Ni-CeCaO3 / Al2O3 catalyst for converting biogas into synthesis gas as well as preparation method and application of Ni-CeCaO3 / Al2O3 catalyst

Abstract

The invention discloses a Ni-CeCaO3 / Al2O3 catalyst for converting biogas into synthesis gas as well as a preparation method and application of the Ni-CeCaO3 / Al2O3 catalyst, and belongs to the technical field of energy catalysis. The Ni-CeCaO3 / Al2O3 catalyst is prepared through a complexing-coprecipitation method, Ni accounts for 7-12 wt% of the catalyst, CeO2 accounts for 24-35 wt% of the catalyst, CaO accounts for 5-16 wt% of the catalyst, a solid solution is formed by CeO2 and CaO, and the balance is Al2O3. According to the invention, Ni is adopted as an active component, so that the production cost of the catalyst is reduced compared with the use of noble metal. The catalyst is prepared through complexation and a coprecipitation method, the preparation method is simple, the dispersity of the active components is improved, high-temperature sintering of the active components is inhibited, and by controlling the content of CeO2 and CaO in a CaCeO3 solid solution, the activity and stability of the catalyst are optimized, the interaction force between an auxiliary carrier and the active components is improved, and the loss of the active components is reduced. The CaCeO3 oxide solid solution is adopted, through two circulation ways, the CO2 adsorption and carbon deposition elimination capability of the catalyst is improved, and the catalyst still can keep good catalytic activity in the presence of VOCs (Volatile Organic Compounds).

Description

Technical Field

[0001] The invention belongs to the technical field of energy catalysis, and specifically relates to a Ni-CeCaO3 / Al2O3 catalyst for converting biogas into synthesis gas, and a preparation method and application thereof. Background Art

[0002] Fossil fuels are the world's most in-demand non-renewable energy source, and as energy demand continues to increase, the use of fossil fuels increases the emission of greenhouse gases such as carbon dioxide. In order to reduce the impact of these emissions and to use renewable energy, it is necessary to increase the use of renewable energy sources such as biogas.

[0003] The main components of biogas are methane and carbon dioxide and a small amount of water. Therefore, biogas can also be used as a raw material for the industrial raw material precursor synthesis gas (H2+CO). Biogas can be converted into synthesis gas through biogas reforming. Biogas reforming is a chemical reaction that occurs at high temperature in the presence of a catalyst, in which methane reacts with carbon dioxide or methane and water to generate synthesis gas. In addition, in industrial production, precious metal catalysts are often not used because of their high prices. Non-precious metal Ni has catalytic activity similar to that of precious metals, but Ni easily forms coke, which is easily lost and sintered in high-temperature and water-containing reactions, resulting in reduced catalyst activity and deactivation. In addition, carbon deposition has a great influence on active components during biogas conversion, and biogas obtained by fermenting raw materials such as kitchen waste, forestry waste, animal feces, and agricultural straw may often contain trace amounts of volatile organic compounds (VOCs). The presence of VOCs will accelerate the formation of carbon deposition, which is easy to affect the activity and stability of the catalyst during the catalytic process.

[0004] CN 101279271A discloses a catalyst for preparing synthesis gas by catalytic partial oxidation of methane and a preparation method thereof. The catalyst comprises a cerium oxide-based composite auxiliary agent and a noble metal ruthenium added to a supported nickel catalyst. The catalyst has good catalytic activity under high space velocity reaction conditions, high selectivity for H2 and CO, and good anti-sintering and anti-carbon deposition properties. However, the noble metal ruthenium is used, resulting in a high production cost, and the stability of the catalyst and the catalytic activity of the catalyst in the presence of VOCs are not explored. Summary of the invention

[0005] In order to solve the above problems in the prior art, the present invention provides a Ni-CeCaO3 / Al2O3 catalyst for converting biogas into synthesis gas.

[0006] Another object of the present invention is to provide a Ni-CeCaO3 / Al2O3 catalyst for converting biogas into synthesis gas and to use the catalyst in preparing synthesis gas.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A Ni-CeCaO3 / Al2O3 catalyst for converting biogas into synthesis gas, the preparation method of which comprises the following steps:

[0009] S1. The soluble nickel salt, the soluble cerium salt, the soluble calcium salt and the aluminum source are mixed in water, the complexing agent is added and mixed, and then the alkaline precipitant is added and heated under mixing to obtain a first precursor;

[0010] S2. The first precursor is calcined and then reduced to obtain the Ni-CeCaO3 / Al2O3 catalyst;

[0011] The catalyst contains 7-12 wt% Ni, 24-35 wt% CeO2, 5-16 wt% CaO, CeO2 and CaO form a solid solution, and the rest is Al2O3.

[0012] The present invention prepares Ni-CeCaO3 / Al2O3 catalyst by complexation-coprecipitation method, firstly adopts the complexing agent to react with metal ions to obtain a complex, then adopts the coprecipitation method, generates CeCaO3 solid solution after calcination, and makes the active component nickel evenly dispersed on CeCaO3 solid solution and Al2O3, thereby improving the dispersibility of the active component nickel and inhibiting the agglomeration of the active component under high temperature sintering. In addition, by controlling the content of CeO2 and CaO in the auxiliary agent CaCeO3 solid solution, the activity and stability of the catalyst are optimized, the interaction force between the auxiliary agent carrier and the active component is enhanced, and the loss of the active component is reduced. Using CeCaO3 solid solution with specific CeO2 and CaO content as a carrier, on the one hand, Ce can be transported by Ce 3+ With Ce 4+ The oxygen cycle between the catalyst and the carbon deposits provides abundant active oxygen to the catalyst, thereby activating the deposited carbon into CO and promoting the removal of carbon deposits. On the other hand, Ca completes the adsorption of water and CO2 through the CaO-CaOH-CaCO3 cycle. CaO adsorbs H2O to generate Ca(OH)2, thereby improving the adsorption of CO2. CO2 can form CO with the deposited carbon on the catalyst surface, thereby promoting the removal of carbon deposits and reducing the deactivation of the catalyst caused by carbon deposits. The two circulation pathways improve the catalyst's ability to adsorb CO2 and eliminate carbon deposits, improve the industrial applicability of biogas reforming, meet its industrial production requirements, and have broad development and application scenarios.

[0013] The present invention adopts low-priced non-precious metal Ni as an active component, which reduces the production cost of the catalyst compared to the use of precious metals, and adopts easily available Al2O3 as a carrier, which reduces the difficulty of obtaining raw materials for industrial production of catalysts. The preparation method of the present invention is simple and convenient for industrial production of catalysts.

[0014] Specifically, the molar ratio of the soluble cerium salt to the soluble calcium salt is (1-2): (1-2).

[0015] The present invention adjusts the contents of CeO2 and CaO in the CeCaO3 solid solution by controlling the molar ratio of the soluble cerium salt and the soluble calcium salt.

[0016] Specifically, the complexing agent is at least two of crown ether, ethylene glycol, cyclodextrin, and polyvinyl pyrrolidone.

[0017] Specifically, the molar ratio of the complexing agent to all metal ions is (0.05-1):1; all metal ions include nickel ions in soluble nickel salts, cerium ions in soluble cerium salts and calcium ions in soluble calcium salts.

[0018] Preferably, the complexing agent is crown ether and ethylene glycol.

[0019] More preferably, the molar ratio of the crown ether to the ethylene glycol is 1:1.

[0020] Crown ether is a macromolecular cyclic compound. The oxygen atom on the ring carries a lone pair of electrons and has a strong coordination effect. The ring structure of crown ether can embed metal cations into it. This structure is conducive to the interaction between metal ions and crown ether molecules, making the formed complex highly stable. Ethylene glycol, as a liquid complexing agent, can effectively promote the interaction between carrier additives and active components, enhance the interaction force, and further improve the stability of the complex.

[0021] Specifically, the alkaline precipitant is at least one of sodium carbonate, ammonium bicarbonate, ammonium carbonate, sodium hydroxide, and ammonia water.

[0022] Specifically, the molar ratio of the alkaline precipitant to all metal ions is (1-3):1.

[0023] Preferably, the alkaline precipitant is ammonium carbonate.

[0024] Specifically, the soluble nickel salt is at least one of nickel acetate, nickel nitrate and nickel chloride.

[0025] Specifically, the soluble cerium salt is at least one of cerium acetate, cerium nitrate and cerium chloride.

[0026] Specifically, the soluble calcium salt is at least one of calcium acetate, calcium nitrate and calcium bicarbonate.

[0027] Specifically, the aluminum source is at least one of aluminum nitrate, aluminum acetate, aluminum oxide, and pseudo-boehmite.

[0028] Specifically, the molar ratio of the soluble nickel salt to the aluminum source (ie, Ni / Al) is (0.5-1.5):(2-4).

[0029] More specifically, the mixing time after adding the complexing agent is 15 to 45 minutes.

[0030] More specifically, the mixing and heating time after adding the alkaline precipitant is 9 to 27 hours.

[0031] More specifically, the temperature of the mixing and heating after adding the alkaline precipitant is 55-75°C.

[0032] It should be noted that after mixing and heating, a slurry is obtained, which needs to be separated, washed and dried to obtain the first precursor.

[0033] More specifically, the calcination temperature is 500-600°C.

[0034] More specifically, the calcination time is 3 to 5 hours.

[0035] The heating rate of the calcination is 1-5°C / min.

[0036] It should be further explained that the reduction is mainly to reduce nickel oxide to nickel element.

[0037] More specifically, the reduction temperature is 500-700°C.

[0038] More specifically, the reduction time is 1 to 3 hours.

[0039] More specifically, the reducing gas is a gas containing hydrogen.

[0040] More specifically, the reducing gas is at least one of hydrogen, a hydrogen-nitrogen mixture, a hydrogen-argon mixture or a hydrogen-helium mixture.

[0041] The present invention also protects the use of the Ni-CeCaO3 / Al2O3 catalyst in catalyzing biogas to prepare synthesis gas.

[0042] Specifically, the biogas contains VOCs.

[0043] More specifically, the VOCs are at least one of ethyl acetate, cyclohexane and propylene.

[0044] Specifically, the temperature for preparing the synthesis gas is 650-800°C.

[0045] Specifically, the raw materials for preparing the synthesis gas include CH4 (biogas), CO2, and H2O.

[0046] More specifically, the biogas is biogas obtained by fermenting urban kitchen waste raw materials.

[0047] More specifically, the volume ratio of CH4, CO2, and H2O is (2-4):(1-3):(0.5-1.5).

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The present invention uses Ni as an active component, which reduces the catalyst production cost compared to the use of precious metals.

[0050] (2) The present invention prepares the catalyst by a complexation-coprecipitation method, which is simple in preparation, improves the dispersibility of the active components, and inhibits the agglomeration of the active components under high-temperature sintering. By controlling the contents of CeO2 and CaO in the solid solution of the auxiliary agent CaCeO3, the catalyst activity and stability are optimized, the interaction between the auxiliary agent carrier and the active components is enhanced, and the loss of the active components is reduced.

[0051] (3) The present invention uses Al2O3 as a carrier, which has a large specific surface area, abundant active sites, and can provide effective dispersion of active components, thereby enhancing the activity and stability of the catalyst.

[0052] (4) The additive of the present invention adopts CaCeO3 oxide solid solution, through Ce 3+ With Ce 4+ The oxygen cycle between them and the CaO-CaOH-CaCO3 cycle enhance the catalyst's ability to adsorb CO2 and eliminate carbon deposits.

[0053] (5) The Ni-CeCaO3 / Al2O3 catalyst prepared by the present invention can still maintain good catalytic activity in the presence of VOCs. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The XRD spectra of Example 1 and Comparative Examples 1 to 3 are shown.

[0055] Figure 2 SEM images of Example 1 before (a) and after (b) the stability evaluation.

[0056] Figure 3 TEM images of Example 1 before (a) and after (b) the stability evaluation.

[0057] Figure 4 Graphs showing the stability evaluation of methane and carbon dioxide for Comparative Example 1(a), Comparative Example 2(b) and Example 1(c).

[0058] Figure 5 The graph shows the methane and carbon dioxide activity conversion rates of Example 1, Comparative Examples 1 and 2.

[0059] Figure 6This is a graph showing the active conversion rates of methane and carbon dioxide in Example 1 in the presence of 500 ppm ethyl acetate. DETAILED DESCRIPTION

[0060] The present invention is further described below in conjunction with examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are usually carried out according to conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets. Any non-substantial changes and substitutions made by those skilled in the art on the basis of the present invention belong to the scope of protection claimed by the present invention.

[0061] Example 1

[0062] A Ni-CeCaO3 / Al2O3 catalyst, the preparation method of which comprises the following steps:

[0063] S1.1 Add nickel acetate tetrahydrate, cerium acetate, calcium acetate and pseudo-boehmite into deionized water and stir; add 0.1381g crown ether (18-crown-6) and stir at room temperature for 30min, then add 0.0324g ethylene glycol and continue stirring for 30min; this is called A;

[0064] S1.2 Weigh 2.88 g of ammonium carbonate and dissolve it in 60 mL of deionized water, stirring to form solution B;

[0065] S1.3 Add solution B dropwise to solution A, and heat the resulting mixture at 65°C for 18 hours under vigorous stirring to obtain a white slurry; cool the white slurry to room temperature, filter, wash with a large amount of deionized water / ethanol aqueous solution, and dry in an oven at 110°C overnight to obtain a first precursor;

[0066] S2. The first precursor is placed in a muffle furnace and heated to 550°C at a heating rate of 2°C / min and calcined for 4 hours, and then reduced in a H2 / N2 mixed gas at 600°C for 2 hours with a H2 / N2 ratio of 1:9 to reduce nickel oxide to Ni to obtain Ni-CeCaO3 / Al2O3.

[0067] Embodiments 2 to 4

[0068] Examples 2 to 4 provide different Ni-CeCaO3 / Al2O3 catalysts, which differ from Example 1 in that the molar ratios of added cerium acetate and calcium acetate are different, and the rest are the same as Example 1.

[0069]

[0070]

[0071] Comparative Example 1

[0072] This comparative example provides a Ni-CaO / Al2O3 catalyst, the preparation method of which is the same as that of Example 1, except that there is no cerium acetate in the raw material, and the mass of calcium acetate is 2.259g. The obtained catalyst contains 10wt% Ni and 40wt% CaO.

[0073] Comparative Example 2

[0074] This comparative example provides a Ni-CeO2 / Al2O3 catalyst, the preparation method of which is the same as that of Example 1, except that there is no calcium acetate in the raw material, and the mass of cerium acetate is 1.476g. The Ni content of the obtained catalyst is 10wt%, and the CeO2 content is 40wt%.

[0075] Comparative Example 3

[0076] This comparative example provides a Ni / Al2O3 catalyst, the preparation method of which is the same as that of Example 1, except that there is no calcium acetate and cerium acetate in the raw materials, and the mass of pseudo-boehmite is 1.799g. The Ni content of the obtained catalyst is 10wt%, and the rest is Al2O3.

[0077] Comparative Example 4

[0078] This comparative example provides a Ru-CeCaO3 / Al2O3 catalyst, the preparation method of which is the same as that of Example 1, except that nickel acetate tetrahydrate is replaced by ruthenium trichloride trihydrate, the mass of which is 0.4455g. The obtained catalyst contains 10wt% of Ru, 26.9wt% of CeO2, and 13.1wt% of CaO.

[0079] Comparative Example 5

[0080] This comparative example provides a Pd-CeCaO3 / Al2O3 catalyst, the preparation method of which is the same as that of Example 1, except that nickel acetate tetrahydrate is replaced with platinum nitrate solution (the content of platinum nitrate in the solution is 15wt%), and the mass of the solution is 1.333g. The Pd content of the obtained catalyst is 10wt%, the CeO2 content is 26.9wt%, and the CaO content is 13.1wt%.

[0081] Comparative Example 6

[0082] This comparative example provides a Pt-CeCaO3 / Al2O3 catalyst, the preparation method of which is the same as that of Example 1, except that nickel acetate tetrahydrate is replaced with palladium nitrate solution (the content of palladium nitrate in the solution is 15wt%), and the mass of the solution is 1.333g. The obtained catalyst contains 10wt% of Pt, 26.9wt% of CeO2, and 13.1wt% of CaO.

[0083] Comparative Example 7

[0084] This comparative example provides a Rh-CeCaO3 / Al2O3 catalyst, the preparation method of which is the same as that of Example 1, except that nickel acetate tetrahydrate is replaced with rhodium nitrate solution (the content of rhodium nitrate in the solution is 35wt%), and the mass of the solution is 0.57g. The obtained catalyst contains 10wt% Ph, 26.9wt% CeO2, and 13.1wt% CaO.

[0085] Test Method

[0086] 200 mg of catalyst was loaded into a quartz tube with an outer diameter of 14 mm and an inner diameter of 10 mm, and the reaction gas and internal standard gas (nitrogen) were introduced for reaction at 650°C, 700°C, 750°C, and 800°C for 2 h, respectively, and the experimental results were recorded by gas chromatography. The reaction gas included: methane (36 ml / min), carbon dioxide (24 ml / min), nitrogen (12 ml / min), and water vapor (32 ml / min). The volume ratio of CH4, CO2, and H2O was 3:2:1, and the space velocity was 31300 mL·g Cat -1 h -1 .

[0087] Figure 1 The XRD spectra of Example 1 and Comparative Examples 1 to 3 are shown in FIG. As can be seen from the figure, the characteristic peaks of Example 1 and Comparative Examples 1 and 2 are the same, which indicates that Ce and Ca form a solid solution during the reaction.

[0088] Table 1

[0089] Sample name Example 1 Comparative Example 1 Comparative Example 2 <![CDATA[S BET (m 2 / g)]]> 202.5 103.7 115.5 <![CDATA[V tot (cm 2 / g)]]> 4.04 2.34 2.55 dr(nm) 7.18 15.52 14.28 Active ingredient mass fraction % (mg / Kg) 10 10 10

[0090] Table 1 shows the BET data and dispersibility data of Example 1 and Comparative Examples 1 and 2. It can be seen from Table 1 that the formation of CaCe solid solution increases the specific surface area (S BET ) and total pore volume (V tot ). dr is the diameter of the active component. The diameter of the active component in Example 1 is smaller than that in Comparative Examples 1 and 2, indicating that the solid solution enhances the intermolecular force between the active component and the carrier, so that the active component does not agglomerate at high temperature, thereby maintaining good dispersibility. Secondly, the addition of the complexing agent during the preparation process further promotes the dispersion of the active component. The mass fractions of the active components contained in Example 1 and Comparative Examples 1 and 2 are basically the same, ensuring the consistency of the variables.

[0091] Table 2

[0092]

[0093]

[0094] Table 2 shows the activity evaluation data of Example 1 and Comparative Examples 4 to 7 at 800°C. It can be seen from Table 2 that the Ni-CeCaO3 / Al2O3 catalyst prepared by the present invention has a catalytic activity similar to that of a noble metal catalyst, and the carbon dioxide conversion rate of Example 1 is slightly higher than that of other noble metal catalysts. Therefore, the preparation method of the present invention is simple, the raw materials are cheap and readily available, the production cost is greatly reduced, and it has a good commercial application prospect. The catalytic activity of Examples 2 to 4 is equivalent to that of Example 1.

[0095] Figure 2 and Figure 3 The SEM and TEM images are respectively before (a) and after (b) the stability evaluation of Example 1. As can be seen from the figure, after 200 hours of catalytic reaction, the structure of the catalyst has not changed much, indicating that the Ni-CeCaO3 / Al2O3 catalyst prepared by the present invention has good structural stability. And no crystalline carbon deposition is found in the SEM spectrum of the catalyst after the reaction, indicating that the Ni-CeCaO3 / Al2O3 catalyst prepared by the present invention has good anti-carbon deposition and anti-sintering properties.

[0096] Figure 4 The stability evaluation graphs of methane and carbon dioxide for Comparative Example 1 (a), Comparative Example 2 (b) and Example 1 (c) show that, compared with Example 1, the conversion rates of methane and carbon dioxide for Comparative Example 1 and 2 samples show a slow downward trend at 100 hours, and the stability is reduced, while Example 1 maintains the original activity and stability, and there is no activity decline trend during the evaluation time of 200 hours.

[0097] Figure 5 The graph is a graph of the methane and carbon dioxide activity conversion rates of Example 1, Comparative Examples 1 and 2. As can be seen from the graph, compared with Comparative Examples 1 and 2, Example 1 exhibits better biogas catalytic activity in the range of 650°C to 800°C.

[0098] Figure 6 The figure is a graph of the methane and carbon dioxide activity conversion rate in the presence of 500 ppm ethyl acetate of Example 1. As can be seen from the figure, under the interference of 500 ppm ethyl acetate, Example 1 can still maintain good biogas catalytic activity in biogas reforming.

[0099] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A Ni-CeCaO3 / Al2O3 catalyst for converting biogas into synthesis gas, characterized in that: The preparation method comprises the following steps: S1. The soluble nickel salt, the soluble cerium salt, the soluble calcium salt and the aluminum source are mixed in water, the complexing agent is added and mixed, and then the alkaline precipitant is added and heated under mixing to obtain a first precursor; S2. The first precursor is calcined and then reduced to obtain the Ni-CeCaO3 / Al2O3 catalyst; The catalyst contains 7-12 wt% Ni, 24-35 wt% CeO2, 5-16 wt% CaO, CeO2 and CaO form a solid solution, and the rest is Al2O3.

2. The catalyst according to claim 1, characterized in that The molar ratio of Ce to Ca in the CeCaO3 is (1-2): (1-2).

3. The catalyst according to claim 1, characterized in that The complexing agent is at least two of crown ether, ethylene glycol, cyclodextrin and polyvinyl pyrrolidone.

4. The catalyst according to claim 1, characterized in that The alkaline precipitant is at least one of sodium carbonate, ammonium bicarbonate, ammonium carbonate, sodium hydroxide and ammonia water.

5. The catalyst according to claim 1, characterized in that The soluble nickel salt is at least one of nickel acetate, nickel nitrate and nickel chloride.

6. The catalyst according to claim 1, characterized in that The soluble cerium salt is at least one of cerium acetate, cerium nitrate and cerium chloride.

7. The catalyst according to claim 1, characterized in that The soluble calcium salt is at least one of calcium acetate, calcium nitrate and calcium bicarbonate.

8. Use of the Ni-CeCaO3 / Al2O3 catalyst as claimed in any one of claims 1 to 7 in catalyzing biogas to produce synthesis gas.

9. The use according to claim 8, characterized in that: The biogas contains VOCs.

10. The use according to claim 9, characterized in that: The VOCs are at least one of ethyl acetate, cyclohexane and propylene.

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