Calcium carbonate hydrogenation decomposition catalyst as well as preparation method and application thereof

Abstract

The invention discloses a calcium carbonate hydrogenation decomposition catalyst and a preparation method and application thereof, the catalyst comprises a CeO2 carrier and Ga species loaded on the CeO2 carrier, and the Ga species account for 1%-10% of the mass of the CeO2 carrier. The active metal gallium in the catalyst is uniform in distribution and low in dosage, so that the cost is relatively low. The catalyst disclosed by the invention can be used for reducing carbon dioxide generated by decomposition of calcium carbonate to generate carbon monoxide under the hydrogen atmosphere of hydrogen-donating molecules, the activity of the catalyst is relatively high, and in-situ reduction of carbon dioxide can be realized at the temperature lower than the pyrolysis temperature of pure calcium carbonate. The catalyst provided by the invention is used in the process of producing metal oxides by thermal decomposition of calcium carbonate, can reduce the reaction temperature, significantly reduces the emission of CO2, and has a significant catalytic effect; the preparation method of the catalyst is simple and easy to implement, low in equipment requirement and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of cerium dioxide composite catalysts, and particularly relates to a calcium carbonate hydrogenation decomposition catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] In the cement, steel, and refractory industries, carbonate thermal decomposition is a key process for preparing metal oxides. However, its high-temperature requirement (>850°C) and high carbon emission problems severely restrict the sustainable development of the industry. Taking cement production as an example, nearly 90% of CO2 emissions come from the clinker burning stage. Among them, the CO2 released by the calcination of limestone to produce quicklime accounts for about 55-70% of the total carbon emissions in the whole production process; while the CO2 generated by the fuel combustion for heat supply required for high-temperature calcination accounts for about 25-40%. Although carbon capture, utilization, and storage (CCUS) technologies have been widely studied for flue gas carbon capture in industries such as cement, their multi-step separation and storage processes have high energy consumption, poor economy, and fail to achieve the conversion and utilization of CO2 into high-value products.

[0003] To solve this problem, it is proposed to couple the decomposition of calcium carbonate with the reverse water gas shift (RWGS) reaction, and use hydrogen to in-situ convert the pyrolytic CO2 into CO. However, the core challenge of this technology lies in designing a catalyst with high temperature efficiency and stability. Among the existing RWGS reaction catalysts, noble metals (such as Pt, Ru) are costly, while transition metals (such as Cu) have a low Tamman temperature and are prone to sintering and deactivation at high temperatures, resulting in poor reaction activity. In addition, conventional carriers (such as Al2O3, SiO2) have limited adsorption capacity for carbon dioxide and are prone to structural collapse at high temperatures, leading to a decrease in metal dispersion and a reduction in catalytic efficiency.

[0004] Therefore, it is necessary to design a calcium carbonate hydrogenation decomposition catalyst with low cost, strong activity, and high stability. Summary of the Invention

[0005] The object of the present invention is to obtain a composite catalyst by loading gallium (Ga) nanoparticles on cerium oxide (CeO2) as a carrier. CeO2, due to its dynamic oxygen vacancies (reversibly generated by Ce 3+ / Ce 4+ reversible conversion) and strong metal-support interaction (SMSI), becomes an ideal carrier: oxygen vacancies serve as CO2 adsorption and activation sites, significantly reducing the dissociation energy barrier of the C=O bond; the SMSI effect inhibits the high-temperature agglomeration of metal particles and improves stability. The active component Ga further optimizes the catalytic performance in cooperation with CeO2. The oxygen vacancies on the surface of CeO2 promote the dissociation of H2 and enhance the hydrogen activation efficiency.

[0006] To achieve the above object, the present invention provides a catalyst for the hydrogenation decomposition of calcium carbonate, which comprises a CeO2 support and Ga species supported on the CeO2 support, and the Ga species accounts for 1%-10% of the mass of the CeO2 support.

[0007] Further, the Ga species accounts for 2%-5% of the mass of the CeO2 support The present invention also provides a method for preparing the above-mentioned catalyst for the hydrogenation decomposition of calcium carbonate, comprising: Mixing a gallium salt solution with a CeO2 support and heating with stirring to obtain a precursor; Drying the precursor and then calcining it to obtain a catalyst for the hydrogenation decomposition of calcium carbonate.

[0008] Further, the temperature is raised to 70-90°C during the heating.

[0009] Further, during the calcination, the temperature is raised to 500-700°C at a heating rate of 1-10°C / min, then kept warm for 3-5 h, and subsequently a reducing gas is introduced and kept warm for 0.5-2 h.

[0010] Further, the method for preparing the CeO2 support comprises: Mixing a cerium salt solution with an alkali solution, and then carrying out a hydrothermal reaction to collect the insoluble matter; Thermally treating the insoluble matter to obtain a CeO2 support.

[0011] Further, the concentrations of the cerium salt solution and the alkali solution are 0.13-0.17 mol / L and 6-9 mol / L respectively; The volume ratio of the cerium salt solution to the alkali solution is 1:1-3.

[0012] Further, the hydrothermal reaction is carried out at 90-120°C for 16-36 h; During the thermal treatment, the temperature is raised to 500-700°C at a heating rate of 1-10°C / min and kept warm for 3-5 h.

[0013] It should be noted that in the present application, the types of gallium salts and cerium salts do not need to be strictly limited. Exemplarily, they can be at least one of gallium nitrate, gallium chloride, etc., and can also have crystal water; the cerium salt can be at least one of cerium nitrate, cerium chloride, etc., and can also have crystal water. The solvents for dissolving gallium salts and cerium salts are not limited. Exemplarily, they can be at least one of water, ethanol, acetone, etc., and water is preferred. The type of alkali solution is not limited, and it is preferably prepared by dissolving an inorganic base such as an aqueous potassium hydroxide solution or an aqueous sodium hydroxide solution in water.

[0014] The present invention also provides the application of the above-mentioned catalyst for the hydrogenation decomposition of calcium carbonate in the reaction of coupling the thermal decomposition of calcium carbonate with hydrogen reduction.

[0015] Further, the application is carried out under the conditions of a material ratio of 1:5 - 15, a temperature of 600 - 700 °C, a space velocity of 30000 - 50000 mL·h -1 ·g -1 and a hydrogen concentration of 30% - 60%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: In the catalyst of the present invention, the active metal gallium is evenly distributed and the dosage is low, so the cost is relatively low. The catalyst of the present invention can reduce carbon dioxide generated by the decomposition of calcium carbonate to produce carbon monoxide in an atmosphere of hydrogen molecules as the hydrogen donor, and the activity of the catalyst is strong, and in-situ reduction of carbon dioxide can be achieved at a temperature lower than the pyrolysis temperature of relatively pure calcium carbonate.

[0017] When the catalyst of the present invention is used in the process of thermally decomposing calcium carbonate to produce metal oxides, the reaction temperature can be reduced, the emission of CO2 can be significantly reduced, and the catalytic effect is remarkable; the preparation method of the catalyst of the present invention is simple and easy to implement, and the equipment requirements are low, which is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 Shows the XRD patterns of the calcium carbonate hydrogenation decomposition catalysts of Examples 1 - 5; Figure 2 Shows the thermogravimetric curves of the thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction under different atmospheres; Figure 3 Shows the performance diagrams of the thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction of the catalysts of Comparative Example 1 and Comparative Example 2, wherein, Figure 3 a is a bar chart of the conversion rate of CO2 and a line chart of the selectivity of CO, Figure 3 b is the calcium carbonate decomposition rate curve; Figure 4 Shows the performance diagrams of the thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction of the calcium carbonate hydrogenation decomposition catalysts of Examples 1 - 4, wherein, Figure 4 a is a bar chart of the conversion rate of CO2 and a line chart of the selectivity of CO, Figure 4 b is the calcium carbonate decomposition rate curve; Figure 5 Shows the performance diagrams of the thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction of the calcium carbonate hydrogenation decomposition catalyst of Example 2 under different hydrogen concentrations, wherein,Figure 5 a is a bar graph of the conversion rate of CO2 and a line graph of the selectivity of CO, Figure 5 b is the calcium carbonate decomposition rate curve; Figure 6 shows the performance graph of the calcium carbonate hydrodecomposition catalyst of Example 2 in the calcium carbonate thermal decomposition coupled hydrogen reduction reaction at different space velocities, where, Figure 6 a is a bar graph of the conversion rate of CO2 and a line graph of the selectivity of CO, Figure 6 b is the calcium carbonate decomposition rate curve; Figure 7 shows the performance graph of the calcium carbonate hydrodecomposition catalyst of Example 2 in the calcium carbonate thermal decomposition coupled hydrogen reduction reaction at different reaction temperatures, where, Figure 7 a is a bar graph of the conversion rate of CO2 and a line graph of the selectivity of CO, Figure 7 b is the calcium carbonate decomposition rate curve; Figure 8 shows the performance graph of the calcium carbonate hydrodecomposition catalyst of Example 2 in the calcium carbonate thermal decomposition coupled hydrogen reduction reaction at different material ratios, where, Figure 8 a is a bar graph of the conversion rate of CO2 and a line graph of the selectivity of CO, Figure 8 b is the calcium carbonate decomposition rate curve. Detailed implementation manners

[0020] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0021] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention. Unless otherwise clearly stated, the technical terms or scientific terms used in the present invention should be understood as the meanings commonly understood by those skilled in the art. Without contradiction, the various embodiments of the present invention and their specific features can be combined arbitrarily. The following listed embodiments are only used to further illustrate the content of the present invention and are not used to limit its protection scope.

[0022] Example 1 A preparation method of a calcium carbonate hydrodecomposition catalyst includes the following steps, S1. Preparation of CeO₂ support: Dissolve 1.3 g of Ce(NO₃)₃·6H₂O in 20 mL of deionized water and stir for 30 min to obtain a 0.15 mol / L cerium nitrate solution; dissolve 14.4 g of NaOH in 40 mL of deionized water and stir evenly to obtain a 9 mol / L NaOH solution; mix the two solutions and continue stirring for 30 min to form a light purple flocculent substance. Transfer the mixed solution into the inner lining of a polytetrafluoroethylene reaction kettle, then put on the reaction kettle, and transfer it to an oven at 100 °C for hydrothermal reaction for 24 h. Subsequently, centrifuge with deionized water and ethanol until the solution is neutral, and place it in an oven at 80 °C for drying for 24 h to obtain a light yellow powder. Heat it to 600 °C at a heating rate of 1 °C / min and keep it calcined for 4 h to obtain the CeO₂ support; S2. Preparation of catalyst: Weigh 0.054 g of Ga(NO₃)₃·6H₂O and dissolve it in 2 mL of deionized water respectively. Add the CeO₂ support, stir at a constant temperature of 80 °C for 1 h, place it in an oven at 80 °C for drying for 24 h, heat it to 600 °C at a heating rate of 1 °C / min and keep it calcined for 4 h, and finally pass 10% H₂ at 500 °C to reduce for 1 h to prepare a calcium carbonate hydrogenation decomposition catalyst with a Ga species loading of 1%, which is simply called the Ga-CeO₂ catalyst.

[0023] Examples 2 - 5 Please refer to the preparation method of Example 1. The difference is that in step S2, 0.16, 0.26, 0.36, and 0.52 g of Ga(NO₃)₃·6H₂O are dissolved in 2 mL of deionized water respectively to obtain Ga-CeO₂ catalysts with Ga species loadings of 3%, 5%, 7%, and 10%.

[0024] The catalysts of Examples 1 - 5 are named x%Ga-CeO₂, where x = 1, 3, 5, 7, 10.

[0025] Comparative Example 1 Ga₂O₃ catalyst. The preparation method includes the following steps. Weigh 1 g of Ga(NO₃)₃·6H₂O, place it in a mortar and grind it into a powder, heat it to 600 °C at a heating rate of 1 °C / min and keep it calcined for 4 h to obtain Ga₂O₃.

[0026] Comparative Example 2 CeO₂ catalyst. The preparation method is the same as that of the CeO₂ support in Example 1, which will not be elaborated here.

[0027] Testing Example Figure 1XRD patterns of catalysts with different Ga loadings are shown. It can be seen from the figure that the diffraction peaks of x%Ga-CeO2 are almost the same as those of CeO2. Even when the Ga loading is 10 wt%, no characteristic peaks of Ga2O3 or other impurity peaks appear. This may be due to the reduction of Ga element to an intermediate valence state and the relatively low Ga loading.

[0028] Figure 2 TG curves of the thermal decomposition of calcium carbonate coupled with hydrogen reduction under different atmospheres are shown. It can be seen from the figure that the initial decomposition temperature of calcium carbonate in air atmosphere is about 720 °C. When hydrogen is coupled and the catalyst of Example 2 is added, the decomposition temperature drops by about 58 °C, indicating that this catalyst can lower the decomposition temperature of calcium carbonate.

[0029] For the evaluation of the catalytic performance of the catalyst for hydrogen reduction coupling, 500 mg of calcium carbonate powder and 50 mg of the catalyst are weighed respectively. The solid mixture is ground in a mortar until evenly mixed. 50 mg of the mixture is weighed and placed at the bottom of the straight tube of the U-shaped glass tube reactor. A mixed gas of H2:Ar = 2:3 mL / min is introduced from below at a total flow rate of 40 mL / min. The reactor is heated to 700 °C. After reacting for 20 min, the tail gas then enters the mass spectrometer for gas composition and concentration analysis.

[0030] Specifically referring to the parameters in Table 1, the Ga2O3 catalyst of Comparative Example 1 and the CeO2 catalyst of Comparative Example 2 are subjected to the co-thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction.

[0031] Table 1

[0032] From Figure 3 a, it can be seen that compared with the reaction without adding a catalyst, both Ga2O3 and the carrier CeO2 can improve the conversion rate of CO2. In addition, during the reaction of all samples, the selectivity of CO can be maintained above 99%. Similarly, in Figure 3 b, the decomposition rate of calcium carbonate during the reaction shows the same trend.

[0033] Table 2

[0034] Specifically referring to the parameters in Table 2, the x%Ga-CeO2 catalysts of Examples 1-4 are subjected to the co-thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction.

[0035] Figure 4 a, Figure 4 b shows the performance differences of catalysts with different Ga loadings of Examples 1-4 for the co-thermal coupling of calcium carbonate with hydrogen reduction. From Figure 3It can be seen that the bar chart of the CO2 conversion performance is in a volcano shape. When the gallium loading is 3%, the conversion rate of CO2 reaches the highest value of 83%, that is, the catalyst in Example 2 has the highest catalytic performance under the same conditions. At the same time, for the catalysts of Examples 1-4, the selectivity of CO can be maintained above 99%. Similarly, in Figure 3 During the reaction process shown in b, the decomposition rate of calcium carbonate under the action of the 3% Ga-CeO2 catalyst also reaches the highest. In addition, comparing Figure 3 a and Figure 4 a as well as Figure 3 b and Figure 4 b, the cerium oxide catalyst loaded with gallium species can further promote the improvement of CO2 conversion due to the strong metal-support interaction (SMSI) between gallium and the carrier cerium oxide.

[0036] Referring to the parameters in Table 3, the catalyst of Example 2 was subjected to the co-thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction at different hydrogen concentrations.

[0037] Table 3

[0038] Figure 5 a, Figure 5 b shows the performance differences of the co-thermal coupling of calcium carbonate with hydrogen reduction at different hydrogen concentrations. As Figure 5 shown in a, when the hydrogen concentration is 40%, the conversion rate of CO2 is 83%; when the hydrogen concentration increases to 70%, the conversion rate only slightly rises to 84.4%, indicating that increasing the hydrogen concentration has a limited promoting effect on the CO2 conversion rate within this range. Therefore, 40% hydrogen is selected as the optimal reaction concentration. In addition, during the reaction process of all samples, the selectivity of CO can be maintained above 99%. As Figure 5 shown in b, under the condition of 10% H2, the decomposition rate of calcium carbonate is low, and the decomposition time is significantly longer than the other two groups; while the decomposition times under the conditions of 40% H2 and 70% H2 are similar, and the decomposition rate differences are not significant. Therefore, considering the reaction efficiency and gas consumption comprehensively, 40% H2 is still the optimal reaction condition.

[0039] Table 4

[0040] Referring to the parameters in Table 4, the catalyst of Example 2 was subjected to the co-thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction at different reaction space velocities.

[0041] Figure 6 a, Figure 6 b shows the performance differences of the co-thermal coupling of calcium carbonate with hydrogen reduction at different space velocities. Figure 6The CO2 conversion performance curve shown in a presents a typical volcano shape. When the total gas flow rate is 40 mL / min and the corresponding space velocity is 48000 mL·h -1 ·g -1 , the CO2 conversion reaches the highest value of 83%. When the gas flow rate is too low, the upper limit of the CO2 concentration that the catalyst can activate has not been reached, and the reaction efficiency has not been fully exerted; while when the flow rate is too high, although the CO2 concentration increases, the excess part cannot fully contact the catalyst and directly passes through the reactor, resulting in a decrease in the conversion rate. Therefore, a space velocity of 48000 mL·h -1 ·g -1 is selected as the optimal reaction condition. In addition, during the reaction of all samples, the selectivity of CO can be maintained above 99%. Similarly, during the reaction shown in Figure 6 b, a space velocity of 48000 mL·h -1 ·g -1 results in the best reaction conditions for the decomposition rate and decomposition time of calcium carbonate.

[0042] Referring to the parameters in Table 5, the catalyst of Example 2 was subjected to the co-thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction at different reaction space velocities.

[0043] Table 5

[0044] Figure 7 a, Figure 7 b shows the performance differences of the co-thermal coupling of calcium carbonate with hydrogen reduction at different reaction temperatures. As can be seen from Figure 7 a, when the reaction temperature is 650 °C, the CO2 conversion is the highest. However, as shown in Figure 7 b, at this temperature, the decomposition rate of calcium carbonate is slow and the decomposition time is long. In contrast, at 700 °C, the CO2 conversion still remains at a relatively high level, while the decomposition rate of calcium carbonate increases and the decomposition time shortens. Compared with 750 °C, 700 °C shows better reaction economy while ensuring a relatively high reaction efficiency, so 700 °C is selected as the more appropriate reaction temperature. In addition, during the reaction of all samples, the selectivity of CO can be maintained above 99%.

[0045] Table 6

[0046] Referring to the parameters in Table 6, the catalyst of Example 2 was subjected to the co-thermal decomposition of calcium carbonate coupled with hydrogen reduction reaction at different material ratios (mass ratio of catalyst to calcium carbonate).

[0047] Figure 8 a, Figure 8 b shows the performance differences of the co-thermal coupling of calcium carbonate with hydrogen reduction at different ratios of calcium carbonate to catalyst. AsFigure 8 As shown in a, when the mass ratio of calcium carbonate to the catalyst is 1:5, the conversion rate, decomposition rate, and decomposition time of CO2 all show the best performance. However, when the ratio increases to 1:10, the CO2 conversion rate only slightly decreases, and the decomposition rate and decomposition time change insignificantly. Considering that the catalytic performance remains basically the same, increasing the ratio helps to reduce the catalyst dosage and reaction cost. Therefore, the final ratio of calcium carbonate to the catalyst is selected as 1:10.

[0048] In summary, the catalyst of the present invention can reduce carbon dioxide generated by the decomposition of calcium carbonate to produce carbon monoxide in a hydrogen atmosphere of a hydrogen-supplying molecule, and the catalyst has strong activity and can realize in-situ reduction of carbon dioxide at a temperature lower than the pyrolysis temperature of relatively pure calcium carbonate. When the catalyst of the present invention is used in the process of thermal decomposition of calcium carbonate to produce metal oxides, the reaction temperature can be reduced, the CO2 emission can be significantly reduced, and the catalytic effect is remarkable; the preparation method of the catalyst of the present invention is simple and easy to operate, and the equipment requirement is low, which is suitable for industrial production.

[0049] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A calcium carbonate hydrogenation decomposition catalyst, characterized in that, It includes a CeO2 support and Ga species loaded on the CeO2 support, and the Ga species account for 1% - 10% of the mass of the CeO2 support.

2. The calcium carbonate hydrocracking catalyst according to claim 1, characterized in that, The Ga species account for 2% - 5% of the mass of the CeO2 support.

3. A method for preparing a calcium carbonate hydrodecomposition catalyst as described in claim 1 or 2, characterized in that, including Mix a gallium salt solution with the CeO2 support and heat it up with stirring to obtain a precursor; Dry the precursor and then calcine it to obtain a calcium carbonate hydrodecomposition catalyst.

4. The preparation method of the calcium carbonate hydrogenation decomposition catalyst according to claim 3, characterized in that, The temperature increase raises the temperature to 60 - 100 °C.

5. The preparation method of the calcium carbonate hydrodecomposition catalyst according to claim 3, characterized in that, During the calcination, it is heated to 500 - 700 °C at a heating rate of 1 - 10 °C / min, then kept warm for 3 - 5 h, and subsequently, a reducing gas is introduced and kept warm for 0.5 - 2 h.

6. The preparation method of the calcium carbonate hydrodecomposition catalyst according to claim 3, characterized in that, The preparation method of the CeO2 support includes Mix a cerium salt solution with an alkali solution, and then carry out a hydrothermal reaction to collect the insoluble matter; Heat-treat the insoluble matter to obtain the CeO2 support.

7. The preparation method of the calcium carbonate hydrocracking catalyst according to claim 6, characterized in that, The concentrations of the cerium salt solution and the alkali solution are 0.13 - 0.17 mol / L and 6 - 9 mol / L respectively; The volume ratio of the cerium salt solution to the alkali solution is 1:1 - 3.

8. The preparation method of the calcium carbonate hydrodecomposition catalyst according to claim 6, characterized in that, The hydrothermal reaction lasts for 16 - 36 h at 90 - 120 °C; The heat treatment is heated to 500 - 700 °C at a heating rate of 1 - 10 °C / min and kept warm for 3 - 5 h.

9. Application of a calcium carbonate hydrodecomposition catalyst as described in claim 1 or 2 in the calcium carbonate thermal decomposition coupled hydrogen reduction reaction.

10. The application according to claim 9, characterized in that, Under the conditions of a material ratio of 1:5 - 15, a temperature of 600 - 700 °C, a space velocity of 30000 - 50000 mL·h -1 ·g -1 and a hydrogen concentration of 30% - 60%.

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