and their composite oxide catalysts. The Co ₃ O ₄ based catalysts disclosed in Chinese patents (CN113786835A, CN113070071A) show relatively excellent propane oxidation activity and low cost, but the preparation process of the catalyst is cumbersome, the energy consumption is high, and a large amount of pollutants such as waste water will be produced , and more importantly, the active components of Co ₃ O ₄ are easy to sinter at high temperature and deactivate easily under water vapor conditions, which inevitably leads to a decrease in catalytic activity. The sandwich Zr/Pt-Pd/Mg-Al ₂ O ₃ catalyst disclosed in Chinese patent CN112958086A has good hydrothermal stability, but because the Pt-Pd active sites are partially covered by the ZrO ₂ protective layer, the catalyst propane catalytic oxidation activity poor. In addition, literature (J.Phys.Chem.C 2021, 125, 19301) reported a Pt/Nb ₂ O ₅ catalyst for propane catalytic combustion, but the full conversion temperature of propane is as high as 370 °C, It is far from meeting the actual exhaust emission requirements. Chinese patent CN109675556A discloses a CeO ₂ nanorod-supported Ru catalyst prepared by hydrothermal and deposition precipitation methods. Ru/CeO ₂ exhibits excellent propane combustion activity, and the full conversion temperature of propane can be as low as 190°C. However, the catalyst preparation process involves a large amount of waste alkali discharge, and the hydrothermal synthesis, high-temperature hydrogen reduction and other production processes have certain safety risks. More importantly, since the active component RuO _x species is constructed through high-temperature reduction, its high-temperature stability remains to be verified. Therefore, there is an urgent need to develop a high-performance catalyst that can meet the elimination of propane tail gas emissions from practical industrial sources.

Contents of the invention

The object of the present invention is to provide a platinum catalyst for catalytic combustion of propane and its preparation method and application in order to overcome the above-mentioned defects in the prior art. The catalyst has the advantages of high activity, high stability, strong resistance to water and CO ₂ , etc., and the preparation process is simple, environmentally friendly and safe, and has good reproducibility.

The object of the present invention can be achieved through the following technical solutions: a platinum catalyst for catalytic combustion of propane, the catalyst is based on Nb ₂ O ₅ as a carrier, Pt as an active component, W as an auxiliary agent, and the loading capacity of Pt is % 0.5-2% of the weight of the carrier, and the loading amount of W is 1%-15% of the weight of the carrier.

Further, the carrier Nb ₂ O ₅ is prepared by a sol-gel method, which specifically includes the following steps: dissolving the Nb source and citric acid in deionized water in proportion, and after the two are fully dissolved, place them in a 60-100°C water bath Heat and stir until a viscous gel begins to appear, then place it in an oven at 80-140°C for 24-48 hours, and finally bake it in air at 700°C for 4 hours, with a heating rate of 4°C/min.

Further, the Nb source includes ammonium niobium oxalate, niobium oxalate and niobium pentachloride, preferably ammonium niobium oxalate.

Further, the molar ratio of the Nb source to citric acid is 2:1, 1:1 or 1:2, preferably 1:2.

Further, the loading amount of Pt is 1% of the weight of the carrier, and the loading amount of W is 5% of the weight of the carrier.

A method for preparing a platinum catalyst for catalytic combustion of propane, comprising the following steps: pretreating the ground Nb ₂ O ₅ carrier with vacuum heating, configuring a Pt impregnating solution and a W impregnating solution, fully stirring the impregnating solution and the carrier, and mixing them evenly , and ultrasonically disperse at room temperature for 10-20min, then stand at room temperature for 12-24h, then place in a 60-100°C oven for 12-48h, and finally bake at 500°C for 4h in a flowing air atmosphere, with a heating rate of 4°C/min. The product is marked as Pt-xW/Nb ₂ O ₅ .

Further, the configuration of the Pt impregnating solution is to dissolve the soluble salt of Pt in deionized solution to prepare a 0.01-0.1 g/ml Pt impregnating solution;

Further, the configuration of the W impregnating solution is to dissolve the soluble salt of W in deionized solution to prepare a 0.01-0.1 g/ml W impregnating solution.

Further, active components and additives are loaded by equal volume co-impregnation.

The application of the above-mentioned platinum catalyst, the catalyst is used in the treatment of low-carbon alkane exhaust gas, including catalytic combustion of propane, high activity at low temperature, no by-products are generated during the reaction process, and the catalyst activity remains unchanged at 200°C for 60 hours. At the same time, the catalyst has excellent resistance to _H2O and _CO2 , cycle reaction stability and thermal stability. Therefore, the Pt-xW/Nb ₂ O ₅ catalyst has a good application prospect in the treatment of low-carbon alkanes such as propane from industrial sources.

The reaction conditions of the propane catalytic combustion are: 0.2vol.% C ₃ H ₈ , 2vol.% O ₂ /Ar or 5vol.% H ₂ O, mass space velocity: 80000mL·h· ^-1 g _cat ^-1 .

Compared with existing technology, the present invention has the following advantages:

(1) The Pt-W/Nb ₂ O ₅ catalyst of the present invention can realize complete oxidation at 250°C (reaction conditions: 0.2 vol.% C ₃ H ₈ , 2 vol.% O ₂ /Ar, mass space velocity: 80000mL·h ^-1 g _cat ^-1 ), even under various harsh actual working conditions (high water vapor and CO ₂ content, long-term reaction stability and multiple cycles, etc.), the catalyst showed excellent catalytic performance active. Further studies found that the excellent propane oxidation performance of the Pt-5W/Nb ₂ O ₅ catalyst was attributed to the enhanced redox property of Nb ₂ O ₅ doped by WO _x , which simultaneously favored the formation of metallic Pt species on the support surface and stable, which greatly facilitates the dissociation of the CH bond as the rate-determining step in the propane oxidation reaction. Besides, the strongly acidic oxide WO _x species also facilitated the adsorption and activation of propane. In addition, the dissociated hydrocarbon fragment ions are oxidatively dehydrogenated into propylene, acrylic acid, carbonate and other oxygen-containing species under the attack of abundant active oxygen species on the catalyst surface, and finally deeply oxidized into CO ₂ and H ₂ O, This degradation pathway is a more efficient propane oxidation pathway.

(2) The Pt-xW/Nb ₂ O ₅ catalyst of the present invention is used in the propane catalytic combustion reaction. When the W loading is 5%, the Pt-5W/Nb ₂ O ₅ catalyst shows the best propane oxidation activity, Propane can be completely catalyzed and oxidized to H ₂ O and CO ₂ at a temperature of 250°C without any other by-products (reaction conditions: 0.2vol.% C ₃ H ₈ , 2vol.% O ₂ /Ar or 5vol.% H ₂ O, mass space velocity: 80000mL·h· ^-1 g _cat ^-1 ), and the Pt-5W/Nb ₂ O ₅ catalyst has the advantages of excellent reaction stability, thermal stability, strong resistance to water and CO ₂ , etc. At the same time, the preparation method of the catalyst is simple and easy, has high repeatability, is environmentally friendly and safe, and can realize large-scale industrial production.

Description of drawings

Figure 1 is the catalytic combustion activity diagram of propane and the CO ₂ yield and selectivity diagram of Pt-xW/Nb ₂ O ₅ catalyst. Specifically, Figure 1a shows the conversion ratio of propane on the surface of different catalysts as a function of temperature, Figure 1b shows the conversion rate of _CO2 in the catalytic combustion of propane over different catalysts, and Figure 1c shows the CO formation in the catalytic combustion of propane on different catalysts. ₂ selectivity map;

Figure 2 shows the cycle stability of the Pt-5W/Nb ₂ O ₅ catalyst propane catalytic combustion reaction under dry and water-containing conditions; where Figure 2a shows the cycle stability test of the Pt-5W/Nb ₂ O ₅ catalyst propane catalytic combustion reaction under dry conditions Fig. 2b is the cycle stability test diagram of Pt-5W/Nb ₂ O ₅ catalyst propane catalytic combustion reaction under the condition of water;

Figure 3 is the long-term reaction stability of propane catalytic combustion with Pt-5W/Nb ₂ O ₅ catalyst under the condition of water or CO ₂ ;

Fig. 4 is the influence of 200-450 ℃ continuous high and low temperature changes on the reactivity of Pt-5W/Nb ₂ O ₅ catalyst propane oxidation;

Fig. 5 is a test diagram of propane oxidation activity of each synthetic sample in Example 2.

Detailed ways

The embodiments of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following implementation example.

Example 1:

A kind of Pt catalyst that is used for propane catalytic combustion and preparation method thereof, comprises the following steps:

_Preparation of _Nb2O5 support:

Dissolve ammonium niobium oxalate and citric acid in proportion (the molar ratio of Nb and citric acid is 1:2) in 80ml of deionized water respectively. After the two are fully dissolved, heat and stir in a water bath at 80°C until a viscous gel begins to appear , and immediately placed the reactor in an oven at 100°C for 36 hours to obtain a brownish-yellow solid powder. Finally, at room temperature at a rate of 4°C/min, the temperature was raised to 700°C in air for 5 hours to obtain white Nb ₂ O ₅ powder.

Preparation of Pt-xW/Nb ₂ O ₅ catalyst:

The loading amount of Pt is 1wt.%, and the loading amount of W is 5wt.%. Take 1g of Nb ₂ O ₅ carrier mechanically and pre-treat it with vacuum heating, prepare 0.04g/ml fresh platinum nitrate impregnation solution and 0.1g/ml ammonium metatungstate impregnation solution respectively. Take 0.25ml of platinum nitrate, 0.5ml of ammonium metatungstate impregnation solution and Nb ₂ O ₅ carrier, mix evenly, and ultrasonically stir at room temperature for 15 minutes, then leave the sample at room temperature for 12 hours, then place it in an oven at 80°C for 24 hours, and finally put the sample Place in a tubular heating furnace under a flowing air atmosphere and bake at 500°C for 4h (air flow rate: 100ml/min), with a heating rate of 4°C/min, to obtain niobium oxide-supported platinum and tungsten catalysts, marked as Pt-5W/Nb ₂ O ₅ .

Pt-1W/Nb ₂ O ₅ , Pt-2W/Nb ₂ O ₅ , Pt-10W/Nb ₂ O ₅ and Pt-15W/Nb ₂ O ₅ catalysts were synthesized by the same preparation method.

Catalyst performance test:

(1) Activity test

The calcined catalyst was pressed into tablets, sieved (40-60 mesh particles were taken), and the propane activity was evaluated in a gas-solid fixed-bed microreactor (inner diameter: 6 mm). The dosage of the catalyst is 30 mg, and the temperature is automatically controlled by a K-type thermocouple. Oxygen at a concentration of 20000ppm is used as the oxidant, the concentration of propane is 2000ppm, the space velocity is 80000mL·h· ^-1 g _cat ^-1 , and the reaction pressure is 0.1MPa. The test results are shown in Figure 1. Figure 1a is the catalytic combustion activity diagram of Pt-xW/Nb ₂ O ₅ catalyst propane. It can be seen from the cluster that Pt-5W/Nb ₂ O ₅ exhibits the best propane oxidation activity. Its full conversion temperature is 250°C, and no other by-products are detected in the gas chromatogram. At the same time, the formation rate of _CO2 (as shown in Figure 1b) is basically the same as the conversion rate of propane, and the selectivity of _CO2 is 100%. (as shown in Figure 1c). These results indicate that propane is fully oxidized to _H2O and _CO2 without any other by-products.

(2) Stability test

The cycle stability of propane catalytic combustion reaction over Pt-5W/Nb ₂ O ₅ catalyst was investigated under dry and aqueous conditions. The specific test process is as follows: reaction gas composition under dry conditions: 0.2vol.% C ₃ H ₈ , 2vol.% O ₂ /Ar, mass space velocity: 80000mL·h· ^-1 g _cat ^-1 ); Gas composition: 0.2vol.% C ₃ H ₈ , 2vol.% O ₂ /Ar, 5vol.% H ₂ O, mass space velocity: 80000mL·h· ^-1 g _cat ^-1 ). Among them, 5vol.% H ₂ O was introduced by injecting 5ml of water from the micro-sampler into the reaction gas through a KDS LEGATO 100 micro-syringe pump (the inner diameter of the micro-sampler was 10.3 mm, and the injection rate was 0.121 ml/h). In addition, the preparation process of the Nb ₂ O ₅ support, the preparation process of the Pt-5W/Nb ₂ O ₅ catalyst and the catalyst performance evaluation conditions are the same as in Example 1, and the results are shown in FIG. 2 . Figure 2a shows the cycle stability of Pt-5W/Nb ₂ O ₅ catalyst propane catalytic combustion reaction under dry conditions, and Figure 2b shows the cycle stability of Pt-5W/Nb ₂ O ₅ catalyst propane catalytic combustion reaction under aqueous conditions, from the figure It can be seen that the catalytic propane oxidation activity of the Pt-5W/Nb _{2 O 5 catalyst remains basically unchanged after 5 consecutive cycles of application under dry or aqueous reaction conditions, indicating that the Pt-5W/Nb 2 O 5 catalyst} Has good reaction stability.

(3) Long-term stability test

The evaluation of the catalyst under the condition of water or _CO2 was investigated (the evaluation of the catalyst under the condition of water is as the above-mentioned stability test; the composition of the reaction gas under the condition of _CO2 : 0.2vol.% _C3H8 , _2vol .% _O2 /Ar, 5vol.%CO ₂ , mass space velocity: 80000mL·h· ^-1 g _cat ^-1 ). Pt-5W/Nb ₂ O ₅ catalyst propane catalytic combustion long-term reaction stability, Nb ₂ O ₅ carrier preparation process and Pt-5W/Nb ₂ O ₅ catalyst preparation process and catalyst performance evaluation conditions are the same as in Example 1, the results are as follows As shown in Figure 3, it can be seen from the figure that the introduction of CO ₂ has basically no effect on the propane oxidation activity of the Pt-5W/Nb ₂ O ₅ catalyst, however, when 5vol.% H ₂ O or 5vol. %CO ₂ and 5 vol.% H ₂ O, the conversion of C ₃ H ₈ on the Pt-5W/Nb ₂ O ₅ catalyst decreased slightly from the initial 93% to 89% stage, and then in 40 hours remain stable inside. Moreover, the conversion of C ₃ H ₈ can be fully recovered after removal of H ₂ O and CO ₂ . These results indicate that the Pt-5W/Nb ₂ O ₅ catalyst has good resistance to H ₂ O.

(4) Effect of continuous high and low temperature changes on catalytic activity

The influence of continuous high and low temperature changes at 200-450°C on the reactivity of Pt-5W/Nb ₂ O ₅ catalyst for propane oxidation was investigated. The specific test process was as follows: the temperature in the tubular heating furnace was stably maintained at 200 °C, the catalyst was continuously operated at the reaction temperature for 10 h. Then the reaction temperature was raised to 450° C. at a heating rate of 5° C./min. The preparation process of the Nb ₂ O ₅ carrier and the preparation process of the Pt-5W/Nb ₂ O ₅ catalyst and the catalyst performance evaluation conditions are the same as in Example 1. The results are shown in Figure 4. It can be seen from the figure that when the reaction temperature is 200 ° C , the conversion rate of propane was stably maintained at 38.5%; when the reaction temperature was rapidly raised to 450°C, the conversion rate of propane immediately rose to 99.9% and could be maintained stably. After several times of heating and cooling, the propane oxidation activity of the catalyst remained unchanged, which indicated that the Pt-5W/Nb ₂ O ₅ catalyst had good thermal stability.

Example 2

A kind of Pt catalyst that is used for propane catalytic combustion and preparation method thereof, comprises the following steps:

_Preparation of _Nb2O5 support:

Dissolve niobium oxalate citric acid in proportion (the molar ratio of Nb and citric acid is 1:1) in 80ml of deionized water respectively. After the two are fully dissolved, heat and stir in a water bath at 60°C until a viscous gel begins to appear. Immediately dissolve The reactor was dried in an oven at 80°C for 48 hours to obtain a brownish-yellow solid powder, and finally heated to 700°C for 4 hours at room temperature at a heating rate of 4°C/min in air to obtain white Nb ₂ O ₅ powder.

Preparation of Pt-xW/Nb ₂ O ₅ catalyst:

The loading amount of Pt is 1wt.%, and the loading amount of W is 5wt.%. Take 1g of Nb ₂ O ₅ carrier and grind it mechanically and heat it in vacuum for pretreatment, prepare 0.01g/ml fresh platinum nitrate impregnation solution and 0.01g/ml ammonium metatungstate impregnation solution respectively. Take 1ml of platinum nitrate, 5ml of ammonium metatungstate impregnation solution and Nb ₂ O ₅ carrier, mix evenly, and ultrasonically stir at room temperature for 15 minutes, then let the sample stand at room temperature for 12 hours, then place it in an oven at 80°C for 24 hours, and finally place the sample in Roast at 500°C for 4 hours in a tubular heating furnace (air flow rate: 100ml/min), and heat up at a rate of 4°C/min to obtain niobium oxide-supported platinum and tungsten catalyst, marked as Pt-5W/Nb ₂ O ₅ .

Using the same preparation method to synthesize 0.5Pt-5W/Nb ₂ O ₅ , 1.5Pt-5W/Nb ₂ O ₅ and 2Pt-5W/Nb ₂ O ₅ catalysts respectively, and using the same synthesis of Pt/Nb ₂ O ₅ as a comparative example 1. Synthesis of 5W/Nb ₂ O ₅ as comparative example 5.

The propane oxidation activity of each of the above synthesized samples was tested, and the results are shown in Figure 5: 5W/Nb ₂ O ₅ has almost no propane oxidation activity at 350°C. In addition, we found that with the increase of Pt loading, the activity of the catalyst gradually increased, and when the Pt loading was greater than 1.5%, the propane oxidation activity of the catalyst remained basically unchanged, so the production cost of the catalyst and the oxidation activity comprehensive It can be seen that the loading of Pt is 1% is the optimal choice. At the same time, the propane oxidation activity of the Pt-5w/Nb ₂ O ₅ catalyst synthesized in Example 2 was significantly lower than that of the Pt-5w/Nb ₂ O ₅ catalyst in Example 1, which may be related to the Nb precursor in the support preparation process. It is related to the ratio of body and citric acid complexing agent. Therefore, in the preparation process of Pt-5W/Nb ₂ O ₅ catalyst, the precursor of Nb is ammonium niobium oxalate and the molar ratio of Nb and citric acid is 1:2.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. A platinum catalyst for propane catalytic combustion, characterized in that the catalyst is based on Nb ₂ O ₅ is a carrier, Pt is an active component, W is an auxiliary agent, and the load of Pt is 0.5-2% of the mass of the carrier. %, the loading amount of W is 1%-15% of the mass of the carrier. 2. The platinum catalyst for propane catalytic combustion according to claim 1, characterized in that, said carrier Nb ₂ O ₅ is prepared by a sol-gel method, specifically comprising the steps of: Nb source and citric acid are respectively proportionally Dissolve in deionized water. After the two are fully dissolved, heat and stir in a water bath at 60-100°C until viscous gel begins to appear, then dry in an oven at 80-140°C for 24-48 hours, and finally in air at 700°C Roast for 4 to 6 hours with a heating rate of 4°C/min. 3. The platinum catalyst for catalytic combustion of propane according to claim 2, wherein the Nb source comprises one of ammonium niobium oxalate, niobium oxalate and niobium pentachloride, preferably ammonium niobium oxalate. 4. the platinum catalyst for propane catalytic combustion according to claim 2, is characterized in that, the consumption molar ratio of described Nb source and citric acid is 2:1, 1:1 or 1:2, preferred 1:2 . 5. The platinum catalyst for propane catalytic combustion according to claim 1, characterized in that, the loading of the Pt is 1% of the mass of the carrier, and the loading of W is 5% of the mass of the carrier. 6. a kind of preparation method for the platinum catalyst of propane catalytic combustion as claimed in claim 1, is characterized in that, comprises the following steps: after grinding Nb ₂ O ₅ carrier vacuum heating pretreatment, configuration Pt impregnation solution and W Impregnation solution, fully stir the impregnation solution and the carrier, mix evenly, and disperse at room temperature for 10-20 minutes ultrasonically, then leave it at room temperature for 12-24 hours, then place it in an oven at 60-100°C for 12-48 hours, and finally place it in a flowing air atmosphere at 500°C Calcined for 4 hours, the heating rate was 4°C/min, and the product was marked as Pt-xW/Nb ₂ O ₅ . 7. the platinum catalyst for propane catalytic combustion according to claim 6, is characterized in that, the configuration of described Pt impregnating solution is that the soluble salt of Pt is dissolved in deionization and is mixed with 0.01-0.1g/ml Pt dipping solution; The configuration of the W impregnating liquid is that the soluble salt of W is dissolved in deionized solution to prepare the W impregnating liquid of 0.01-0.1 g/ml. 8. The platinum catalyst for catalytic combustion of propane according to claim 6, characterized in that the active components and auxiliary agents are loaded by equal-volume co-impregnation. 9. The application of the platinum catalyst for catalytic combustion of propane as claimed in claim 1, characterized in that, the catalyst is used in the treatment of low-carbon alkane waste gas, including catalytic combustion of propane. 10. The platinum catalyst for catalytic combustion of propane according to claim 1, characterized in that the reaction conditions for catalytic combustion of propane are: 0.2vol.% _C3H8 , _2vol .% _O2 /Ar or 5vol.% H ₂ O, mass space velocity: 80000mL·h· ^-1 g _cat ^-1 .

Images