CN104475098A - Catalyst for preparing synthetic gas by partially oxidizing methane and preparation method of catalyst - Google Patents

Abstract

The invention discloses a catalyst for preparing a synthetic gas by partially oxidizing methane and a preparation method of the catalyst, and relates to nano catalysts for preparing synthetic gases. The catalyst for preparing the synthetic gas by partially oxidizing methane takes SiO2 as a carrier and CeO2 as an additive, and is prepared from the following components in percentage by mass: 0.005-1% of an active component Rh, 5-30% of an additive CeO2 and the balance of SiO2, wherein the particle size of Rh is 1-2nm and the specific surface area of Rh is 350-450m<2>/g. The preparation method comprises the following steps: 1) soaking the carrier in a nitric acid solution, washing till the pH value is 6.5-7.0 and drying for later use; 2) respectively preparing a rhodate solution and a cerate solution according to the content ratios of the components of the catalyst, and mixing the solutions into a mixed steeping liquid according to the ratios of the components of the catalyst; and 3) mixing SiO2 obtained in the step 1) with the steeping liquid obtained in the step 2), steeping, drying, and roasting, so as to obtain the catalyst for preparing the synthetic gas by partially oxidizing methane.

Description

Catalyst for producing synthesis gas by partial oxidation of methane and preparation method thereof

technical field

The invention relates to a nanometer catalyst for preparing synthesis gas, in particular to a catalyst for preparing synthesis gas by partial oxidation of methane and a preparation method thereof.

Background technique

The main component of natural gas and shale gas is methane. With the large-scale exploitation and utilization of natural gas and shale gas, the effective utilization of methane has attracted more and more attention. One of the effective ways to convert methane into high value-added products is to convert it into synthesis gas, which is then used to produce methanol, liquid fuels and other chemical products. Compared with the traditional steam reforming of methane to synthesis gas, partial oxidation of methane to synthesis gas has the advantages of small reactor volume, fast reaction rate, low energy consumption, and the carbon-hydrogen ratio of the product is suitable for subsequent methanol and Fischer-Tropsch synthesis. Therefore, the partial oxidation of methane to synthesis gas has attracted much attention in recent years.

Catalysts for partial oxidation of methane to synthesis gas are mainly supported metal catalysts, which can be divided into two categories: one is supported nickel and cobalt catalysts, nickel catalysts are prone to carbon deposition and active components are easy to lose, while cobalt catalysts are relatively less active , the active phase is easily oxidized; the other is a supported noble metal catalyst, which has reliable stability and excellent activity and selectivity, but its price is relatively expensive.

Rhodium catalyst has the characteristics of high stability and strong oxidation resistance, so it shows excellent reaction performance. 1wt%Rh/SiO ₂ catalyst has shown good catalytic activity at 450°C (J.Catal.2004,226,247-259). Due to the high price of rhodium, the preparation of catalysts with low loading and stable catalytic performance is an important step to promote this reaction to industrialization. Literature (ChemCatChem 2012, 4, 1368-1375) synthesized Rh nanoparticles with a particle size of only about 1.3nm by the ethylene glycol reduction method and loaded them on γ-Al ₂ O ₃ to prepare a catalyst for this reaction. The dispersion degree of the catalyst is very high, and when the loading amount of Rh is as low as 0.005wt%, it can still show good catalytic activity and stability. However, the preparation method of the catalyst is complicated and only applicable to the reaction conditions with low space velocity. Therefore, it is an effective way to reduce the amount of rhodium to further improve the activity, selectivity and stability of the catalyst by adding suitable auxiliary agents. CeO ₂ has a unique redox property, which can store and release oxygen. At the same time, a solid solution can be formed between CeO ₂ and Rh, which prevents the migration of Rh on the catalyst surface and improves the stability of the catalyst.

Contents of the invention

The object of the present invention is to provide a catalyst for producing synthesis gas by partial oxidation of methane and a preparation method thereof.

The catalyst for the partial oxidation of methane to synthesis gas uses _SiO2 as a carrier, _CeO2 as an auxiliary agent, the content of the active component Rh is 0.005% to 1%, and the auxiliary agent _CeO2 is 5% to 30% by mass percentage, The rest is SiO ₂ ; preferably the content of the active component Rh is 0.01%-1%, the additive CeO ₂ is 5%-30%, and the rest is SiO ₂ . The particle diameter of Rh is 1-2 nm, and the specific surface area is 350-450 m ² /g.

The preparation method of the catalyst for the partial oxidation of methane to synthesis gas comprises the following steps:

1) Soak the carrier _SiO2 in nitric acid solution, wash to pH=6.5-7.0, and dry it for later use;

2) Prepare rhodium salt solution and cerium salt solution respectively according to the content ratio of each component of the catalyst, and combine them into a mixed impregnating solution according to the ratio of each component of the catalyst;

3) Mix the SiO ₂ obtained in step 1) with the impregnating liquid obtained in step 2), impregnate, dry, and roast to prepare a catalyst (Rh-CeO ₂ /SiO ₂ catalyst) for partial oxidation of methane to synthesis gas.

In step 1), the soaking condition can be soaked in a nitric acid solution with a mass concentration of 20% for 12 to 24 hours; the washing can be washed with distilled water; the drying condition can be 12 hours at 110 to 120°C ;

In step 2), the precursor salt used in the rhodium and cerium salt solution is rhodium acetylacetonate and cerium acetylacetonate, and the solvent is acetylacetone or toluene.

In step 3), the soaking time is at least 12 hours; the drying condition can be 110-120°C in an air atmosphere for 2 hours; the roasting condition can be: the temperature is 800°C, and the heating rate is 1 ~10°C/min, the atmosphere is air, and the firing time is 2~4h.

Catalyst of the present invention is used in the performance evaluation of methane partial oxidation synthesis gas reaction to carry out on the miniature fixed-bed flow reaction device, adopts the quartz reactor that internal diameter is 6mm, is used for the K type (nickel-chromium-nickel-aluminum) of temperature control The thermocouple is fixed on the outer wall of the quartz tube, and its temperature measuring end is close to the outer wall of the reaction tube in the first half of the catalyst bed. The catalyst was pre-reduced at 700°C for 1 h under hydrogen atmosphere to react. According to the molar ratio, the composition of raw gas is CH ₄ /O ₂ =2 (with or without diluent gas), the space velocity of raw gas is 100000h ^-1 , the reaction pressure is 0.1MPa, and the reaction temperature is 700-800°C. The catalyst was used continuously for 400 hours, and the activity did not change significantly. The catalyst is suitable for a wide ratio of methane and oxygen raw material gas system, and can be suitable for a system without inert gas dilution.

The invention relates to a high-dispersion anti-sintering loaded rhodium-based catalyst with silicon dioxide as a carrier and cerium oxide as an auxiliary agent and a preparation method thereof, and is used for preparing synthesis gas by partial oxidation of methane. In the present invention, silica is selected as the carrier, surface residues are cleaned by nitric acid solution to expose surface hydroxyl groups, and the dispersion of rhodium precursor salt on the surface of the silica carrier is promoted, while cerium oxide is added to prevent the sintering and agglomeration of rhodium in processes such as roasting and reduction. , so as to prepare a Rh-CeO ₂ /SiO ₂ catalyst with high dispersion and high stability, and use the catalyst for partial oxidation of methane to synthesize gas, and study its catalytic performance.

The advantage of the catalyst provided by the present invention is: cerium dioxide layered spread on the surface of silicon dioxide, the active phase rhodium and layered cerium dioxide form a solid solution, which overcomes the shortcoming of weak interaction between rhodium and silicon dioxide surface; at the same time Ceria possesses unique redox properties, capable of storing and releasing oxygen, which significantly enhances catalyst performance. The preparation process of the present invention is simple, the required precious metal content is extremely low, the cost advantage is high, and the catalytic activity is high, the conversion rate of methane is close to the thermodynamic equilibrium value at the corresponding reaction temperature, the selection of _H2 and CO is high, and it has excellent resistance to carbon deposition Performance and stability: During the test period of 400 hours of continuous reaction at high space velocity, the activity of the catalyst remains stable, and there is no carbon deposit on the surface of the catalyst after the reaction.

Description of drawings

Fig. 1 is a transmission electron microscope image of a 0.5%Rh-10%CeO ₂ /SiO ₂ catalyst calcined at 800°C for 2h and reduced at 700°C for 1h.

Detailed ways

Example 1

Catalyst preparation: select 10g _{of SiO2} as a carrier, soak it in 20% nitric acid solution for 24 hours, wash it with distilled water to pH=6.5-7.0, dry it for later use; weigh 0.0098g of rhodium acetylacetonate and dissolve it in 20ml of acetylacetone solution , then weighed 0.0763g of cerium acetylacetonate and dissolved it in 60ml of acetylacetone, mixed the two solvents to form a mixed impregnation solution, weighed 0.5g of SiO ₂ that had been treated and added it to the mixed impregnation solution for immersion for 24 hours, stirred several times during the period, and then The solution was evaporated to dryness at 110° C., and calcined at 800° C. in air for 2 hours with a heating rate of 1° C./min to obtain a catalyst of 0.5% Rh-5% CeO ₂ /SiO ₂ .

Evaluation conditions: Before the reaction, the catalyst was reduced with hydrogen at 700°C for 1 hour. The reaction was carried out in a continuous injection fixed-bed quartz reactor, the reaction temperature was 700°C, the feed gas composition was CH ₄ : O ₂ : Ar=2:1:4 (molar ratio), the space velocity was 1×10 ⁵ h ^-1 , and the product After condensing to remove water, it was analyzed online by gas chromatography. The evaluation results are shown in Table 1.

See Figure 1 for the transmission electron micrograph of the 0.5%Rh-10%CeO ₂ /SiO ₂ catalyst calcined at 800°C for 2h and reduced at 700°C for 1h.

Example 2

Catalyst preparation Referring to Example 1, the solvent was changed from acetylacetone to toluene, and other conditions were the same to obtain a catalyst 0.5%Rh-10%CeO ₂ /SiO ₂ The evaluation conditions were the same as in Example 1, and the evaluation results are shown in Table 1.

Table 1

Examples 3-5: Catalyst Preparation Referring to Example 1, the mass of cerium acetylacetonate was changed to 0.1525g, 0.3050g, and 0.4575g respectively, and the rest of the conditions were the same to obtain a catalyst of 0.5%Rh-10%CeO ₂ /SiO ₂ , 0.5% Rh-20% _CeO2 / _SiO2 , 0.5%Rh-30% _CeO2 / _SiO2 . The evaluation conditions are the same as in Example 1, and the evaluation results are shown in Table 2.

Table 2

Comparative example 1

Catalyst preparation Referring to Example 1, weigh 0.0098 rhodium acetylacetonate and dissolve it in 20ml of acetylacetone solution, weigh 0.5g of treated SiO ₂ and add it to the mixed impregnation solution for immersion for 24 hours, stir several times during the period, and then place The solution was evaporated to dryness and calcined at 800°C for 2h in air with a heating rate of 1°C/min to obtain a 0.5%Rh/SiO ₂ -catalyst. The evaluation conditions are the same as in Example 1, and the evaluation results are shown in Table 3.

table 3

Embodiment 6～7

Catalyst preparation Referring to Example 1, the mass of rhodium acetylacetonate was changed to 0.0050g and 0.0020g respectively, and the mass of cerium acetylacetonate was changed to 0.1525g to obtain catalyst 0.25%Rh-10%CeO ₂ /SiO ₂ and 0.1%Rh -10% CeO ₂ /SiO ₂ and other conditions are the same. The evaluation conditions are the same as in Example 1, and the evaluation results are shown in Table 4.

Table 4

Comparative example 2~3

Catalyst preparation Referring to Comparative Example 1, the mass of rhodium acetylacetonate was changed to 0.0050 g and 0.0020 g respectively to prepare 0.25% Rh/SiO ₂ and 0.1% Rh/SiO ₂ , and the rest of the conditions were the same. The evaluation conditions are the same as in Example 1, and the evaluation results are shown in Table 5.

table 5

Embodiment 8～9

Catalyst preparation Referring to Example 1, the mass of rhodium acetylacetonate was changed to 0.0005g and 0.0002g respectively, and the mass of cerium acetylacetonate was changed to 0.1525g to obtain a catalyst of 0.025%Rh-10%CeO ₂ /SiO ₂ and 0.01% Rh-10%CeO ₂ /SiO ₂ and other conditions are the same. The reaction temperature was increased from 700°C to 800°C, and other evaluation conditions were the same as in Example 1. The results are shown in Table 6.

Table 6

Example 10

The preparation of the catalyst is the same as that in Example 1. The mass of rhodium acetylacetonate is changed to 0.0050g, and the mass of cerium acetylacetonate is changed to 0.1525g to obtain a catalyst of 0.25%Rh-10%CeO ₂ /SiO _{2 .} CH ₄ : O ₂ : Ar = 2: 1: 4 (molar ratio) was changed to CH ₄ : O ₂ = 2: 1 (without diluent gas). Other evaluation conditions were the same as in Example 1. The evaluation results are shown in Table 6.

Example 11

The preparation of the catalyst is the same as that in Example 1. The mass of rhodium acetylacetonate is changed to 0.0050g, and the mass of cerium acetylacetonate is changed to 0.1525g to obtain a catalyst of 0.25%Rh-10%CeO ₂ /SiO _{2 .} Change from CH ₄ : O ₂ : Ar = 2: 1: 4 (molar ratio) to CH ₄ : O ₂ = 2: 1 (without diluent gas), and increase the reaction temperature from 700°C to 800°C, other evaluation conditions Same as Example 1, the evaluation results are shown in Table 7.

Table 7

Example 12

Catalyst preparation Referring to Example 1, the mass of rhodium acetylacetonate was changed to 0.005 g, the mass of cerium acetylacetonate was changed to 0.1525 g, and the rest of the conditions were the same to prepare a catalyst of 0.25% Rh-10% CeO ₂ /SiO ₂ . The reaction raw material gas composition was CH ₄ :O ₂ :Ar=2:1:4 (molar ratio), the evaluation conditions were the same as in Example 1, and the catalyst life was evaluated, and the results are shown in Table 8.

Table 8

The preparation process of the present invention is simple, the required precious metal content is extremely low, the cost advantage is high, and the catalytic activity is high, the conversion rate of methane is close to the thermodynamic equilibrium value at the corresponding reaction temperature, the selection of _H2 and CO is high, and it has excellent resistance to carbon deposition performance and stability.

Claims (10)

1. a catalyst for producing synthesis gas by partial oxidation of methane is characterized in that with SiO ₂ as carrier, CeO as auxiliary agent, by mass percentage, the _content of active component Rh is 0.005%～1%, auxiliary agent CeO ₂ is 5%-30%, the rest is SiO ₂ . 2. the catalyst of a kind of methane partial oxidation synthesis gas as claimed in claim 1 is characterized in that by mass percentage, the content of active component Rh is 0.01%～1%, and auxiliary agent _CeO is 5%-30%, The remainder is SiO ₂ . 3. the preparation method of the catalyst of the partial oxidation of methane as claimed in claim 1, is characterized in that comprising the following steps: 1) Soak the carrier _SiO2 in nitric acid solution, wash to pH=6.5-7.0, and dry it for later use; 2) Prepare rhodium salt solution and cerium salt solution respectively according to the content ratio of each component of the catalyst, and combine them into a mixed impregnating solution according to the ratio of each component of the catalyst; 3) Mixing the _SiO2 obtained in step 1) with the impregnating solution obtained in step 2), impregnating, drying, and roasting to prepare a catalyst for the partial oxidation of methane to synthesis gas. 4. The preparation method of the catalyst for preparing synthesis gas by partial oxidation of methane as claimed in claim 3, characterized in that in step 1), the soaking condition is soaking in a nitric acid solution with a mass concentration of 20% for 12 to 24 hours. 5. the preparation method of the catalyst of partial oxidation of methane as claimed in claim 3, is characterized in that in step 1), described washing adopts distilled water washing. 6 . The preparation method of the catalyst for the partial oxidation of methane to synthesis gas according to claim 3 , characterized in that in step 1), the drying condition is 12 hours at 110-120° C. 7. as claimed in claim 3, the preparation method of the catalyst of methane partial oxidation synthesis gas is characterized in that in step 2), the precursor salt used in the salt solution of rhodium and cerium is rhodium acetylacetonate and cerium acetylacetonate, solvent For acetylacetone or toluene. 8. The preparation method of the catalyst for producing synthesis gas by partial oxidation of methane as claimed in claim 3, characterized in that in step 3), the soaking time is at least 12h. 9. The preparation method of the catalyst for the partial oxidation of methane to synthesis gas according to claim 3, characterized in that in step 3), the drying condition is 110-120°C in an air atmosphere for 2 hours. 10. The preparation method of the catalyst for the partial oxidation of methane to synthesis gas as claimed in claim 3, characterized in that in step 3), the conditions of the roasting are: the temperature is 800° C., and the heating rate is 1 to 10° C./min , the atmosphere is air, and the firing time is 2 to 4 hours.