A cascaded bifunctional catalyst, its preparation method and its application in the high-value-added catalytic conversion of CO2.

Abstract

The application discloses a kind of cascade bifunctional catalyst, its preparation method and its application in CO2 high value-added catalytic conversion, belong to chemical catalysis technical field.The cascade bifunctional catalyst is composed of sodium iron cobalt catalyst and potassium copper zinc aluminum catalyst and molecular sieve, and the catalyst can realize high selectivity of carbon dioxide (CO2) hydrogenation by ethanol coupling olefin conversion route Preparation of aromatic hydrocarbon.The new reaction path proposed by the cascade bifunctional catalyst constructed by the application can effectively regulate the front reaction product distribution, significantly optimize the mass transfer and heat transfer performance of catalyst, and then improve the selectivity and reaction efficiency of target product.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalysis technology, specifically relating to a cascaded bifunctional catalyst, its preparation method, and its application in the high-value-added catalytic conversion of CO2. Background Technology

[0002] The widespread use of fossil fuels such as coal, oil, and natural gas has driven the rapid development of human society, but it has also been accompanied by a sharp increase in CO2 emissions. This has directly led to a series of ecological and environmental problems such as global warming and rising sea levels, seriously threatening human survival and development. The efficient conversion of CO2 into value-added chemicals not only helps reduce the concentration of greenhouse gases in the atmosphere and alleviate climate change, but also provides a promising strategic approach for the production of high-value-added chemicals. Among many high-value-added chemicals, aromatics, as a cornerstone of modern industry, are of paramount strategic importance. Aromatics, represented by benzene, toluene, and xylene, account for more than 30% of global petrochemical products. Traditionally, 90% of aromatics are produced from naphtha catalytic reforming / steam cracking, with each ton of aromatics production emitting 4.2 tons of CO2; while the biomass route is limited by feedstock supply (requiring 8 tons of corn to produce 1 ton of aromatics), making large-scale production difficult. The one-step preparation of aromatics via CO2 hydrogenation can achieve high carbon utilization, significantly reduce the carbon footprint throughout the entire life cycle, alleviate energy security and resource shortages, and form a resource closed loop. It is one of the key technological directions for addressing climate change and promoting green chemistry.

[0003] Traditional catalytic reactions for the hydrogenation of CO2 to aromatics mainly focus on two differentiated reaction pathways: the methanol-mediated route (CO2 → methanol → aromatics) and the olefin-mediated route (CO2 → olefins → aromatics). Both pathways involve constructing bifunctional catalysts to further dehydrogenate and condense methanol or olefin intermediates within the porous structure of HZSM-5 molecular sieves to produce aromatics. The methanol route can achieve aromatics selectivity of over 60%, but its CO2 single-pass conversion is typically below 20%, accompanied by 30%–40% CO byproduct generation, significantly limiting the space-time yield of aromatics. Furthermore, the methanol aromatization process requires prior CC coupling within the molecular sieve, which has a high kinetic barrier (approximately 1.5 eV), further reducing the aromatics synthesis rate. In contrast, the olefin route exhibits a high CO2 conversion of up to 50% and a CO selectivity of less than 10%, demonstrating significant potential for scale-up in terms of aromatics synthesis efficiency. However, due to the competitive olefin hydrogenolysis side reaction, its aromatic selectivity is generally less than 40%, which has become the core bottleneck restricting the industrial application of this technology.

[0004] Therefore, it is necessary to seek a new reaction route that can simultaneously achieve high aromatic selectivity, high CO2 conversion rate, and low CO selectivity. Summary of the Invention

[0005] This invention proposes a novel reaction pathway for the hydrogenation of CO2 to aromatics by constructing a cascaded bifunctional catalyst, aiming to solve the problem of the inability to simultaneously achieve high aromatic selectivity, high CO2 conversion, and low CO selectivity in current reaction pathways. The constructed cascaded bifunctional catalyst can effectively regulate the product distribution of the upstream reaction, significantly improving aromatic selectivity, while simultaneously achieving high CO2 conversion and low CO selectivity, thus significantly enhancing reaction efficiency.

[0006] This invention provides a cascaded bifunctional catalyst, which is composed of the following components in parts by mass: 1-10 parts of sodium iron cobalt catalyst, 1-10 parts of potassium copper zinc aluminum catalyst, and 10-30 parts of molecular sieve.

[0007] In one specific embodiment, the cascaded bifunctional catalyst is composed of the following components in parts by mass: 6 parts sodium iron cobalt catalyst, 6 parts potassium copper zinc aluminum catalyst, and 20 parts molecular sieve.

[0008] In this invention, the sodium-iron-cobalt catalyst is prepared by the following method: Ferric nitrate nonahydrate, cobalt nitrate hexahydrate, and urea were dissolved in water and stirred at 80-90°C for 1-3 hours. Then, the mixture was aged at 80-90°C for 10-20 hours. After centrifugation, the reddish-brown product was collected and calcined at 300-400°C for 2-6 hours to obtain an iron-cobalt bimetallic catalyst. The catalyst was then impregnated with a sodium salt solution and dried to obtain a sodium-iron-cobalt catalyst.

[0009] In the above preparation method of sodium iron cobalt catalyst, the raw materials are selected from the following parts by mass: 10-15 parts of ferric nitrate nonahydrate, 1-5 parts of cobalt nitrate hexahydrate, 20-50 parts of urea, and 200-500 parts of water.

[0010] In the above method for preparing sodium-iron-cobalt catalyst, the sodium salt solution is a sodium carbonate solution with a concentration of 0.3~0.8 mol / L.

[0011] In this invention, the potassium-copper-zinc-aluminum catalyst is prepared by the following method. Copper nitrate trihydrate, zinc nitrate hexahydrate, aluminum nitrate nonahydrate, and urea were dissolved in water and stirred at 90-100°C for 1-3 hours. The mixture was then aged at 90-100°C for 15-30 hours. After centrifugation, the dark gray product was collected and calcined at 300-400°C for 2-6 hours to obtain a copper-zinc-aluminum catalyst. This catalyst was then impregnated with a potassium salt solution, and after impregnation, dried to obtain a potassium-copper-zinc-aluminum catalyst.

[0012] In the above preparation method of potassium copper zinc aluminum catalyst, the raw materials are selected from the following parts by mass: 20-50 parts of copper nitrate trihydrate, 10-30 parts of zinc nitrate hexahydrate, 5-20 parts of aluminum nitrate nonahydrate, 40-100 parts of urea, and 500-1000 parts of water.

[0013] In the above method for preparing potassium-copper-zinc-aluminum catalysts, the potassium salt solution is a potassium nitrate solution with a concentration of 0.2~0.6 mol / L.

[0014] In this invention, the molecular sieve is HZSM-5 molecular sieve; the HZSM-5 molecular sieve is prepared by the following method: Sodium aluminate, tetrapropylammonium bromide, and n-butylamine were dissolved in water, and then silica sol was slowly added dropwise while stirring until homogeneous. The mixture was then subjected to a hydrothermal reaction at 150-200℃ for 36-72 hours. After cooling to room temperature, the emulsion was washed and dried to obtain the HZSM-5 precursor. The HZSM-5 precursor was ground into powder and calcined at 500-600℃ for 5-10 hours to obtain the twinned HZSM-5 molecular sieve.

[0015] In the above preparation method of HZSM-5 molecular sieve, the raw materials are selected from the following parts by mass: sodium aluminate 0.3~0.6 parts, tetrapropylammonium bromide 1~2 parts, n-butylamine 2~5 parts, water 80~100 parts, and silica sol 15~30 parts.

[0016] This invention provides a method for preparing the above-mentioned cascaded bifunctional catalyst, the steps of which are as follows: Sodium iron cobalt catalyst was mixed with potassium copper zinc aluminum catalyst and granulated; then mixed with HZSM-5 molecular sieve particles to obtain a cascaded bifunctional catalyst.

[0017] This invention provides the application of the above-mentioned cascaded bifunctional catalyst in the high-value-added catalytic conversion of CO2; preferably, the application is the catalytic hydrogenation of CO2 to produce aromatics.

[0018] This invention provides a method for preparing aromatics by CO2 hydrogenation, comprising the following steps: The cascaded bifunctional catalyst was placed in a fixed-bed reactor and activated in a pure H2 atmosphere at 400℃ for 1-4 h. After cooling to room temperature, a mixture of reaction gases was added to carry out the reaction and obtain aromatics.

[0019] In the above method for preparing aromatics by CO2 hydrogenation, the reaction gas mixture is composed of CO2, H2 and an inert gas; the inert gas is preferably argon; the volume ratio of CO2 to H2 is preferably 1:3, and the volume content of argon is preferably 3.9%.

[0020] In the above method for preparing aromatics by CO2 hydrogenation, the reaction conditions are as follows: reaction temperature is 260~360℃, reaction pressure is 2~10MPa, flow rate is 5~100 mL / min, corresponding space velocity is 1500~30000 mL / g / h, and reaction time is 12~48 h.

[0021] The beneficial effects of this invention are as follows: This invention presents a cascaded bifunctional catalyst composed of sodium-iron-cobalt catalyst, potassium-copper-zinc-aluminum catalyst, and a molecular sieve. This catalyst enables highly selective hydrogenation of carbon dioxide (CO2) to aromatics via an ethanol-coupled olefin conversion pathway. The novel reaction pathway proposed by this invention through the constructed cascaded bifunctional catalyst effectively regulates the distribution of upstream reaction products, significantly optimizes the mass and heat transfer performance of the catalyst, and thus improves the selectivity and reaction efficiency of the target product. Detailed Implementation

[0022] Besides olefins and methanol, ethanol can also serve as a precursor for aromatization, generating aromatics within the porous structure of HZSM-5. Furthermore, the water molecules resulting from ethanol dehydration can promote the deprotonation of cyclopentene cations and optimize the mass and heat transfer processes during olefin aromatization, thereby improving the selectivity of aromatic products in the catalytic process. In addition, compared to the methanol route, ethanol dehydration directly generates ethylene, eliminating the need for the energy-intensive CC coupling step, which significantly improves the efficiency of aromatic synthesis. Therefore, ethanol-coupled ethylene co-aromatization holds promise for addressing the insufficient aromatic selectivity of the olefin route. Thus, this invention attempts to construct a novel reaction route mediated by ethanol that simultaneously achieves high aromatic selectivity, high CO2 conversion, and low CO selectivity.

[0023] The steps for preparing the sodium-iron-cobalt catalyst are as follows: 12.12 g of ferric nitrate nonahydrate, 2.91 g of cobalt nitrate hexahydrate, and 33.03 g of urea were dissolved in 330 mL of deionized water to form a homogeneous solution. This solution was placed in an oil bath and heated to 85 °C with stirring for 2 h. Subsequently, it was aged at 85 °C for 12 h. The reddish-brown product was separated and collected by centrifugation, washed four times with deionized water, and then dried overnight in a 70 °C oven. Next, the reddish-brown product was calcined at 350 °C for 4 h in air at a heating rate of 5 °C / min to obtain an iron-cobalt bimetallic catalyst. The catalyst was then impregnated with a sodium carbonate solution (0.63 mol / L) for 3% sodium impregnation, followed by drying overnight in a 70 °C oven to obtain a sodium-iron-cobalt catalyst, named NaFeCo.

[0024] The steps for preparing potassium-copper-zinc-aluminum catalysts are as follows: 26.81 g of copper nitrate trihydrate, 13.38 g of zinc nitrate hexahydrate, 11.25 g of aluminum nitrate nonahydrate, and 48.29 g of urea were dissolved in 750 mL of deionized water to form a homogeneous solution. This solution was placed in an oil bath and heated to 95 °C with stirring for 2 h. Subsequently, it was subjected to a sedimentation aging treatment at 95 °C for 24 h. The blackish-gray product was separated and collected by centrifugation, washed four times with deionized water, and then dried overnight in an oven at 70 °C. Next, the blackish-gray product was calcined at 350 °C for 3 h under air atmosphere at a heating rate of 5 °C / min to obtain a copper-zinc-aluminum catalyst. The catalyst was then impregnated with a potassium nitrate solution (0.40 mol / L) for a 5% potassium impregnation treatment, followed by drying overnight in an oven at 70 °C to obtain a potassium-copper-zinc-aluminum catalyst, named KCZA.

[0025] The steps for preparing ZSM-5 molecular sieves are as follows: 91.50 g of deionized water was added to a 200 mL polytetrafluoroethylene (PTFE) bottle. Then, while stirring, 0.48 g of sodium aluminate, 1.83 g of tetrapropylammonium bromide, and 3.92 g of n-butylamine were added, and the mixture was magnetically stirred for 15 min to ensure complete dissolution. Next, 22.53 g of silica sol was slowly added dropwise, and stirring was continued for 30 min. The resulting solution was evenly poured into two stainless steel reactors lined with PTFE. After being tightly sealed to ensure no leakage, the reactors were transferred to a rotary drying oven and fixed on a rotating support. The temperature was increased to 180 °C at a rate of 10 °C / min, controlled at 5.6 rpm, and maintained for 48 h. After the hydrothermal treatment ended and the reactor temperature naturally cooled to room temperature, the resulting emulsion was washed three times with deionized water by centrifugation and then dried overnight in a 60 °C rotary drying oven to obtain the HZSM-5 precursor. The HZSM-5 precursor was appropriately ground in an agate mortar and heated to 550 °C in an air atmosphere in a muffle furnace at a heating rate of 5 °C / min, held for 6 h, and calcined to remove the organic template agent, thus obtaining the twinned HZSM-5 molecular sieve.

[0026] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way.

[0027] Example 1 The steps for preparing a cascaded bifunctional catalyst are as follows: 0.6 g of NaFeCo powder and 0.6 g of KCZA powder were mixed evenly, poured into a mold, and pressed into shape using a tablet press at 10 MPa. After removal, the mixture was crushed and sieved using a stainless steel sieve to obtain NaFeCo & KCZA catalyst particles in the range of 20-40 mesh. Next, 2 g of HZSM-5 molecular sieve powder was poured into a mold, pressed into shape using a tablet press at 20 MPa, and then crushed and sieved using a stainless steel sieve to obtain HZSM-5 molecular sieve particles in the range of 20-40 mesh. The NaFeCo & KCZA catalyst particles and HZSM-5 molecular sieve particles were then mixed evenly to obtain a cascaded bifunctional catalyst.

[0028] I. Catalytic Conversion of CO2 The catalyst was mixed evenly with 1 g of quartz sand particles and packed into a fixed-bed reactor (reaction tube inner diameter 8 mm). 2.0 g of quartz sand was added to the top of the catalyst bed to promote fluid agitation, and quartz wool was appropriately filled at the top and bottom of the reactor to seal and support the catalyst bed and prevent catalyst particles from falling off. The catalyst was first pretreated by reduction in an H2 atmosphere at 400 °C for 4 h. The catalyst was then placed in the reaction tube, and a mixed gas (containing 3.9% Ar, 24.3% CO2, and 71.8% H2) was introduced at a flow rate of 10 mL / min. The reaction was carried out at 320 °C and 3.0 MPa for 24 h. The products were analyzed by gas chromatography, and the reaction results are shown in Table 1.

[0029] Table 1 Reaction performance of CO2 hydrogenation to aromatics Note: Reduction conditions were 400 ℃, H2 reduction for 4 h. Reaction conditions were 320 ℃, space velocity 3000 mL / g / h, H2 / CO2 = 3, TOS = 24 h. C2 = -C4 = This refers to olefin products ranging from C2 to C4, where C2... o -C4 o This refers to C2-C4 alkane products, C 5+ α C represents non-aromatic hydrocarbons 5+ The product, Oxy, indicates oxygen-containing compounds, Aro. indicates aromatic products, and BTX in Aro. indicates the proportion of light aromatics in the total aromatics.

[0030] Table 1 shows that the NaFeCo single catalytic system performed poorly in terms of CO2 conversion (30.1%) and product selectivity, with CO and low-carbon olefin selectivities of 15.7% and 24.3%, respectively. When constructing the NaFeCo-HZSM-5 bifunctional catalyst (olefin route), although the CO selectivity decreased slightly to 13.8%, the CO2 conversion (29.8%) and aromatics selectivity (23.8%) remained at low levels. In contrast, the NaFeCo&KCZA cascade catalytic system exhibited significantly improved catalytic performance, with CO2 conversion increasing to 48.4% and CO selectivity decreasing to 6.7%, particularly achieving a breakthrough in ethanol selectivity at 26.6%. By designing the NaFeCo&KCZA-HZSM-5 cascade bifunctional catalyst (ethanol-olefin coupling route), the catalytic system achieved synergistic optimization, obtaining a CO2 conversion of 55.4%, while significantly increasing aromatics selectivity to 51.5% and controlling CO selectivity to a minimum level (3.4%). Experimental results show that a reasonable catalyst cascade design can effectively optimize the reaction pathway and significantly improve the selectivity and synthesis efficiency of aromatic products.

[0031] The ethanol selectivity becomes very low after coupling with HZSM-5 because HZSM-5 converts almost all ethanol and olefins into aromatic compounds. The role of the molecular sieve component is aromatization; coupling with the molecular sieve enables the target product to be converted from ethanol / olefins to aromatics with high selectivity (i.e., the mentioned ethanol-olefin coupled aromatization route). General catalysts (such as NaFeCo) have low ethanol selectivity, and consequently, low aromatic selectivity after coupling with the molecular sieve. This demonstrates that the ethanol-olefin coupled aromatization route has a higher aromatic production capacity.

[0032] In short, without molecular sieve coupling, NaFeCo&KCZA can efficiently generate ethanol and alkenes. After coupling with molecular sieve, it can efficiently generate aromatics through an ethanol-alkene coupled aromatization route.

[0033] In summary, the cascaded bifunctional catalyst prepared in this invention has a first functional component of sodium iron cobalt potassium copper zinc aluminum catalyst, which can efficiently convert CO2 into olefins and ethanol intermediates via reverse water-gas shift reaction and Fischer-Tropsch synthesis reaction; and a second functional component of HZSM-5 molecular sieve, which can further convert the generated olefins and ethanol intermediates into aromatic components.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A cascaded bifunctional catalyst, characterized in that, Composed of the following ingredients in parts by mass Composition: 1-10 parts sodium iron cobalt catalyst, 1-10 parts potassium copper zinc aluminum catalyst, 10-30 parts HZSM-5 molecular sieve; The potassium-copper-zinc-aluminum catalyst is prepared by the following method: Copper nitrate trihydrate, zinc nitrate hexahydrate, aluminum nitrate nonahydrate, and urea were dissolved in water and stirred at 90-100℃ for 1-3 hours. Then, the mixture was aged at 90-100℃ for 15-30 hours. After centrifugation, the blackish-gray product was collected and calcined at 300-400℃ for 2-6 hours to obtain a copper-zinc-aluminum catalyst. The catalyst was then impregnated with a potassium salt solution and dried to obtain a potassium-copper-zinc-aluminum catalyst. The sodium-iron-cobalt catalyst is prepared by the following method: Ferric nitrate nonahydrate, cobalt nitrate hexahydrate, and urea were dissolved in water and stirred at 80-90°C for 1-3 hours. Then, the mixture was aged at 80-90°C for 10-20 hours. After centrifugation, the reddish-brown product was collected and calcined at 300-400°C for 2-6 hours to obtain an iron-cobalt bimetallic catalyst. The catalyst was then impregnated with a sodium salt solution and dried to obtain a sodium-iron-cobalt catalyst.

2. The cascaded bifunctional catalyst according to claim 1, characterized in that, In the preparation method of the potassium copper zinc aluminum catalyst, the raw materials are selected from the following parts by mass: 20-50 parts of copper nitrate trihydrate, 10-30 parts of zinc nitrate hexahydrate, 5-20 parts of aluminum nitrate nonahydrate, 40-100 parts of urea, and 500-1000 parts of water.

3. The cascaded bifunctional catalyst according to claim 1, characterized in that, In the preparation method of the sodium-iron-cobalt catalyst, the raw materials are selected from the following parts by mass: 10-15 parts of ferric nitrate nonahydrate, 1-5 parts of cobalt nitrate hexahydrate, 20-50 parts of urea, and 200-500 parts of water.

4. The cascaded bifunctional catalyst according to claim 1, characterized in that, The HZSM-5 molecular sieve is prepared by the following method: Sodium aluminate, tetrapropylammonium bromide, and n-butylamine were dissolved in water, and then silica sol was slowly added dropwise while stirring until homogeneous. The mixture was then subjected to a hydrothermal reaction at 150-200℃ for 36-72 hours. After cooling to room temperature, the emulsion was washed and dried to obtain the HZSM-5 precursor. The HZSM-5 precursor was ground into powder and calcined at 500-600℃ for 5-10 hours to obtain the twinned HZSM-5 molecular sieve.

5. The cascaded bifunctional catalyst according to claim 4, characterized in that, The raw materials are selected from the following parts by weight: sodium aluminate 0.3~0.6 parts, tetrapropylammonium bromide 1~2 parts, n-butylamine 2~5 parts, water 80~100 parts, and silica sol 15~30 parts.

6. The method for preparing the cascaded bifunctional catalyst according to claim 1, characterized in that, The steps are as follows: Sodium iron cobalt catalyst was mixed with potassium copper zinc aluminum catalyst and granulated; then mixed with HZSM-5 molecular sieve particles to obtain a cascaded bifunctional catalyst.

7. The application of the cascaded bifunctional catalyst of claim 1 in the high-value-added catalytic conversion of CO2.

8. A method for preparing aromatics by CO2 hydrogenation, characterized in that, The steps are as follows: The cascaded bifunctional catalyst described in claim 1 is placed in a fixed-bed reactor, activated at 400°C in a pure H2 atmosphere for 1-4 hours, cooled to room temperature, and then a reaction gas mixture is added to carry out the reaction to obtain aromatics.

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