Catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalysts, in particular to a catalyst and a preparation method and application thereof. The catalyst comprises an active component, an auxiliary agent and a carrier, the active component comprises a first active component and a second active component, the first active component is Pt, and the second active component is Cr; the carrier comprises more than 70 wt% of MgO and the balance of heterogeneous oxide; the heterogeneous oxide is selected from at least two of CeO2, TiO2, In2O3, Bi2O3, WO3 and MnO2; the auxiliary agent comprises at least one of La, Ga, Nd and Si. According to the catalyst disclosed by the invention, the initial conversion rate of methyl cyclohexane dehydrogenation is obviously improved by improving the dispersibility of active components; the sintering resistance and the carbon deposition resistance of the catalyst are remarkably improved by enhancing the interaction among the active components, the interaction between the active components and the carrier and the alkalinity of the carrier, so that the dehydrogenation reaction stability of methylcyclohexane is improved.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, in particular to a catalyst and a preparation method and application thereof. Background Art

[0002] Hydrogen is an ideal clean energy fuel that can replace traditional hydrocarbon feedstocks. Because its gravimetric energy density of 141.6 MJ / kg is three times that of gasoline, while producing only water as a byproduct, it is widely used in polymer electrolyte membrane fuel cells (PEMFCs). Challenges facing these applications relate to efficient hydrogen storage. Currently, most technologies rely on compression and liquefaction, which introduce safety concerns, low storage density, and high transportation, evaporation losses, and other cost issues. Liquid organic hydrogen carriers (LOHCs) represent a promising approach for storing hydrogen within chemical bonds, potentially addressing many of the limitations of current technologies. Reversible LOHC systems typically consist of hydrogen-poor and hydrogen-rich organic compounds and store hydrogen through hydrogenation and dehydrogenation processes, showing great potential for mobile applications. Cycloalkanes and aromatic hydrocarbons containing one or more six-membered rings are promising reversible LOHC systems. These stable compounds have high storage capacities (6 wt%–7 wt%) and can be dehydrogenated / hydrogenated under relatively mild conditions. The hydrogenation process is relatively mature, while the dehydrogenation process is mostly performed using supported Pt nanoparticle catalysts. Chiyoda Corporation has developed a methylcyclohexane (MCH) / toluene dehydrogenation / hydrogenation LOHC system based on a sulfided Pt nanoparticle catalyst (S-Pt / Al2O3), demonstrating its feasibility and advantages in hydrogen storage and transportation (CN116171197 A, International Journal of Hydrogen Energy 31 (2006) 1348–1356). However, the high cost and low natural abundance of Pt have limited its further application. Preparing highly dispersed and stable Pt catalysts is an effective method to improve Pt atomic efficiency and reduce investment costs.

[0003] CN 113070058 B discloses a composite-supported single-atom catalyst for dehydrogenation of organic hydrogen storage media and its preparation method. The composite support is composed of Al2O3 and one or two of ZrO2, MgO, and TiO2. The prepared Pt-based composite oxide catalyst has a Pt content exceeding 1.0 wt%. CN 117943079 A discloses a method for preparing a platinum / spherical cerium dioxide catalyst for dehydrogenation of methylcyclohexane. The three-dimensional Pt / CeO2 dehydrogenation catalyst is prepared by utilizing the large specific surface area of ​​spherical CeO2 to promote Pt dispersion. After 72 hours of catalytic reaction, the hydrogen overflow concentration is reduced by 3.2%. CN 106622228 B discloses a method for preparing a catalyst using Ce-Mg-Al or Zr-Mg-Al hydrotalcite impregnated with active components such as Pt, Pd, or Ru. The hydrotalcite structure promotes the dispersion of Pt on the carrier, resulting in excellent catalytic activity and hydrogen production rates under relatively mild reaction conditions, but the precious metal content is 0.5-2.0%. CN111686718B discloses a cyclohexane dehydrogenation catalyst and its preparation method. The Pt / γ-Al2O3 dehydrogenation catalyst is prepared through amine complexation, improving dehydrogenation activity, but the precious metal content is greater than 0.5%. CN114011431A discloses a long-life, low-platinum bimetallic catalyst for methylcyclohexane and its preparation method. The precious metal Pt content is 0.05-0.2%, and sulfur species are introduced into the carrier to stabilize the active components. CN115805073A discloses a dehydrogenation catalyst, a preparation method and application thereof, and a method for producing hydrogen by dehydrogenating methylcyclohexane. The base metal elements M are Fe, Co, Sn, In, Zn, Pb, Cu, Mn and Al to stabilize Pt, and the content of the precious metal Pt is 0.2-1.5%.

[0004] In summary, to improve the activity and stability of dehydrogenation catalysts, researchers have sought to improve the support type, increase the specific surface area to facilitate the dispersion of active components, increase the loading of precious metals, and introduce bimetallic stabilization of Pt. However, the methylcyclohexane dehydrogenation reaction is prone to carbon deposition as a side reaction, and at high temperatures, the active components of the catalyst tend to aggregate. Existing catalyst technologies have struggled to achieve a balance between low cost, stability, and activity. Therefore, a low-cost, efficient, and stable methylcyclohexane dehydrogenation catalyst is urgently needed. Summary of the Invention

[0005] The purpose of the present invention is to solve the defects of low cost, stability and activity of noble metal catalysts for methylcyclohexane dehydrogenation, so as to obtain a highly dispersed and stable Pt-based catalyst for methylcyclohexane dehydrogenation and a preparation method thereof, which can be applied to the field of methylcyclohexane hydrogen storage.

[0006] Based on this, the present invention has the following technical solutions: In a first aspect, the present invention provides a catalyst comprising an active component, a promoter and a carrier; The active component includes a first active component and a second active component, the first active component is Pt, and the second active component is Cr; The support comprises more than 70 wt% of MgO and the remainder is a heterogeneous oxide; The heterogeneous oxides are at least two of CeO2, TiO2, In2O3, Bi2O3, WO3, and MnO2; The auxiliary agent includes at least one of La, Ga, Nd and Si.

[0007] The present invention enhances the alkalinity and weakens the acidity of the surface of the carrier with MgO as the main component, thereby suppressing the carbon deposition side reaction during the dehydrogenation reaction of methylcyclohexane; prepares a heterogeneous oxide carrier by compounding a reducible oxide with the alkaline earth metal MgO, constructs a heterogeneous interface, and controls the ascorbic acid concentration and immersion time to adjust the defects on the carrier, thereby promoting the high dispersion of the Pt active component and improving the activity.

[0008] According to the catalyst provided by the present invention, the mass ratio of the first active component to the second active component is (0.1-0.3): (0.5-2.0).

[0009] By controlling the above-mentioned dosage relationship and introducing Cr and precious metal Pt for synergistic catalytic dehydrogenation, the interaction between active components and between active components and the support can be enhanced, further improving the catalyst's resistance to sintering and carbon deposition, thereby improving the stability of the methylcyclohexane dehydrogenation reaction.

[0010] According to the catalyst provided by the present invention, the catalyst includes the following components in the following amounts: The first active component is 0.1~0.3%; The second active component is 0.5~2.0%; Additives 3.0~7.0%; Carrier remainder.

[0011] According to the catalyst provided by the present invention, the specific surface area of ​​the catalyst is 25~50 m 2 / g, pore volume is 0.3~0.5mL / g, and pore diameter is 7~12 nm.

[0012] The dehydrogenation catalyst prepared by the present invention can have an outer shape of a five-pointed star with a circular arc, which can increase the surface area of ​​the catalyst and reduce the diffusion effect.

[0013] According to the catalyst provided by the present invention, the equivalent diameter of the arc-shaped five-pointed star is 4.5±0.1 mm and the height is 3±0.1 mm.

[0014] In a second aspect, the present invention provides a method for preparing the catalyst, comprising: S1: A heterogeneous oxide precursor, an auxiliary agent precursor, and magnesium nitrate are prepared into a mixed solution, the pH value of the mixed solution is adjusted to 8.8-10.2, and an aging treatment is performed at 75-98°C and 0.2-0.5 MPa. The product is filtered, washed, dried, and calcined at 500-650°C to obtain a heterogeneous oxide MgO-based support; S2: dispersing the heterogeneous oxide MgO-based carrier in a 5.0-15.0 mmol / L ascorbic acid aqueous solution, filtering, washing, drying, adding additives, and pressing to obtain a molded carrier; S3: The pH value of the Pt- and Cr-containing precursor salt solution is adjusted to 0.5-1.5, and after adding a complexing agent to fully dissolve it, it is evenly sprayed on the forming support, allowed to stand, and then dried at 100-130°C, and then calcined at 300-450°C, and then calcined in a reducing atmosphere at 300-400°C; preferably, the calcination adopts programmed temperature rise, and the heating rate is 5-10°C.

[0015] The present invention has found that when the calcination temperature in S3 exceeds the above range, the catalyst is fragile and has poor stability before the reaction.

[0016] Preferably, the reducing atmosphere is an N2 atmosphere with a hydrogen content of 3-7%.

[0017] Preferably, the preparation method of the catalyst comprises: S1: Prepare a mixed solution of a certain concentration of a heterogeneous oxide precursor, a nitrate as an additive precursor, and magnesium nitrate, titrate it with NaOH at 45-65 °C to a pH of 8.8-10.2, age it in an autoclave at 75-98 °C for 4-15 h, filter and wash it, dry it at 90-120 °C for 4-8 h, and calcine it in a muffle furnace at 500-650 °C for 2-5 h to obtain a heterogeneous oxide MgO-based support; S2: The heterogeneous oxide MgO-based support was dispersed in a 5.0-15.0 mmol / L ascorbic acid aqueous solution, vigorously stirred at room temperature for 3-5 minutes, filtered, washed, and vacuum-dried at 50-70°C overnight. An additive was added, and the support was pressed into a five-pointed star shape with a rounded arc to obtain a shaped support. S3: The precursor salt solution containing Pt and Cr is converted into an aqueous solution with a pH of 0.5~1.5. After adding a complexing agent to fully dissolve it, it is evenly sprayed on the stirring shaped support. After standing for 1~8 hours, it is dried at 120°C for 5~7 hours. Combined with hydrothermal treatment, it is calcined at 300~450°C in an intermittent atmosphere rotary kiln for 2~4 hours, and reduced at 300~400°C in a 3~7% H2 / N2 atmosphere for 3~5 hours to obtain a dehydrogenation catalyst.

[0018] The present invention can enhance the interaction between the active component Pt-Cr and the heterogeneous interface on the carrier by the above-mentioned hydrothermal treatment of the Pt catalyst, thereby improving the dispersibility and stability of the active component.

[0019] According to the preparation method of the catalyst provided by the present invention, the additive is at least one of aluminum sol, silica sol, montmorillonite, sesbania powder, rosin soap and polyethylene glycol; preferably, the mass of the additive is 2% to 7% of the mass of the catalyst.

[0020] According to the preparation method of the catalyst provided by the present invention, the complexing agent is one or more of EDTA, citric acid, Pluronic P123, Pluronic F127, PVP and hydroxyphenylbutazone; preferably, the mass of the complexing agent is 0.2% to 2% of the mass of the catalyst.

[0021] According to the preparation method of the catalyst provided by the present invention, the precursor salt of Pt is chloroplatinic acid, and the precursor salt of Cr is chromic anhydride; the precursors of La, Ga, Nd, and Si in the auxiliary agent are lanthanum nitrate, gallium nitrate, neodymium nitrate, and tetraethyl orthosilicate, respectively; and the precursors of CeO2, TiO2, In2O3, Bi2O3, WO3, and MnO2 in the heterogeneous oxide are cerium nitrate, titanyl sulfate, indium nitrate, bismuth nitrate, ammonium metatungstate, and manganese nitrate, respectively.

[0022] In a third aspect, the present invention provides use of the catalyst in the dehydrogenation reaction of methylcyclohexane.

[0023] According to the application provided by the present invention, during the dehydrogenation reaction, the reaction temperature is 320-350 ° C, the reaction pressure is 0.1-1.0 MPa, and the liquid space velocity is 0.5-4 h -1 , the amount of hydrogen introduced is 10~15%.

[0024] Based on this, the technical solution of the present invention has the following beneficial effects: The catalyst of the present invention significantly improves the initial conversion rate of methylcyclohexane dehydrogenation by improving the dispersibility of the active components; significantly improves the catalyst's resistance to sintering and carbon deposition by enhancing the interactions between the active components and between the active components and the carrier, as well as the basicity of the carrier, thereby improving the stability of the methylcyclohexane dehydrogenation reaction. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, the various raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0027] The specific surface area of ​​the catalysts prepared in the following examples is 25~50 m 2 / g, pore volume is 0.3~0.5 mL / g, and pore diameter is 7~12 nm.

[0028] Example 1 This embodiment provides a catalyst, and its preparation method specifically includes the following steps: Step 1: Weigh 57.96 g of cerium nitrate hexahydrate, 14.68 g of gallium nitrate, and 456.33 g of magnesium nitrate hexahydrate to prepare a 2 L mixed solution, titrate the mixture with 1.0 mol / L NaOH solution at 50 °C to control the endpoint pH at 9.2, age the mixture in an autoclave at 85 °C and 0.25 MPa for 8 h, filter, wash, dry at 105 °C for 6 h, and calcine in a muffle furnace at 550 °C for 3 h to obtain a heterogeneous oxide Ga-CeO2-MgO support. Step 2: The heterogeneous oxide Ga-CeO2-MgO support was dispersed in a 10.0 mmol / L ascorbic acid aqueous solution, vigorously stirred at room temperature for 5 min, filtered, washed, and vacuum-dried at 60°C overnight. 5 g of aluminum sol was added and pressed into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 1.6667 g of 15% Pt content chloroplatinic acid solution and 1.9200 g of chromic anhydride to prepare an aqueous solution with a pH of 1.2, add 0.5 g of Pluronic P123 and fully dissolve it, then evenly spray it on the stirred molding carrier, let it stand for 2 hours, and dry it at 120 ° C for 6 hours. During the calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 3000 h -1 , calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 350 °C for 2 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst MDH-1.

[0029] Example 2 This embodiment provides a catalyst, and its preparation method specifically includes the following steps: Step 1: Weigh 12.60 g of cerium nitrate hexahydrate, 10.85 g of indium nitrate, 15.20 g of neodymium nitrate hexahydrate, and 531.38 g of magnesium nitrate to prepare a 2 L mixed solution, which is co-titrated with 1.5 mol / L NaOH at 65 °C to an endpoint pH of 9.6. The solution is aged in an autoclave at 75 °C and 0.25 MPa for 10 h, filtered, washed, dried at 120 °C for 6 h, and calcined in a muffle furnace at 600 °C for 4 h to obtain a heterogeneous oxide Nd-In2O3-CeO2-MgO support. Step 2: Disperse the heterogeneous oxide Nd-In2O3-CeO2-MgO support in a 15.0 mmol / L ascorbic acid aqueous solution, vigorously stir at room temperature for 3 min, filter, wash, and vacuum dry at 60°C overnight. Add 6.00 g of rosin soap and press into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 1.6667 g of 15% Pt content chloroplatinic acid solution and 2.3040 g of chromic anhydride to prepare an aqueous solution with a pH of 1.5, add 0.4 g of Pluronic F127 and fully dissolve it, then evenly spray it on the stirred molding carrier, let it stand for 4 hours, and dry it at 120 ° C for 6 hours. During the calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 2000 h -1 , calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 300 °C for 2 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst MDH-2.

[0030] Example 3 This embodiment provides a catalyst, and its preparation method specifically includes the following steps: Step 1: Weigh 30.00 g of titanyl sulfate, 44.52 g of ethyl orthosilicate, and 494.17 g of magnesium nitrate to prepare a 2 L mixed solution, titrate with 1.0 mol / L NaOH at 55 °C, and the end point pH is 10.0. The solution is aged in an autoclave at 80 °C and 0.35 MPa for 6 h, filtered, washed, dried at 120 °C for 6 h, and calcined in a muffle furnace at 650 °C for 3 h to obtain a heterogeneous oxide Si-TiO2-MgO support. Step 2: Disperse the heterogeneous oxide Si-TiO2-MgO support in a 15.0 mmol / L ascorbic acid aqueous solution, vigorously stir at room temperature for 3 min, filter, wash, and vacuum dry at 60°C overnight. Add 4.50 g of montmorillonite and press into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 2.0000 g of 15% Pt content chloroplatinic acid solution and 1.9200 g of chromic anhydride to prepare an aqueous solution with a pH of 1.3, add 0.8 g of hydroxyphenylbutazone and fully dissolve it, then evenly spray it on the stirred molding carrier, let it stand for 3 hours, and then dry it at 120 ° C for 6 hours. During the calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 2000 h -1 , calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 400 °C for 2 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst MDH-3.

[0031] Example 4 This embodiment provides a catalyst, and its preparation method specifically includes the following steps: Step 1: Weigh 45.32 g of manganese nitrate, 10.92 g of lanthanum nitrate hexahydrate, and 461.42 g of magnesium nitrate to prepare a 2 L mixed solution, which is co-titrated with 0.8 mol / L NaOH at 60 °C to an endpoint pH of 9.5. The solution is aged in an autoclave at 75 °C and 0.25 MPa for 7 h, filtered, washed, dried at 110 °C for 8 h, and calcined in a muffle furnace at 600 °C for 4 h to obtain a heterogeneous oxide La-MnO2-MgO support. Step 2: The heterogeneous oxide La-MnO2-MgO support was dispersed in an 8 mmol / L ascorbic acid aqueous solution, vigorously stirred at room temperature for 4 min, filtered, washed, and vacuum-dried at 60°C overnight. 5.00 g of silica sol was added and pressed into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 1.0000 g of 15% Pt content chloroplatinic acid solution and 3.4560 g of chromic anhydride to prepare a pH 1.0 aqueous solution, add 1.0 g of PVP and fully dissolve it, then evenly spray it on the stirred molding carrier, let it stand for 2 hours, and dry it at 120 ° C for 6 hours. During the calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 3000 h -1 , calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 350 °C for 3 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst MDH-4.

[0032] Example 5 This embodiment provides a catalyst, and its preparation method specifically includes the following steps: Step 1: Weigh 41.60 g of bismuth nitrate pentahydrate, 12.48 g of lanthanum nitrate hexahydrate, and 472.55 g of magnesium nitrate to prepare a 2 L mixed solution, which is co-titrated with 1.5 mol / L NaOH at 65 °C to an endpoint pH of 10.2. The solution is aged in an autoclave at 90 °C and 0.25 MPa for 5 h, filtered, washed, dried at 120 °C for 6 h, and calcined in a muffle furnace at 500 °C for 5 h to obtain a heterogeneous oxide La-Bi2O3-MgO support. Step 2: The heterogeneous oxide La-Bi2O3-MgO support was dispersed in a 10.0 mmol / L ascorbic acid aqueous solution, stirred vigorously at room temperature for 5 min, filtered, washed, and dried overnight in a vacuum at 60°C. 3.00 g of sesbania powder was added and pressed into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 1.3333 g of 15% Pt content chloroplatinic acid solution and 2.8800 g of chromic anhydride to prepare an aqueous solution with a pH of 1.5, add 1.5 g of citric acid and fully dissolve it, then evenly spray it on the stirred molded support. After standing for 3 hours, dry it at 120 ° C for 6 hours. During the calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 4000 h -1 , calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 400 °C for 2 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst MDH-5.

[0033] Example 6 This embodiment provides a catalyst, and its preparation method specifically includes the following steps: Step 1: Weigh 15.90 g of ammonium metatungstate, 18.35 g of gallium nitrate, and 494.94 g of magnesium nitrate to prepare a 2 L mixed solution, which is co-titrated with 1.5 mol / L NaOH at 45 °C to an endpoint pH of 9.4. The solution is aged in an autoclave at 75 °C and 0.25 MPa for 5 h, filtered, washed, dried at 105 °C for 8 h, and baked in a muffle furnace at 550 °C for 4 h to obtain a heterogeneous oxide Ga-WO3-MgO support. Step 2: Disperse the heterogeneous oxide Ga-WO3-MgO in a 15.0 mmol / L ascorbic acid aqueous solution, vigorously stir at room temperature for 4 minutes, filter, wash, and vacuum dry at 60°C overnight. Add 4.50 g of silica sol and press into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 1.2000 g of 15% Pt content chloroplatinic acid solution and 3.8400 g of chromic anhydride to prepare an aqueous solution with a pH of 0.8, add 2.00 g of EDTA and fully dissolve it, then evenly spray it on the stirred molding carrier, let it stand for 3 hours, and dry it at 120℃ for 6 hours. During the calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 3500 h -1 , calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 350 °C for 2 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst MDH-6.

[0034] Example 7 This embodiment provides a catalyst, and its preparation method specifically includes the following steps: Step 1: Weigh 25.20 g of cerium nitrate, 21.28 g of neodymium nitrate hexahydrate, and 521.52 g of magnesium nitrate to prepare a 2 L mixed solution, titrate with 1.0 mol / L NaOH at 60 °C, and the end point pH is 8.9. The solution is aged in an autoclave at 80 °C and 0.20 MPa for 8 h, filtered, washed, dried at 120 °C for 5 h, and calcined in a muffle furnace at 600 °C for 3 h to obtain a heterogeneous oxide Nd-CeO2-MgO support. Step 2: Disperse the heterogeneous oxide Nd-CeO2-MgO support in a 12.0 mmol / L ascorbic acid aqueous solution, vigorously stir at room temperature for 4 minutes, filter, wash, and vacuum dry at 60°C overnight. Add 3.50 g of aluminum sol and press into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 1.3333 g of 15% Pt content chloroplatinic acid solution and 1.5360 g of chromic anhydride to prepare an aqueous solution with a pH of 1.3, add 1.20 g of Pluronic P123 and fully dissolve it, then evenly spray it on the stirred molding carrier, let it stand for 1 hour, and dry it at 120 ° C for 6 hours. During the calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 2500 h -1 , calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 300 °C for 3 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst MDH-7.

[0035] Example 8 This embodiment provides a catalyst, and its preparation method specifically includes the following steps: Step 1: Weigh 21.70 g of indium nitrate, 15.60 g of lanthanum nitrate hexahydrate, and 532.14 g of magnesium nitrate to prepare a 2 L mixed solution, which is co-titrated with 1.0 mol / L NaOH at 60 °C to an endpoint pH of 9.2. The solution is aged in an autoclave at 90 °C and 0.25 MPa for 4 h, filtered, washed, dried at 120 °C for 6 h, and calcined in a muffle furnace at 650 °C for 2 h to obtain a heterogeneous oxide La-In2O3-MgO support. Step 2: The heterogeneous oxide La-In2O3-MgO support was dispersed in a 10.0 mmol / L ascorbic acid aqueous solution, vigorously stirred at room temperature for 5 min, filtered, washed, and dried in a vacuum at 60°C overnight. 6.00 g of polyethylene glycol was added and pressed into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 0.8667 g of 15% Pt content chloroplatinic acid solution and 2.3040 g of chromic anhydride to prepare an aqueous solution with a pH of 1.5, add 1.50 g of EDTA and fully dissolve it, then evenly spray it on the stirred molded support. After standing for 6 hours, dry it at 120°C for 6 hours. During calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 5000 h -1 , calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 380 °C for 3 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst MDH-8.

[0036] Comparative Example 1 This comparative example provides a catalyst. In this comparative example 1, the carrier does not use a heterogeneous oxide MgO-based carrier material. The preparation method specifically includes: Step 1: Weigh 626.78 g of magnesium nitrate and prepare a 2 L mixed solution. Co-titrate with 1.0 mol / L NaOH at 60 °C to an endpoint pH of 9.6. Aged in an autoclave at 85 °C and 0.30 MPa for 6 h, filtered, washed, dried at 120 °C for 6 h, and calcined in a muffle furnace at 650 °C for 2 h to obtain a MgO support. Step 2: The MgO support was filtered, washed, and vacuum-dried at 60°C overnight. 5.00 g of montmorillonite was added and pressed into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 1.6667 g of 15% Pt content chloroplatinic acid solution and 2.3040 g of chromic anhydride to prepare a pH 1.0 aqueous solution, add 0.50 g of PVP and fully dissolve it, then evenly spray it on the stirred molding carrier, let it stand for 3 hours, and dry it at 120 ° C for 6 hours. During the calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 3000 h -1, calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 350 °C for 3 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst RS-1.

[0037] Comparative Example 2 This comparative example provides a catalyst. In this comparative example 2, the catalyst carrier uses pure γ-Al2O3 to increase the content of precious metal Pt. The preparation method is as follows: Step 1: calcining 99.60 g of pseudo-boehmite at 450 °C for 4 h to obtain the carrier γ-Al2O3; Step 2: Add 3.00 g of aluminum sol to the carrier material and press it into a five-pointed star shape with a circular arc to obtain a shaped carrier; Step 3: Weigh 3.3333 g of 15% Pt content chloroplatinic acid solution and dilute it to 39.84 g of aqueous solution. Add 1.00 g of hydroxyphenylbutazone and fully dissolve it. Then spray it evenly on the stirred molded support. After standing for 2 hours, dry it at 120°C for 6 hours, then calcine it at 350°C in an air atmosphere for 2 hours, and reduce it at 350°C in a 5% H2 / N2 atmosphere for 4 hours to obtain dehydrogenation catalyst RS-2.

[0038] Comparative Example 3 This comparative example provides a catalyst. Compared with Example 8, this comparative example does not use a batch atmosphere rotary kiln and water vapor treatment to impregnate the Pt catalyst. The specific preparation method is as follows: Step 1: Weigh 21.70 g of indium nitrate, 15.60 g of lanthanum nitrate hexahydrate, and 532.14 g of magnesium nitrate to prepare a 2 L mixed solution, which is co-titrated with 1.0 mol / L NaOH at 60 °C to an endpoint pH of 9.2. The solution is aged in an autoclave at 90 °C and 0.25 MPa for 4 h, filtered, washed, dried at 120 °C for 6 h, and calcined in a muffle furnace at 650 °C for 2 h to obtain a heterogeneous oxide La-In2O3-MgO support. Step 2: The heterogeneous oxide La-In2O3-MgO support was dispersed in a 10.0 mmol / L ascorbic acid aqueous solution, vigorously stirred at room temperature for 5 min, filtered, washed, and dried in a vacuum at 60°C overnight. 6.00 g of polyethylene glycol was added and pressed into a five-pointed star shape with a rounded arc to obtain a shaped support. Step 3: Weigh 0.8667 g of 15% Pt content chloroplatinic acid solution and 2.3040 g of chromic anhydride to prepare an aqueous solution with a pH of 1.5, add 1.50 g of EDTA and fully dissolve it, then evenly spray it on the stirring molded support. After standing for 6 hours, dry it at 120°C for 6 hours, calcine it at 380°C in an air atmosphere for 3 hours, and reduce it at 350°C in a 5% H2 / N2 atmosphere for 4 hours to obtain dehydrogenation catalyst RS-3.

[0039] Comparative Example 4 This comparative example provides a catalyst. In this comparative example 4, the carrier does not use a heterogeneous oxide MgO-based carrier material, and no Cr active component is added. The preparation method is specifically as follows: Step 1: Weigh 636.09 g of magnesium nitrate and prepare a 2 L mixed solution. Co-titrate with 1.0 mol / L NaOH at 60 °C to an endpoint pH of 9.6. Aged in an autoclave at 85 °C and 0.25 MPa for 6 h, filtered, washed, dried at 120 °C for 6 h, and calcined in a muffle furnace at 650 °C for 2 h to obtain a MgO support. Step 2: The MgO carrier was filtered, washed, and vacuum-dried at 60°C overnight. 4.50 g of rosin soap was added and pressed into a five-pointed star shape with a circular arc to obtain a shaped carrier. Step 3: Weigh 2.0000 g of 15% Pt content chloroplatinic acid and dissolve it in a certain amount of aqueous solution. Add 0.80 g of citric acid and dissolve it fully. Then spray it evenly on the stirred molded support. After standing for 4 hours, dry it at 120 ° C for 6 hours. During the calcination, the intermittent atmosphere rotary kiln is fed with a gas space velocity of 3000 h -1 , calcined at 300 °C for 1 h in a 10% H2O / N2 atmosphere, then calcined at 350 °C for 3 h in an air atmosphere, and reduced at 350 °C for 4 h in a 5% H2 / N2 atmosphere to obtain the dehydrogenation catalyst RS-4.

[0040] Test example catalyst performance test The catalysts prepared in Examples 1-8 and Comparative Examples 1-4 were respectively subjected to methylcyclohexane dehydrogenation activity evaluation and carbon deposit content test using a fixed bed reactor. The catalysts did not need to be reactivated before testing. Each catalyst was evaluated for activity for 50 h, and the evaluated catalysts were then subjected to carbon deposition test. Dehydrogenation performance evaluation conditions: catalyst loading of 15 g, inert material of 75 g, methylcyclohexane liquid space velocity of 2.0 h -1 The reaction was carried out at a pressure of 0.2 MPa and a temperature of 330°C, supplemented with 12% H₂ of the volume of vaporized methylcyclohexane. The reaction tube had an inner diameter of 20 mm and a bed (catalyst + inert material) height of 159 mm.

[0041] Table 1 Test results of the catalyst performance of the present invention for catalytic dehydrogenation of cycloalkanes

[0042] As can be seen from the results in Table 1, the catalyst of the present invention significantly improves the initial conversion rate of methylcyclohexane dehydrogenation by improving the dispersibility of the active components; and significantly improves the catalyst's resistance to sintering and carbon deposition by enhancing the interactions between the active components and between the active components and the support, as well as the basicity of the support, thereby improving the stability of the methylcyclohexane dehydrogenation reaction.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A catalyst, characterized in that including active ingredients, adjuvants and carriers; The active component includes a first active component and a second active component, the first active component is Pt, and the second active component is Cr; The support comprises more than 70 wt% of MgO and the remainder is a heterogeneous oxide; The heterogeneous oxides are at least two of CeO2, TiO2, In2O3, Bi2O3, WO3, and MnO2; The auxiliary agent includes at least one of La, Ga, Nd and Si.

2. The catalyst according to claim 1, characterized in that The mass ratio of the first active component to the second active component is (0.1-0.3): (0.5-2.0).

3. The catalyst according to claim 1 or 2, characterized in that The catalyst includes the following components in the following amounts: The first active component is 0.1~0.3%; The second active component is 0.5~2.0%; Additives 3.0~7.0%; Carrier remainder.

4. The catalyst according to any one of claims 1 to 3, characterized in that The specific surface area of ​​the catalyst is 25~50 m 2 / g, pore volume is 0.3~0.5 mL / g, and pore diameter is 7~12 nm.

5. The method for preparing the catalyst according to any one of claims 1 to 4, characterized in that: include: S1: A heterogeneous oxide precursor, an auxiliary agent precursor, and magnesium nitrate are prepared into a mixed solution, the pH value of the mixed solution is adjusted to 8.8-10.2, and an aging treatment is performed at 75-98°C and 0.2-0.5 MPa. The product is filtered, washed, dried, and calcined at 500-650°C to obtain a heterogeneous oxide MgO-based support; S2: dispersing the heterogeneous oxide MgO-based carrier in a 5.0-15.0 mmol / L ascorbic acid aqueous solution, filtering, washing, drying, adding additives, and pressing to obtain a molded carrier; S3: The pH value of the Pt- and Cr-containing precursor salt solution is adjusted to 0.5-1.5, and after adding a complexing agent to fully dissolve it, it is evenly sprayed on the forming support, allowed to stand, and then dried at 100-130°C, and then calcined at 300-450°C, and then calcined in a reducing atmosphere at 300-400°C; preferably, the calcination adopts programmed temperature rise, and the heating rate is 5-10°C.

6. The method for preparing the catalyst according to claim 5, characterized in that: The additive is at least one of aluminum sol, silica sol, montmorillonite, sesbania powder, rosin soap and polyethylene glycol; preferably, the mass of the additive is 2% to 7% of the mass of the catalyst.

7. The method for preparing the catalyst according to claim 5 or 6, characterized in that: The complexing agent is one or more of EDTA, citric acid, Pluronic P123, Pluronic F127, PVP and hydroxyphenylbutazone; preferably, the mass of the complexing agent is 0.2% to 2% of the mass of the catalyst.

8. The method for preparing the catalyst according to any one of claims 5 to 7, characterized in that: The precursor salt of Pt is chloroplatinic acid, and the precursor salt of Cr is chromic anhydride; the precursors of La, Ga, Nd, and Si in the additive are lanthanum nitrate, gallium nitrate, neodymium nitrate, and tetraethyl orthosilicate, respectively; the precursors of CeO2, TiO2, In2O3, Bi2O3, WO3, and MnO2 in the heterogeneous oxide are cerium nitrate, titanyl sulfate, indium nitrate, bismuth nitrate, ammonium metatungstate, and manganese nitrate, respectively.

9. Use of the catalyst according to any one of claims 1 to 4 or the catalyst prepared by the preparation method according to any one of claims 5 to 8 in the dehydrogenation reaction of methylcyclohexane.

10. The use according to claim 9, characterized in that During the dehydrogenation reaction, the reaction temperature is 320~350℃, the reaction pressure is 0.1~1.0 MPa, and the liquid space velocity is 0.5~4 h -1 , the amount of hydrogen introduced is 10~15%.

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