A supported TiOx core-shell structure catalyst and a preparation method and application thereof

Abstract

This invention belongs to the field of supported catalyst technology and discloses a supported TiO2 catalyst. x Core-shell structured catalysts, their preparation methods and applications, with Ni@TiO supported on an Al2O3 support. x The core-shell structure consists of a metallic Ni core and TiO2. x The outer shell was prepared by first adding aluminum alkoxide, organotitanium compounds, and surfactants to isopropanol solvent and stirring until homogeneous. Then, dilute nitric acid was added dropwise for hydrolysis until complete. The resulting sol was aged at room temperature until complete and then dried completely under vacuum. The resulting solid was then calcined in steps. After being immersed in Ni(NO3)3·6H2O solution and ultrasonically dispersed until homogeneous, the solid was dried completely. Finally, the resulting solid was calcined and reduced to obtain Al2O3-supported Ni@TiO2. x Core-shell structured catalyst. The catalyst obtained by this invention has high activity comparable to industrial noble metal catalysts, accompanied by high selectivity and stability. It overcomes the limitation of low activity of oxide-based catalysts, which do not meet the requirements of industrial applications, and can be used as a catalyst in the dehydrogenation of low-carbon alkanes to olefins.

Description

Technical Field

[0001] This invention belongs to the field of supported catalyst technology, specifically, it relates to a supported TiO2 catalyst. x Core-shell structured catalysts, their preparation methods, and applications. Background Technology

[0002] Propylene is one of the essential basic chemical raw materials for industrial production. Depending on its propylene content, it can be used to produce different downstream chemical products. Refinery-grade propylene (50%-70%) is suitable for producing isopropanol or cumene, etc.; chemical-grade propylene (92%-96%) is suitable for producing carbonyl alcohols, acrylonitrile, acrylic acid, propylene oxide, isopropanol, cumene, etc.; and polymerization-grade propylene (greater than 99.5%) can be used to produce polypropylene, ethylene propylene rubber, and allyl chloride, etc. These products exhibit excellent performance and are widely used in building materials, textiles, automobiles, and other industries. In recent years, global demand for propylene has surged, driving rapid growth in its production capacity. It is predicted that propylene demand will grow at an average annual rate of 2% to 3% until 2035. Currently, propylene supply mainly comes from byproducts of two major processes: steam cracking and fluid catalytic cracking (FCC) of petroleum hydrocarbons. However, in recent years, with the rapid development of hydraulic fracturing technology, shale gas condensate (NGLS), rich in low-carbon alkanes such as methane, ethane, and propane, can be extracted and exploited on a large scale at a relatively low cost, resulting in a significant increase in propane production. Meanwhile, the feedstock for steam cracking processes, which primarily produce ethylene and produce propylene as a byproduct, has shifted from naphtha to ethane based on shale gas due to the lower cost of shale gas. Steam cracking units have been dismantled or converted into ethane cracking units. This has further reduced the supply of propylene, causing a sharp rise in propylene prices. The combined effect of these two factors has led to a continuous widening of the propylene-propane price spread since 2016. Propane dehydrogenation technology, with its cost advantage and significant capacity increase, has become a more economical choice.

[0003] The reaction formula for propane dehydrogenation is: △H 298K =124.3 kJ / g·mol. This reaction is a strongly endothermic equilibrium reaction with an increasing number of molecules. It is thermodynamically confined, and high temperature and low pressure conditions favor the reaction. Supported CrO x Pt catalysts are two important types of industrial catalysts, used in the industrialized production processes of propane dehydrogenation, namely Lummus's Catofin process and UOP's Oleflex process. The Catofin process uses CrO2. x The catalyst is plagued by carbon buildup and deactivation, requiring frequent regeneration. Meanwhile, CrO... xIt also causes serious environmental pollution. The Pt-based catalyst used in the Oleflex process has excellent ability to activate C-H bonds in alkanes, but as a noble metal, the application of Pt is strongly limited by its high price. In summary, cheap and environmentally friendly alternative catalysts have received extensive attention.

[0004] Oxides such as ZrO2, TiO2 and WO3 have long been considered to have no catalytic activity for propane dehydrogenation. However, in recent years, some studies have shown that when the stoichiometric oxide surface undergoes partial reduction to form oxygen vacancies and coordination-unsaturated metal cation sites, the catalytic activity is improved, indicating that such oxides also have potential activity. Among them, TiO2 is abundant in reserves, cheap and easily available, and is a promising catalyst. The current problem is that the intrinsic activity of TiO2 as an active species is still relatively low, and it does not have the value for industrial application as a catalyst. Summary of the Invention

[0005] The present invention aims to solve the technical problem of low catalytic activity of existing TiO2-based catalysts, and provides a supported TiO x core-shell structure catalyst, a preparation method therefor and an application thereof. The catalyst has high activity comparable to industrial noble metal catalysts, accompanied by high selectivity and stability, breaks through the limitation that oxide-based catalysts have low activity and do not meet the requirements of industrial application, and can be used as a catalyst in the dehydrogenation of low-carbon alkanes to produce olefins.

[0006] In order to solve the above technical problem, the present invention is achieved by the following technical solution:

[0007] According to one aspect of the present invention, there is provided a supported TiO x core-shell structure catalyst, which uses Al2O3 as a carrier, and the Al2O3 carrier is loaded with Ni@TiO x core-shell structure, said Ni@TiO x core-shell structure comprises a metallic Ni core and TiO x (1<x<2) shell; the molecular formula of the catalyst is recorded as NimTin / Al2O3, wherein m:n=1:(1-6).

[0008] Further, based on the mass of the Al2O3 carrier, the TiO x has a mass percentage content of 5%-15%.

[0009] Further, said m:n=1:4.

[0010] According to another aspect of the present invention, there is provided a method for preparing the above supported TiO x core-shell structure catalyst, comprising the following steps:

[0011] (1) Add aluminum alkoxide, organotitanium compound and surfactant to isopropanol solvent and stir until uniformly mixed;

[0012] (2) Add dilute nitric acid dropwise to the mixture obtained in step (1) and hydrolyze until complete;

[0013] (3) The sol obtained in step (2) is aged at room temperature until complete and then dried completely under vacuum.

[0014] (4) The solid obtained in step (3) is calcined in stages;

[0015] (5) The solid obtained in step (4) is immersed in Ni(NO3)3·6H2O solution, ultrasonically dispersed evenly, and then completely dried;

[0016] (6) The solid obtained in step (5) is calcined and then reduced at 400-700℃ to obtain Al2O3-supported Ni@TiO. x Core-shell structured catalysts.

[0017] Further, in step (1), the aluminum alkoxide is one of aluminum sec-butoxide (ATSB) and aluminum isopropoxide (Al(Opri)3); the organotitanium compound is one of tetrabutyl titanate (TTB) and isopropyl titanate (TTP); the surfactant is one of hexadecyltrimethylammonium bromide (CTAB) and hexadecyltrimethylammonium chloride (CTAC); and the organic alcohol solvent is isopropanol or ethanol.

[0018] Furthermore, in step (3), the vacuum drying is carried out in a vacuum oven at 60-80°C for 18-24 hours.

[0019] Furthermore, in step (4), the stepwise calcination is first calcined at 200-300℃ for 2-3 hours, and then calcined at 500-600℃ for 3-4 hours.

[0020] Furthermore, in step (6), the calcination temperature is 500-600℃, the calcination time is 2-4h, and the reduction time is 1-2h.

[0021] According to another aspect of the present invention, a supported TiO2 type is provided. x Application of core-shell structured catalysts in the dehydrogenation of low-carbon alkanes to olefins.

[0022] Furthermore, the low-carbon alkane is propane, and the olefin is propylene.

[0023] The beneficial effects of this invention are:

[0024] The supported TiO of the present invention x Core-shell structured catalysts, using inexpensive and readily available non-precious metal oxides such as TiO2.x As the active component, it exhibits high activity comparable to commonly used industrial noble metal Pt-based catalysts while significantly reducing catalyst costs. Strong metal-Ni nanoparticle cores and TiO2 shells are constructed using strong metal-Ni nanoparticle interactions (SMSI). x Ni@TiO x Core-shell structure, utilizing subsurface metallic Ni as an electronic additive and surface TiO2. x The interaction between them modulates the active site TiO x The coordination environment and electronic properties of TiO2 accelerate the activation of CH bonds and H2 desorption during the dehydrogenation reaction, significantly improving the efficiency of TiO2. x The intrinsic catalytic activity of TiO₂ was confirmed by various characterization methods, showing that the catalytic activity increases with increasing reduction temperature. x The shell coating covers the exposed Ni sites, preventing the adverse effects of Ni sites with high CH and C bond cleaving activity on dehydrogenation selectivity, thus maintaining the TiO₂ content. x High selectivity of dehydrogenation catalysts.

[0025] The catalyst of this invention is prepared by sol-gel method and co-impregnation method. The raw materials are readily available, the process is simple and highly reproducible, and it has certain industrial significance.

[0026] The catalyst of this invention exhibits excellent catalytic performance for the dehydrogenation of low-carbon alkanes to olefins. Under high-temperature conditions, the conversion rate of low-carbon alkanes can reach over 40%, the olefin selectivity can reach over 93%, and the propylene yield, based on catalyst mass, can reach approximately 16.70 mmol·g. cat -1 ·h -1 It possesses high activity comparable to industrial catalysts, overcoming the limitation that oxide-based catalysts have low activity and do not meet the requirements of industrial applications. Attached Figure Description

[0027] Figure 1 The figures show the catalytic performance of the catalysts prepared in Examples 1-6; where (a) is the curve of propane conversion as a function of time, and (b) is the curve of propylene selectivity as a function of time.

[0028] Figure 2 This is a comparison chart of the catalytic performance of the catalysts prepared in Examples 1 and 16;

[0029] Figure 3 The graphs show the catalytic performance of the catalysts prepared in Examples 1, 7, and 8.

[0030] Figure 4 This is a graph showing the long-term regeneration stability test of the catalyst prepared in Example 1.

[0031] Figure 5Spherical aberration-corrected scanning transmission electron microscopy images of the catalysts prepared in Examples 1, 11 and 12 under in-situ reduction conditions;

[0032] Figure 6 Electron energy loss spectroscopy line scanning results corresponding to the spherical aberration-corrected scanning transmission electron microscopy image of the catalyst prepared in Example 1 under in-situ reduction conditions;

[0033] Figure 7 Comparison diagram of CO adsorption infrared results of the catalysts prepared in Examples 1, 11, 13 and 14 under in-situ reduction conditions;

[0034] Figure 8 Comparison diagram of XPS results of the catalysts prepared in Examples 1 and 5 under in-situ atmosphere conditions; wherein, (a) and (b) respectively correspond to the catalysts prepared in Example 5 and Example 1;

[0035] Figure 9 Comparison diagram of EPR results of the catalysts prepared in Examples 1 and 5;

[0036] Figure 10 Comparison diagram of fitting analysis results of extended X-ray absorption fine structure of Ti K-edge X-ray absorption for the catalysts prepared in Examples 1 and 5;

[0037] Figure 11 Diagram of propane surface reaction test results of the catalysts prepared in Examples 1 and 5; wherein, (a) and (b) respectively correspond to the catalysts prepared in Example 5 and Example 1. Detailed Description of the Embodiments

[0038] The present invention provides a supported TiO x core-shell structured catalyst, which uses Al2O3 as a support, and the Al2O3 support is loaded with Ni@TiO x core-shell structure, Ni@TiO x core-shell structure comprises a metallic Ni core and a TiO x (1<x<2) shell; the molecular formula of the catalyst is recorded as NimTin / Al2O3, wherein m:n=1:(1-6), and most preferably m:n=1:4.

[0039] In a preferred embodiment of the present invention, based on the mass of the Al2O3 support, the TiO x has a mass percentage content of 5%-15%.

[0040] The present invention also provides a method for preparing a supported TiO x core-shell structured catalyst, comprising the following steps:

[0041] (1) Adding aluminum alkoxide, an organotitanium compound and a surfactant into an isopropanol solvent and stirring until the mixture is uniform.

[0042] In a preferred embodiment of the present invention, the aluminum alkoxide is one of aluminum sec-butoxide (ATSB) and aluminum isopropoxide (Al(Opri)3);

[0043] In a preferred embodiment of the present invention, the organotitanium compound is one of tetrabutyl titanate (TTB) and isopropyl titanate (TTP);

[0044] In a preferred embodiment of the present invention, the surfactant is one of cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC);

[0045] In a preferred embodiment of the present invention, the organic alcohol solvent is isopropanol or ethanol.

[0046] (2) Add dilute nitric acid dropwise to the mixture obtained in step (1) until hydrolysis is complete.

[0047] In some embodiments of the present invention, the hydrolysis time is 1 hour.

[0048] (3) The sol obtained in step (2) is aged at room temperature until complete and then dried completely under vacuum.

[0049] In a preferred embodiment of the present invention, complete drying under vacuum conditions involves continuing drying in a vacuum oven at 60-80°C for 18-24 hours.

[0050] In a preferred embodiment of the present invention, the aging time is 24 hours.

[0051] (4) The solid obtained in step (3) is roasted in stages.

[0052] In a preferred embodiment of the present invention, the stepwise calcination involves first calcining at 200-300°C for 2-3 hours, and then calcining at 500-600°C for 3-4 hours.

[0053] (5) The solid obtained in step (4) is immersed in Ni(NO3)3·6H2O solution, ultrasonically dispersed and then completely dried.

[0054] (6) The solid obtained in step (5) is calcined and then reduced at 400-700℃ to obtain Al2O3-supported Ni@TiO. x Core-shell structured catalysts.

[0055] In a preferred embodiment of the present invention, the calcination temperature is 500-600℃ and the calcination time is 2-4h.

[0056] In a preferred embodiment of the present invention, the reduction time is 1-2 hours.

[0057] The present invention also provides the above-mentioned supported TiO2.x Application of core-shell structured catalysts in the dehydrogenation of low-carbon alkanes to olefins, especially in the dehydrogenation of propane to propylene.

[0058] The present invention will be further described in detail below through specific embodiments. These embodiments will enable those skilled in the art to have a more comprehensive understanding of the present invention, but will not limit the present invention in any way.

[0059] Example 1

[0060] (1) Add 2.174 parts by weight of aluminum sec-butoxide (ATSB), 0.425 parts by weight of tetrabutyl titanate (TTB), and 0.182 parts by weight of surfactant cetyltrimethylammonium bromide (CTAB) to isopropanol solvent and stir for 1.5 h to achieve uniform mixing;

[0061] (2) Add 3.726 parts by mass of dilute nitric acid dropwise to the mixture obtained in step (1) and hydrolyze for 1 hour;

[0062] (3) After aging the sol obtained in step (2) at room temperature for 24 hours, continue to dry it in a vacuum oven at 60-80℃ for 18-24 hours;

[0063] (4) The solid obtained in step (3) is calcined in stages at 200-300℃ for 2-3 hours and then heated to 500-600℃ for 3-4 hours.

[0064] (5) Dissolve 0.09 parts by mass of Ni(NO3)3·6H2O in 1 mL of deionized water;

[0065] (6) Immerse 1 part by mass of the solid obtained in step (4) in the solution obtained in step (5), sonicate for 0.5-1h, then air dry at room temperature for 12h, and then dry completely at 80-100℃;

[0066] (7) The solid obtained in (6) was calcined at 600°C in air for 3 h, and then reduced at 600°C for 1 h to obtain Al2O3-supported Ni@TiO. x Core-shell structured catalyst, wherein the mass of the support is used as a basis, TiO2 x The mass percentage content is 10%, and the molecular formula is Ni1Ti4 / Al2O3;

[0067] (8) The prepared Al2O3-supported Ni@TiO x The catalyst tablets are 20-40 mesh granular catalysts;

[0068] (9) Ni@TiO3 loaded with Al2O3 tablets xA granular catalyst was loaded into a fixed-bed reactor, and a reaction gas was introduced to carry out the reaction. The molar ratio of hydrogen to propane in the reaction gas was 1:1, and the propane mass hourly space velocity was 4 h⁻¹. -1 The equilibrium gas is nitrogen.

[0069] (10) Ni@TiO3 supported on Al2O3 after reaction x The granular catalyst was regenerated by passing air through it at 500-550℃ for 0.5 h, followed by reduction at 600℃ for 1 h to obtain regenerated Al2O3-supported Ni@TiO. x Particulate catalyst.

[0070] Example 2:

[0071] The preparation and reaction were carried out using the method of Example 1, the only difference being that 0.06 parts by mass of Ni(NO3)3·6H2O were used in step (5); the resulting catalyst was based on the mass of the support, and TiO2... x The mass percentage is 10%, and the molecular formula is Ni1Ti6 / Al2O3.

[0072] Example 3:

[0073] The preparation and reaction were carried out using the method of Example 1, the only difference being that 0.12 parts by mass of Ni(NO3)3·6H2O were used in step (5); the resulting catalyst was based on the mass of the support, and TiO2... x The mass percentage is 10%, and the molecular formula is Ni1Ti3 / Al2O3.

[0074] Example 4:

[0075] The preparation and reaction were carried out using the method of Example 1, the only difference being that 0.36 parts by mass of Ni(NO3)3·6H2O were used in step (5); the resulting catalyst was based on the mass of the support, and TiO2... x The mass percentage is 10%, and the molecular formula is Ni1Ti1 / Al2O3.

[0076] Example 5:

[0077] The preparation and reaction were carried out using the method of Example 1, the only difference being that 0 parts by mass of Ni(NO3)3·6H2O were used in step (5); the resulting catalyst was based on the mass of the support, and TiO2 was used. x The mass percentage content is 10%, and the molecular formula is TiO2. x / Al2O3.

[0078] Example 6:

[0079] (1) Dissolve 0.09 parts by mass of Ni(NO3)3·6H2O in 1 mL of deionized water;

[0080] (2) Immerse 1 part by mass of Al2O3 in the above solution, sonicate for 0.5-1 h, air dry at room temperature for 12 h, and then dry completely at 80-100℃;

[0081] (3) The solid obtained in (2) was calcined at 600°C in air for 3 h and reduced at 600°C for 1 h to obtain Ni catalyst supported on Al2O3, with the molecular formula Ni / Al2O3.

[0082] (4) The prepared Al2O3-supported Ni catalyst and the Al2O3-supported TiO2 catalyst prepared by the method in Example 5 were combined. x Catalyst mechanical mixing, denoted as Ni / Al+TiO x / Al, tableted as 20-40 mesh granular catalyst;

[0083] (5) The tableted granular catalyst is loaded into a fixed-bed reactor, and a reaction gas is introduced to carry out the reaction. The molar ratio of hydrogen to propane in the reaction gas is 1:1, and the propane mass hourly space velocity is 4 h⁻¹. -1 The equilibrium gas is nitrogen.

[0084] Example 7:

[0085] The preparation and reaction were carried out using the method of Example 1, the only difference being that in step (1), 2.294 parts by mass of aluminum sec-butoxide (ATSB) and 0.212 parts by mass of tetrabutyl titanate (TTB) were used. The catalyst was prepared based on the mass of the support, and TiO₂ was used. x The mass percentage content is 5%.

[0086] Example 8:

[0087] The preparation and reaction were carried out using the method of Example 1, the only difference being that in step (1), 1.932 parts by mass of aluminum sec-butoxide (ATSB) and 0.85 parts by mass of tetrabutyl titanate (TTB) were used. The catalyst was prepared based on the mass of the support, and TiO₂ was used. x The mass percentage content is 20%.

[0088] Example 9:

[0089] The preparation and reaction were carried out using the method of Example 1, the only difference being that the calcination temperature in step (7) was 500°C.

[0090] Example 10:

[0091] The preparation and reaction were carried out using the method of Example 1, the only difference being that the calcination time in step (7) was 4 hours.

[0092] Example 11:

[0093] The preparation and reaction were carried out using the method of Example 1, the only difference being that the reduction temperature in step (3) was 400°C.

[0094] Example 12:

[0095] The preparation and reaction were carried out using the method of Example 1, the only difference being that the reduction temperature in step (3) was 500°C.

[0096] Example 13:

[0097] The preparation and reaction were carried out using the method of Example 1, the only difference being that the reduction temperature in step (3) was 550°C.

[0098] Example 14:

[0099] The preparation and reaction were carried out using the method of Example 1, the only difference being that the reduction temperature in step (3) was 700°C.

[0100] Example 15:

[0101] The preparation and reaction were carried out using the method of Example 1, the only difference being that the reduction time in step (3) was 2 hours.

[0102] Example 16:

[0103] (1) Dissolve 0.526 parts by mass of Cr(NO3)3·9H2O in 1 mL of deionized water;

[0104] (2) Immerse 1 part by mass of Al2O3 in the above solution, sonicate for 0.5-1 h, air dry at room temperature for 12 h, and then dry completely at 80-100℃;

[0105] (3) The solid obtained in (2) was calcined at 600℃ in air for 3 h and then reduced at 600℃ for 1 h to obtain Al2O3-supported CrO. x Catalyst, molecular formula CrO x / Al2O3; This catalyst, based on the mass of its support, contains CrO x The mass percentage content is 10%;

[0106] (4) The prepared Al2O3-supported Ni catalyst and the Al2O3-supported TiO2 catalyst prepared by the method in Example 5 were combined. x Catalyst mechanical mixing, denoted as Ni / Al+TiO x / Al, tableted as 20-40 mesh granular catalyst;

[0107] (5) The tableted granular catalyst is loaded into a fixed-bed reactor, and a reaction gas is introduced to carry out the reaction. The molar ratio of hydrogen to propane in the reaction gas is 1:1, and the propane mass hourly space velocity is 4 h⁻¹. -1The equilibrium gas is nitrogen.

[0108] The catalytic performance of the catalysts prepared in the above examples for propane dehydrogenation was tested. The catalyst activity was expressed as propane conversion, propylene selectivity, propylene yield, and deactivation rate. The results are discussed below based on the calculations.

[0109] The propane dehydrogenation performance of different NimTin / Al2O3 catalysts corresponding to Examples 1-6 was tested, and the catalytic performance is as follows: Figure 1 As shown, (a) is the propane conversion rate versus time, and (b) is the propylene selectivity versus time. (This is related to the relationship between Ni / Al₂O₃ and TiO₂.) x Compared to Al2O3 catalysts, Ni1Ti4 / Al2O3 (m:n = 1:(1-6)) exhibits higher propylene selectivity and dehydrogenation activity. Specifically, the Ni1Ti4 / Al2O3 catalyst maintains high propylene selectivity while demonstrating significantly improved catalytic activity, with an initial conversion of approximately 40% and a propylene yield of approximately 16.70 mmol·g based on catalyst mass. cat -1 ·h -1 ,according to Figure 2 The catalytic performance comparison charts for the catalysts in Examples 1 and 16 show their performance compared to industrial CrO. x High activity comparable to Al2O3 catalysts. Meanwhile, Ni / Al2O3 and TiO2O3... x Mechanical mixing of Ni / Al+TiO3 with Al2O3 x Due to the more prominent C / C bond activation ability of Ni sites, the Ni / Al catalyst initially exhibits a catalytic behavior similar to that of the Ni / Al2O3 catalyst. However, in the later stages of the reaction, as the highly active Ni sites are covered by carbon deposits, its catalytic behavior gradually shifts towards that of TiO2. x The Al2O3 catalyst transformation significantly improved propylene yield. These results reflect the interaction between metallic Ni and TiO2 in the mechanically mixed catalyst. x Species cannot effectively interact to form Ni@TiO due to differences in spatial distribution. x The core-shell structure, with exposed Ni sites on the surface, further confirms the presence of TiO₂ based on significant differences in catalytic performance. x The shell is Ni@TiO x Active sites for propane dehydrogenation on Al2O3.

[0110] Examples 1, 7, and 8 show different TiO₂. x The catalyst prepared by mass percentage (based on the support mass) and its catalytic performance in the propane dehydrogenation to olefins reaction are as follows: Figure 3 As shown, it can be seen that when TiO xWhen the mass percentage content decreased to 5%, the induction period of methanogenesis was re-observed, possibly corresponding to a higher Ni / TiO content. x The ratio leads to the exposure of some Ni sites. When TiO2... x The catalytic performance is optimal when the content is 10%.

[0111] The long-term regeneration stability of the catalyst corresponding to Example 1 was also tested, and the results are as follows: Figure 4 As shown, the catalyst can be completely restored to its initial activity after regeneration in continuous dehydrogenation regeneration cycles, and its high selectivity for propylene remains steady, exhibiting excellent stability. The deactivation rate constants at reaction temperatures of 550, 575, and 600 °C are 0.007, 0.018, and 0.073 h⁻¹, respectively. -1 It is far lower than that of industrial CrO under the same testing conditions. x The deactivation rate constant of the Al2O3 catalyst at 600℃ is 0.32 h⁻¹. -1 ).

[0112] Figure 5 and Figure 6 The images shown are spherical aberration-scanning transmission electron microscopy (TEM) images under in-situ reduction conditions for Examples 11, 12, and 1 (Ni1Ti4 / Al2O3 corresponding to H2 reduction temperatures of 400, 500, and 600 °C), and the electron energy loss spectral scan results corresponding to Example 1. Starting from Experiment 11 at 400 °C, metallic Ni nanoparticles with an average diameter of approximately 6.8 nm can be observed. When the reduction temperature is increased to 500 °C, TiO2 is observed on the surface of the Ni nanoparticles. x The formation of the coating layer but TiO x The coating layer exhibits a discrete and non-uniform morphology until the reduction temperature is increased to 600℃, forming a uniform and relatively thick (1-2 nm) TiO₂ layer. x The shell completely encapsulates the metallic Ni nanoparticles. This result is consistent with... Figure 7 The infrared comparison results of CO adsorption under in-situ reduction conditions in Examples 11, 13, 1, and 14 (Ni1Ti4 / Al2O3 corresponding to H2 reduction temperatures of 400, 550, 600, and 700℃) are consistent. At a reduction temperature of 400℃, the Ni1Ti4 / Al2O3 catalyst has a CO adsorption capacity of 2055 cm⁻¹. -1 The CO adsorption band attributable to metallic Ni was prominent, but it gradually decreased and eventually disappeared as the reduction temperature increased above 550℃. This indicates that as the reduction temperature increased, the exposed Ni sites on the catalyst surface were gradually covered, confirming the strong interaction-induced TiO₂ adsorption. x The occurrence of reverse Ni coating phenomenon. Figure 6The study specifically demonstrated the elemental distribution of Ni1Ti4 / Al2O3 after reduction at 600℃. The observed interatomic distances between Ni-Ni and Ti-Ti atoms were 0.20 nm and 0.25 nm, respectively, with the latter corresponding to the Ni-TiO3 atoms formed during the reduction process. x The formation of the interface causes a shortening of the d-interface spacing of rutile phase titanium oxide (110). Ti L 2,3 Line scan results of edge electron energy loss spectroscopy confirm the coating distribution of Ti at the edges of nanoparticles where Ni is absent.

[0113] In-situ XPS spectroscopy analysis was performed on the catalysts of Examples 1 and 5 to analyze the changes in chemical bonding and valence state distribution of surface Ti and O species with varying atmosphere. The results are as follows: Figure 8 As shown, (a) and (b) correspond to the catalysts prepared in Example 5 and Example 1, respectively. After H2 reduction treatment at 600°C, the TiO2 catalysts corresponding to Example 5 were obtained. x Compared to the Al2O3 catalyst, the Ni@TiO catalyst in Experimental Example 1 x The presence of the +3 Ti peak at a lower binding energy (457.5 eV) in the Al2O3 catalyst leads to a more pronounced peak asymmetry in the dominant +4 Ti peak. Peak deconvolution results show that Ti... 3+ / (Ti 3+ +Ti 4+ The proportion is approximately TiO2 x Twice that of Al2O3 indicates more O vacancies formed. This result is consistent with... Figure 9 The EPR comparison results of the catalysts in Examples 1 and 5 are consistent with those of the TiO2 catalyst in Experimental Example 5. x Compared to the Al2O3 catalyst, the Ni@TiO catalyst in Experimental Example 1 x Al2O3 catalysts belong to TiO2 with oxygen vacancies. x The significantly increased signal strength of the species indicates that TiO2 x The concentration of oxygen vacancies and adjacent coordinating unsaturated Ti sites increases.

[0114] Further X-ray absorption extended X-ray absorption fine structure fitting analysis was performed on the catalysts of Examples 1 and 5 to obtain the specific details of the Ti atom coordination environment, such as... Figure 10 As shown, the TiO2 corresponding to Experimental Example 5 x Compared to the Al2O3 catalyst, the Ni@TiO catalyst in Experimental Example 1 x The Ti-O coordination number of the Ni@TiOx / Al2O3 catalyst decreased from 4.2 to 3.8, further providing clear experimental evidence for the increased concentration of coordinatingly unsaturated Ti sites. Based on these results, it is proposed that the higher catalytic activity of the Ni@TiOx / Al2O3 catalyst originates from Ni@TiOx. xThe formation of a core-shell structure. Strong metal-oxide interactions lead to the formation of TiO₂ during H₂ reduction treatment. x The reverse coating of metallic Ni by the capping layer, during the formation of this special "adhesive" structure, metallic Ni and TiO x The tight contact of the capping layer allows for easier hydrogen overflow, leading to more O vacancies and the formation of corresponding coordinatingly unsaturated Ti sites. And the coordinatingly unsaturated Ti... 4C The site is an active site for propane dehydrogenation reaction with stronger CH bond activation ability, a lower CH activation barrier, and a significantly reduced apparent reaction barrier, thus exhibiting higher propane dehydrogenation activity.

[0115] Propane-surface reaction tests were performed on the catalysts of Examples 1 and 5 to characterize the ability of the catalytic active sites to activate CH bonds. The results are as follows: Figure 11 As shown, (a) and (b) correspond to the catalysts prepared in Example 5 and Example 1, respectively. To avoid interference from the H2 signal caused by the desorption of adsorbed H species remaining on the catalyst surface after H2 reduction treatment, the reduction atmosphere was changed from H2 to D2 to ensure that H2... 1 The sole source is the CH cleavage of propane molecules, and the recorded HD signal serves as a standard for the initial CH activation temperature. It can be seen that Experimental Example 5, with its lower oxygen vacancies and corresponding concentrations of coordinatingly unsaturated Ti sites, corresponds to TiO₂. x The activation temperature of the Al2O3 dehydrogenation reaction is around 332℃, while the experimental example 1, which has a high concentration of oxygen vacancies and corresponding coordinatingly unsaturated Ti sites, corresponds to Ni@TiO. x The activation temperature of the Al2O3 dehydrogenation reaction decreased to around 251℃, confirming that Ni@TiO x / Al2O3 lowers the activation barrier for CH and increases propane dehydrogenation activity.

[0116] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many specific modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and these modifications all fall within the scope of protection of the present invention.

Claims

1. A supported TiO2 x The application of a core-shell structured catalyst in the dehydrogenation of low-carbon alkanes to olefins, wherein the catalyst uses Al₂O₃ as a support, is characterized by... The Al2O3 support is loaded with Ni@TiO x core-shell structure, wherein the Ni@TiO x core-shell structure comprises a metallic Ni core and TiO x shell, 1<x<2; wherein the TiO x shell serves as an active site for propane dehydrogenation; based on the mass of the Al2O3 support, the TiO x has a mass percentage content of 10%-15%; the molecular formula of the catalyst is recorded as NimTin / Al2O3, wherein m:n=1: (1- 6).

2. A supported TiO2 type according to claim 1 x The application of core-shell structured catalysts in the dehydrogenation of low-carbon alkanes to olefins is characterized by, The ratio m:n is 1:

4.

3. A supported TiO2 type according to claim 1 x The application of core-shell structured catalysts in the dehydrogenation of low-carbon alkanes to olefins is characterized by, The supported TiO x The preparation method of core-shell structured catalysts includes the following steps: (1) Add aluminum alkoxide, organotitanium compound and surfactant to organic alcohol solvent and stir until uniformly mixed; (2) Add dilute nitric acid dropwise to the mixture obtained in step (1) until hydrolysis is complete; (3) The sol obtained in step (2) is aged at room temperature until complete and then dried completely under vacuum conditions; (4) The solid obtained in step (3) is roasted in stages, that is, first roasted at 200-300 ℃, and then roasted at 500-600 ℃. (5) The solid obtained in step (4) is immersed in Ni(NO3)3·6H2O solution, ultrasonically dispersed evenly, and then completely dried; (6) The solid obtained in step (5) is calcined and then reduced at 550-700 °C to obtain Al2O3-supported Ni@TiO. x Core-shell structured catalysts.

4. A supported TiO2 type according to claim 3 x The application of core-shell structured catalysts in the dehydrogenation of low-carbon alkanes to olefins is characterized by, In step (1), the aluminum alkoxide is one of aluminum sec-butoxide (ATSB) and aluminum isopropoxide (Al(Opri)3); the organotitanium compound is one of tetrabutyl titanate (TTB) and isopropyl titanate (TTP); the surfactant is one of hexadecyltrimethylammonium bromide (CTAB) and hexadecyltrimethylammonium chloride (CTAC); and the organic alcohol solvent is isopropanol or ethanol.

5. A supported TiO2 type according to claim 3 x The application of core-shell structured catalysts in the dehydrogenation of low-carbon alkanes to olefins is characterized by, In step (3), the complete drying under vacuum conditions is to dry in a vacuum oven at 60-80 ℃ for 18-24 hours.

6. A supported TiO2 type according to claim 3 x The application of core-shell structured catalysts in the dehydrogenation of low-carbon alkanes to olefins is characterized by, In step (4), the stepwise calcination is to first calcinate at 200-300 ℃ for 2-3 h, and then calcinate at 500-600 ℃ for 3-4 h.

7. A supported TiO2 type according to claim 3 x The application of core-shell structured catalysts in the dehydrogenation of low-carbon alkanes to olefins is characterized by, In step (6), the calcination temperature is 500-600 ℃, the calcination time is 2-4 h, and the reduction time is 1-2 h.

8. A supported TiO2 type according to claim 1 x The application of core-shell structured catalysts in the dehydrogenation of low-carbon alkanes to olefins is characterized by, The low-carbon alkane is propane, and the olefin is propylene.

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