Application of a Specific Facet-Type Noble Metal MoC Catalyst

Abstract

The present invention discloses the application of a noble metal-like MoC catalyst with specific crystal planes, specifically the application of an α-MoC catalyst with specific crystal planes in low-temperature water-gas shift for hydrogen production. The catalyst is prepared by directly nitriding and then carbonizing commercial MoO3 nanorods, which can regulate the exposure of a large number of (200) crystal planes on the surface, thereby achieving complete conversion of CO at 175 °C in the water-gas shift reaction. The reaction rate per unit mass is about 4.5 times higher than that of ordinary α-MoC (mainly with (111) crystal planes) and about 1.8 times higher than that of industrial CuZnAl catalysts, and it has better stability.

Description

Technical Field

[0001] The present invention relates to the application of a specific crystal plane type noble metal MoC catalyst, and specifically to the application of an α-MoC catalyst exposing a specific crystal plane in the low-temperature water-gas shift reaction. Background Art

[0002] New energy sources such as hydrogen energy, wind energy, and biomass energy are the main targets of energy-related research. Among them, hydrogen energy has the advantages of high energy density, zero pollution of products, and stability, and is an ideal secondary energy source (Renew. Sust. Energ. Rev., 9 (2005), 255-271). At present, the conversion of hydrogen energy into electrical energy has been realized. By using a proton exchange membrane fuel cell, electrical energy is generated during the process of converting H2 into H2O, converting chemical energy into electrical energy, and at the same time, no CO2 is generated. However, trace amounts of CO in the hydrogen source used in such industrial batteries have a serious poisoning effect on the battery electrode materials, and the content of CO needs to be reduced to less than 50-100 ppm (J. Power Sources, 111 (2) (2002), 239-247). In addition, trace amounts of CO in the industrial process of synthesizing ammonia also have a strong poisoning effect on the catalyst and need to be eliminated (Catal. Sci. Technol., 7 (2017), 4806-4817). At present, the main goal of eliminating CO is achieved through the water-gas shift (WGS) reaction (J. Power Sources, 159 (2006), 943).

[0003] The water-gas shift reaction is as follows:

[0004]

[0005] This process is divided into two steps: a high-temperature section and a low-temperature section. The high-temperature WGS temperature is 300-450 °C, and Fe-Cr catalysts are mainly used. This temperature section can be used to accelerate the reaction process. However, due to the exothermic nature of the reaction, it is limited by the thermodynamic equilibrium, the CO conversion rate is low, and the metal Cr itself is toxic and will pollute the environment. The low-temperature WGS temperature is 200-270 °C, and the catalysts used are represented by Cu-Zn-Al. In the low-temperature section, the CO conversion rate can reach nearly 100%. Combining with the high-temperature section can achieve the optimal CO conversion route (Appl. Energy., 258 (2020), 114078). However, the Cu-Zn-Al catalyst in the low-temperature section has problems such as flammability, sulfur and chlorine intolerance. Achieving a high conversion rate in the low-temperature section helps to reduce the energy consumption in the high-temperature section while meeting the production target, solve the cost and improve the economic benefits.

[0006] Noble metal catalysts have become a research hotspot for WGS catalysts due to their high catalytic activity in WGS. Commonly used noble metal catalysts mainly include Pt, Au, Pd, etc. (Renew. Sust. Energy Rev., 75 (2017), 1101 - 1129). However, the low reserves and high price of noble metals result in very high catalyst costs, increasing industrial production costs. Therefore, it is of great research significance to develop substitutes for noble metal catalysts in low-temperature WGS reactions.

[0007] Transition metal carbides refer to a class of compounds formed by carbonizing transition non-noble metals. For example, molybdenum carbide material is a type of interstitial metal compound formed by carbon atoms filling the lattice of transition metal molybdenum. The electronic effect between molybdenum and carbon changes the electron density of states near the Fermi level of the transition metal, resulting in noble metal-like properties, which is one of the options for noble metal substitution (Chem. Rev., 96 (1996), 1477 - 1498). Currently, MoC is an important research object for WGS catalysts, with a large specific surface area. However, it is easily oxidized to MoO3 on the surface and quickly deactivates. Researchers have loaded MoC with other metals to obtain catalysts with high catalytic activity. The Thompson team loaded Pt on Mo2C, and due to the strong interaction between Mo2C and Pt, Pt shows a valve-like distribution, demonstrating better catalytic performance than industrial CuZnAl catalysts and most other oxide-supported Pt catalysts (J. Am. Chem. Soc., 133 (2011), 2378–2381). The Martin team at Peking University loaded Pt on α-MoC and found that H2O dissociates on the surface of MoC to form -OH, and -OH combines with CO adsorbed on Pt to form CO2. However, when the Pt loading is 0.02%, the catalyst quickly deactivates. When the Pt loading is increased to 2%, the stability of the catalyst is greatly improved, and a catalyst with high stability and high CO conversion rate is obtained (Nature, 589 (2021), 396 - 401). Our team prepared an Ir / MoC catalyst with Ir single atoms as promoters and found that the presence of Ir single atoms greatly enhances the catalytic activity of MoC (ACS Catal., 11 (2021), 5942 - 5950). However, these works often add a large amount of noble metals to quickly eliminate surface oxygen species of the catalyst and thus improve the stability of the catalyst, which brings problems such as high catalyst price and increased process cost for practical applications. So far, there has been no report on the application of highly efficient and highly stable non-noble metal carbide catalysts in low-temperature water-gas shift reactions. Summary of the Invention

[0008] The object of the present invention is to provide an application of a noble metal-like carbide catalyst, which can be used for low-temperature and highly efficient hydrogen production by water-gas shift reaction.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A MoC catalyst prepared from commercial nanorod-shaped MoO3 as a precursor and applied to low-temperature water vapor reforming for hydrogen production. The catalyst is prepared by a calcination method, and commercial MoO3 nanorods are nitrided and carbonized to obtain the final MoC catalyst. The specific process is to place a certain amount of nanorod-shaped MoO3 in a tubular furnace and treat it in a nitrogen-containing atmosphere to obtain MoN x . The sample MoN x is then placed back in the tubular furnace and carbonized in an atmosphere of a CH4 / H2 mixture to obtain MoC x , and then O2 / Ar is continuously introduced for passivation to obtain the required catalyst.

[0011] An application of a noble metal-like MoC catalyst, which is obtained by nitriding and carbonizing MoO3 with a nanorod morphology, to obtain an α-phase MoC nanorod catalyst with a surface-exposed (200) crystal plane accounting for 50%-80%, and is used for low-temperature water gas shift hydrogen production reaction. Thus, high-efficiency and stable low-temperature water gas shift hydrogen production performance is achieved.

[0012] Further, in the above technical solution, the low temperature is 100-200 °C.

[0013] Further, in the above technical solution, in the MoO3 crystal with a nanorod morphology, the (020) and its parallel crystal planes account for 70%-100% of the total crystal plane content, the length is 1-500 μm, and the diameter is 1-300 nm.

[0014] Further, in the above technical solution, the conditions for the low-temperature water gas shift hydrogen production reaction are: the CO concentration is 1%-10% (volume fraction), water vapor is introduced into the reactor by bubbling, and the total flow rate is 20-100 ml / min. The water vapor content in the reaction gas is obtained by controlling the temperature of the water bath.

[0015] Further, in the above technical solution, the catalyst needs to be activated before application, and the conditions are 500-700 °C, treated for 1-3 h, and the heating rate is 2-20 °C / min; the treatment atmosphere is 1-100% CH4 / H2, 1-100% H2 / He or 1-100% H2 / Ar.

[0016] Further, in the above technical solution, the MoC catalyst is finally obtained by nitriding and carbonizing MoO3 with a nanorod morphology; the specific preparation steps are as follows:

[0017] 1) Place MoO3 with a nanorod morphology in a reaction device and perform nitriding treatment at 600-900 °C in a nitrogen-containing atmosphere to obtain MoN x .

[0018] 2) The nitrided MoN x is continuously placed in a reaction device and carbonized at 1-100% CH4 / H4 mixed gas and 600-900 °C to obtain MoC x catalyst.

[0019] 3) 0.1-10% O2 / Ar or air is introduced onto the MoC x catalyst, and passivation is carried out at 10-50 °C to obtain a MoC catalyst.

[0020] Furthermore, in the above technical solution, in step 1), the heating rate of the nitriding treatment is 2-20 °C / min, the heat preservation duration is 60-240 min, and the nitrogen-containing atmosphere is NH3, N2, 1-100% NH3 / He, 1-100% N2 / He, 1-100% NH3 / Ar or 1-100% N2 / Ar.

[0021] Furthermore, in the above technical solution, in step 2), the heating rate of the carbonization is 2-20 °C / min, and the heat preservation duration is 60-240 min.

[0022] Furthermore, in the above technical solution, in step 3), the passivation time is 10-20 h.

[0023] Compared with the existing technology, the substantial features of the present invention are:

[0024] 1. After nitriding and carbonizing commercial MoO3 nanorods, the present invention obtains a noble metal-like MoC catalyst with specific exposed crystal planes (denoted as MoC NR, where NR represents nanorods), which is used for the low-temperature water-gas shift reaction, realizing the complete conversion of CO at low temperature (below 200 °C) without loading noble metals, filling the gap in the field of applying highly efficient and highly stable non-noble metal carbide catalysts to the low-temperature water-gas shift hydrogen production reaction.

[0025] 2. Compared with ordinary MoC, the catalyst of the present invention has better stability, solving the problem of poor catalyst stability caused by the oxidation inactivation of conventional MoC.

[0026] 3. It is expected to replace noble metal catalysts for low-temperature water-gas reactions, thus solving the problem that the high cost of catalysts due to the low reserves and high price of noble metals increases the industrial production cost. Description of the Drawings

[0027] Figure 1 Activity comparison among MoC NR prepared in Example 1, MoC prepared in Comparative Example 1, β-MoC prepared in Comparative Example 2, and industrial CuZnAl catalyst.

[0028] Figure 2 Stability comparison among MoCNR prepared in Example 1, MoC prepared in Comparative Example 1, and industrial CuZnAl catalyst.

[0029] Figure 3 Reaction rates of MoCNR prepared in Example 1 and MoC prepared in Comparative Example 1 at 150 °C.

[0030] Figure 4 XRD characterization results of granular MoO3, MoO3NR, MoC prepared in Comparative Example 1, and MoCNR prepared in Example 1.

[0031] Figure 5 TEM electron microscope image of MoC prepared in Comparative Example 1.

[0032] Figure 6 TEM electron microscope image of MoCNR prepared in Example 1.

[0033] Figure 7 SEM electron microscope images of MoCNR prepared in Example 1 and MoC prepared in Comparative Example 1. Detailed implementation manners

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] Example 1:

[0036] Place 1 g of MoO3NR in a tubular furnace, introduce NH3, heat it to 700 °C at a rate of 10 °C / min, and hold for 2 h. After cooling to room temperature, introduce 20% CH4 / H2 and calcine at 700 °C for 2 h. After cooling, introduce 1% O2 / Ar to passivate for 12 h to prepare a MoCNR catalyst with a (200) crystal plane ratio of 70%-80%. (MoO3NR refers to MoO3 crystals with a nanorod morphology, where the (020) crystal plane and its parallel crystal planes account for 70%-100% of the total crystal plane content, with a length of 1-500 μm and a diameter of 1-300 nm).

[0037] Example 2:

[0038] Place 1 g of MoO3NR in a tubular furnace, introduce 80% NH3 / Ar, heat it up to 700 °C at a rate of 10 °C / min, and hold for 2 h. After cooling to room temperature, introduce 20% CH4 / H2, and calcine at 700 °C for 2 h. After cooling, introduce 1% O2 / Ar to passivate for 12 h to prepare a MoCNR catalyst with about 60% content of (200) crystal plane.

[0039] Example 3:

[0040] Place 1 g of MoO3NR in a tubular furnace, introduce NH3, heat it up to 700 °C at a rate of 10 °C / min, and hold for 2 h. After cooling to room temperature, introduce 30% CH4 / H2, and calcine at 700 °C for 2 h. After cooling, introduce 1% O2 / Ar to passivate for 12 h to prepare a MoC NR catalyst with about 70% content of (200) crystal plane.

[0041] Example 4:

[0042] Place 1 g of MoO3NR in a tubular furnace, introduce NH3, heat it up to 700 °C at a rate of 10 °C / min, and hold for 2 h. After cooling to room temperature, introduce 20% CH4 / H2, and calcine at 600 °C for 2 h. After cooling, introduce 1% O2 / Ar to passivate for 12 h to prepare a MoC NR catalyst with N-containing species on the surface and about 50% of (200) crystal plane.

[0043] Example 5:

[0044] Place 1 g of MoO3NR in a tubular furnace, introduce NH3, heat it up to 700 °C at a rate of 10 °C / min, and hold for 2 h. After cooling to room temperature, introduce 20% CH4 / H2, and calcine at 800 °C for 2 h. After cooling, introduce 1% O2 / Ar to passivate for 12 h to prepare a MoC NR catalyst with a small part of excessive carbonization on the surface and about 70% content of (200) crystal plane.

[0045] Comparative Example 1:

[0046] Place 1 g of granular MoO3 in a tubular furnace, introduce NH3, heat it up to 700 °C at a rate of 10 °C / min, and hold for 2 h. After cooling to room temperature, introduce 20% CH4 / H2, and calcine at 700 °C for 2 h. After cooling, introduce 1% O2 / Ar to passivate for 12 h to prepare MoC (mainly with (111) crystal plane, the proportion of (111) crystal plane is 40 - 60%, and the proportion of (200) crystal plane is about 20%).

[0047] Comparative Example 2:

[0048] Place 1 g of granular MoO3 in a tubular furnace, introduce 20% CH4 / H2, and calcine at 700 °C for 2 h. After cooling, introduce 1% O2 / Ar to passivate for 12 h to prepare β-MoC.

[0049] Application Example 1:

[0050] To evaluate the catalytic performance of the prepared catalyst, a microreactor evaluation device was used to test the CO water-gas shift reaction activity of the catalyst. The test conditions were as follows: a tubular furnace and a fixed-bed reactor were used, the catalyst dosage was 100 mg, the gas volume composition was 2% CO and 10% H2O, He was used as the balance gas, the total flow rate was 30 ml / min, and the mass space velocity was 1.8x10 4 mlg cat -1 h -1 . Before the test, the catalyst was pre-carbonized at 590 °C for 2 h in a 20 vol% CH4 / H2 atmosphere. After cooling to room temperature, a temperature-programmed activity test was carried out. After maintaining a constant temperature for 20 min at each temperature point to be measured, a sample was taken. The gas composition at the reactor outlet was detected by chromatography, and the conversion rate was calculated.

[0051] The calculation method of the CO conversion rate is as follows:

[0052] CO Conversion(%) = {([CO] in – [CO] out ) / [CO] in} × 100%

[0053] Where: [CO] in is the chromatographic peak area of the feed CO, and [CO] out is the chromatographic peak area of the outlet CO.

[0054] It can be seen from Figure 1 that under the reaction conditions below 150 °C, the conversion rate of CO by the MoCNR catalyst prepared in the present invention exceeds 90%, and complete conversion is achieved at 175 °C. Under the same conditions, the conventional MoC, CuZnAl, and β-MoC do not achieve complete conversion of CO.

[0055] It can be seen from Figure 2 that the MoCNR catalyst prepared in the present invention has the best stability. Under the same conditions, the catalytic performance stabilities of the conventional MoC and CuZnAl are relatively unstable.

[0056] It can be seen from Figure 3 that at 150 °C, the catalytic reaction rate of the MoCNR catalyst prepared in the present invention for converting CO is about 4.5 times that of ordinary MoC, showing strong catalytic performance.

[0057] It can be seen from Figure 4It can be seen that the XRD pattern shows that compared with the precursor nanorod-shaped MoO3 NR and granular MoO3, the intensities of the (020), (040), and (060) crystal planes are stronger, and after nitridation and carbonization treatment, the nanorod-shaped MoCNR has a stronger (200) crystal plane intensity and a higher content.

[0058] From Figure 5 It can be seen that according to the TEM results, MoC presents a granular morphology, and the surface is mainly the (111) crystal plane.

[0059] From Figure 6 It can be seen that according to the TEM results, MoCNR presents a nanorod-shaped morphology, and the surface is mainly the (200) crystal plane.

[0060] From Figure 7 It can be seen that according to the SEM results, MoC presents a granular morphology, and MoC NR presents a nanorod-shaped morphology.

Claims

1. Application of a noble metal-like MoC catalyst, characterized in that: By nitriding and carbonizing nanorod-shaped MoO3, an α-phase MoC nanorod catalyst with 50%-80% of the surface-exposed (200) crystal plane is obtained for the low-temperature water-gas shift reaction for hydrogen production; The low temperature is 100-200 °C; The MoC catalyst is finally obtained by nitriding and carbonizing nanorod-shaped MoO3; the specific preparation steps are as follows: 1) Place the nanorod-shaped MoO3 in a reaction device and perform nitridation treatment at 600 - 900 °C in a nitrogen-containing atmosphere to obtain MoN x ; 2) The nitrided MoN x is continuously placed in a reaction device and carbonized at 1-100% CH4 / H4 mixed gas and 600-900 °C to obtain MoC x catalyst; 3) Introduce 0.1-10% O2 / Ar or air onto the MoC x catalyst and passivate it at 10-50 °C to obtain the MoC catalyst.

2. The application according to claim 1, wherein: In the nanorod-shaped MoO3 crystal, (020) and its parallel crystal planes account for 70%-100% of the total crystal plane content, with a length of 1-500 μm and a diameter of 1-300 nm.

3. The application according to claim 1, wherein: The conditions for the low-temperature water-gas shift reaction for hydrogen production are: the CO concentration is 1%-10% by volume percentage, water vapor is introduced into the reactor by bubbling, and the total flow rate is 20-100 ml / min.

4. The application according to claim 1, characterized in that: Before the catalyst is applied, it needs to be activated under the conditions of 500-700 °C for 1-3 h, with a heating rate of 2-20 °C / min; the treatment atmosphere is 1%-100% CH4 / H2, 1%-100% H2 / He or 1%-100% H2 / Ar.

5. The application according to claim 1, wherein: The heating rate of the nitriding treatment is 2-20 °C / min, and the heat preservation time is 60-240 min. The nitrogen-containing atmosphere is NH3, N2, 1%-100% NH3 / He, 1%-100% N2 / He, 1%-100% NH3 / Ar or 1%-100% N2 / Ar.

6. The application according to claim 1, wherein: The heating rate of the carbonization is 2-20 °C / min, and the heat preservation time is 60-240 min.

7. The application according to claim 1, characterized in that: The passivation time is 10-20 h.

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