CN102600854A - Catalyst for carbon dioxide methanation and preparation method thereof - Google Patents

Abstract

The invention discloses a carbon dioxide methanation catalyst and a preparation method thereof, belonging to the technical field of carbon dioxide methanation. The invention provides a catalyst for carbon dioxide methanation, which is composed of composite carrier and active component, composite carrier: active component=84-90wt%: 10-16wt%; wherein, the composite carrier is made of γ- _{Al2O 3} and water-soluble metal oxides, the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxides is 77-86:2-10; the active component is Ni, which exists in the catalyst in the form of NiO . The catalyst of the invention has high activity and low cost, and the catalyst can be used for the methanation reaction of carbon dioxide under normal pressure conditions, and has good stability.

Description

Catalyst for carbon dioxide methanation and preparation method thereof

technical field

The invention belongs to the technical field of carbon dioxide methanation, and in particular relates to a catalyst for carbon dioxide methanation and a preparation method thereof.

Background technique

Carbon dioxide is one of the most abundant carbon sources on earth. With the increasing depletion of petroleum resources and the serious ecological and environmental problems caused by the massive emission of carbon dioxide into the atmosphere, the transformation of greenhouse gas _CO2 into high value-added chemical products has become a hot topic of research and discussion in domestic and foreign industries and academic circles. In 1902, French chemist Paul sabatier first reported the catalytic hydrogenation reduction technology of carbon dioxide (that is, the methanation reaction of CO ₂ ): CO ₂ (g)+4H ₂ (g)=CH ₄ (g)+2H ₂ O( g) Δ _R H ⁰ 298K=-252.9KJ·mol ^-1 , hydrogenation of CO ₂ to synthesize methane gas, on the one hand turning CO ₂ The generated methane can be used as high-quality city gas, and the technological process is simple, the investment is small, and the cost is low.

Jiang Qi et al. (Jiang Qi, Deng Guocai, Chen Rongti, Huang Zhongtao. Acta Catalytica Sinica 18 (1997) 42-45) reported that γ-Al ₂ O ₃ carrier was impregnated with 10wt% nickel nitrate aqueous solution, calcined in 450°C air atmosphere, and prepared A 10 wt% Ni/γ- _Al2O3 catalyst was used for the _CO2 methanation reaction, _and it was found that the conversion of _CO2 was only 15.2% at 300 °C, and the selectivity of _CH4 was 97.5%. Chu Wei et al. (Mengdie Cai, Jie Wen, Wei Chu, Xueqing Cheng, Zejun Li. Journal of Natural Gas Chemistry20(2011): 318-324) reported that 12wt%Ni/88%γ-Al ₂ O ₃ catalyst was used In the _CO2 methanation reaction, it was found that there was no reactivity below 240 °C. With the increase of the reaction temperature, the conversion rate of _CO2 and the yield of _CH4 showed an obvious upward trend. At 360 °C, the conversion of _CO2 The yield of CH ₄ was 24.8%, and the yield of CH 4 was 24.3%. Then the reaction stability of the 12wt% Ni/γ-Al ₂ O ₃ catalyst at 360°C was investigated, and it was found that the active component metal nickel The aggregation and carbon deposition of the reaction caused the conversion rate of _CO2 to drop to 16.5% after 50 h of reaction, indicating that the catalyst had poor reactivity and stability performance.

In order to improve the activity of the Ni catalyst, as described in Chinese patent CN9510367.2, the catalyst prepared by adding noble metal Ru to the catalyst has higher activity, but the addition of Ru will inevitably increase the production cost of the catalyst. Chinese patent CN101884927 discloses a catalyst for complete methanation of carbon dioxide and its preparation method. The mass percent composition of each component in the catalyst is: γ-Al ₂ O ₃ : 60-80%; NiO: 10-20% ; Fe ₂ O ₃ : 5-15%; MgO: 1-10%; La ₂ O ₃ or CeO ₂ : 1-10%, but this catalyst is mainly suitable for the complete methanation of carbon dioxide at medium pressure 3.0-5.0MPa, The catalyst we reported in Example 1 of this patent (the main components of the catalyst and its proportioning ratio are: 16.9% NiO-6.5% Fe ₂ O ₃ -3.3% MgO-2.8% CeO ₂ -70.5% γ-Al ₂ O ₃ ) Applied to the carbon dioxide methanation reaction under normal pressure conditions, it was found that the conversion rate of _CO2 was 87.5% and the methane selectivity was 100% at 360 °C, but after a 100h stability test, the conversion rate of _CO2 dropped to 80.3%, The selectivity of _CH4 is also reduced to 99.4%, indicating that the catalyst for complete methanation of carbon dioxide disclosed in Chinese patent CN101884927 is only suitable for _CO2 methanation reaction under medium pressure, and due to the aggregation and surface area of the active components of the catalyst during the reaction process The formation of carbon leads to a decrease in the activity of the catalyst, and the reaction stability of the catalyst is poor.

Contents of the invention

Aiming at the above defects, the present invention provides a carbon dioxide methanation catalyst, which has high activity and low cost, can be used for carbon dioxide methanation reaction under normal pressure conditions, and has good stability.

Technical scheme of the present invention is:

The invention provides a catalyst for carbon dioxide methanation, which is composed of composite carrier and active component, composite carrier: active component=84-90wt%: 10-16wt%; wherein, the composite carrier is made of γ- _{Al2O 3} and water-soluble metal oxides, the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxides is 77-86:2-10; the active component is Ni, which exists in the catalyst in the form of NiO .

The water-soluble metal oxide is at least one of CeO ₂ , ZrO ₂ or La ₂ O ₃ .

Preferably, the mass ratio of each component in the catalyst is: composite support: active component = 84-88: 12-16; the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxide in the composite support is 78-86 : 2-6.

More preferably, the mass ratio of each component in the catalyst is: composite support:active component=84.7:15.3; the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxide in the composite support is 78.7:6.

More preferably, the mass ratio of each component in the catalyst is: composite support:active component=87.3:12.7; the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxide in the composite support is 81.3:6.

The composite support is at least one of CeO ₂ /γ-Al ₂ O ₃ , ZrO ₂ /γ-Al ₂ O ₃ or La ₂ O ₃ /γ-Al ₂ O ₃ ; preferably CeO ₂ /γ-Al ₂ O ₃ .

The preparation method of the catalyst for methanation of carbon dioxide in the present invention is specifically as follows: first, the composite carrier is prepared by the impregnation-precipitation method, and then the composite carrier and the active component salt solution are prepared by the impregnation method to obtain the catalyst precursor; the catalyst precursor is dried and plasma treated After that, the carbon dioxide methanation catalyst of the present invention is obtained.

The concrete steps of the present invention's preparation above-mentioned carbon dioxide methanation catalyst method are:

1) Prepare the composite carrier by impregnation-precipitation method: impregnate the salt solution corresponding to the water-soluble metal oxide on the γ-Al ₂ O ₃ carrier at room temperature, and then introduce a precipitant until the pH of the solution is 8-10. After 2-4 hours, filter, wash, dry, and heat to decompose to obtain a composite carrier; wherein, the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxide is 77-86:2-10; the precipitating agent is NH ₃ H ₂ O, Na ₂ CO ₃ , NaOH;

2) Preparation of the catalyst precursor: the active component salt solution is loaded on the composite carrier obtained in step 1) by an equal-volume impregnation method; wherein, the composite carrier: active component=84-90%: 10-16%; impregnation The temperature is normal temperature, and the soaking time is 3-5 hours;

3) Preparation of the catalyst: the catalyst precursor obtained in step 2) is dried and subjected to plasma treatment at normal temperature and pressure to obtain the carbon dioxide methanation catalyst of the present invention.

Further, the present invention also provides a method for using the above-mentioned catalyst for carbon dioxide methanation, the application conditions of the catalyst for catalyzing the carbon dioxide methanation reaction are: the reaction pressure is normal pressure, and the volume space velocity of the raw material gas is 8100-15000ml/(h·g _cat ), the molar ratio of H ₂ /CO ₂ is 2/1-4/1.

Preferably, the volume space velocity of the raw material gas is 10000 ml/(h·g _cat ), and the molar ratio of H ₂ /CO ₂ is 4:1.

Beneficial effects of the present invention:

The addition of water-soluble metal oxides in the composite carrier of the catalyst of the present invention improves the dispersion degree of the active component Ni on the base carrier γ-Al ₂ O _3. Before the water-soluble metal oxide content does not reach the maximum dispersion, the Ni content The degree of dispersion increases with the increase of the water-soluble metal oxide content; the present invention has explored the addition of appropriate metal oxide (if its addition is too large, it is easy to agglomerate on the one hand and is not conducive to the dispersion of NiO on the carrier surface, and on the other hand On the one hand, metal oxides may form solid solutions with NiO to hinder its reduction), and the resulting catalysts have high _CO2 conversion and 100% _CH4 selectivity.

In addition, the present invention introduces plasma technology to replace the high-temperature calcination treatment in the existing preparation method (the catalyst for methanation of carbon dioxide in the prior art is usually loaded on the surface of the oxide by impregnation with salts of transition metals, and then roasted at high temperature to reduce and prepared), because the high-temperature roasting process is avoided, the particle size of the active component of the catalyst is small, and the dispersion of the active component on the surface of the carrier is more uniform, and NiO changes from crystal to highly dispersed amorphous phase on the surface of the catalyst. It has extremely high catalytic activity and good stability, and the catalyst can catalyze the complete methanation reaction of carbon dioxide under normal pressure and certain H ₂ /CO ₂ conditions. At the same time, because the method of the invention does not need to use noble metals, its cost is greatly reduced compared with noble metal catalysts.

The present invention uses plasma to modify the catalyst, and the catalyst is placed in a plasma reactor to carry out modification treatment under certain conditions. The low-temperature catalytic conversion ability of the obtained _catalyst is significantly improved. It can reach about 85-90%. Compared with traditional catalyst preparation methods, the preparation of catalysts by plasma technology has the advantages of simple operation, short process flow, low energy consumption, intuitive and easy-to-control catalyst change process, clean and pollution-free, etc.; the catalyst prepared by using plasma technology has a large specific surface area, The reduction rate is fast, the number of active centers is large, the catalyst particles are small, and the dispersion is high.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

Fig. 2 is a diagram of the plasma generator of the present invention.

Fig. 3 is the 12.7wt% NiO/6wt% CeO ₂ /81.3wt% γ-Al ₂ O ₃ catalyst prepared in Example 2 and the 12.7wt% NiO/87.3wt% γ-Al ₂ O ₃ prepared in Comparative Example 2 Temperature-programmed reduction test (TPR) diagram. As can be seen from Figure 3, the catalyst prepared in Comparative Example 2 has two reduction peaks, located at 318°C and 692°C, which belong to the free NiO crystal phase with weak interaction with the support γ-Al ₂ O ₃ and the support γ-Al 2 O 3 Reduction peaks _{of Al2O3} strongly _{interacting NiAl2O4} spinel. However, the catalyst prepared in Example 2 has four reduction peaks, and the area of the reduction peaks is larger than that of the catalyst of Comparative Example 2. This indicates that after the addition of _CeO2 , the interaction between Ni-Al is adjusted, on the one hand, it promotes _the interaction between _the surface NiO crystal phase and the support γ- _Al2O3 , and on the other hand, it weakens the interaction between the entering _Al2O3 The strong interaction between Ni ²⁺ and Al ₂ O ₃ in the crystal lattice makes most of the nickel elements in the catalyst form xNiO-Al ₂ O ₃ solid solution structure, while CeO ₂ promotes the reduction of NiO species. Compared with the catalyst of Comparative Example 2, the reduction peak shape of the catalyst in Example 2 has changed, and a shoulder peak appears at about 402°C, which belongs to the reduction peak of _CeO2 lattice oxygen, except for the main reduction peak at about 587°C , a shoulder peak appeared around 742°C, which belonged to the reduction peak of the NiO-CeO ₂ solid solution, indicating that there was obviously a strong interaction between NiO and CeO ₂ in the catalyst prepared in Example 2, and this strong interaction was very beneficial to the catalyst Reduction of surface NiO species.

Figure 4 is the 12.7wt% NiO/6wt% CeO ₂ /81.3wt% γ- _{Al 2} O ₃ catalyst prepared in Example 2 and the 12.7wt% NiO/87.3wt% γ-Al ₂ O ₃ catalyst prepared in Comparative Example 2 X-ray diffraction pattern (XRD) after firing. As can be seen from the figure, the intensity of each characteristic diffraction peak of NiO in the catalyst prepared in Example 2 is weaker than that of the catalyst prepared in Comparative Example 2, especially on the catalyst of Example 2, the (220) crystal plane of NiO becomes very sharp. Clearly, illustrate that the grain size of the corresponding catalyst NiO of embodiment 2 is smaller than the corresponding value of the catalyst of comparative example 2, further illustrate, add _CeO The dispersion degree of the nickel-based catalyst active metal NiO that the composite carrier prepared is loaded is better, combines According to the TPR characterization, it can be considered that there is an interaction between the supported CeO ₂ species and NiO, and this interaction increases the dispersion of each other.

Fig. 5(a) is the scanning electron microscope and X-ray energy spectrum analysis pattern (SEM-EDX) of the 12.7wt% NiO/6wt% CeO ₂ /81.3wt% γ-Al ₂ O ₃ catalyst prepared in Example 2. Fig. 5(b) is the scanning electron microscope and X-ray energy spectrum analysis pattern of the 12.7wt% NiO/87.3wt% γ-Al ₂ O ₃ catalyst prepared in Comparative Example 2. As can be seen from the photo in Figure 5, the size of the catalyst surface active metal particles prepared in Comparative Example 2 is larger than that of the catalyst surface particles prepared in Example 2, and the latter is much more uniform. Combining the X-ray diffraction pattern and the temperature-programmed reduction characterization, it is further explained After the addition of CeO ₂ , the interaction of the additive CeO ₂ with the active metal Ni promotes the dispersion of the active metal Ni on the catalyst surface.

Figure 6 shows the 12.7wt% NiO/6wt% CeO ₂ /81.3wt% γ-Al ₂ O ₃ catalyst prepared in Example 1 and the 12.7wt% NiO/87.3wt% γ-Al ₂ O ₃ catalyst prepared in Comparative Example 2. Graph of _CO2 conversion in _CO2 methanation reaction as a function of reaction time. As can be seen from Figure 6, as the reaction proceeds, the activity of the catalyst prepared in Comparative Example 2 gradually decreases, and after 26 hours, the rate of decline in activity significantly accelerates, and the _CO conversion rate is only about 41.2% in 100 hours; while the catalyst prepared in Example 1 Although the catalytic activity of the catalyst decreased, the decline was not large. When the reaction lasted for 100 hours, the _CO2 conversion rate was still as high as about 80.3%. This shows that the rare earth metal oxide _CeO2 can not only improve the reactivity of the nickel-based catalyst, but also significantly improve the stability of the nickel-based catalyst and prolong the service life of the catalyst.

Detailed ways

The invention provides a catalyst for carbon dioxide methanation, which is composed of composite carrier and active component, composite carrier: active component=84-90wt%: 10-16wt%; wherein, the composite carrier is made of γ- _{Al2O 3} and water-soluble metal oxides, the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxides is 77-86:2-10; the active component is Ni, which exists in the catalyst in the form of NiO ; and the catalyst is treated with plasma before use.

The present invention introduces plasma technology to replace the high-temperature roasting treatment in the existing preparation method. Since the high-temperature roasting process is avoided, the particle size of the active component of the catalyst is small, and the obtained catalyst has a large specific surface area, a fast reduction rate, and a large number of active centers. The size of the active components is small, the dispersion is high, and there will be no sintering and agglomeration during the preparation process, so it shows high catalytic activity and good stability in the reaction.

In the catalyst of the present invention, when the loading amount of the active component is too small, Ni ²⁺ easily enters the Al ₂ O ₃ lattice during the calcination process to form NiAl ₂ O ₄ with tetrahedral coordination. This spinel structure makes the species due to It is difficult to reduce in hydrogen and affect the activity; when the loading is too high, free NiO will appear, and the appearance of NiO may not only cause waste of active metals, but also cause sintering, which needs to be avoided; choose a suitable loading Quantity can both increase conversion rate and save cost. The addition of water-soluble metals can improve the physical and chemical properties of the support surface, which is beneficial to the dispersion of active metals, but if the loading amount is too high, water-soluble metal oxides will aggregate on the surface of γ-Al ₂ O ₃ , which is not conducive to the active metal NiO dispersion on the surface.

The present invention also provides a preparation method of the above-mentioned carbon dioxide methanation catalyst, which changes the roasting treatment in the existing preparation method of the carbon dioxide methanation catalyst to plasma treatment. Specifically: the composite carrier is first prepared by the impregnation-precipitation method, and then the composite carrier and the active component salt solution are impregnated with an equal volume to obtain the catalyst precursor; the catalyst precursor is dried and plasma treated to obtain the carbon dioxide methane of the present invention. chemical catalyst.

The concrete steps of the catalyst preparation method for carbon dioxide methanation of the present invention are:

1) Prepare the composite carrier by impregnation-precipitation method: impregnate the salt solution corresponding to the water-soluble metal oxide on the γ-Al ₂ O ₃ carrier by stirring at room temperature, and the immersion time is 4-6 hours to make the water-soluble metal oxide The corresponding salt solution completely enters the gamma-Al ₂ O ₃ carrier; and then introduces the precipitating agent until the pH value of the solution is 8-10 (the Ce(OH) ₃ precipitate begins to form when the pH value is ≥8, and the pH value is 8-10 In an alkaline environment, it is easy to form small crystal grains with good dispersion. If the pH value is too high, the particles will be agglomerated sharply). The purpose of adding a precipitant is to better evenly load the salt solution corresponding to the water-soluble metal oxide On the surface of the base carrier γ-Al ₂ O ₃ ; after the solution is uniformly precipitated, it is allowed to stand for 2-4 hours to allow the crystal grains to form and grow to a certain particle size, and then filter, wash, dry, and heat to decompose to obtain a composite carrier;

Wherein, the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxide is 77-86:2-10; the precipitant is NH ₃ ·H ₂ O, Na ₂ CO ₃ , NaOH; the drying condition is 100- Drying at 120°C for 12-24 hours; thermal decomposition means roasting at 450-600°C for 4-6 hours, preferably at 550°C for 5 hours; the concentration of precipitant is preferably 0.8mol/L;

2) Preparation of the catalyst precursor: the active component salt solution is loaded on the composite carrier obtained in step 1) by an equal-volume impregnation method; wherein, the composite carrier: active component=84-90wt%: 10-16wt%; impregnation The temperature is normal temperature, and the soaking time is 3-5 hours; preferably 4 hours;

3) Preparation of the catalyst: After the catalyst precursor obtained in step 2) is dried, the plasma treatment is carried out under normal temperature and pressure, wherein the plasma treatment conditions are: the degree of vacuum is 2-200Pa, the treatment time is 45-120min, and the drying condition is : Dry at 100-120°C for 12-24 hours to obtain the carbon dioxide methanation catalyst of the present invention.

The present invention introduces plasma technology to replace the high-temperature roasting treatment in the existing preparation method (the catalyst for methanation of carbon dioxide in the prior art is usually prepared by impregnating and loading the oxide surface with salts of transition metals, and then roasting at high temperature and reducing it. get), due to avoiding the high-temperature roasting process (the temperature in the plasma discharge region is very low), thereby avoiding many adverse reactions at high temperatures, it is not easy to agglomerate and sinter, and the obtained catalyst active component particle size is small, and the dispersion is better, making The stability of the catalyst has also been significantly improved. In addition, plasma technology can enhance and improve the adhesion and interaction between the metal and the carrier, increase the reduction degree of the catalytic active metal and the number of surface active centers, thereby enhancing the reduction ability of the catalyst and improving the dispersion. In addition, the catalyst prepared by plasma technology has the characteristics of large specific surface area, fast reduction rate and large number of active centers.

The present invention preferably adopts non-equilibrium cold plasma treatment, which is characterized by high electron temperature (10 ⁴ -10 ⁵ K) and relatively low gas temperature, which can effectively avoid the damage to catalyst structure and crystal form during high temperature treatment; radio frequency plasma As a kind of non-equilibrium cold plasma, the bulk technology can excite, dissociate and ionize the reactant molecules by using external energy on the molecular scale, and generate a large number of non-equilibrium high-energy activated species. Due to the bombardment of high-energy electrons and ions on the surface, it can Lowering the decomposition temperature and reduction temperature of the catalyst precursor, its thermal and chemical effects can effectively promote the interaction between the catalyst active components and the support.

The selection of the degree of vacuum in the present invention is based on the fact that the treatment atmosphere has a better treatment effect without the influence of air, and the influence of air cannot be ignored when the degree of vacuum is higher than 200Pa. The treatment time should be controlled when Ni ^O and NiO exist simultaneously on the surface of the catalyst, so that the catalyst will have high catalytic activity and stability; when the treatment time is less than 45 minutes, the catalyst will not be completely decomposed, and the treatment time is more than 120 minutes , more Ni ⁰ phases are formed, and the plasma treatment gas electron temperature is as high as 10 ⁴ K, too long treatment time will affect the interaction between the metal and the support, which is not conducive to the effective dispersion of the active metal.

Preferably, the plasma treatment conditions in the above method are: input voltage 60-120V, gas flow rate 20-45ml/min, radio frequency 13.56MHz; discharge parameters: positive current 100±10mA, grid current 50±10mA; gas is N ₂ , H ₂ , air or Ar.

Further, the present invention also provides a method for using the above-mentioned catalyst for carbon dioxide methanation, the application conditions of the catalyst for catalyzing the carbon dioxide methanation reaction are: the reaction pressure is normal pressure, and the volume space velocity of the raw material gas is 8100-15000ml/(h·g _cat ), the molar ratio of H ₂ /CO ₂ is 2/1-4/1. Gas volume space velocity is: under specified conditions, the volume of raw material gas per unit mass of catalyst per unit time, that is: space velocity = raw gas volume flow rate/catalyst mass. And the larger the space velocity, the shorter the residence time, the lower the reaction depth, but the enhanced processing capacity; the smaller the space velocity, the longer the residence time, the increased reaction depth, but the reduced processing capacity.

Preferably, the volume space velocity of the raw material gas is 10000 ml/(h·g _cat ), and the molar ratio of H ₂ /CO ₂ is 4:1.

The present invention is specifically described below by the examples, it is necessary to point out that the examples are only used to further illustrate the present invention, and can not be interpreted as limiting the protection scope of the present invention, those skilled in the art can make some non-essential according to the present invention improvements and adjustments.

Example 1 Preparation of 12.7wt% NiO/6.0wt% CeO ₂ -81.3wt% γ-Al ₂ O ₃ catalyst

A: First, prepare the CeO ₂ /γ-Al ₂ O ₃ composite carrier by the dipping-precipitation method: weigh 1.06g Ce(NO ₃ ) ₃ 6H ₂ O in a beaker, add 20ml of deionized water and stir to dissolve it; Weigh 4.65g γ-Al ₂ O ₃ into the above solution, stir at room temperature for 60min, then slowly add the precipitant NH ₃ ·H ₂ O (0.8mol/L) dropwise to pH = 9, stir for 2 hours to make the precipitation uniform After aging (aging means standing at room temperature) for 2 hours, filter, wash, dry overnight at 120°C, and then bake at 550°C for 5 hours to obtain a CeO ₂ /γ-Al ₂ O ₃ composite carrier, wherein the mass of CeO ₂ The fraction is 6.0wt%;

Preparation of B catalyst precursor: Weigh 2.83g Ni(NO ₃ ) ₂ (analytical grade, commercially available) in a beaker, add 20ml of deionized water and stir to dissolve it; weigh 5g of CeO ₂ /γ -Al ₂ O ₃ composite carrier was placed in a magnetic crucible, and the prepared Ni(NO ₃ ) ₂ impregnating solution was added dropwise into the crucible at room temperature, adsorbed and impregnated for 4 hours, and kept stirring until all the impregnated solution was completely impregnated into the CeO ₂ /γ-Al ₂ O ₃ composite support;

Preparation of catalyst C: After the catalyst precursor obtained in step B was evaporated to dryness in a water bath at 80°C, it was placed in a drying oven and dried overnight at 110°C, and the dried sample was placed in a glass desiccator for later use; at room temperature, weigh the above Spread 1.0 g of the sample in a discharge glass tube, conduct plasma treatment under the condition of vacuum degree of 100Pa, pass in discharge gas N ₂ (the flow rate is 30ml/min), adjust the input voltage to 100V, radio frequency to 13.56MHz, and the processing time to 60min. A finished catalyst is obtained.

The mass percentage composition of each component in the catalyst is as follows: NiO: 12.7%; γ-Al ₂ O ₃ : 81.3%; CeO ₂ : 6.0%.

Example 2-11

Compared with Example 1, only the content of catalyst components or the types of nickel salt and water-soluble metal salt used are different, and other processes are the same as in Example 1 to obtain various finished catalysts. The catalyst compositions of Examples 2 to 11 and the nickel salts and water-soluble metal salts used are shown in Table 1.

Table 1 Catalyst Composition Table

The catalyst obtained in Examples 1-11 was pressed into tablets and sieved to obtain 60-80 mesh catalyst particles, and 200 mg was filled in a fixed-bed reactor, and hydrogen was used for in-situ reduction. The reduction temperature was 450 ° C, and the reaction pressure was normal pressure. The raw material gas ratio is n(H ₂ ):n(CO ₂ )=4:1, the gas volume space velocity is 10000ml/h·g _cat , and the temperature range of investigation is 240-360°C. The GC-1690 gas chromatograph (TCD ) TDX01 chromatographic column to analyze the tail gas composition, and the data is recorded by the chromatographic workstation N2000.

The conversion rate, selectivity and productive rate of reaction are calculated as follows:

x _p ＝f _p ·A _p /∑(f _i ·A _i )

X(CO ₂ )＝(F _in x _in (CO ₂ )-F _out x _out (CO ₂ ))/(F _in x _in (CO ₂ ))×100%

X(H ₂ )＝(F _in x _in (H ₂ )-F _out x _out (H ₂ ))/(F _in x _in (H ₂ ))×100%

S(CH ₄ )＝F _out x _out (CH ₄ )/(F _in x _in (CO ₂ )-F _out x _out (CO ₂ ))×100%

Y(CH ₄ )=X(CO ₂ )·S(CH ₄ )×100%

In the formula: x _p - the percentage content of species p; f _p - the correction factor of species p; F - gas flow rate;

A _p - peak area of species p; X - conversion; Y - yield; S - selectivity

The activity test results of the catalysts obtained in Examples 1-11 (that is, the conversion rate of CO _{2 CO 2} /% and the selectivity S _{CH 4 /% of CH 4} ) are shown in Table 2. In addition, we counted the activity of the catalysts obtained in the examples corresponding to different CeO ₂ contents, and the evaluation results (CO ₂ conversion rate) are shown in Table 3.

Comparative Example 1 Preparation of 12.7wt% NiO/87.3wt% γ-Al ₂ O ₃ catalyst - plasma method

The present invention also studies the nickel catalyst with γ-Al ₂ O ₃ as a single carrier. The specific preparation process is as follows: 1) Weigh 2.83g Ni(NO ₃ ) ₂ (analytically pure, commercially available) in a beaker, add Stir with 20ml of deionized water to dissolve it; weigh 5g of γ-Al ₂ O ₃ and place it in a magnetic crucible, add the prepared impregnation solution drop by drop into the crucible, absorb and impregnate at room temperature for 4 hours, and keep stirring until all impregnation The solution was completely immersed in γ-Al ₂ O ₃ ; after that, it was evaporated to dryness in a water bath at 80°C, and then placed in a drying oven to dry overnight at 110°C; the dried samples were placed in a glass desiccator for later use. 2) At room temperature, weigh 1.0 g of the above-mentioned sample and lay it flat in a discharge glass tube, conduct plasma treatment under the condition of vacuum degree of 100 Pa, and pass in discharge gas N ₂ (flow rate is 30ml/min), adjust the input voltage to 100V, The radio frequency was 13.56 MHz, and the treatment time was 60 minutes to obtain a finished catalyst. The mass percent composition of each component in the catalyst is: γ-Al ₂ O ₃ : 87.3%; NiO: 12.7%. The activity test results of the obtained catalysts (i.e. _CO2 conversion rate X _CO2 /% and _CH4 selectivity S _CH4 /%) are shown in Table 2.

Comparative Example 2 Preparation of 12.7wt% NiO/87.3wt% γ-Al ₂ O ₃ catalyst - conventional equal volume impregnation method

The present invention also prepares the NiO/γ-Al ₂ O ₃ catalyst according to the conventional impregnation method reported in the literature. The specific implementation process is as follows: using the equal volume impregnation method, weigh 2.83g Ni(NO ₃ ) ₂ (analytical pure, commercially available) Put it in a beaker, add 20ml of deionized water and stir to dissolve it; weigh 5g of γ-Al ₂ O ₃ and place it in a magnetic crucible, add the prepared impregnating solution dropwise into the crucible, and absorb and impregnate it at room temperature for 4 hours. Stop stirring until all the impregnation liquid is completely impregnated into γ-Al ₂ O ₃ , then evaporate to dryness in a water bath at 80°C with constant stirring, put it in a drying oven at 110°C to dry overnight, and then bake at 500°C for 5 hours in an air atmosphere , to obtain the finished catalyst. The mass percent of each component in this catalyst is composed of: γ-Al ₂ O ₃ : 87.3%; NiO: 12.7%; the activity test result of gained catalyst (that is CO ₂ conversion rate × _{CO 2} /% and CH _Selectivity S _CH4 /%) as shown in Table 2.

Comparative Example 3 Preparation of 16.9wt% NiO-6.5wt% Fe ₂ O ₃ /3.3wt% MgO-6wt% CeO ₂ -70.5wt% Al ₂ O ₃ catalyst

The present invention also studies the catalyst disclosed in Chinese patent application CN101884927. The specific preparation process is: weigh Mg(NO ₃ ) ₂ ·6H ₂ O 1.5g, Ce(NO ₃ ) ₃ ·6H ₂ O 0.5g, dissolve in 20ml of deionized water, stirred and dissolved to make an impregnating liquid, put 5g of γ-Al ₂ O ₃ in the impregnating liquid, immerse at room temperature for 4 hours, evaporate to dryness in a water bath at 80°C, and put it in a drying oven at 110°C to dry overnight. Then bake at 500°C for 5 hours in an air atmosphere to obtain a carrier sample of the impregnation aid component; take Ni(NO ₃ ) ₂ ·6H ₂ O 4.68g, Fe(NO ₃ ) ₃ ·9H ₂ 02.32g, dissolve in Prepare an aqueous solution in 20ml of deionized water, then mix the aqueous solution with the carrier sample of the impregnation aid component, soak at room temperature for 4 hours, then evaporate to dryness in a water bath at 80°C with constant stirring, and put it in a drying oven to dry overnight at 110°C. A finished catalyst is obtained. The mass percent composition of each component in the catalyst is: γ-Al ₂ O ₃ : 70.5%; NiO: 16.9%; Fe ₂ O ₃ : 6.5%; MgO: 3.3%; CeO ₂ : 6%.

The experimental conditions for the catalyst activity evaluation of the comparative example are the same as those in Example 1, and the test results are shown in Table 2.

Table 2 Catalyst activity evaluation results

Table 3 Catalyst Activity Evaluation Results with Different CeO ₂ Contents

The present invention has also studied CeO ₂ content (represented by CeO ₂ content accounts for the weight ratio of catalyzer) to the active influence of catalyst, as shown in table 3, can find out by table 3, the introduction of rare earth metal oxide CeO ₂ can obviously improve The CO ₂ methanation reaction activity of NiO/γ-Al ₂ O ₃ catalyst, with the increase of CeO ₂ content, the activity of the catalyst (CO ₂ conversion rate increases when applied to carbon dioxide methanation reaction) increases, but when CeO ₂ When the content exceeds 6wt%, its catalytic effect decreases instead. Theoretically, the amount of _CeO2 added should not be too much to prevent the metal particles from clogging the pores, causing the mechanical strength of the catalyst to decrease and causing the catalyst to be pulverized. Furthermore, there is a threshold value for the dispersion degree of the metal oxide CeO ₂ on the base carrier Al ₂ O ₃ , and when the CeO ₂ content exceeds the threshold value, the CeO ₂ is unevenly dispersed on the base carrier Al ₂ O ₃ and easily accumulates into large particles. Particles are not conducive to the uniform dispersion of active metal Ni on the support, so the addition of metal _CeO2 is selected to be 6wt%.

In addition, the present invention has carried out a stability test on the catalyst (12.7wt% NiO/6.0wt% CeO ₂ /81.3wt% γ-Al ₂ O ₃ ) obtained in Example 1, specifically: catalyst stability test experimental device and activity evaluation In the same way, 200 mg of catalyst (60-80 mesh) was filled in a fixed-bed reactor, hydrogen was used for in-situ reduction, the reduction temperature was 450°C, the reaction pressure was normal pressure, and the raw material gas ratio was n(H ₂ ):n(CO ₂ ) = 4:1, gas volume space velocity 10000ml/h·g _cat , reaction temperature 360°C, gas chromatography on-line analysis, TDX-01 column, TCD detection. Catalyst stability is represented by the conversion ratio of _CO and _CH The selectivity and reaction time relation, the result shows: after the 100h stability test, when the catalyst obtained by the present invention is used for the carbon dioxide methanation reaction, the conversion ratio of _CO only drops 5.3%, the _CH4 selectivity is also reduced to 99.5%. And the catalyst reported in Example 1 of Chinese patent application CN101884927 (the main components of the catalyst and its mass proportion are _: 16.9%NiO-6.5% _Fe2O3-3.3 %MgO-2.8% _CeO2-70.5 %γ- _{Al2O 3} ) Applied to the carbon dioxide methanation reaction under normal pressure conditions, it was found that the conversion rate of _CO2 was 87.5% at 360°C, and the selectivity of methane was 100%, but after a 100h stability test, the conversion rate of _CO2 dropped to 80.3 % (the conversion of _CO2 decreased by 7.2%), and the _CH4 selectivity also decreased to 99.4%. It can be seen that the stability of the catalyst obtained in the present invention is better.

In summary, the present invention does not add active component Fe and auxiliary agent Mg, and under the situation that active component content is lower, the catalyst obtained in the present invention is applied to carbon dioxide methanation reaction catalytic effect under normal pressure condition better (contrast Example 9 and Comparative Example 3), and the catalyst obtained by the present invention has better stability, lower cost, and is more suitable for large-scale industrial production.

Claims (10)

1. Catalyst for methanation of carbon dioxide, characterized in that, is made up of composite carrier and active component, composite carrier: active component=84-90wt%: 10-16wt%; Wherein, described composite carrier is made of γ-Al ₂ O ₃ and water-soluble metal oxides, the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxides is 77-86:2-10; the active component is Ni, which exists in the catalyst in the form of NiO . 2 . The catalyst for carbon dioxide methanation according to claim 1 , wherein the water-soluble metal oxide is at least one of CeO ₂ , ZrO ₂ or La ₂ O ₃ . 3. The catalyst for carbon dioxide methanation according to claim 1 or 2, characterized in that, the mass ratio of each component in the catalyst is: composite carrier: active component=84-88: 12-16; - The mass ratio of Al ₂ O ₃ to water-soluble metal oxide is 78-86:2-6. 4. The catalyst for carbon dioxide methanation according to claim 1 or 2, characterized in that, the mass ratio of each component in the catalyst is: composite carrier: active component=84.7: 15.3; in the composite carrier, γ-Al ₂ O The mass ratio of ₃ to water-soluble metal oxide is 78.7:6. 5. The catalyst for carbon dioxide methanation according to claim 1 or 2, characterized in that, the mass ratio of each component in the catalyst is: composite carrier: active component=87.3: 12.7; in the composite carrier, γ-Al ₂ O The mass ratio of ₃ to water-soluble metal oxide is 81.3:6. The catalyst for carbon dioxide methanation according to claim 1 or 2, characterized in that the composite carrier is CeO ₂ /γ-Al ₂ O ₃ . 7. The preparation method of the carbon dioxide methanation catalyst described in any one of claims 1-6, is characterized in that, first adopts impregnation-precipitation method to prepare composite carrier, then composite carrier and active component salt solution are adopted impregnation method to make Catalyst precursor: The catalyst for carbon dioxide methanation of the present invention can be obtained after the catalyst precursor is dried and treated with plasma. 8. the preparation method of carbon dioxide methanation catalyst according to claim 7, concrete steps are: 1) Prepare the composite carrier by impregnation-precipitation method: impregnate the salt solution corresponding to the water-soluble metal oxide on the γ-Al ₂ O ₃ carrier at room temperature, and then introduce a precipitant until the pH of the solution is 8-10. After 2-4 hours, filter, wash, dry, and heat to decompose to obtain a composite carrier; wherein, the mass ratio of γ-Al ₂ O ₃ to water-soluble metal oxide is 77-86:2-10; the precipitating agent is NH ₃ H ₂ O, Na ₂ CO ₃ , NaOH; 2) Preparation of the catalyst precursor: the active component salt solution is loaded on the composite carrier obtained in step 1) by an equal-volume impregnation method; wherein, the composite carrier: active component=84-90wt%: 10-16wt%; impregnation The temperature is normal temperature, and the soaking time is 3-5 hours; 3) Preparation of the catalyst: the catalyst precursor obtained in step 2) is dried and subjected to plasma treatment at normal temperature and pressure to obtain the carbon dioxide methanation catalyst of the present invention. 9. the using method of the carbon dioxide methanation described in any one of claim 1-6 is characterized in that, the application condition of this catalyst catalyzed carbon dioxide methanation reaction is: reaction pressure is normal pressure, and raw material gas volume space velocity is 8100-15000ml/(h·g _cat ), the molar ratio of H ₂ /CO ₂ is 2/1-4/1. 10. The method for using the catalyst for carbon dioxide methanation according to claim 9, characterized in that the volume space velocity of the raw material gas is 10000 ml/(h·g _cat ), and the molar ratio of H ₂ /CO ₂ is 4:1.

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