CN115430450B - Preparation method and application of Rh nanoparticle-modified group III nitrogen oxide Si catalyst - Google Patents

Abstract

The invention relates to the technical field of thermal catalysts, in particular to a preparation method and application of a Rh nano-particle modified III-nitride Si catalyst. The preparation method has the advantages of simple operation, controllable height and low manufacturing cost. The prepared thermal catalyst is applied to the reaction of CO ₂ in the thermal catalytic hydrogenation to CO, so that severe experimental conditions such as high temperature, high pressure and the like are avoided, and the rate of CO production by CO ₂ hydrogenation is greatly improved. Rh NPs have high dispersivity, and ensure that efficient and long-acting catalysis of CO ₂ hydrogenation reaction occurs. Compared with the existing commercial catalytic system, the hydrogenation activity of CO ₂ is higher by 4 orders of magnitude, and the catalyst has a great application prospect.

Description

Preparation method and application of Rh nanoparticle-modified group III nitrogen oxide Si catalyst

Technical Field

The invention relates to the technical field of thermal catalysts, and in particular to a preparation method and application of a Rh nanoparticle-modified group III nitrogen oxide Si catalyst.

Background technique

_CO2 emission is one of the serious problems currently facing mankind. The fixation and refining of _CO2 and its conversion into other high-value-added chemicals and high-energy-density synthetic fuels are of great significance for solving the current greenhouse effect and alleviating the problem of energy shortage. As one of the products of _CO2 hydrogenation, CO is the main raw material for Fischer-Tropsch synthesis and plays a vital role in the process of chemical refining and production of chemicals and fuels. At the same time, compared with other hydrogenation products of _CO2 , the conversion process of CO is relatively easy in terms of kinetics and thermodynamics. Therefore, converting _CO2 hydrogenation into CO is a good choice. Compared with other conversion technologies (biocatalysis, electrocatalysis), thermal catalytic technology has a large _CO2 processing capacity and is highly compatible with existing industrial facilities, which reduces the cost of use and promotion to a certain extent. However, the bond energy of _CO2 is relatively high, and it is a great challenge to produce CO with high activity and selectivity at a lower temperature. Judging from the current research status, most thermal catalytic refining methods still require harsh conditions of high temperature and high pressure, which places extremely high demands on refining equipment. In addition, the low CO yield and poor catalytic stability further increase the application cost of _CO2 hydrogenation technology, making it still have a considerable gap with industrialization.

In previous studies, Rh was considered to be a metal that efficiently catalyzes _CO2 hydrogenation. However, when loaded on conventional carriers (alumina, cerium oxide, etc.), high temperature and high pressure conditions are still required, and the yield of CO is low. This is largely attributed to the limitations of conventional carriers, which make it difficult for them to play an excellent synergistic role with Rh. Therefore, developing a new carrier to enhance the synergistic ability with Rh will greatly promote the occurrence of _CO2 hydrogenation reaction.

Summary of the invention

The purpose of the present invention is to provide a preparation method and application of a Rh nanoparticle-modified III-nitride Si catalyst, wherein a III-nitride NWs/Si carrier is prepared by combining molecular beam epitaxy (MBE) with high temperature annealing, and Rh NPs are anchored on the carrier surface by photodeposition. The prepared thermal catalyst is applied to the reaction of thermal catalytic hydrogenation of _CO2 to CO, thereby avoiding high temperature and high pressure reaction conditions and improving the reaction rate.

The III-nitride NWs/Si epitaxial wafer was grown by molecular beam epitaxy (MBE), the surface of the III-nitride NWs/Si epitaxial wafer was partially oxidized by high-temperature annealing to prepare the III-nitride oxide NWs/Si carrier, and finally the Rh/III-nitride oxide NWs/Si thermal catalyst was prepared by photodeposition.

To achieve the above object, the present invention adopts the following technical solutions:

A method for preparing a Rh nanoparticle-modified group III nitrogen oxide Si catalyst, characterized in that the specific steps include:

Step 1, using a cleaning agent to clean a silicon wafer, using the silicon wafer as a substrate, and growing a group III nitride NWs/Si carrier by molecular beam epitaxy;

Step 2, annealing the group III nitride NWs/Si at high temperature in an air atmosphere to obtain a group III nitride oxide NWs/Si carrier;

Step 3: Load Rh on the group III nitride NWs/Si by photodeposition to prepare the Rh/group III nitride NWs/Si thermal catalyst.

As a further improvement of the present invention, the cleaning agent includes any one or both of an organic solvent and an acidic solvent.

As a further improvement of the present invention, the growth conditions of the molecular beam epitaxy method include a Ga beam equivalent pressure (BEP) of 5×10 ⁻⁸ Torr and a forward plasma power of 350W.

As a further improvement of the present invention, the bottom III-nitride layer is first grown in situ to serve as a template for the III-nitride NWs.

As a further improvement of the present invention, the growth conditions also include a substrate temperature of 680° C. to 720° C. and a growth time of 45 min to 75 min.

As a further improvement of the present invention, the high temperature annealing temperature is 150° C. to 250° C., and the temperature is kept for 1 to 2 hours.

As a further improvement of the present invention, the photodeposition method includes placing group III nitride NWs/Si in a reactor, adding a mixed solution of an organic alcohol solvent and water, and a Rh precursor H ₂ RhCl ₆ respectively, and using a xenon lamp as a photodeposition light source to illuminate in a vacuum state of an argon atmosphere to obtain a Rh/group III nitride NWs/Si thermal catalyst.

As a further improvement of the present invention, the lighting time is 0.5 hours.

An application of a Rh nanoparticle-modified III-group nitrogen oxide Si catalyst, wherein the catalyst prepared by the above method is applied to the reaction of thermal catalytic _CO2 hydrogenation to produce CO.

As a further improvement of the present invention, the thermal catalytic _CO2 production CO reaction can be controlled at a minimum of 170°C.

Compared with the prior art, the present invention is beneficial in that:

1. The present invention develops a new III-nitride carrier. Different from traditional catalytic carriers such as alumina and cerium oxide, the III-nitride has a good one-dimensional morphology and a high specific surface area, which is conducive to the high dispersion of the co-catalyst; it has excellent adsorption and activation effects on linear _CO2 molecules; and it can be modified at the atomic level.

2. A III-nitride oxide NWs/Si carrier was prepared by combining MBE with air atmosphere annealing, and RhNPs were anchored on its surface by photodeposition. By reducing the activation energy of the key elementary reaction and changing the rate-determining step, a lower reaction start-up temperature was obtained and efficient and long-term _CO2 hydrogenation refining was achieved.

3. The preparation method of the present invention has the advantages of simple operation and low manufacturing cost.

4. The Rh-loaded III-group nitrogen oxide thermal catalyst prepared by the present invention is applied to the reaction of thermal catalytic _CO2 to CO, avoiding harsh experimental conditions such as high temperature and high pressure, and greatly improving the rate of _CO2 hydrogenation to CO. RhNPs have high dispersibility, ensuring the occurrence of efficient and long-term catalytic _CO2 hydrogenation reaction. Compared with the existing commercial catalytic system, the _CO2 hydrogenation activity is 4 orders of magnitude higher, and has great application prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the CO ₂ hydrogenation activity of Rh/III-nitride NWs/Si and Rh/III-oxide NWs/Si at different reaction temperatures.

Figure 2 shows the CO ₂ hydrogenation conversion frequency (TOF) of Rh/III-group nitrogen oxide NWs/Si at different reaction temperatures.

Figure 3 shows the CO ₂ hydrogenation activity of Rh/III-nitride NWs/Si-250 and Rh/III-nitride TP/Sapphire at 260°C.

Figure 4 is the CO ₂ hydrogenation activity of Rh/III-nitride/NWs/Si-250 and Rh/Al ₂ O ₃ at 260 °C.

Figure 5 shows the stability of Rh/III-group nitrogen oxide NWs/Si-250 catalyzing CO ₂ hydrogenation at 260 °C.

Detailed ways

The technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of the present invention.

Example 1

Preparation of Group III Nitride Supports

The III-nitride oxide NWs were epitaxially grown using a Veeco Gen II MBE system equipped with an RF plasma assisted nitrogen source. A 4-inch silicon (111) wafer was used as the substrate. Before loading into the MBE chamber, the silicon wafer was cleaned with acetone and methanol to remove organic contaminants and then rinsed with ¹⁰ % hydrofluoric acid to remove silicon oxide. The growth conditions of these nanowires included a Ga beam equivalent pressure (BEP) of 5× ^10-8 Torr and a forward plasma power of 350W. The nitrogen flow rate was set to 1.0 standard cubic centimeter per minute (sccm), ensuring a nitrogen-rich atmosphere to promote the formation of the N-terminal side surface (m-plane) of the nanowires. In addition, a Ga seed layer was used to promote the formation of a Ga polar basal plane for N termination. The substrate temperature of the growth was about 700°C. Typically, a bottom III-nitride layer is first grown in situ to serve as a template for the III-nitride NWs. After a growth time of 1 hour, the III-nitride NWs/Si support was obtained.

Example 2

Preparation of Rh/III-nitride NWs/Si thermal catalyst

The III-nitride NWs/Si (geometric surface area of about 0.2 cm ² ) was pre-treated by rinsing with deionized water and then placed in a 0.4L glass reactor equipped with a top quartz window. 60mL of a mixed solution of methanol/water (volume ratio 1/5) was poured into the reactor, and then 70μL of a Rh precursor (0.2mol/L H ₂ RhCl ₆ ) was added. After the reactor chamber was evacuated for about 2 minutes, the chamber was evacuated and degassed with argon gas 5 times to remove residual air in the system. A 300W xenon lamp (AuLight, CEL-HLF300-T3) was used as the light source for photodeposition, and the illumination time was 0.5 hours. Rinse thoroughly with deionized water to remove carbon residues, and the Rh/III-nitride NWs/Si thermal catalyst was prepared.

Embodiment 3-5

Preparation of Rh/III-group Nitrogen Oxide NWs/Si Catalyst

The group III nitride NWs/Si is placed in a thermal reaction kettle, kept in contact with air and the pressure in the kettle is kept at normal pressure, then gradually raised to annealing temperature and kept warm for one hour, and then cooled to room temperature after the insulation is completed to obtain a group III nitride NWs/Si carrier.

The III-nitride NWs/Si (geometric surface area ~0.2 cm ² ) was pre-treated by rinsing with deionized water and then placed in a 0.4L glass reactor equipped with a top quartz window. 60mL of a mixed solution of methanol/water (volume ratio 1/5) was poured into the reactor, and then 70μL of a Rh precursor (0.2mol/L H ₂ RhCl ₆ ) was added. After the reactor chamber was evacuated for about 2 minutes, the chamber was evacuated and degassed with argon gas 5 times to remove residual air in the system. A 300W xenon lamp (AuLight, CEL-HLF300-T3) was used as the light source for photodeposition, and the illumination time was 0.5 hours. Rinse thoroughly with deionized water to remove carbon residues, and the Rh/III-nitride NWs/Si thermal catalyst was prepared. The specific experimental conditions and product nomenclature are shown in Table 1 below.

Table 1 Experimental conditions and products of Examples 3-5

Example 6

Preparation of Rh/III-nitride TP/Sapphire catalyst

A commercial III-nitride film with sapphire as substrate (denoted as III-nitride TP/Sapphire, geometric surface area ~0.2 cm ² ) was pre-treated by rinsing with deionized water, and then placed in a 0.4L glass reactor equipped with a top quartz window. 60mL of a mixed solution of methanol/water (volume ratio 1/5) was poured into the reactor, and then 70μL of a Rh precursor (0.2mol/L H ₂ RhCl ₆ ) was added. After the reactor chamber was evacuated for about 2 minutes, the chamber was evacuated and degassed with argon gas 5 times to remove residual air in the system. A 300W xenon lamp (AuLight, CEL-HLF300-T3) was used as the light source for photodeposition, and the illumination time was 0.5 hours. Rinse thoroughly with deionized water to remove carbon residues, and the Rh/III-nitride TP/Sapphire thermal catalyst was prepared.

Example 7

Application experiment of thermal catalyst

The thermal catalysts prepared in Examples 2-6 and Rh/Al ₂ O ₃ (Shaanxi Kaida Chemical Co., Ltd.) were respectively used for the experiment of catalytic hydrogenation of CO ₂ to produce CO. The specific steps are as follows: Add the catalyst (the amount of commercial catalyst Rh/Al ₂ O ₃ added is 1 g) to a sealed 0.25L stainless steel reactor, seal the kettle body and completely evacuate it to vacuum, and then introduce a mixed gas of CO ₂ and H ₂ (CO ₂ :H ₂ =10:1) into the kettle to normal pressure. The temperature is gradually increased and kept at different reaction temperatures (170°C, 200°C, 230°C, 260°C and 290°C) for one hour. After cooling to room temperature, 50mL of gas is taken out with a syringe and injected into a gas chromatograph with an FID detector to detect the CO production.

As shown in Figures 1 and 2, the catalytic activity of Rh/III-nitride NWs/Si and Rh/III-nitride NWs/Si for CO ₂ hydrogenation is positively correlated with the reaction temperature: the higher the reaction temperature, the faster the CO ₂ hydrogenation rate. After the surface of the III-nitride was partially oxidized, the minimum temperature for the reaction to start was reduced to 170°C, and the reaction activity gradually increased with the deepening of the oxidation degree (increase in oxidation temperature). When the oxidation temperature reached 250°C (Rh/III-nitride NWs/Si-250), a high CO yield of 127 mmol·g ^-1 ·h ^-1 was obtained at a reaction temperature of 290°C, which was 47.8% higher than that of Rh/III-nitride NWs/Si (85.9 mmol·g ^-1 ·h ^-1 ). At the same time, the conversion frequency (TOF) of Rh/III-nitride NWs/Si-250 reached 270.2 molCO per mol of Rh.

As shown in Figures 3 and 4, at a reaction temperature of 260°C, Rh/III-nitride NWs/Si-250 achieved a CO generation rate of 106.4 mmol·g ^-1 ·h ^-1 , which is 39 times higher than the CO generation rate of Rh/III-nitride TP/Sapphire (2.7 mmol·g ^-1 ·h ^-1 ) based on commercial III-nitride TP/Sapphire at the same temperature, and 6259 times higher than the CO generation rate of commercial catalyst Rh/Al ₂ O ₃ (0.017 mmol·g ^-1 ·h ^-1 ). This proves that the III-nitride NWs catalytic system we developed has a higher CO generation rate than the commercial catalytic system at the same temperature.

As can be seen from Figure 5, after 9 cycles of stability testing totaling 45 hours, Rh/III-nitrogen oxide NWs/Si-250 obtained a total CO production of 1.22 mol and an intrinsic activity (TON) of 2616 mol CO per mole of Rh, and the catalytic activity did not decay significantly.

Claims (10)

1. A method for preparing a Rh nanoparticle-modified group III nitrogen oxide Si catalyst, characterized in that: the specific steps include: Step 1, using a cleaning agent to clean a silicon wafer, using the silicon wafer as a substrate, and growing a group III nitride NWs/Si carrier by molecular beam epitaxy; Step 2, annealing the group III nitride NWs/Si at high temperature in an air atmosphere to obtain a group III nitride oxide NWs/Si carrier; Step 3: Load Rh on the group III nitride NWs/Si by photodeposition to prepare the Rh/group III nitride NWs/Si thermal catalyst. 2. The method for preparing a Rh nanoparticle modified group III nitrogen oxide Si catalyst according to claim 1, characterized in that the cleaning agent comprises any one or both of an organic solvent and an acidic solvent. 3 . The method for preparing a Rh nanoparticle modified group III oxynitride Si catalyst according to claim 1 , wherein the growth conditions of the molecular beam epitaxy method include a Ga beam equivalent pressure of 5×10 ⁻⁸ Torr and a forward plasma power of 350 W. 4. The method for preparing a Rh nanoparticle modified III-nitride Si catalyst according to claim 1, characterized in that: a bottom III-nitride layer is first grown in situ to serve as a template for the III-nitride NWs. 5. The method for preparing a Rh nanoparticle modified group III nitride Si catalyst according to claim 3, characterized in that: the growth conditions also include a substrate temperature of 680°C to 720°C and a growth time of 45min to 75min. 6. The method for preparing a Rh nanoparticle modified III-group nitrogen oxide Si catalyst according to claim 1, characterized in that: the temperature of the high temperature annealing is 150°C to 250℃, keep warm for 1 to 2 hours. 7. The method for preparing a Rh nanoparticle modified III-group nitride Si catalyst according to claim 1, characterized in that: the photodeposition method comprises placing the III-group nitride NWs/Si in a reactor, adding a mixed solution of an organic alcohol solvent and water, and a Rh precursor H ₂ RhCl ₆ , respectively, and using a xenon lamp as a photodeposition light source to illuminate in a vacuum state of an argon atmosphere to obtain a Rh/III-group nitride NWs/Si thermal catalyst. 8 . The method for preparing a Rh nanoparticle-modified group III nitrogen oxide Si catalyst according to claim 7 , wherein the illumination time is 0.5 hours. 9. An application of a Rh nanoparticle modified III-group nitrogen oxide Si catalyst, characterized in that the thermal catalyst prepared by the method of claim 1 is applied to the reaction of thermal catalytic _CO2 hydrogenation to produce CO. 10. The use of a Rh nanoparticle modified III-group nitrogen oxide Si catalyst according to claim 9, characterized in that the thermal catalytic _CO2 to CO reaction can be controlled at a minimum of 170°C.