Carbon modified catalyst for methane dry reforming reaction as well as preparation method and application of carbon modified catalyst

Abstract

The invention discloses a carbon modified catalyst for a methane dry reforming reaction as well as a preparation method and application thereof. The catalyst comprises a nickel-based catalyst and carbon black modified on the surface of the nickel-based catalyst, the nickel-based catalyst comprises an oxide carrier and Ni particles loaded on the surface of the oxide carrier. The prepared carbon-modified nickel-based catalyst is applied to methane and carbon dioxide reforming reaction, the initial carbon dioxide conversion rate is 97.9%, the methane conversion rate is 88.4%, the carbon dioxide conversion rate is 96.4% after the reaction is carried out for 50 hours, and the methane conversion rate is 88.7% after the reaction is carried out for 50 hours. The prepared catalyst has high catalytic activity and stability, and the purposes of effectively reducing the carbon deposition rate, protecting Ni particle sintering and keeping the stability of the catalyst can be achieved.

Description

Technical Field

[0001] The invention belongs to the field of carbon-modified catalysts, and in particular relates to a carbon-modified catalyst for methane dry reforming reaction, a preparation method and an application thereof. Background Art

[0002] Global warming caused by excessive CO2 emissions has become a common concern of countries around the world. Based on this, my country clearly proposed the "carbon peak" and "carbon neutrality" goals in 2020, striving to effectively reduce CO2 emissions by accelerating the research and development of energy-saving and carbon-reduction technologies, and at the same time use advanced and efficient technologies to convert it into high-value-added chemicals to achieve resource utilization of CO2. Carbon dioxide methane dry reforming (CO2-CH4) technology (CH4+CO2=2CO+2H2,ΔH θ (298K) = 247kJ / mol) can simultaneously convert two greenhouse gases, CO2 and CH4, into synthesis gas (H2 / CO). This technology has regained widespread attention due to the large amount of CO2 emissions in recent years. However, this reaction is a strongly endothermic reaction in thermodynamics, and the reaction temperature is above 700°C to have a high reaction efficiency, so the serious problem brought about is catalyst deactivation. In the CH4-CO2 reforming reaction, precious metals such as Pd, Pt, Rh, and Ru catalysts have high catalytic activity and excellent anti-carbon deposition performance. However, due to the high price and scarce resources of precious metals, their large-scale application in industry is limited. A large number of studies have confirmed that non-precious metal Ni shows high catalytic activity in the CH4-CO2 reforming reaction, which is comparable to precious metals, and the price of Ni is relatively low. However, Ni-based catalysts are prone to catalyst deactivation due to poor anti-carbon deposition and easy sintering. In order to solve the carbon deposition and sintering problems of Ni-based catalysts, researchers have conducted a lot of research work, including surface modification and structural modification of Ni-based catalysts, such as core-shell structure design, alloying modification, and establishment of pores, etc., to improve the thermal stability and anti-carbon deposition performance of Ni-based catalysts. For example, in Chinese patent publication number CN109663593B, Ma Qingxiang et al. prepared a dual-porous nickel-based catalyst, in which both mesopores and macropores exist in the structure. The mesopores have a large specific surface area, which is conducive to improving the catalyst activity and thus improving the conversion rate of the raw materials; the macropores are conducive to the mass transfer of reactant molecules, which can effectively solve the problem of catalyst carbon deposition.

[0003] In summary, although some progress has been made in the research of CH4-CO2 reforming catalysts, there are still deficiencies in catalyst reaction activity, anti-carbon deposition and anti-sintering performance, which makes it difficult to meet the industrial application of CH4-CO2 reforming. Summary of the invention

[0004] The technical problem to be solved by the present invention is the bottleneck problem that the current nickel-based reforming catalyst is prone to carbon deposition and sintering in application. Therefore, the present invention provides a carbon-modified catalyst for methane dry reforming reaction and its preparation method and application, which can achieve the purpose of effectively reducing the carbon deposition rate, protecting Ni particles from sintering and maintaining catalyst stability.

[0005] To achieve the above object, the technical solution of the present invention is as follows: On the one hand, the present invention provides a carbon-modified catalyst for methane dry reforming reaction, including a nickel-based catalyst and carbon black modified on the surface of the nickel-based catalyst; the nickel-based catalyst includes an oxide carrier and Ni particles loaded on the surface of the oxide carrier. Carbon surface modification can effectively protect Ni particles from sintering, inhibit reaction carbon deposition on the surface of Ni particles, and thus promote the catalytic activity and catalytic stability of Ni. By using carbon modification to cover Ni active sites to varying degrees, the metal Ni particles are spatially protected, which can not only effectively inhibit the agglomeration of metal Ni particles due to high-temperature sintering, but also spatially isolate carbon deposition to prevent deposition on the surface of Ni active sites. Carbon surface modification can effectively protect Ni particles from sintering, inhibit reaction carbon deposition on the surface of Ni particles, and thus promote the catalytic activity and catalytic stability of Ni.

[0006] In the above scheme, further, the mass ratio of carbon black to nickel-based catalyst is 0.3-1:90-100. By using a trace amount of carbon black with high temperature thermal stability to modify the surface of Ni / ZrO2, the metal Ni 0 The electrical structure of the surface modified carbon changes to varying degrees. Because the surface modified carbon has semiconductor properties, when it is combined with metal Ni 0 When heterogeneous contacts occur, due to Ni 0 The work function of Ni is slightly lower than that of surface carbon. 0 The electrons inevitably transfer to the carbon until their Fermi levels are equal, resulting in the formation of a small amount of positive Ni δ+ Species (Ni 0 It is an active site for CH4 cracking), thereby reducing the cracking rate of CH4 and reducing the occurrence of carbon deposition.

[0007] In the above scheme, further, the mass ratio of Ni particles to oxide carriers in the nickel-based catalyst is 0.9-1.1:1.8-2.2.

[0008] In the above scheme, further, the oxide carrier is selected from one of zirconium dioxide, silicon dioxide, aluminum oxide, and cerium dioxide. The present invention selects zirconium dioxide as the oxide carrier. The selected ZrO2 has redox properties. The surface carbon modification can replace the ZrO2 lattice oxygen, so that the formation energy of oxygen vacancies is significantly reduced, thereby promoting the formation of more oxygen vacancies (O v The oxygen vacancies formed can activate CO2(O v+CO2=CO+O * ), which generates reactive oxygen species O * It can react with the carbon deposits produced by CH4 cracking to produce an oxidation reaction, thereby achieving the purpose of eliminating carbon deposits; on the other hand, the surface-modified carbon can inhibit the cracking of methane. The occurrence of carbon deposition can effectively reduce the occurrence of carbon deposition and promote a more complete conversion of methane and carbon dioxide reforming reaction.

[0009] In the above scheme, further, the particle size of the oxide carrier is 20 to 40 nm; the particle size of the Ni particles is 15 to 25 nm.

[0010] Another aspect of the present invention provides a method for preparing a carbon-modified catalyst for a methane dry reforming reaction, comprising the following steps: (1) taking oxide carrier powder, Ni(NO3)2·6H2O and carbon black, grinding them in a mortar to obtain a mixed powder; (2) The mixed powder is subjected to a calcination reaction at a high temperature in an inert atmosphere to obtain a carbon-modified catalyst.

[0011] In the above scheme, further, in step (2), the heating rate is 5 to 15°C / min; the roasting temperature is 650 to 750°C, and the roasting time is 1 to 3h.

[0012] In the above scheme, further, the inert atmosphere is selected from one of argon, helium and neon, and the ventilation rate of the inert gas is 30-50 mL / min.

[0013] On the other hand, the present invention provides an application of a carbon-modified catalyst for a methane dry reforming reaction, comprising the steps of heating the carbon-modified catalyst to a reaction temperature under N2 protection, and switching the reaction gas to carry out a catalytic reaction.

[0014] In the above scheme, the reaction temperature is 700-800°C.

[0015] In the above scheme, further, the reaction gas is composed of nitrogen, carbon dioxide and methane; the volume ratio of nitrogen, carbon dioxide and methane is V(N2):V(CO2):V(CH4)=60:10:10; the ventilation flow rate of the reaction gas is 80mL / min.

[0016] The beneficial effects of the present invention are as follows: the carbon-modified catalyst for methane carbon dioxide reforming reaction prepared by the present invention can effectively reduce the carbon deposition rate, protect the sintering of Ni particles and improve the stability of the catalyst, can better maintain the activity of the catalyst in the catalytic application of carbon dioxide methane reforming reaction, and can be further applied in large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1This is a comparison chart of CO2 conversion rates in the catalyst stability test of Examples 1 to 3 and Comparative Example 4.

[0018] Figure 2 This is a comparison chart of CH4 conversion rates in the catalyst stability test of Examples 1 to 3 and Comparative Example 4.

[0019] Figure 3 It is a comparison chart of the H2 / CO ratio of the reaction gas in Application Examples 1 to 3 and Comparative Application Example 4.

[0020] Figure 4 This is the SEM image of the Ni / ZrO2 catalyst prepared in Comparative Example 4 before the reaction.

[0021] Figure 5 This is the SEM image of the C@Ni / ZrO2-10 catalyst prepared in Example 2 before the reaction.

[0022] Figure 6 This is the SEM image of the Ni / ZrO2 catalyst prepared in Comparative Example 4 after the reaction.

[0023] Figure 7 This is the SEM image of the C@Ni / ZrO2-10 catalyst prepared in Example 2 after the reaction. DETAILED DESCRIPTION

[0024] The present invention provides a carbon-modified catalyst for methane dry reforming reaction, wherein the catalyst uses zirconium dioxide as a carrier, loads Ni particles, and uses carbon black for surface modification. By using carbon modification to cover Ni active sites to varying degrees, a spatial protection effect is played on metal Ni particles, which can not only effectively inhibit the agglomeration of metal Ni particles due to high-temperature sintering, but also spatially isolate carbon deposits to prevent deposition on the surface of Ni active sites. Carbon surface modification can effectively protect Ni particles from sintering, inhibit reaction carbon deposits from depositing on the surface of Ni particles, and thus promote the catalytic activity and catalytic stability of Ni. From the perspective of catalyst carrier structure, Ni particle surface electrical properties, and Ni particle spatial shielding, a carbon-surface-modified ZrO2-loaded Ni catalyst is designed and constructed to achieve the purpose of effectively protecting Ni particles from sintering, reducing carbon deposition rate, and cleaning carbon.

[0025] In some embodiments provided by the present invention, the mass ratio of zirconium dioxide is 63.85-64.27wt%, the mass ratio of Ni(NO3)2·6H2O is 35.18-35.41wt% and the mass ratio of carbon black is 0.32-0.96wt%. By using a trace amount of carbon black with high temperature thermal stability to modify the surface of Ni / ZrO2, the metal Ni 0 The electrical structure of the surface modified carbon changes to varying degrees. Because the surface modified carbon has semiconductor properties, when it is combined with metal Ni 0 When heterogeneous contacts occur, due to Ni 0The work function of Ni is slightly lower than that of surface carbon. 0 The electrons inevitably transfer to the carbon until their Fermi levels are equal, resulting in the formation of a small amount of positive Ni δ+ Species (Ni 0 On the other hand, the selected ZrO2 has redox properties, and the surface carbon modification can replace the ZrO2 lattice oxygen, which significantly reduces the formation of oxygen vacancies, thereby promoting the formation of more oxygen vacancies (O v The oxygen vacancies formed can activate CO2(O v +CO2=CO+O * ), which generates reactive oxygen species O * It can react with the carbon deposits produced by CH4 cracking to produce an oxidation reaction, thereby achieving the purpose of eliminating carbon deposits; on the other hand, the surface-modified carbon can inhibit the cracking of methane. The occurrence of carbon deposition can effectively reduce the occurrence of carbon deposition and promote a more complete conversion of methane and carbon dioxide reforming reaction.

[0026] The present invention also provides a method for preparing a carbon-modified catalyst for a methane dry reforming reaction, comprising the following steps: (1) zirconium dioxide powder, Ni(NO3)2·6H2O and carbon black are put into a mortar and ground to obtain a mixed powder; (2) The powder is placed in a tubular furnace, an inert gas is passed through, and the temperature is increased to calcine to obtain a Ni / ZrO2 catalyst modified with a carbon surface.

[0027] In some embodiments provided by the present invention, the heating rate is 10° C. / min.

[0028] In some embodiments provided by the present invention, the heating temperature is 700°C and the calcination time is 2 hours. Carbon dioxide methane dry reforming (CO2-CH4) technology (CH4+CO2=2CO+2H2, ΔH θ (298K) = 247kJ / mol) can simultaneously convert CO2 and CH4, two greenhouse gases, into synthesis gas (H2 / CO). This reaction is a strong endothermic reaction in thermodynamics. The reaction efficiency is high only when the reaction temperature is above 700°C. Therefore, the serious problem brought about by this is catalyst deactivation. Based on the above conditions, the present invention selects the preparation condition of 700°C to maintain a high reaction efficiency under the condition of catalyst activity.

[0029] In some embodiments provided by the present invention, the inert atmosphere is selected from one of argon, helium and neon, and the ventilation rate of the inert gas is 40 mL / min.

[0030] The present invention further provides an application of a carbon-modified catalyst for a methane dry reforming reaction, characterized in that the application comprises the following steps: heating the carbon-modified catalyst to a reaction temperature under N2 protection, and switching the reaction gas to perform a catalytic reaction.

[0031] In some embodiments provided by the present invention, the reaction gas is composed of nitrogen, carbon dioxide and methane; the volume ratio of nitrogen, carbon dioxide and methane is V(N2):V(CO2):V(CH4)=60:10:10; the ventilation flow rate of the reaction gas is 80mL / min.

[0032] In some embodiments provided by the present invention, the prepared catalyst is ground to 30-60 mesh for use in applications.

[0033] The present invention is further described in detail below in conjunction with specific examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry.

[0034] Example 1 Weigh 1 g of commercial zirconium dioxide powder (particle size), 0.551 g of Ni(NO3)2·6H2O and 5 mg of carbon black, put them into an agate grinding jar and grind them for 1 h to mix them thoroughly, then put them into a quartz tube furnace, and heat them to 700 °C at a heating rate of 10 °C / min under Ar atmosphere (40 mL / min), calcine them for 2 h, and then cool them to room temperature to finally prepare the carbon surface-modified C@Ni / ZrO2-5 ​​catalyst.

[0035] Application Example 1: Application of the carbon surface modified C@Ni / ZrO2-5 ​​catalyst prepared in Example 1 in the methane carbon dioxide reforming reaction: The catalytic activity of the prepared catalyst was tested using a normal pressure quartz tube fixed bed reactor (inner diameter 8mm, length 40mm). 0.1g of carbon surface modified C@Ni / ZrO2-5 ​​catalyst (30-60 mesh) was weighed and loaded into the reactor. Both ends were fixed by quartz wool, and the catalyst bed temperature was measured by a K-type thermocouple. N2 (30mL / min) was introduced into the reactor and heated to a reaction temperature of 750°C at a heating rate of 10°C / min. Then the reaction gas was switched. The volume ratio of the reaction gas was V(N2) / V(CO2) / V(CH4)=60 / 10 / 10 (flow rate 80mL / min). After 0.5h of reaction, the gas after the reaction was analyzed. The reaction time was 100h. The Ni / ZrO2 catalyst was heated to 750°C under the protection of N2, and the reaction gas was switched for catalytic reaction. The reaction gas is condensed by a cold trap and then analyzed by online gas chromatography, thereby obtaining the CO2 and CH4 conversion rates and the H2 / CO molar ratio under the action of the catalyst in Example 1.

[0036] Example 2 Weigh 1 g of commercial zirconium dioxide powder, 0.551 g of Ni(NO3)2·6H2O and 10 mg of carbon black, put them into an agate grinding jar and grind them for 1 h to mix them thoroughly. Then put them into a quartz tube furnace and heat them to 700 °C at a heating rate of 10 °C / min under Ar atmosphere (40 mL / min), calcine them for 2 h, and then cool them to room temperature to prepare the carbon surface-modified C@Ni / ZrO2-10 catalyst.

[0037] Application Example 2 Application of the carbon surface modified C@Ni / ZrO2-10 catalyst prepared in Example 2 in the methane carbon dioxide reforming reaction: The catalytic activity of the prepared catalyst was tested using a normal pressure quartz tube fixed bed reactor (inner diameter 8mm, length 40mm). 0.1g of carbon surface modified C@Ni / ZrO2-10 catalyst (30-60 mesh) was weighed and loaded into the reactor. Both ends were fixed by quartz wool, and the catalyst bed temperature was measured by a K-type thermocouple. N2 (30mL / min) was introduced into the reactor and heated to a reaction temperature of 750°C at a heating rate of 10°C / min. Then the reaction gas was switched. The volume ratio of the reaction gas was V(N2) / V(CO2) / V(CH4)=60 / 10 / 10 (flow rate 80mL / min). After 0.5h of reaction, the gas after the reaction was analyzed. The reaction time was 100h. The Ni / ZrO2 catalyst was heated to 750°C under the protection of N2, and the reaction gas was switched for catalytic reaction. The reaction gas is condensed by a cold trap and then analyzed by online gas chromatography, thereby obtaining the CO2 and CH4 conversion rates and the H2 / CO molar ratio under the action of the catalyst in Example 2.

[0038] Example 3 Weigh 1 g of commercial zirconium dioxide powder, 0.551 g of Ni(NO3)2·6H2O and 15 mg of carbon black, put them into an agate grinding jar and grind them for 1 h to mix them thoroughly. Then put them into a quartz tube furnace and heat them to 700 °C at a heating rate of 10 °C / min under Ar atmosphere (40 mL / min), calcine them for 2 h, and then cool them to room temperature to prepare the carbon surface-modified C@Ni / ZrO2-15 catalyst.

[0039] Application Example 3 Application of the carbon surface modified C@Ni / ZrO2-15 catalyst prepared in Example 3 in the methane carbon dioxide reforming reaction: The catalytic activity of the prepared catalyst was tested using a normal pressure quartz tube fixed bed reactor (inner diameter 8mm, length 40mm). 0.1g of carbon surface modified C@Ni / ZrO2-15 catalyst (30-60 mesh) was weighed and loaded into the reactor. Both ends were fixed by quartz wool, and the catalyst bed temperature was measured by a K-type thermocouple. N2 (30mL / min) was introduced into the reactor and heated to a reaction temperature of 750°C at a heating rate of 10°C / min. Then the reaction gas was switched. The volume ratio of the reaction gas was V(N2) / V(CO2) / V(CH4)=60 / 10 / 10 (flow rate 80mL / min). After 0.5h of reaction, the gas after the reaction was analyzed. The reaction time was 100h. The Ni / ZrO2 catalyst was heated to 750°C under the protection of N2, and the reaction gas was switched for catalytic reaction. The reaction gas is condensed by a cold trap and then analyzed by online gas chromatography, thereby obtaining the CO2 and CH4 conversion rates and the H2 / CO molar ratio under the action of the catalyst in Example 3.

[0040] Comparative Example 1 Weigh 1 g of commercial cerium dioxide powder, 0.551 g of Ni(NO3)2·6H2O and 10 mg of carbon black, put them into an agate grinding jar and grind them for 1 h to mix them thoroughly. Then put them into a quartz tube furnace and heat them to 700 °C at a heating rate of 10 °C / min under Ar atmosphere (40 mL / min), calcine them for 2 h, and then cool them to room temperature to prepare the carbon surface-modified C@Ni / CeO2-10 catalyst.

[0041] Comparative application example 1 Application of the carbon surface modified C@Ni / CeO2-10 catalyst prepared in Comparative Example 1 in the methane carbon dioxide reforming reaction: The catalytic activity of the prepared catalyst was tested using a normal pressure quartz tube fixed bed reactor (inner diameter 8mm, length 40mm). 0.1g of carbon surface modified C@Ni / CeO2-10 catalyst (30-60 mesh) was weighed and loaded into the reactor. Both ends were fixed by quartz wool, and the catalyst bed temperature was measured by a K-type thermocouple. N2 (30mL / min) was introduced into the reactor and heated to a reaction temperature of 750°C at a heating rate of 10°C / min. Then the reaction gas was switched. The volume ratio of the reaction gas was V(N2) / V(CO2) / V(CH4)=60 / 10 / 10 (flow rate 80mL / min). After 0.5h of reaction, the gas after the reaction was analyzed. The reaction time was 100h. The Ni / ZrO2 catalyst was heated to 750°C under the protection of N2, and the reaction gas was switched for catalytic reaction. The reaction gas is condensed by a cold trap and then analyzed by online gas chromatography, thereby obtaining the CO2 and CH4 conversion rates and the H2 / CO molar ratio under the action of the catalyst in Comparative Example 1.

[0042] Comparative Example 2 Weigh 1 g of commercial silica powder, 0.551 g of Ni(NO3)2·6H2O and 10 mg of carbon black, put them into an agate grinding jar and grind them for 1 h to mix them thoroughly. Then put them into a quartz tube furnace and heat them to 700 °C at a heating rate of 10 °C / min under Ar atmosphere (40 mL / min), calcine them for 2 h, and then cool them to room temperature to prepare the carbon surface-modified C@Ni / SiO2-10 catalyst.

[0043] Comparative Application Example 2 Application of the carbon surface modified C@Ni / SiO2-10 catalyst prepared in Comparative Example 2 in the methane carbon dioxide reforming reaction: The catalytic activity of the prepared catalyst was tested using a normal pressure quartz tube fixed bed reactor (inner diameter 8mm, length 40mm). 0.1g of carbon surface modified C@Ni / SiO2-10 catalyst (30-60 mesh) was weighed and loaded into the reactor. Both ends were fixed by quartz wool, and the catalyst bed temperature was measured by a K-type thermocouple. N2 (30mL / min) was introduced into the reactor and heated to a reaction temperature of 750°C at a heating rate of 10°C / min. Then the reaction gas was switched. The volume ratio of the reaction gas was V(N2) / V(CO2) / V(CH4)=60 / 10 / 10 (flow rate 80mL / min). After 0.5h of reaction, the gas after the reaction was analyzed. The reaction time was 100h. The Ni / ZrO2 catalyst was heated to 750°C under the protection of N2, and the reaction gas was switched for catalytic reaction. The reaction gas is condensed by a cold trap and then analyzed by online gas chromatography, thereby obtaining the CO2 and CH4 conversion rates and the H2 / CO molar ratio under the action of the catalyst in Comparative Example 2.

[0044] Comparative Example 3 Weigh 1 g of commercial alumina powder, 0.551 g of Ni(NO3)2·6H2O and 10 mg of carbon black, put them into an agate grinding jar and grind them for 1 h to mix them thoroughly. Then put them into a quartz tube furnace and heat them to 700 °C at a heating rate of 10 °C / min under Ar atmosphere (40 mL / min), calcine them for 2 h, and then cool them to room temperature to prepare the carbon surface-modified C@Ni / Al3O2-10 catalyst.

[0045] Comparative Application Example 3 Application of the carbon surface modified C@Ni / Al3O2-10 catalyst prepared in Comparative Example 3 in the methane carbon dioxide reforming reaction: The catalytic activity of the prepared catalyst was tested using a normal pressure quartz tube fixed bed reactor (inner diameter 8mm, length 40mm). 0.1g of carbon surface modified C@Ni / Al3O2-10 catalyst (30-60 mesh) was weighed and loaded into the reactor. Both ends were fixed by quartz wool, and the catalyst bed temperature was measured by a K-type thermocouple. N2 (30mL / min) was introduced into the reactor and heated to a reaction temperature of 750°C at a heating rate of 10°C / min. Then the reaction gas was switched. The volume ratio of the reaction gas was V(N2) / V(CO2) / V(CH4)=60 / 10 / 10 (flow rate 80mL / min). After 0.5h of reaction, the gas after the reaction was analyzed. The reaction time was 100h. The Ni / ZrO2 catalyst was heated to 750°C under the protection of N2, and the reaction gas was switched for catalytic reaction. The reaction gas is condensed by a cold trap and then analyzed by online gas chromatography, thereby obtaining the CO2 and CH4 conversion rates and the H2 / CO molar ratio under the action of the catalyst in Comparative Example 3.

[0046] Comparative Example 4 Weigh 1 g of commercial zirconium dioxide powder and 0.551 g of Ni(NO3)2·6H2O, put them into an agate grinding jar and grind them for 1 h to mix them thoroughly, then put them into a muffle furnace and calcine them for 2 h in an air atmosphere and cool them to room temperature to finally prepare a Ni / ZrO2 catalyst.

[0047] Comparative Application Example 4 Application of the Ni / ZrO2 catalyst prepared in Comparative Example 4 in the methane carbon dioxide reforming reaction: The catalytic activity of the prepared catalyst was tested using a normal pressure quartz tube fixed bed reactor (inner diameter 8mm, length 40mm). 0.1g of Ni / ZrO2 catalyst (30-60 mesh) was weighed and loaded into the reactor. Both ends were fixed by quartz wool, and the catalyst bed temperature was measured by a K-type thermocouple. N2 (30mL / min) was introduced into the reactor and heated to a reaction temperature of 750°C at a heating rate of 10°C / min. Then the reaction gas was switched. The volume ratio of the reaction gas was V(N2) / V(CO2) / V(CH4)=60 / 10 / 10 (flow rate 80mL / min). After 0.5h of reaction, the gas after the reaction was analyzed. The reaction time was 100h. Before the reaction of the Ni / ZrO2 catalyst, it was required to be reduced at 500°C for 2h by a reducing gas of V(N2) / V(H2)=9 / 1 (flow rate 30mL / min), and then N2 was protected to heat up to 750°C, and the reaction gas was switched for catalytic reaction. The reaction gas is condensed by a cold trap and then analyzed by online gas chromatography, thereby obtaining the CO2 and CH4 conversion rates and the H2 / CO molar ratio under the action of the catalyst in Comparative Example 4.

[0048] like Figure 1 , Figure 2 and Figure 3 The comparison chart of the catalytic activity test shows that the Ni / ZrO2 catalyst in Comparative Example 4 can show a high catalytic activity at the beginning of the catalytic reaction, but its resistance to carbon deposition is poor. After 3 hours of reaction, the catalyst has serious carbon deposition and the catalyst bed is blocked. The reaction is forced to terminate, resulting in a low conversion rate. The carbon-modified Ni / ZrO2 catalyst in Example 2 shows higher catalytic stability than the Ni / ZrO2 in Comparative Example 4, indicating that carbon modification can improve the carbon deposition resistance of the Ni catalyst. At the same time, the carbon content has a significant effect on the catalytic activity and stability. With the increase of carbon content, even if the catalytic activity gradually decreases, its catalytic stability is greatly promoted. After 100 hours of reaction, no catalytic activity deactivation was observed. By combining the SEM images of the catalyst in the attached drawings of the specification, it is concluded that, Figure 4 Ni / ZrO2 before reaction and Figure 5 The SEM image of C@Ni / ZrO2-10 before reaction shows that there is no filamentary graphite carbon. Figure 6 The surface of the catalyst shown in the reaction Ni / ZrO2 is entangled with a large amount of filamentous carbon, resulting in the Ni active site being covered and the catalyst activity being lost. Different from the reaction Ni / ZrO2, such as Figure 7 After the reaction, a small amount of filamentous carbon is shown on the surface of C@Ni / ZrO2-10, which has little effect on the catalytic activity and catalytic stability and can be ignored. Therefore, the C@Ni / ZrO2-10 catalyst has better anti-carbon deposition performance in the CH4-CO2 reforming reaction and shows stable catalytic activity.

[0049] As shown in the experimental data of comparative examples 1, 2 and 3, all of them are carbon-modified Ni / ZrO2 catalysts, and the variable is the different mass of carbon black added for carbon modification, and the added amount is 5mg, 10mg and 15mg respectively. From the catalytic activity test, it can be compared that the catalytic performance of catalysts with different mass of carbon black added is also different. Example 1 adds 5mg carbon black for carbon modification and shows good catalytic activity, but the carbon deposition resistance is poor, and the reactor is blocked and cannot continue to react after 100h of reaction; Example 2 adds 10mg carbon black for carbon modification and the catalytic activity is worse than that of Example 1, but the reactor is not blocked for a long time of reaction, and the carbon deposition resistance is good; Example 3 adds 15mg carbon black for modification and the catalytic activity is worse than that of Example 2, and the carbon deposition resistance is good, and the reactor is not blocked for a long time of reaction. Example 1 compares the conversion rates of Example 2 and Example 3 after 10h and 20h of reaction, and it is found that the conversion rate of Example 1 decreases faster, indicating that the catalytic activity of the catalyst with 5mg of carbon black is not stable enough. The catalyst in Example 2 has the most stable catalytic activity, and the CO2 conversion rate can be close to 98% and can be stable at more than 96% for a long time, while the conversion rate of Example 3 is lower than that of Example 2. The comparison shows that the preferred choice is that when 10mg of carbon black is added to Example 2, it can have better catalytic activity and good carbon deposition resistance.

[0050] Comparative Example 2 and Comparative Example 1, the metal oxide carriers are different, and the mass of carbon modification addition is the same. The metal oxide carrier of Example 2 is zirconium dioxide, and the metal oxide carrier of Comparative Example 1 is cerium dioxide. It can be seen from the catalyst activity test data that the reactor of Comparative Example 1 was blocked after 20 hours of reaction. Even though carbon black was added like Example 2, the carbon deposition resistance was poor, and the conversion rate after 10 hours of reaction was lower than that of Example 2 of the same period. The catalytic activity of Comparative Example 1 is poorer than that of Example 2. Comparative Example 2 and Comparative Example 2, the metal oxide carriers are different, and the mass of carbon modification addition is the same. The metal oxide carrier of Example 2 is zirconium dioxide, and the metal oxide carrier of Comparative Example 2 is silicon dioxide. It can be seen from the catalyst activity test data that the silicon dioxide used in Comparative Example 2 did not block the reactor after 100 hours of reaction, indicating that the carbon deposition resistance of the metal oxide is also good, but compared with the conversion rate of Example 2, the catalytic activity of Comparative Example 2 is poor. Comparing Example 3 and Comparative Example 3, the mass of carbon black added in the two schemes is the same, and Comparative Example 3 uses aluminum oxide with similar properties to zirconium dioxide. Comparing the catalyst activity data, the reactor of Comparative Example 3 was blocked at 100h of reaction and the carbon deposition resistance was poor. Comparing the conversion rate data of 10h and 20h of reaction, it was found that the conversion rate decreased rapidly, and the catalytic activity deteriorated with the increase of reaction time. By contrast, it can be seen that the present invention selects zirconium dioxide as a more suitable metal oxide carrier. The selected ZrO2 has redox properties, and the surface carbon modification can replace the ZrO2 lattice oxygen, so that the formation of oxygen vacancies can be significantly reduced, thereby promoting the formation of more oxygen vacancies (O v The oxygen vacancies formed can activate CO2(O v +CO2=CO+O * ), which generates reactive oxygen species O * It undergoes an oxidation reaction with the carbon deposits produced by the cracking of CH4, thereby achieving the purpose of eliminating the carbon deposits.

[0051] In summary, the present invention enhances the anti-carbon deposition ability and catalytic stability of the Ni-based catalyst by carbon surface modification of the Ni-based catalyst with ZrO2 as the carrier. The main reason for this is that the carbon modification hinders the carbon deposition produced by methane cracking to a certain extent, and at the same time can spatially shield the carbon deposition produced by it from being deposited on the surface of Ni particles; in addition, the carbon modification can reduce the surface lattice oxygen of ZrO2 and promote the formation of more surface oxygen vacancies. The presence of oxygen vacancies produces active oxygen species due to the activation of CO2, which can oxidize the carbon deposits produced in the reaction to achieve the purpose of carbon removal.

Claims

1. A carbon-modified catalyst for methane dry reforming reaction, characterized in that: It includes a nickel-based catalyst and carbon black modified on the surface of the nickel-based catalyst; the nickel-based catalyst includes an oxide carrier and Ni particles loaded on the surface of the oxide carrier.

2. The carbon-modified catalyst for methane dry reforming reaction according to claim 1, characterized in that: The mass ratio of carbon black to nickel-based catalyst is 0.3-1:90-100.

3. The carbon-modified catalyst for methane dry reforming reaction according to claim 1, characterized in that: The mass ratio of Ni particles to oxide carriers in the nickel-based catalyst is 0.9-1.1:1.8-2.

2.

4. The carbon-modified catalyst for methane dry reforming reaction according to claim 1, characterized in that: The oxide is selected from one of zirconium dioxide, silicon dioxide, aluminum oxide and cerium dioxide.

5. A carbon-modified catalyst for methane dry reforming reaction according to claim 1 or 3, characterized in that: The particle size of the oxide carrier is 20 to 40 nm; The particle size of Ni particles is 15 to 25 nm.

6. A method for preparing a carbon-modified catalyst for methane dry reforming reaction according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) taking zirconium dioxide powder, nickel salt and carbon black and mixing them uniformly to obtain a mixed powder; (2) The mixed powder is calcined in an inert atmosphere to obtain a carbon-modified catalyst.

7. The method for preparing a carbon-modified catalyst for methane dry reforming reaction according to claim 6, characterized in that: The heating rate of the heating is 5 to 15° C. / min; the heating temperature is 650 to 750° C., and the calcination time is 1 to 3 hours.

8. The method for preparing a carbon-modified catalyst for methane dry reforming reaction according to claim 6, characterized in that: The ventilation rate of the inert atmosphere is 30 to 50 mL / min.

9. Use of a carbon-modified catalyst for methane dry reforming reaction as claimed in any one of claims 1 to 5, characterized in that: The steps are heating to the reaction temperature under N2 protection and switching the reaction gas to carry out catalytic reaction.

10. The use of a carbon-modified catalyst for methane dry reforming reaction according to claim 9, characterized in that: Reaction temperature 700~800℃.

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