Preparation method of Zn-Cr spinel oxide catalyst and application of Zn-Cr spinel oxide catalyst in CO2-assisted ethane dehydrogenation

Abstract

The invention provides a preparation method of a Zn-Cr spinel oxide catalyst and application of the Zn-Cr spinel oxide catalyst in CO2-assisted ethane dehydrogenation, and relates to the technical field of composite catalysts. Wherein the Zn-Cr spinel oxide catalyst is prepared by firstly preparing a Zn1Crx oxide carrier by adopting a coprecipitation method and then loading Cr on the surface of the Zn1Crx oxide carrier by adopting an impregnation method, and in the process, strong metal-carrier interaction can be formed between the loading of Cr on the surface of the carrier and the Zn1Crx oxide carrier, so that the oxygen vacancy concentration on the surface of the catalyst is regulated and controlled and the desorption of ethylene is promoted; according to the present invention, the Zn1Crx carrier is used as the catalyst to inhibit the excessive oxidation of the Zn1Crx carrier so as to significantly improve the selectivity of ethylene, and the metal Cr forms the compact covering layer on the surface of the Zn1Crx carrier so as to reduce the number of the strong oxidation active sites, synergistically promote the rapid desorption of ethylene, and inhibit the occurrence of the side reactions such as dry reforming and hydrogenolysis.

Description

Technical Field

[0001] The present invention relates to the technical field of composite catalysts, and in particular to a preparation method of a Zn-Cr spinel oxide catalyst and application thereof in CO2-assisted ethane dehydrogenation. Background Art

[0002] Ethylene is an important basic raw material in the petrochemical industry, and its demand is constantly increasing. Ethane dehydrogenation to ethylene has attracted widespread attention as an alternative process to traditional naphtha cracking. Among them, CO2-assisted ethane dehydrogenation to ethylene has become one of the most promising alternative technologies due to its ability to take into account CO2 utilization. Supported Cr-based catalysts are considered one of the most promising catalysts due to their superior catalytic performance. As an important component of supported catalysts, the properties of the support directly regulate the acid-base properties of the Cr-based catalyst, the dispersion and chemical state of the surface chromium species, and thus affect important properties such as the catalyst's reactivity and selectivity.

[0003] In order to improve the catalytic activity of Cr-based catalysts, a common method is to dope metal elements in the catalyst. For example, in the prior art, Liu et al. (titled J.Liu, Y.Liu, Y.Ni, H.Liu, W.Zhu, Z.Liu. Enhanced propanedehydrogenation to propylene over zinc-promoted chromium catalysts. Catalysis Science & Technology, 2020, 10 (6): 1739-1746.) introduced Zn into ZnCr2O4. Zn can be used to induce the formation of more defect sites around ZnCr2O4 particles and at the interface with Cr2O3, and reduce the apparent activation energy of ZnCr2O4, thereby improving the catalytic performance of the catalyst. However, due to its own volatility, Zn may destroy the structure of spinel when used in a high temperature environment, thereby affecting the catalytic performance; in addition, Zn may also trigger some side reactions, such as excessive dehydrogenation of ethane to form carbon deposits, affecting the efficiency of ethane dehydrogenation to produce ethylene.

[0004] In view of this, it is necessary to design an improved preparation method of Zn-Cr spinel oxide catalyst and its application in CO2-assisted ethane dehydrogenation to solve the above problems. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a Zn-Cr spinel oxide catalyst and its application in CO2-assisted ethane dehydrogenation.

[0006] To achieve the above-mentioned object of the invention, the present invention provides a Zn-Cr spinel oxide catalyst, comprising Zn1Cr x An oxide carrier and Cr loaded on the surface of the carrier, wherein the loading amount of Cr is 10 wt %, and the range of x is 1-7.

[0007] Preferably, x is any value of 1, 2, 3, 5, or 7.

[0008] On the other hand, the present invention also provides a method for preparing the Zn-Cr spinel oxide catalyst, comprising the following steps:

[0009] Zn 2+ Salt and Cr 3+ The salt was dissolved in water to obtain a mixed solution; under stirring conditions, (NH4)2CO3 solution was slowly added to the mixed solution to form a mixed suspension, the pH value of the mixed suspension was 7.0; then, the mixed suspension was aged at 60-80°C for 3 hours, and the obtained product was dried and calcined to obtain Zn1Cr x oxide supports;

[0010] The Zn1Cr x Oxide support added Cr 3+ After being immersed in an aqueous solution, the catalyst is immersed at 70° C. for 2-12 hours under stirring to obtain a slurry; the slurry is dried and then subjected to a secondary calcination treatment to obtain a Zn-Cr spinel oxide catalyst.

[0011] Preferably, the mixed solution contains Zn 2+ and Cr 3+ The total concentration is 1 mol / L.

[0012] Preferably, the concentration of the (NH4)2CO3 solution is 1.0 mol / L.

[0013] Preferably, the calcination temperature is 500° C. and the calcination time is 5 hours.

[0014] Preferably, the Cr 3+ The concentration of the aqueous solution is 5-15%.

[0015] Preferably, the temperature of the secondary calcination treatment is 700° C., and the calcination time is 5 hours.

[0016] Preferably, the heating rate during the secondary calcination process is 5°C / min.

[0017] In particular, the Zn-Cr spinel oxide catalyst prepared by the preparation method proposed in the present invention can be applied to CO2-assisted ethane dehydrogenation.

[0018] The beneficial effects of the present invention are:

[0019] 1. The preparation method of the Zn-Cr spinel oxide catalyst provided by the present invention comprises the following steps: firstly preparing Zn1Cr by coprecipitation method; x After the oxide support, Cr is loaded on its surface by impregnation method to prepare Zn-Cr spinel oxide catalyst. In this process, the loading of Cr on the support surface can be the same as that of Zn1Cr x The oxide supports form a strong metal-support interaction to regulate the oxygen vacancy concentration on the catalyst surface, promote the desorption of ethylene, and inhibit its over-oxidation, thereby significantly improving the selectivity of ethylene. x The dense coating formed on the support surface reduces the number of strong oxidative active sites, synergistically promoting rapid ethylene desorption and suppressing side reactions such as dry reforming and hydrogenolysis. The preparation method proposed in this invention produces a Zn-Cr spinel oxide catalyst with high catalytic activity and stability suitable for CO2-assisted ethane dehydrogenation.

[0020] 2. The preparation method of the Zn-Cr spinel oxide catalyst provided by the present invention is to adjust the Zn1Cr x The molar ratio of Cr and Zn in the oxide support gives the non-stoichiometric Zn1Cr x The oxide supports are rich in coordination unsaturated defects Cr 3+ These defects and oxygen vacancies can promote the adsorption of ethane on the catalyst surface and enhance the activation ability of ethane. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Zn1Cr prepared in Examples 1-5 of the present invention x XRD patterns of oxide supports;

[0022] Figure 2 Cr / Zn1Cr prepared in Examples 1-5 of the present invention x XRD pattern of the catalyst;

[0023] Figure 3 TEM image and EDS-mapping image of the Zn1Cr3 oxide support prepared in the embodiment of the present invention;

[0024] Figure 4 TEM image and EDS-mapping image of the Cr / Zn1Cr3 catalyst prepared in the embodiment of the present invention;

[0025] Figure 5 Zn1Cr prepared in Examples 1-5 of the present invention x Oxide supports and Cr / Zn1Cr xadsorption–desorption isotherms of the catalyst;

[0026] Figure 6 Zn1Cr prepared in Examples 1 to 5 of the present invention x Oxide supports and Cr / Zn1Cr x Raman spectrum of the catalyst;

[0027] Figure 7 XPS graphs of the Zn1Cr3 oxide support, Cr / Zn1Cr3 catalyst and pure Cr2O3 prepared in the present invention;

[0028] Figure 8 Zn1Cr prepared in Examples 1 to 5 of the present invention x Oxide supports and Cr / Zn1Cr x Catalyst reducibility test results;

[0029] Figure 9 The Zn1Cr prepared by the present invention x Application performance of oxide supports in CO2-assisted ethane dehydrogenation catalysis;

[0030] Figure 10 Cr / Zn1Cr prepared by the present invention x Application performance of the catalyst in CO2-assisted ethane dehydrogenation. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] It should also be noted here that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0033] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0034] In one aspect, the present invention provides a Zn-Cr spinel oxide catalyst comprising: Zn1Cr x The oxide support and Cr supported on the surface thereof, wherein the Cr loading amount is 10 wt %. Specifically, x ranges from 1 to 7, and may be 1, 2, 3, 5, or 7.

[0035] On the other hand, the present invention also provides a method for preparing the above-mentioned Zn-Cr spinel oxide catalyst, comprising the following steps:

[0036] Zn1Cr x Preparation of oxide support: Zn 2+ Salt and Cr 3+ The salt is dissolved in water to obtain a mixed solution; under stirring conditions, (NH4)2CO3 solution is slowly added to the mixed solution to form a mixed suspension, and the addition is stopped when the pH value of the mixed suspension reaches 7.0; then, the mixed suspension is aged at 60-80°C for 3 hours, the solid product is collected by centrifugation, dried at 105°C, and then calcined to obtain Zn1Cr x oxide supports;

[0037] Preparation of Zn-Cr spinel oxide catalyst: Zn1Cr prepared in the above steps x Oxide support added Cr 3+ After being immersed in the aqueous solution, it is immersed at 70℃ for 2-12h under stirring conditions until the liquid surface of the mixed liquid disappears completely and loses fluidity to obtain a slurry; after the obtained slurry is dried at 105℃, it is subjected to secondary calcination treatment to obtain Zn1Cr x The surface of the oxide support is loaded with Cr, and the loading amount of Cr is 10 wt% (i.e., the ratio of the mass of the loaded Cr to the mass of the support and the loaded Cr), and Cr / Zn1Cr is prepared. x catalyst.

[0038] In the above technical solution, Zn1Cr is first prepared by coprecipitation method. x After the oxide support is formed, a certain amount of Cr is loaded on its surface. The strong metal-support interaction formed between Cr and the support can be used to regulate the oxygen vacancy concentration on the catalyst surface, promote the desorption of ethylene, and inhibit its over-oxidation, thereby significantly improving the catalyst's selectivity for ethylene. At the same time, metal Cr in Zn1Cr x The dense coating formed on the surface of the support reduces the number of strong oxidative active sites, synergistically promotes the rapid desorption of ethylene and inhibits the occurrence of side reactions such as dry reforming and hydrogenolysis; in addition, Zn1Cr x The oxide support itself has abundant coordination unsaturated defects Cr 3+ The non-stoichiometric Zn-Cr spinel oxide obtained after Cr loading has more coordination unsaturated defects Cr than the support. 3+ These defects and oxygen vacancies can promote the adsorption of ethane on the catalyst surface and enhance the activation ability of ethane.

[0039] Secondly, by regulating Zn1Cr xThe molar ratio of Cr and Zn in the oxide support can affect the coordination unsaturation defect Cr 3+ The oxygen storage capacity of the carrier can be regulated by regulating the Cr and oxygen vacancies. At the same time, the strong metal-carrier interaction formed between Cr in the catalyst and the carrier can be used to jointly improve the anti-carbon deposition performance of the catalyst.

[0040] In some embodiments, the total concentration of metal ions in the mixed solution is 1 mol / L (ie, Zn 2+ and Cr 3+ Specifically, Zn 2+ Salt and Cr 3+ The salt is a soluble metal salt, such as Zn(NO3)2·6H2O, Cr(NO3)3·9H2O. In other embodiments, other soluble metal salts can also be selected as needed, as long as they can meet the actual application requirements, and this is not limited here.

[0041] In some embodiments, the calcination temperature is 500° C., the calcination time is 5 h, and the calcination process is carried out at a heating rate of 5° C. / min from 25° C. to 500° C.

[0042] In some embodiments, the concentration of (NH 4 ) 2 CO 3 solution is 1.0 mol / L, which is used as a precipitant.

[0043] In some embodiments, Cr 3+ The concentration of aqueous solution is 5-15%, which is soluble Cr 3+ Obtained when salt dissolves in water, such as Cr(NO3)3·9H2O.

[0044] In some embodiments, the secondary calcination treatment is performed at a temperature of 700° C., the calcination time is 5 h, and the calcination process is performed at a heating rate of 5° C. / min from 25° C. to 700° C.

[0045] The preparation method of the Zn-Cr spinel oxide catalyst proposed by the present invention and its application in CO2-assisted ethane dehydrogenation are further described below with reference to specific examples:

[0046] Example 1

[0047] In this example, a Zn-Cr spinel oxide catalyst was prepared, and the preparation method thereof is as follows:

[0048] Weigh a certain amount of Zn(NO3)2·6H2O and Cr(NO3)3·9H2O and dissolve them in a certain amount of deionized water to prepare Zn 2+ and Cr 3+A mixed solution with a total concentration of 1 mol / L and a molar ratio of Zn to Cr of 1:1 was prepared. Under mechanical stirring, a (NH4)2CO3 solution with a concentration of 1 mol / L was added to the mixed solution until the pH of the mixed suspension reached about 7.0, and then the addition was stopped. The solution was then aged in a constant temperature water bath at 70°C for 3 h. The solid product was then recovered by centrifugation and washed multiple times with deionized water until the supernatant pH reached 7. The resulting precipitate was transferred to a 105°C oven and dried overnight. The product was then heated to 500°C at a heating rate of 5°C / min and calcined for 5 h to obtain a ZnCr oxide support.

[0049] 3.078 g of Cr(NO3)3·9H2O was dissolved in deionized water, and 3.6 g of a ZnCr oxide support was added. The mixture was then stirred and impregnated in a 70°C constant temperature water bath for 5 h until the slurry surface completely disappeared and lost fluidity. The resulting slurry was transferred to a 105°C oven and dried overnight. Finally, the temperature was increased to 700°C at a heating rate of 5°C / min and calcined for 5 h to obtain a Cr / ZnCr catalyst. It should be noted that, unless otherwise specified, the reagents and raw materials used in the examples of the present invention can be obtained commercially.

[0050] Examples 2 to 5

[0051] The only difference between Examples 2 to 5 and Example 1 is that the molar ratio of Zn to Cr is different when preparing ZnCr oxide, specifically 1:2 (Example 2), 1:3 (Example 3), 1:5 (Example 4) and 1:7 (Example 5). x The XRD pattern of the oxide support is shown in Figure 1 As shown in the figure, it can be seen that only the characteristic diffraction peaks of the ZnCr2O4 spinel phase are observed in the Zn1Cr2 sample. The Cr:Zn ratio of the Zn1Cr1 sample is much less than 2:1, indicating that there is an excess of ZnO in the sample. However, there are only extremely weak ZnO characteristic peaks in its XRD spectrum. This may be because the ZnO phase is highly dispersed on the surface of the ZnCr2O4 spinel. In samples with a Cr:Zn ratio of 3:1 to 7:1, in addition to the ZnCr2O4 spinel phase, obvious Cr2O3 diffraction peaks are detected. Moreover, with the increase of the Cr / Zn ratio, the intensity of the Cr2O3 diffraction peak in the sample gradually increases, while the intensity of the diffraction peak of the ZnCr2O4 spinel gradually decreases. In the single-component Cr2O3 sample, only the diffraction peak of Cr2O3 is observed. x The XRD pattern of the catalyst is shown in Figure 2As shown in the figure, it can be seen that after further loading of Cr, the diffraction peak of the ZnCr2O4 spinel phase becomes sharper and the peak width becomes narrower, which indicates that after further high-temperature calcination during the loading process, the order of the crystal is improved, the size of the grain is increased, and the crystallinity is better. Subsequent TEM images also further verified this conclusion; in addition, after loading of metal Cr, no Cr2O3 diffraction peak is still observed in the Cr / Zn1Cr1 catalyst. This may be because the addition of Cr in the loading process balances part of the excess Zn, which promotes the formation of more stable ZnCr2O4 spinel phases. The formation of spinel phase occurs at the same time, there is still excess ZnO in the catalyst, so a weak ZnO phase can still be observed in the XRD pattern of the Cr / Zn1Cr1 catalyst. The loading of metal Cr also causes the appearance of Cr2O3 diffraction peak in the Cr / Zn1Cr2 catalyst. In addition, it is found that after further loading of metal Cr, the diffraction peaks of the ZnCr2O4 spinel phase and the Cr2O3 phase both shift slightly to the right, which may be due to the interaction between the Cr metal particles and the Zn-Cr oxide support causing changes in local stress.

[0052] TEM image of Zn1Cr3 oxide support Figure 3 As shown in (a), the particle size of Zn1Cr3 oxide particles is about 5nm; HRTEM image Figure 3 (be) shown, Figure 3 (b) shows the lattice fringes of the (220) and (311) crystal planes of spinel ZnCr2O4, as well as the lattice fringes of the (110) crystal plane of Cr2O3, which are consistent with the phase composition results obtained by XRD. Figure 3 (c) and (d) show the lattice spacing of the (220) and (311) planes of spinel ZnCr2O4, which are measured to be 0.29 nm and 0.251 nm, respectively. Figure 3 (e) also shows the lattice spacing of the (110) crystal plane of Cr2O3, which is measured to be 0.248nm; EDS-mapping diagram as shown Figure 3 As shown in (fi), the results show that all elements in the Zn1Cr3 sample, including Zn, Cr, and O, are uniformly distributed.

[0053] The TEM image of the Cr / Zn1Cr3 catalyst obtained after loading metal Cr is shown in Figure 2. Figure 4 As shown in (a), the results show that its structural characteristics are significantly different from those of Zn1Cr3. This is because after high-temperature calcination during the loading process, the particle size of ZnCr2O4 spinel is significantly increased, showing a cubic structure with a particle size of about 10nm. At the same time, the crystallinity and order of the grains are also significantly improved, which is consistent with the XRD results; HRTEM pictures are shown in Figure 4(bg) shows the lattice fringes of the (311), (220) and (110) planes of spinel ZnCr2O4. Figure 4 (c), (d) and (e) show the lattice spacing of (311), (220) and (110) crystal planes respectively. The test values of the lattice spacing are 0.25nm, 0.47nm and 0.29nm respectively. EDS-mapping diagram is shown in Figure 2. Figure 4 (fi) shows that, from Figure 4 In (f), spherical particles of Cr2O3 with a particle size of about 10 nm can be observed, and the lattice spacing of the (110) crystal plane is measured to be 0.247 nm. The corresponding element distribution characterization results of high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) Figure 4 (jl) shows that the three elements Zn, Cr, and O in the Cr / Zn1Cr3 catalyst are also evenly distributed.

[0054] Zn1Cr prepared in Examples 1 to 5 x Oxide supports and Cr / Zn1Cr x The specific surface area and pore structure test results of the catalyst are shown in Table 1. From the analysis of the data in the table, it can be found that Zn1Cr x With the increase of Cr content, the specific surface area and pore volume of Zn-Cr oxide first increase and then decrease. Among them, the specific surface area of Zn1Cr3 sample is the largest, which is 72.438m 2 ·g -1 , and a larger specific surface area is conducive to the dispersion of the subsequent loaded Cr species. The specific surface area of the Zn1Cr1 sample is much smaller than that of other samples. This is because the larger particle size ZnO phase appears in the spinel structure, which reduces the specific surface area of the catalyst. It is found that the specific surface area of the pure Cr2O3 sample is very small. Therefore, when the Cr / Zn ratio is too high, too much Cr2O3 phase will appear in the Zn-Cr oxide sample, thereby reducing the specific surface area of the sample. For the Cr / Zn1Cr after loading metal Cr, x The specific surface area and pore volume of the catalyst decreased because the impregnated Cr species blocked part of the pores of the Zn-Cr oxide support, thereby preventing the adsorption of nitrogen molecules. However, the pore size of the catalyst increased significantly after impregnation and loading. This may be because the loaded metal Cr interacted with the surface of the Zn-Cr oxide support, changing the pore structure of the support and causing the pore size to increase.

[0055] N2 physical adsorption-desorption isotherm Figure 5 As shown, Figure 5 (a) Zn1Cr x Adsorption-desorption isotherms of spinel oxides, Figure 5 (b) Cr / Zn1Cr xAdsorption-desorption isotherms of catalysts, spinel support and Cr / Zn1Cr x The catalysts all exhibited type IV mesoporous isotherms with H3-type hysteresis loops, proving that all samples were mainly mesoporous structures, which may be due to the accumulation of oxide particles to form slit-like pores.

[0056] Table 1 Zn1Cr prepared in Examples 1 to 5 x Oxide supports and Cr / Zn1Cr x Catalyst specific surface area and pore structure test results

[0057]

[0058] Zn1Cr prepared in Examples 1 to 5 x Oxide supports and Cr / Zn1Cr x The Raman spectrum of the catalyst is shown in Figure 6 As shown in the figure, it can be seen that the Cr / Zn1Cr prepared after loading Cr x catalyst( Figure 6 b) Compared with Zn1Cr x Oxide support ( Figure 6 a) As for the Raman response, there is a significant change. Due to the loading of metallic chromium, the Raman spectrum of the Cr / Zn1Cr2 catalyst changes significantly at 300, 345, and 545 cm -1 A new peak attributed to crystalline Cr2O3 appeared at 600 cm -1 and 1000cm -1 Aggregate Cr 6+ The characteristic peaks of species. In the Cr / Zn1Cr3 catalyst, the vibration mode of ZnCr2O4 spinel was observed after the loading of metallic chromium. This may be because the high temperature calcination after the loading of chromium makes the spinel structure more stable, and the interaction between the loaded metallic Cr and the ZnCr oxide support enhances the molecular vibration of the ZnCr2O4 spinel in the support. The Cr / Zn1Cr5 and Cr / Zn1Cr7 catalysts also showed weak spinel A. 1g The peaks of chromate in Cr / Zn1Cr2 and Cr / Zn1Cr3 catalysts are enhanced with the addition of Cr, which indicates that the Cr loading increases the Cr content in the catalyst. 6+The number of species is small, while the characteristic peaks of Cr2O3 and polychromate do not appear in the Cr / Zn1Cr1 catalyst. This may be because the added Cr reacts preferentially with the excess Zn to form more thermodynamically stable ZnCr2O4 spinel phases instead of Cr2O3 phases. This result is consistent with the XRD results.

[0059] The XPS patterns of Zn1Cr3 oxide support, Cr / Zn1Cr3 catalyst and pure Cr2O3 are shown in Figure 2. Figure 7 As shown, Figure 7 (a) is the XPS spectrum of Cr2p orbitals, where the peaks at 587eV and 577eV correspond to Cr 2p 1 / 2 and Cr 2p 3 / 2 Spin orbit, through the sample Cr 2p 3 / 2 After deconvolution of the orbital, it was found that the chromium species in Zn1Cr3 oxide mainly present three forms: the peak at 579.48eV is attributed to Cr 6+ , the main peak at 577.22 eV is attributed to Cr 3+ , the Cr at the peak of 576.10eV corresponds to the Cr in the surface crystalline Cr2O3 3+ Comparing the XPS spectra of Zn1Cr3 and Cr2O3, it was found that the introduction of Zn in Zn1Cr3 oxide caused the characteristic binding energy of Cr species to produce a positive (high BE) shift. This shift may be attributed to the formation of ZnCr2O4 spinel structure, which increases the energy required for Cr ionization by enhancing the covalency of Cr-O bond. Quantitative analysis shows that there are more Cr in Cr2O3 than in Zn1Cr3 sample. 6+ This result is consistent with the H2-TPR result. According to the XPS element quantitative results in Table 2, it was found that the Zn content on the surface of the Cr / Zn1Cr3 catalyst was very low, which confirmed that the metal Cr loaded by the impregnation method formed a dense covering layer on the surface of the Zn1Cr3 oxide support. Figure 7 As shown in (a), the loading of Cr causes the characteristic peak of Cr to shift slightly toward the low BE direction, which may be attributed to the interaction between metal Cr and Zn1Cr3 oxide support, which increases the electron cloud density of Cr. Quantitative analysis shows that the Cr in Cr / Zn1Cr3 catalyst 6+ The species and Cr2O3 contents are higher than those of Zn1Cr3 oxide, which is consistent with the characterization analysis results above. Figure 7(b) is the O1s orbital XPS spectrum. The fitted surface O1s peak is divided into three oxygen chemical states: lattice oxygen (OL), with a peak at (530.5±0.5eV); oxygen vacancy (OV), with a peak at (532.0±0.2eV); and chemically adsorbed oxygen (OC), with a peak at (533.3±0.2eV). Table 2 lists the relative contents of the three oxygen states. It was observed that the oxygen vacancy concentration in Zn1Cr3 oxide was the highest. With the loading of Cr, the oxygen vacancy concentration decreased, while the oxygen vacancy concentration of the pure Cr2O3 sample was the lowest. In addition, the formation of oxygen vacancies is generally accompanied by the appearance of coordinated unsaturated metal ions. This result further confirms that the activity of ethane dehydrogenation reaction is closely related to the defects and oxygen vacancies in Zn-Cr oxide. In addition, the introduction of Zn causes a positive shift of the O element, which is also attributed to the formation of the ZnCr2O4 spinel structure; and the loading of Cr causes a slight shift of the characteristic peak of the O element toward the high BE direction, indicating that electron transfer occurs between Cr and O, confirming the existence of interaction between Cr and the support. This result also shows that the concentration of oxygen vacancies in Zn-Cr oxide can be controlled by adjusting the Cr / Zn ratio in the non-stoichiometric Zn-Cr spinel oxide.

[0060] Table 2 XPS analysis results of Zn1Cr3, Cr / Zn1Cr3 and Cr2O3 samples

[0061]

[0062] Furthermore, the present invention also uses H2-TPR (temperature programmed reduction analysis with hydrogen as reducing gas) to explore the Zn1Cr x Oxide supports and Cr / Zn1Cr x The reducibility of the catalyst, the specific analysis results are as follows Figure 8 As shown, Figure 8 (a) Zn1Cr prepared with different Cr / Zn molar ratios x The H2-TPR curve of the oxide support shows that the pure Cr2O3 sample has an obvious main reduction peak at 303℃, which may be attributed to the presence of a small amount of Cr on the Cr2O3 oxide. 6 + Species are reduced to Cr 3+ After the introduction of Zn, the position of the main reduction peak changed significantly. The H2-TPR spectrum showed that all Zn-Cr oxides had an obvious hydrogen reduction peak near 220 ° C, which may be attributed to the reduction of non-stoichiometric Zn-Cr spinel. It is speculated that H2 is mainly caused by the unsaturated defect Cr 3+ species consumed, while Cr / Zn1Cr x The catalyst has more defects due to Cr 3+and oxygen vacancies, which makes it show better reduction properties, and the defective Cr 3+ The presence of oxygen vacancies can promote the adsorption of reactants on the catalyst surface, thereby effectively improving the catalytic activity. Figure 8 (b) is the H2-TPR diagram of Zn1Cr3 oxide support and Cr / Zn1Cr3 catalyst. The results show that the H2 consumption of Cr / Zn1Cr3 catalyst is significantly lower than that of Zn1Cr3 oxide, among which the reduction peak intensity corresponding to Zn-Cr spinel defects and oxygen vacancies is significantly weakened, which may be related to the secondary high-temperature calcination during the Cr loading process. Further high-temperature calcination may lead to a reduction in defects and oxygen vacancies in the spinel. At the same time, with the loading of metal Cr, the reduction temperature corresponding to the reduction peak at 221℃ shifts toward high temperature, indicating that there is a strong interaction between metal Cr and Zn-Cr oxide support. The significant decrease in the low-temperature reduction peak intensity of Cr / Zn1Cr3 catalyst is accompanied by a shift toward high temperature. This change explains the reason why side reactions such as reforming are suppressed, and provides a reasonable explanation for the significant improvement of ethylene selectivity of Cr / Zn1Cr3 catalyst. In addition, new reduction peaks appear at 345℃ and 442℃ on Cr / Zn1Cr3 catalyst, which may be attributed to some Cr species on the catalyst surface. 6+ Reduction (Cr 6+ →Cr 3+ ).

[0063] The H2-TPR results are shown in Table 3. From the data in the table, it can be seen that among the Zn-Cr oxides with different Cr / Zn ratios, the Zn1Cr3 sample shows the highest H2 consumption, and the results of the H2 consumption of the Zn-Cr oxide are positively correlated with the ethane conversion results in the activity test. Therefore, it is speculated that the activity of the ethane dehydrogenation reaction is related to the coordination unsaturated defect Cr in the Zn-Cr oxide. 3+ Closely related to oxygen vacancies, a small amount of defective Cr also appeared in the Cr2O3 sample. 3+ The reduction peak caused by the presence of Cr species may be due to the structural defects formed during the preparation of the material. At the same time, Zn1Cr5 and Zn1Cr3 oxides also showed a small reduction peak near 300 °C, which may also be attributed to the small amount of Cr in the sample. 6+ Reduced to Cr 3+ , and Cr 6+ The intensity of the reduction peak increases with the increase of Cr content in Zn-Cr oxide.

[0064] Table 3 H2-TPR results of spinel oxide and Cr / Zn1Cr3 catalysts

[0065]

[0066] In particular, the present invention also explores Zn1Crx Oxide supports and Cr / Zn1Cr x Application performance of Zn1Cr catalyst in CO2-assisted ethane dehydrogenation x The application results of oxide supports are as follows Figure 9 As shown, Figure 9 (a) is the ethane conversion result, the results show that Zn1Cr x The ethane conversion rate of spinel oxides showed a trend of first increasing and then decreasing with the increase of Cr content. Among them, Zn1Cr3 oxide had the highest initial ethane conversion rate, reaching 84.9%. Zn1Cr2 and Zn1Cr5 oxides also showed extremely high initial conversion rates, 72.0% and 80.2%, respectively. This activity test result was positively correlated with the hydrogen consumption of spinel oxide H2-TPR, indicating that the coordination unsaturated defect Cr in Zn-Cr oxide 3+ Species and oxygen vacancies are active sites for ethane dehydrogenation, and these defects and oxygen vacancies can promote the adsorption of reactants on the catalyst surface, improve the CH bond activation ability, and thus effectively enhance the catalytic dehydrogenation activity of ethane; Figure 9 (b) is the ethylene yield result. The ethylene yield increases with time in the early stage of the reaction, which may be due to the partial suppression of side reactions such as ethane dry reforming and hydrogenolysis during the reaction process; Figure 9 (c) Product selectivity results (reaction time 130min), as can be seen from the figure, all Zn1Cr x The ethylene selectivity of spinel oxides is very low, and the reaction process is accompanied by the generation of a large amount of CO and CH4 by-products, which may be attributed to the x The active sites of spinel oxide have strong ability to oxidize and activate ethane. While catalyzing the breakage of CH, CC or C=C also breaks. Moreover, the ethylene selectivity increases first and then decreases with the increase of Cr content, indicating that the introduction of appropriate amount of Zn helps the desorption of ethylene, thereby improving its selectivity. x The ethylene yield of spinel oxide is extremely low, only 1.3%, indicating that the Zn site is not the main active site for ethane dehydrogenation to ethylene.

[0067] Under the same conditions, Cr / Zn1Cr x The results of using the catalyst to catalyze CO2-assisted ethane dehydrogenation are as follows Figure 10 As shown, Figure 10 (a) is the ethane conversion result, and Figure 9 (a) By comparison, it can be seen that Cr / Zn1Cr x The ethane conversion rate of the catalyst is the same as that of Zn1Cr xThe spinel oxides are similar, and with the increase of Cr content, they show a trend of first increasing and then decreasing. Among them, the initial ethane conversion rate of Cr / Zn1Cr3 catalyst is the highest, which is 62.0%. Figure 9 (a)Zn1Cr x The conversion rate of spinel oxide was found to be Cr / Zn1Cr after loading metal Cr. x The ethane conversion of the catalyst decreased significantly, which may be due to the coordination unsaturation defect Cr in the supported catalyst. 3+ It is related to the reduction of oxygen vacancies. Figure 10 (b) Ethylene yield results and Figure 10 (c) Product selectivity results (reaction time 130 min) show that the Cr / Zn1Cr ratio after loading metal Cr is 0.04. x The selectivity and yield of the catalyst were significantly improved, which may be due to the presence of metal Cr in Zn1Cr. x A covering layer is formed on the surface of spinel oxide, which reduces the number of strong oxidative active sites, promotes the desorption of ethylene and inhibits the occurrence of side reactions such as dry reforming and hydrogenolysis. In addition, the loaded metal Cr and Zn1Cr x The strong interaction formed by spinel oxides can also regulate the surface oxygen vacancy concentration, hindering the over-oxidation of ethylene and thereby improving ethylene selectivity.

[0068] Furthermore, at 650℃, Zn1Cr x Spinel oxide and Cr / Zn1Cr x The stability test of CO2-assisted ethane dehydrogenation was carried out on the catalysts (x=2, 3, 5). Figure 10 (df), where Figure 10 (d) is the ethane conversion rate of the stability test, Figure 10 (e) is the ethylene selectivity of the stability test, Figure 10 (f) shows the ethylene yield from the stability test. As can be seen, the ethane conversion of all samples decreased slightly over time. This is likely due to a slight deactivation of the active sites caused by the formation of a small amount of carbon deposits. Ethylene selectivity, on the other hand, gradually increased over time, presumably due to the partial suppression of side reactions such as dry reforming and hydrogenolysis as the reaction proceeded.

[0069] observe Figure 10 (f) It was found that the Cr / Zn1Cr3 catalyst showed the best ethylene yield, and its ethylene yield was stably maintained at 33% within a 10-h reaction period, and its stability was significantly improved compared with the support. x The excellent stability may be attributed to the spinel structure of Zn1Cr x The oxide support has excellent chemical and thermal stability, Zn1Cr xOxide supports can inhibit the migration and agglomeration of Cr species, thereby slowing down the sintering of surface metal Cr. x No obvious black carbon layer was observed on the catalyst after the reaction, indicating that the catalyst has certain anti-carbon deposition performance at 650°C. This may be attributed to the activation of CO2 by oxygen vacancies on the surface of Zn-Cr spinel oxide, which promotes the carbon removal reaction. At the same time, the strong interaction between the surface Cr species and Zn-Cr spinel oxide can also accelerate the oxidation rate of carbon deposits. The synergistic effect of the adjustable oxygen storage capacity of the Zn-Cr spinel oxide support and the strong interaction between the Cr species and the Zn-Cr oxide support makes the catalyst still show excellent stability at a high temperature of 650°C.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A Zn-Cr spinel oxide catalyst, characterized in that: Including Zn1Cr x An oxide carrier and Cr loaded on the surface of the carrier, wherein the loading amount of Cr is 10 wt %, and the range of x is 1-7.

2. The Zn-Cr spinel oxide catalyst according to claim 1, characterized in that x is any value among 1, 2, 3, 5, and 7.

3. A method for preparing a Zn-Cr spinel oxide catalyst, characterized in that: The steps include: Zn 2+ Salt and Cr 3+ The salt was dissolved in water to obtain a mixed solution; under stirring conditions, (NH4)2CO3 solution was slowly added to the mixed solution to form a mixed suspension, the pH value of the mixed suspension was 7.0; then, the mixed suspension was aged at 60-80°C for 3 hours, and the obtained product was dried and calcined to obtain Zn1Cr x oxide supports; The Zn1Cr x Oxide support added Cr 3+ After being immersed in an aqueous solution, the catalyst is immersed at 70° C. for 2-12 hours under stirring to obtain a slurry; the slurry is dried and then subjected to a secondary calcination treatment to obtain a Zn-Cr spinel oxide catalyst.

4. The preparation method according to claim 3, characterized in that The mixed solution contains Zn 2+ and Cr 3+ The total concentration is 1 mol / L.

5. The preparation method according to claim 3, characterized in that The concentration of the (NH4)2CO3 solution is 1.0 mol / L.

6. The preparation method according to claim 3, characterized in that The calcination temperature is 500° C. and the calcination time is 5 hours.

7. The preparation method according to claim 3, characterized in that The Cr 3+ The concentration of the aqueous solution is 5-15%.

8. The preparation method according to claim 3, characterized in that The temperature of the secondary calcination treatment is 700° C., and the calcination time is 5 hours.

9. The preparation method according to claim 8, characterized in that The heating rate of the secondary calcination process is 5°C / min.

10. Use of the Zn-Cr spinel oxide catalyst according to any one of claims 1 to 2 or the Zn-Cr spinel oxide catalyst prepared by any one of the preparation methods according to claims 3 to 9 in CO2-assisted ethane dehydrogenation.

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