A carbon material for thermal catalytic reduction of impure CO2 and its preparation method

Abstract

The present invention provides a carbon material for the thermal catalytic reduction of impure CO2 and a preparation method thereof. The components of the carbon material include 20-50 wt.% Ni, 30-70 wt.% CeO2, and 10-20 wt.% carbon deposits. The CeO2 is a carrier, and the Ni and carbon deposits are active components for the thermal catalytic conversion of CO2. The carbon deposits are generated in situ by the cracking of CH4 on Ni-modified cerium metal oxide. The carbon deposits generated in situ by the cracking can promote the reduction of CO2. The chemical formula is: MeO x ‑C+CO2→2CO+MeO x The carbon material catalyst of the present invention has high oxygen resistance and can achieve efficient reduction of CO2 in an atmosphere of non-pure CO2 (a mixture of CO2 and air) with a content of 20 to 100 vol.%. The carbon material catalyst of the present invention directionally reduces non-pure CO2 to CO with a CO selectivity of 100% and a yield of up to 18.53 to 20.18 mmol / g, which is 4.50 to 9.43 times that of traditional metal oxides, greatly improving the catalytic conversion efficiency of non-pure CO2.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 catalytic conversion, and specifically relates to a carbon material for thermal catalytic reduction of impure CO2 and a preparation method thereof. Background Art

[0002] Chemical looping dry reforming is a novel and highly efficient CO2 conversion technology with broad application prospects in CO2 resource utilization. In existing technologies, metal oxides can serve as an oxygen source to induce the selective oxidation of CH4 to produce high-quality syngas (2H2 + CO). Simultaneously, the metal oxide is reduced. The reduced metal oxide acts as a catalyst for CO2 activation, converting CO2 to CO while releasing a certain amount of heat for the CH4 oxidation reaction, achieving a step-by-step energy utilization. Therefore, the metal oxide can simultaneously serve as an oxygen source for the partial oxidation of CH4 and a catalyst for the reduction of CO2, connecting the reduction and oxidation reactors to form a redox closed-loop reaction.

[0003] Metal oxides are key to the operation of chemical chaining systems. Currently, nickel-based, iron-based, copper-based, cerium-based composite metal oxides and oxides with special structures such as perovskites and hexaaluminates all have high CH4 / CO2 redox activity and strong thermal stability; however, the aforementioned metal oxides are all designed and constructed for the conversion of pure CO2, and the efficiency of catalytic conversion of CO2 and air mixtures is low. The energy consumption of CO2 gas purification increases exponentially with the increase of target purity, and the purification process of obtaining pure CO2 is energy-intensive and complex; in addition, in the technology of CO2 catalytic conversion, the output of CO will be limited by the storage / release capacity of metal oxides, resulting in low efficiency of CO2 thermal catalytic conversion. Summary of the Invention

[0004] In response to the defects and shortcomings of the existing technology, the present invention proposes a carbon material for the thermal catalytic reduction of impure CO2 and a preparation method thereof. The purpose is to improve the efficiency of the thermal catalytic reduction of impure CO2 by replacing the traditional metal oxide catalyst with a new carbon material catalyst, and solve the problems of high energy consumption for purifying CO2 and low CO production during the thermal catalytic conversion of CO2.

[0005] The present invention discloses a carbon material for thermal catalytic reduction of impure CO2. The components of the carbon material specifically include 20-50 wt.% of Ni, 10-20 wt.% of carbon deposits and 30-70 wt.% of CeO2 used as a carrier.

[0006] The present invention provides a method for preparing a carbon material for thermal catalytic reduction of impure CO2 as follows:

[0007] (1) dissolving nickel nitrate and cerium nitrate in deionized water respectively, and then mixing the obtained nickel nitrate solution and cerium nitrate solution to obtain a precursor solution; adding ethylene glycol and citric acid to the precursor solution, after the citric acid and ethylene glycol are evenly mixed, placing the precursor solution in a water bath and heating and stirring until the water evaporates and becomes a gel; then drying and calcining to obtain Ni-modified cerium metal oxide;

[0008] (2) The Ni-modified cerium metal oxide is placed in a fixed-bed reactor, heated to the cracking temperature under nitrogen protection, and switched to a CH4 atmosphere. The CH4 is cracked on the Ni-modified cerium metal oxide to generate carbon deposits in situ. The carbon deposits adhere to the metal oxide, thereby obtaining a carbon material that is not subjected to thermal catalytic reduction of pure CO2.

[0009] Preferably, the concentration of cerium nitrate and nickel nitrate in the precursor solution in step (1) is 0.1 to 0.5 M;

[0010] Preferably, the mass ratio of nickel nitrate to cerium nitrate in step (1) is 0.50 to 2.70;

[0011] Preferably, the amount of citric acid added in step (1) is Ni 2+ ions and Ce 3+ 1 to 3 times the amount of the total amount of ion substances, the amount of ethylene glycol added is Ni 2+ ions and Ce 3+ 1 to 6 times the amount of the total ion substance;

[0012] Preferably, in step (1), the precursor solution is heated in a water bath at a temperature of 60 to 90° C., the drying temperature is 100 to 120° C., and the calcination temperature is 500 to 900° C.;

[0013] Preferably, the cracking temperature in step (2) is 700-900°C, and the flow rate of CH4 is 40-150 mL / min;

[0014] Preferably, the prepared carbon material comprises: 20-50 wt.% Ni, 10-20 wt.% carbon deposits and 30-70 wt.% CeO2 used as a carrier;

[0015] Preferably, the conversion rate of the prepared carbon material for the thermal catalytic reduction of impure CO2 with a content of 20 to 100 vol.% is 70 to 90%.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. Compared with the existing thermal reduction CO2 catalyst, the carbon material catalyst of the present invention has higher oxygen resistance and can achieve efficient reduction of CO2 in an atmosphere of non-pure CO2 (a mixture of CO2 and air) with a content of 20 to 100 vol.%.

[0018] 2. The carbon material catalyst of the present invention directionally reduces impure CO2 to CO with a CO selectivity of 100% and a yield of up to 18.53 to 20.18 mmol / g, which is 4.50 to 9.43 times that of traditional metal oxides, greatly improving the catalytic conversion efficiency of impure CO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The X-ray powder diffraction spectra of the catalysts of Examples 1-3 and Comparative Examples 1-3 of the present invention are shown in FIG.

[0020] Figure 2 This is the Raman spectrum of the carbon material catalyst of Example 1 of the present invention.

[0021] Figure 3 This is the Raman spectrum of the carbon material catalyst of Example 2 of the present invention.

[0022] Figure 4 This is the Raman spectrum of the carbon material catalyst of Example 3 of the present invention.

[0023] Figure 5 The activity diagram of the non-pure CO2 reduction reaction of the carbon material catalyst of Examples 1-3 of the present invention is shown in FIG.

[0024] Figure 6 The activity diagram of the non-pure CO2 reduction reaction of the conventional metal oxide catalysts in comparative examples 1-3 of the present invention is shown in FIG.

[0025] Figure 7 2 is a comparison chart of the CO2 temperature-programmed reduction curves of the catalysts in Example 2 of the present invention and Comparative Example 4. DETAILED DESCRIPTION

[0026] In order to better understand the content of the present invention, the present invention will be further described below in conjunction with specific examples and drawings. The following examples are based on the technical solution of the present invention and provide detailed implementation methods and operating steps, but the protection scope of the present invention is not limited to the following examples.

[0027] The present invention discloses a carbon material for the thermal catalytic reduction of impure CO2, comprising 20-50 wt.% Ni, 30-70 wt.% CeO2, and 10-20 wt.% carbon deposits. The CeO2 serves as a carrier, and the Ni and carbon deposits serve as active components for the thermal catalytic conversion of CO2. The carbon deposits are generated in situ by the cracking of CH4 on Ni-modified cerium metal oxides. The carbon deposits generated in situ by the cracking can promote the reduction of CO2. The chemical formula is: MeO x -C+CO2→2CO+MeO x ; The present invention undergoes a reduction reaction with CO2 in non-pure CO2 (i.e., a mixture of CO2 and air) under the action of a carbon material catalyst to generate CO. The carbon material catalyst is a composite material of carbon deposits wrapped in metal oxides for thermal catalytic reduction of non-pure CO2. It has high oxygen resistance and high reaction activity, and achieves efficient reduction of CO2 in a non-pure CO2 atmosphere with a CO2 content of 20 to 100 vol.%, with a CO selectivity of 100%. The yield of generated CO is as high as 18.53 to 20.18 mmol / g, which is 4.50 to 9.43 times that of traditional metal oxide catalytic reduction of CO2.

[0028] The present invention provides a method for preparing a carbon material for thermal catalytic reduction of impure CO2, which specifically comprises the following steps:

[0029] (1) nickel nitrate and cerium nitrate are dissolved in deionized water at a mass ratio of nickel nitrate to cerium nitrate = 0.5 to 2.7, and then the obtained nickel nitrate solution and cerium nitrate solution are mixed to obtain a precursor solution; citric acid and ethylene glycol are added to the precursor solution in sequence, wherein citric acid serves as a complexing agent and ethylene glycol can improve the dispersion of metal ions in the precursor solution; after the citric acid and ethylene glycol are evenly mixed, the precursor solution is placed in a water bath at 60 to 90° C. and heated and stirred until the water evaporates and becomes a gel; then the precursor solution is dried and calcined to obtain Ni-modified cerium metal oxide, wherein the drying temperature is 100 to 120° C. and the calcination temperature is 500 to 900° C.;

[0030] (2) The Ni-modified cerium metal oxide is placed in a fixed bed reactor, and the temperature is raised to 700-900°C under a nitrogen atmosphere. The atmosphere is switched to CH4 with a CH4 flow rate of 40-150 mL / min. CH4 is cracked on the Ni-modified cerium metal oxide to generate carbon deposits in situ. The chemical equation of the cracking reaction is: CH4+MeO x →2H2+MeO x -C, carbon deposits adhere to the metal oxide, that is, a carbon material that is not pure CO2 thermal catalytic reduction is obtained.

[0031] The concentrations of cerium nitrate and nickel nitrate in the precursor solution of step (1) are 0.1-0.5M, and the amount of citric acid added is the amount of metal cations (Ni 2+ and Ce 3+ ions) is 1 to 3 times the amount of the total substance, and the amount of ethylene glycol added is the amount of metal cations (Ni 2+ and Ce 3+ ions) is 1 to 6 times the amount of the total substance.

[0032] The present invention is described in detail below with specific embodiments:

[0033] Example 1:

[0034] The carbon material prepared for the thermal catalytic reduction of impure CO2 is a 20wt.% Ni / CeO2-C catalyst, and the specific steps are as follows:

[0035] 2.6173 g of nickel nitrate and 4.9658 g of cerium nitrate were dissolved in 90 mL and 50 mL of deionized water, respectively. The nickel nitrate solution and the cerium nitrate solution were then mixed and stirred to obtain a precursor solution. 11.7727 g of citric acid and 1.5656 mL of ethylene glycol were added to the precursor solution, mixed evenly, and stirred in an 80°C water bath until the water evaporated and turned into a gel. The gel was then dried in a drying oven at 110°C. After drying, it was ground and calcined in a muffle furnace at 500°C for 4 h to obtain a Ni content of 20 wt.%. Ni-modified cerium metal oxide Ni / CeO2 (hereinafter referred to as 20wt.% Ni / CeO2, the same in other embodiments); 20wt.% Ni / CeO2 is placed in a fixed bed reactor, the temperature is raised to 850°C under nitrogen protection, and the CH4 atmosphere is switched (the flow rate of CH4 is 100mL / min). CH4 is cracked on the 20wt.% Ni / CeO2 to produce in situ carbon deposits (carbon deposit content is 10wt.%) attached to the metal oxide, and a 20wt.% Ni / CeO2-C catalyst can be obtained.

[0036] Example 2:

[0037] The carbon material prepared for the thermal catalytic reduction of impure CO2 is a 40wt.% Ni / CeO2-C catalyst, and the specific steps are as follows:

[0038] 4.9438 g of nickel nitrate and 3.0887 g of cerium nitrate were dissolved in 34 mL and 70 mL of deionized water, respectively. The nickel nitrate solution and the cerium nitrate solution were mixed and stirred to obtain a precursor solution. 9.2600 g of citric acid and 0.6245 mL of ethylene glycol were added to the precursor solution. After mixing evenly, the mixture was placed in a 90°C water bath and stirred until the water evaporated and turned into a gel. The gel was then placed in a drying oven at 100°C for drying. After drying, it was ground and placed in a 700°C oven. Calcinate in a muffle furnace for 4 hours to obtain 40wt.% Ni / CeO2; place 40wt.% Ni / CeO2 in a fixed bed reactor, heat to 900℃ under nitrogen protection, switch to CH4 atmosphere (CH4 flow rate is 40mL / min), CH4 is cracked on 40wt.% Ni / CeO2 to produce carbon deposits in situ (carbon deposit content is 14wt.%) attached to the metal oxide, and a 40wt.% Ni / CeO2-C catalyst can be obtained.

[0039] Example 3:

[0040] The carbon material prepared for the thermal catalytic reduction of impure CO2 is a 50wt.% Ni / CeO2-C catalyst, and the specific steps are as follows:

[0041] 4.9438 g of nickel nitrate and 1.8304 g of cerium nitrate were dissolved in 85 mL and 40 mL of deionized water, respectively. The nickel nitrate solution and the cerium nitrate solution were mixed and stirred to obtain a precursor solution. 7.3375 g of citric acid and 1.4631 mL of ethylene glycol were added to the precursor solution. After mixing evenly, the mixture was placed in a 60°C water bath and stirred until the water evaporated and turned into a gel. The gel was then placed in a drying oven at 120°C for drying. After drying, it was ground and placed in a 900°C oven. Calcinate in a muffle furnace for 4 hours to obtain 50wt.% Ni / CeO2; place 50wt.% Ni / CeO2 in a fixed bed reactor, raise the temperature to 900℃ under nitrogen protection, switch to CH4 atmosphere (CH4 flow rate is 150mL / min), CH4 is cracked on 50wt.% Ni / CeO2 to produce carbon deposits in situ (carbon deposit content is 20wt.%) attached to the metal oxide, and a 50wt.% Ni / CeO2-C catalyst can be obtained.

[0042] Comparative Example 1:

[0043] The conventional metal oxide 20 wt.% Ni / CeO2 catalyst was prepared by the following steps:

[0044] 2.6173g of nickel nitrate and 4.9658g of cerium nitrate were dissolved in 90mL and 50mL of deionized water, respectively. The nickel nitrate solution and the cerium nitrate solution were mixed and stirred to obtain a precursor solution. 11.7727g of citric acid and 1.5656mL of ethylene glycol were added to the precursor solution, mixed evenly, and placed in an 80°C water bath and stirred until the water evaporated and turned into a gel. The gel was then placed in a drying oven at 110°C to dry. After drying, it was ground and placed in a muffle furnace at 500°C for calcination for 4h. Finally, it was reduced under H2 atmosphere to obtain a 20wt.% Ni / CeO2 catalyst.

[0045] Comparative Example 2:

[0046] The conventional metal oxide 40 wt.% Ni / CeO2 catalyst was prepared by the following steps:

[0047] 4.9438g of nickel nitrate and 3.0887g of cerium nitrate were dissolved in 34mL and 70mL of deionized water, respectively. The nickel nitrate solution and the cerium nitrate solution were mixed and stirred to obtain a precursor solution. 9.2600g of citric acid and 0.6245mL of ethylene glycol were added to the precursor solution, mixed evenly, and placed in a 90°C water bath and stirred until the water evaporated and turned into a gel. The gel was then placed in a drying oven at 100°C for drying. After drying, it was ground and placed in a muffle furnace at 700°C for calcination for 4h. Finally, it was reduced under H2 atmosphere to obtain a 40wt.% Ni / CeO2 catalyst.

[0048] Comparative Example 3:

[0049] The conventional metal oxide 50wt.% Ni / CeO2 catalyst was prepared by the following steps:

[0050] 4.9438g of nickel nitrate and 1.8304g of cerium nitrate were dissolved in 85mL and 40mL of deionized water, respectively. The nickel nitrate solution and the cerium nitrate solution were mixed and stirred to obtain a precursor solution. 7.3375g of citric acid and 1.4631mL of ethylene glycol were added to the precursor solution, mixed evenly, and placed in a 60°C water bath and stirred until the water evaporated and turned into a gel. The gel was then placed in a drying oven at 120°C to dry. After drying, it was ground and placed in a muffle furnace at 900°C for calcination for 4h. Finally, it was reduced under H2 atmosphere to obtain a 50wt.% Ni / CeO2 catalyst.

[0051] Figure 1 The X-ray powder diffraction spectra of the catalysts of Examples 1-3 and Comparative Examples 1-3 of the present invention were obtained. During the test, the light source was a copper target Kα line (λ = 0.15406 nm), the X-ray tube voltage was U = 40 kV, the current was I = 40 mA, and the scanning range was 10-80°. Figure 1The crystal phase structure of the catalyst can be seen: the carbon material catalysts prepared in Examples 1-3 of the present invention and the traditional metal oxide catalysts in Comparative Examples 1-3 have the same crystal phase, both showing a coexisting crystal phase of Ni and CeO2; but since no signal peak of C was observed on the carbon material catalysts prepared in Examples 1-3, most of the carbon deposits formed by the cracking of CH4 on 20wt.%, 40wt.% and 50wt.% Ni / CeO2-C are amorphous.

[0052] Figure 2-4 The Raman spectra of the carbon material catalysts of Examples 1-3 of the present invention are shown. During the test, the excitation wavelength was 532 nm and the scanning range was 100-2000 cm -1 ;Depend on Figure 2 It can be seen that there are two band peaks on the carbon material catalysts prepared in Examples 1-3 of the present invention: 1343 cm -1 D band at 1575cm -1 The G band peak at , where the G band is attributed to the stretching vibration of the C-C bond in the graphite layer plane, and the D band is attributed to the structural defects of graphite or a disordered structure. The degree of graphitization of carbon material catalysts can be measured by the peak intensity ratio of D and G bands (I D / I G ) is represented by: I of the carbon material obtained by calculating Example 1-3 D / I G The ratios of are 0.6132, 0.6113, and 0.5938, respectively; therefore, the carbon materials prepared in Examples 1-3 contain some graphite.

[0053] Figure 5-6 This is an activity diagram of the non-pure CO2 reduction reaction of the carbon material catalyst of Examples 1-3 of the present invention and the traditional metal oxide catalyst of Comparative Examples 1-3. The non-pure CO2 reduction reaction activity of the Ni / CeO2-C catalyst and the Ni / CeO2 catalyst was carried out in a fixed bed reactor at 700°C under normal pressure, wherein the amount of the catalyst was 200 mg, the reaction temperature of CO2 was 700°C, and the CO2 reduction test was carried out in 5 vol.% CO2 / air, 50 vol.% CO2 / air, and pure CO2 atmospheres for Examples 1-3 and Comparative Examples 1-3, respectively; Figure 5-6 It can be seen that the carbon material catalyst prepared in the present invention has a non-pure CO2 conversion rate of 70-90%, and a CO production of 18.54-20.18 mmol / g. Compared to the conventional metal oxide catalysts prepared in Comparative Examples 1-3, the non-pure CO2 conversion rate was 30-40%, and the CO production was 2.04-4.12 mmol / g. Through the above comparison, the carbon material catalyst has a non-CO2 conversion rate of 1.75-3 times that of the conventional metal oxide catalyst under the same experimental conditions, and a CO production of 4.50-9.43 times that of the conventional metal oxide catalyst.

[0054] Comparative Example 4: Using existing C (McLean) as a catalyst, this comparative example and Example 2 were subjected to a CO2 programmed temperature reduction test. The test was carried out in a fixed-bed reactor at atmospheric pressure, and a multi-component gas online analysis mass spectrometer was used for gas detection and recording.

[0055] Figure 7 The comparison diagram of CO2 temperature-programmed reduction curves of the catalysts in Example 2 of the present invention and Comparative Example 4 is shown in FIG. Figure 7 It can be seen that no obvious CO2 consumption peak was observed for the C catalyst in the entire temperature window of 100-900°C, indicating that graphite C alone is inert to CO2; while the in situ generated carbon material in Example 2, as a catalyst, sharply increased CO2 consumption in the high temperature zone (above 500°C). The comparison shows that the carbon material in situ generated on Ni-modified cerium metal oxide has high catalytic reaction activity for CO2.

[0056] The present invention can have other embodiments according to the above preparation method, which are not listed one by one. Therefore, any simple modification, equivalent change and modification made by any person skilled in the art to the above embodiment according to the technical essence of the present invention without departing from the scope of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A carbon material for the thermal catalytic reduction of impure CO2, characterized in that: The components specifically include 20-50 wt.% of Ni, 10-20 wt.% of carbon deposits, and 30-70 wt.% of CeO2 used as a carrier; The method for preparing the carbon material for the thermal catalytic reduction of impure CO2 specifically comprises the following steps: (1) Dissolve nickel nitrate and cerium nitrate in deionized water respectively, and then mix the obtained nickel nitrate solution and cerium nitrate solution to prepare a precursor solution, wherein the concentration of cerium nitrate and nickel nitrate in the precursor solution is 0.1-0.5 M, and the mass ratio of nickel nitrate to cerium nitrate is 0.50-2.70; add ethylene glycol and citric acid to the precursor solution, mix the citric acid and ethylene glycol evenly, and then place the precursor solution in a water bath and heat and stir until the water evaporates and becomes a gel; then dry and calcine to obtain Ni-modified cerium metal oxide; (2) The Ni-modified cerium metal oxide is placed in a fixed-bed reactor, and the temperature is raised to a cracking temperature of 700-900°C under nitrogen protection. The atmosphere is switched to CH4 with a flow rate of 40-150 mL / min. CH4 is cracked on the Ni-modified cerium metal oxide to generate carbon deposits in situ. The carbon deposits adhere to the metal oxide, and a non-pure CO2 thermal catalytic reduction carbon material is obtained.

2. A carbon material for thermal catalytic reduction of impure CO2 according to claim 1, characterized in that: The amount of citric acid added in step (1) is Ni 2+ ions and Ce 3+ 1 to 3 times the amount of the total amount of ion substances, the amount of ethylene glycol added is Ni 2+ ions and Ce 3+ 1 to 6 times the amount of the total ion substance.

3. The carbon material for thermal catalytic reduction of impure CO2 according to claim 1, characterized in that: In the step (1), the precursor solution is heated in a water bath at a temperature of 60 to 90° C., the drying temperature is 100 to 120° C., and the calcination temperature is 500 to 900° C.

4. The use of a carbon material for the thermal catalytic reduction of impure CO2 as claimed in claim 1 in the thermal catalytic directional reduction of impure CO2 to CO, characterized in that: The conversion rate of the prepared carbon material for the thermal catalytic reduction of impure CO2 with a content of 20 to 100 vol.% is 70 to 90%, wherein the impure CO2 specifically refers to a mixture of CO2 and air.

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