Patent Application
20240091747
The present disclosure relates to the technical fields of catalytic materials preparation and instrument analysis, and in particular to a Ni-based catalyst for an unsteady-state trace CO, methanation reaction, and a preparation method thereof.
In many scenarios of scientific research and industrial production, there is a demand for the detection of a content of trace CO or CO2. The content of CO, can be as low as a few or tens of parts per million (ppm). Common detection method is Gas chromatography (GC), in which a suitable chromatographic column could be used to separate CO and CO2, the chromatographic column is connected to a methanation furnace at its rear end, and in the methanation furnace, CO and CO2 each react with H2 to generate CH4, and then a content of each of CO and CO2 could be determined through a sensitive response of chromatography flame ionization detection (FID) to trace CH4. Currently, the methanation furnace is generally set at a working temperature of 400° C. or higher. This is because, on the one hand, the existing commercial Ni-based catalysts can only show high methanation activity at about 400° C., and on the other hand, the higher temperature results in great reduction in quantity of physical adsorption on the catalyst surface, making a chemical adsorption reaction reach equilibrium as soon as possible. However, for the chromatographic upgrading in the future, the methanation furnace will be improved to lower the working temperature and reduce the energy consumption. Therefore, it is required to develop a Ni-based methanation catalyst with high activity at a low temperature.
Reactions of methanation catalysts reported in literatures are evaluated as steady-state reactions, and a ratio of H2 to CON in a reaction gas is usually a stoichiometric ratio. Given that the reaction in the methanation furnaces is performed under a condition of unsteady-state intermittent pulse and the ratio of H2 to COx in a reaction gas is usually far beyond the stoichiometric ratio, it is further required to develop a Ni-based catalyst with high activity at a low temperature which is suitable for the methanation reaction of an unsteady-state trace CON.
A common Ni-based catalyst is usually obtained by loading an active metal Ni onto a metal oxide support, and the support mainly plays a role of supporting and fixing the active metal Ni. It is generally believed that, in a CO2 methanation reaction, the dissociation of H2 occurs on Ni particles, the support is responsible for adsorbing and activating CO2, and a synergistic effect of the active metal Ni and the support promotes the generation of CH4. Studies have shown that, compared with the use of an inert oxide such as SiO2, MgO, and Al2O3 as a support for a Ni-based catalyst, the use of a rare earth oxide (REO) such as Eu2O3, Sm2O3, La2O3, and CeO2 as the support could significantly improve the activity of CO2 methanation. This is because homogeneously-dispersed Ni could partly form interfacial active sites with nearby metal oxides, and carbon species (derived from CO2) adsorbed at the sites could be quickly hydrogenated to produce CH4. When the co-precipitation is adopted for the preparation of the catalyst, the mutual dispersion of Ni and a metal oxide could be strengthened, resulting in smaller size of Ni particles, which makes it possible to increase the number of active sites at a metal-support interface and thereby lead to superior low-temperature methanation activity.
The steady-state reaction experiment is generally used for evaluating a reaction. In such experiment, the species evolution on a surface of the catalyst is in a steady state, and the adsorption and desorption of carbon species on the metal oxide support reach a dynamic equilibrium. However, in an actual operation of a methanation furnace, during a unit sample injection time, a trace reaction gas passes through a catalyst bed in a very short period of time, and the catalyst bed is purged with H2 in the remaining time. During the very short period of time in which the reaction gas passes through the catalyst bed, if CO2 adsorbed on the metal oxide support cannot be completely hydrogenated, CH4 will be continuously generated during the subsequent H2 purging process. According to the chromatographic detection principle, such CH4 slowly generated cannot be completely detected in the unit sample injection time, which is reflected by the ultra-long tailing of a CH4 peak in a chromatogram, and a calculated COX conversion rate will be greatly reduced, which greatly reduces the detection accuracy.
Preliminary experimental results show that a Ni-based catalyst with an REO as a support which works well in a steady state works poorly in an unsteady-state pulse reaction; this is because the REO support has a strong adsorption effect for CO2. It is reported by Tatsuro Horiuchi et al. that the addition of different REOs into Al2O3 makes it possible to significantly increase a retention time of CO2, and a value of adsorption heat would be increased sharply with the increase of the addition amount (see Effect of added basic metal oxides on CO2 adsorption on alumina at elevated temperatures, Applied Catalysis A: General 167.2 (1998): 195-202). It is reported by Thien An Le et al. that the high activity of a Ni/CeO2 catalyst in CO and CO2 methanation reactions is inseparable from the strong adsorption of the catalyst for CO2 (see CO and CO2 methanation over supported Ni catalysts, Catalysis Today 293 (2017): 89-96). For Ni-based catalysts with the REO as a support, since Ni on the interface of the catalyst could provide a large amount of H, CO2 adsorbed by the REO at the interface could be rapidly hydrogenated to generate CH4. While the REO, which is far away from the interface and accounts for the vast majority, mainly plays a supporting role, and CO2 adsorbed thereon could only be hydrogenated slowly to generate CH4. The chromatographic detection results show that this part of CO2 is not converted. That is, the catalyst shows poor unsteady-state activity. In addition, because a CO, content to be detected is on the order of ppm, no matter how small an amount of CO, adsorbed on the catalyst is, its proportion in a total amount cannot be ignored. In conclusion, the Ni-based catalysts with the REO as a support are not suitable for the application scenarios proposed herein.
The present disclosure is intended to provide a Ni-based catalyst and a preparation method thereof. The Ni-based catalyst is suitable for an unsteady-state pulse trace COX methanation reaction, and makes it possible to achieve 98% or more methanation conversion at 200° C. to 300° C. The chromatographic results show that the peak of the product CH4 does not have a broadening or tailing phenomenon. The Ni-based catalyst of the present disclosure makes it possible to replace the existing catalyst in a methanation furnace arranged for chromatography.
The Ni-based catalyst provided in the present disclosure is composed of an active metal Ni and an oxide support, wherein the oxide support is composed of an REO and an inert oxide; and the rare earth oxide and the inert oxide exhibit an excellent synergistic effect to ensure both high reactivity and weak adsorption and desorption interference. The Ni-based catalyst has a mass percentage of the active metal Ni of 40 wt. % to 90 wt. %, and a mass percentage of the REO of 0.5 wt. % to 20 wt. %, a balance being the inert oxide.
The preparation method provided in the present disclosure is a co-precipitation method, including a direct mixing for co-precipitation, a constant-speed dropwise addition for co-precipitation, and a microchannel mixing for co-precipitation. A precipitate obtained by the co-precipitation is separated through a centrifugation, a drying, and a calcination to obtain the Ni-based catalyst with high activity at a low temperature.
The method for preparing the Ni-based catalyst comprises steps of:
Provided is also use of the Ni-based catalyst in an unsteady-state pulse CO, methanation reaction, and specifically, the use is performed as follows:
The Ni-based catalyst provided by the present disclosure has the following advantages:
In a Ni-based catalyst according to the present disclosure, an inert oxide is used as a primary support, which plays a major supporting and fixing role and meanwhile shows weak adsorption for CO2, without causing interference, and on the other hand, the REO is used as a secondary support, which could reduce the content of REO but ensure the dispersion of REO, resulting in that a large number of Ni-REO support interfaces are still formed to ensure the CO2 methanation activity. The catalyst combines the properties of the two oxides and is fully suitable for the unsteady-state pulse COx methanation reaction proposed herein.
The Ni-based catalyst provided in the present disclosure is composed of an active metal Ni and an oxide support, wherein the oxide support is composed of an REO and an inert oxide; and the rare earth oxide and the inert oxide exhibit an excellent synergistic effect to ensure both high reactivity and weak adsorption and desorption interference. The Ni-based catalyst has a mass percentage of the active metal Ni of 40 wt. % to 90 wt. %, and a mass percentage of the REO of 0.5 wt. % to 20 wt. %, a balance being the inert oxide.
In the present disclosure, the REO in the oxide support of the Ni-based catalyst may be one or more selected from the group consisting of CeO2, La2O3, Eu203, and Sm203, and the REO accounts for 0.5 wt. % to 20 wt. % of a total mass of the catalyst. The inert oxide in the oxide support may be one or more selected from the group consisting of SiO2, MgO, and Al2O3, and the inert oxide accounts for 2 wt. % to 60 wt. % of a total mass of the catalyst.
The preparation method provided in the present disclosure is a co-precipitation method, including a direct mixing for co-precipitation, a constant-speed dropwise addition for co-precipitation, and a microchannel mixing for co-precipitation. A precipitate obtained by the preparation method is separated through a centrifugation, a drying, and a calcination to obtain the Ni-based catalyst with high activity at a low temperature. The method for preparing the Ni-based catalyst comprises steps of:
The present disclosure is further described below with reference to examples, but the embodiments of the present disclosure are not limited thereto.
The catalyst in the example was subjected to a granulation, and 100 mg of the catalyst with 40 to 60 mesh was taken and packed in a quartz tube. Before an activity test, the catalyst was activated through reduction at 400° C. for 2 h with 40 mL/min pure H2 as a reducing gas.
After the catalyst was reduced, the activity test was directly conducted in situ as follows: during a single chromatographic acquisition time of 9.8 min, a reaction gas consisting of 100 ppm of CO 2 and 100 ppm of CH 4 (internal standard) in a chromatographic quantification loop (with a volume of 250 μL) was intermittently pumped through a shut-off valve into a methanation furnace at a flow rate of 20 mL/min, and a carrier gas (i.e. a high-purity H2) was continuously introduced into the methanation furnace at a flow rate of 40 mL/min. After trace CO2 in the reaction gas was converted into CH4 through a methanation reaction, a concentration of the product CH4 was determined by an FID (peak area: 363,497) and a concentration of an internal standard CH4 was determined by an FID (peak area: 368,454), and the two were compared to calculate a conversion rate of CO2 methanation corresponding to the catalyst, which was 98.65%. The methanation reaction was performed at a temperature of 270° C. and a pressure of 1 bar. The Shimadzu Nexis GC-2030 chromatography system was used for detection. It can be known that the catalyst is suitable for an unsteady-state COx methanation reaction and exhibits excellent reactivity.
The catalyst in the example was subjected to a granulation, and 100 mg of the catalyst with 40 to 60 mesh was taken and packed in a quartz tube. Before an activity test, the catalyst was activated through reduction at 400° C. for 2 h with 40 mL/min pure H2 as a reducing gas.
After the catalyst was reduced, the activity test was directly conducted in situ as follows: during a single chromatographic acquisition time of 9.8 min, a reaction gas consisting of 1,000 ppm of CO2 and 1,000 ppm of CH4 (internal standard) in a chromatographic quantification loop (with a volume of 250 μL) was intermittently pumped through a shut-off valve into a methanation furnace at a flow rate of 20 mL/min, and a carrier gas (i.e. a high-purity H2) was continuously introduced into the methanation furnace at a flow rate of 40 mL/min. After trace CO2 in the reaction gas was converted into CH4 through a methanation reaction, a concentration of the product CH4 was determined by an FID (peak area: 4,079,000) and a concentration of an internal standard CH4 was determined by an FID (peak area: 4,146,243), and the two were compared to calculate a conversion rate of CO2 methanation corresponding to the catalyst, which was 98.38%. The methanation reaction was performed at a temperature of 300° C. and a pressure of 1 bar. The Shimadzu Nexis GC-2030 chromatography system was used for detection. It can be known that the catalyst is suitable for an unsteady-state COx methanation reaction and exhibits excellent reactivity.
The catalyst in the example was subjected to a granulation, and 100 mg of the catalyst with 40 to 50 mesh was taken and packed in a quartz tube. Before an activity test, the catalyst was activated through reduction at 400° C. for 2 h with 40 mL/min pure H2 as a reducing gas.
After the catalyst was reduced, the activity test was directly conducted in situ as follows: during a single chromatographic acquisition time of 9.8 min, a reaction gas consisting of 100 ppm of CO 2 and 100 ppm of CH 4 (internal standard) in a chromatographic quantification loop (with a volume of 250 μL) was intermittently pumped through a shut-off valve into a methanation furnace at a flow rate of 20 mL/min, and a carrier gas (i.e. a high-purity H2) was continuously introduced into the methanation furnace at a flow rate of 40 mL/min. After trace CO2 in the reaction gas was converted into CH4 through a methanation reaction, a concentration of the product CH4 was determined by an FID (peak area: 361774) and a concentration of an internal standard CH4 was determined by an FID (peak area: 368552), and the two were compared to calculate a conversion rate of CO2 methanation corresponding to the catalyst, which was 98.16%. The methanation reaction was performed at a temperature of 290° C. and a pressure of 1 bar. The Shimadzu Nexis GC-2030 chromatography system was used for detection. It can be known that the catalyst is suitable for an unsteady-state COx methanation reaction and exhibits excellent reactivity.
The catalyst in the example was subjected to a granulation, and 100 mg of the catalyst with 40 to 50 mesh was taken and packed in a quartz tube. Before an activity test, the catalyst was activated through reduction at 400° C. for 2 h with 40 mL/min pure H2 as a reducing gas.
After the catalyst was reduced, the activity test was directly conducted in situ as follows: during a single chromatographic acquisition time of 9.8 min, a reaction gas consisting of 5,000 ppm of CO 2 and 5,000 ppm of CH 4 (internal standard) in a chromatographic quantification loop (with a volume of 250 μL) was intermittently pumped through a shut-off valve into a methanation furnace at a flow rate of 20 mL/min, and a carrier gas (i.e. a high-purity H2) was continuously introduced into the methanation furnace at a flow rate of 40 mL/min. After trace CO2 in the reaction gas was converted into CH4 through a methanation reaction, a concentration of the product CH4 was determined by an FID (peak area: 17,993,400) and a concentration of an internal standard CH4 was determined by an FID (peak area: 18,351,600), and the two were compared to calculate a conversion rate of CO2 methanation corresponding to the catalyst, which was 98.05%. The methanation reaction was performed at a temperature of 290° C. and a pressure of 1 bar. The Shimadzu Nexis GC-2030 chromatography system was used for detection. It can be known that the catalyst is suitable for an unsteady-state COx methanation reaction and exhibits excellent reactivity.
The catalyst in the example was subjected to a granulation, and 100 mg of the catalyst with 60 to 80 mesh was taken and packed in a quartz tube. Before an activity test, the catalyst was activated through reduction at 400° C. for 1.5 h with 40 mL/min pure H2 as a reducing gas.
After the catalyst was reduced, the activity test was directly conducted in situ as follows: during a single chromatographic acquisition time of 9.8 min, a reaction gas consisting of 100 ppm of CO and 100 ppm of CH 4 (internal standard) in a chromatographic quantification loop (with a volume of 250 μL) was intermittently pumped through a shut-off valve into a methanation furnace at a flow rate of 20 mL/min, and a carrier gas (i.e. a mixture of H2 and Ar with 50% of H2) was continuously introduced into the methanation furnace at a flow rate of 40 mL/min. After trace CO in the reaction gas was converted into CH4 through the methanation reaction, a concentration of the product CH4 was determined by an FID (peak area: 355,972) and a concentration of an internal standard CH4 was determined by an FID (peak area: 359,106), and the two were compared to calculate a conversion rate of CO methanation corresponding to the catalyst, which was 99.13%. The methanation reaction was performed at a temperature of 275° C. and a pressure of 1 bar. The Shimadzu Nexis GC-2030 chromatography system was used for detection. It can be known that the catalyst is suitable for an unsteady-state COx methanation reaction and exhibits excellent reactivity.
The catalyst in the example was subjected to a granulation, and 100 mg of the catalyst with 40 to 60 mesh was taken and packed in a quartz tube. Before an activity test, the catalyst was activated through reduction at 400° C. for 2.5 h with 40 mL/min pure H2 as a reducing gas.
After the catalyst was reduced, the activity test was directly conducted in situ as follows: during a single chromatographic acquisition time of 9.8 min, a reaction gas consisting of 100 ppm of CO, 100 ppm of CO2, and 100 ppm of CH4 (internal standard) in a chromatographic quantification loop (with a volume of 250 μL) was intermittently pumped through a shut-off valve into a methanation furnace at a flow rate of 20 mL/min, and a carrier gas (i.e. a mixture of H2 and Ar with 20% of H2) was continuously introduced into the methanation furnace at a flow rate of 40 mL/min. After trace CO in the reaction gas was converted into CH4 through the methanation reaction, a concentration of the product CH4 of CO methanation was determined by an FID (peak area: 356,873) and a concentration of the product CH4 of CO2 methanation was determined by an FID (peak area: 360,069), which were each compared with a concentration of an internal standard CH4 determined by an FID (peak area: 361,674) to calculate a conversion rate of CO methanation (98.67%) and a conversion rate of CO2 methanation (99.56%) corresponding to the catalyst. The methanation reaction was performed at a temperature of 300° C. and a pressure of 1 bar. The Shimadzu Nexis GC-2030 chromatography system was used for detection. It can be known that the catalyst is suitable for an unsteady-state COx methanation reaction and exhibits excellent reactivity.
