Pd-Ag / g-C3N4 catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of hydrogenation, and discloses a Pd-Ag / g-C3N4 catalyst and a preparation method and application thereof.The catalyst comprises a carrier and active components loaded on the carrier, the carrier is g-C3N4, and the active components comprise Pd and Ag; and the particle size of the active component is 2-15 nm. The method for preparing the Pd-Ag / g-C3N4 catalyst comprises the step that active components are loaded on a carrier, the carrier is g-C3N4, and the active components comprise Pd and Ag. The catalyst provided by the invention can improve the selectivity of olefin, especially the selectivity of ethylene.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogenation, and particularly relates to a Pd-Ag / g-C3N4 catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] In the industrial production of ethylene, the olefin-alkane mixture generated by steam thermal cracking of hydrocarbon raw materials such as naphtha is subjected to cryogenic separation to obtain products such as ethylene, propylene, and butadiene. In the C2 fraction obtained in the separation process, ethane, ethylene, and acetylene are contained. During rectification separation, acetylene will be enriched in ethylene, affecting the downstream utilization of ethylene. By adopting the process route of selective hydrogenation of acetylene to ethylene, while removing acetylene impurities, the ethylene production is increased. So far, the supported Pd-based catalyst with Pd as the active component and Al2O3 as the carrier prepared by the conventional impregnation method is still recognized as the best industrial catalyst for acetylene hydrogenation. The acetylene catalytic hydrogenation reaction is a gas-solid phase reaction, including four processes: diffusion, adsorption, reaction, and desorption of reactants (acetylene and hydrogen). Only when the ethylene generated by acetylene hydrogenation has weak adsorption on the catalyst surface can it be effectively desorbed to avoid side reactions caused by over-hydrogenation to generate ethane or oligomers of 1,3-butadiene (commonly known as green oil). The existence of side reactions not only reduces the ethylene yield, but also the generated green oil will shorten the operation cycle of the catalyst and the service life of the reactor. Therefore, it is crucial to develop a Pd-based hydrogenation catalyst with high activity, high selectivity, and high stability. g-C3N4 not only has visible light response, high chemical stability, and appropriate C2p and N2p orbital bands, but also has ideal N coordination, and has now been widely used as a photocatalyst. The metal-support interaction plays a key role in regulating the charge density and d-orbital distribution of the supported metal species. At present, the industrial acetylene selective hydrogenation catalyst is still mainly Pd-Ag / Al2O3. Although it can achieve the purpose of removing acetylene at a relatively low temperature (usually 70-90 °C), its ethylene selectivity is still not ideal. Therefore, there is an urgent need to provide an acetylene hydrogenation catalyst that has high ethylene selectivity at a relatively low temperature. Summary of the Invention

[0003] The purpose of the present invention is to overcome the problem that the olefin (especially ethylene) selectivity of the existing hydrogenation catalyst is relatively low, and to provide a Pd-Ag / g-C3N4 catalyst, a preparation method thereof, and an application thereof.

[0004] To achieve the above purpose, in the first aspect of the present invention, a Pd-Ag / g-C3N4 catalyst is provided. The catalyst includes a carrier and active components supported on the carrier. The carrier is g-C3N4, and the active components include Pd and Ag; the particle size of the active components is 2-15 nm.

[0005] The second aspect of the present invention provides a method for preparing a Pd-Ag / g-C3N4 catalyst, which includes: loading active components on a carrier, wherein the carrier is g-C3N4, and the active components include Pd and Ag.

[0006] The third aspect of the present invention provides the catalyst prepared by the above-mentioned method.

[0007] The fourth aspect of the present invention provides the application of the above-mentioned catalyst and / or the catalyst prepared by the above-mentioned method in alkyne hydrogenation, preferably in acetylene hydrogenation.

[0008] The fifth aspect of the present invention provides a method for alkyne hydrogenation, which includes: carrying out hydrogenation reaction on the alkyne in the raw material gas in the presence of the above-mentioned catalyst and / or the catalyst prepared by the above-mentioned method.

[0009] Through the above technical solutions, the present invention has achieved the following beneficial effects:

[0010] (1) The catalyst of the present invention has a smaller particle size of the active components. The catalyst of the present invention can improve the selectivity of olefins, especially the selectivity of ethylene. Preferably, the catalyst of the present invention can ensure a high olefin selectivity while obtaining a high alkyne conversion rate.

[0011] (2) The present invention uses the photodeposition method to deposit Pd-Ag on the g-C3N4 carrier to prepare the catalyst. The method provided by the present invention can prepare the catalyst under mild conditions (such as normal temperature and pressure conditions). Compared with the existing hydrogenation catalysts, the catalyst prepared by the photodeposition method of the present invention does not need to carry out the steps of high-temperature sintering and hydrogen reduction to prepare the catalyst containing Pd(0), which simplifies the preparation process of the catalyst. Moreover, the catalyst prepared by the method of the present invention has a smaller particle size of the active components and the active components are more uniformly dispersed. Description of the Drawings

[0012] Figure 1 is a photo of the fluidized photochemical reaction system;

[0013] Figure 2 is the XRD pattern of the C3N4 carrier in Example 1;

[0014] Figure 3 is the XPS pattern of the active component Pd 3d of the Pd-Ag / g-C3N4 catalyst in Example 1;

[0015] Figure 4 is the TEM image of the Pd-Ag / g-C3N4 catalyst in Example 1;

[0016] Figure 5It is the TEM image of the Pd-Ag / g-C3N4 catalyst after hydrogen reduction in Example 8;

[0017] Figure 6 It is the TEM image of the Pd-Ag / g-C3N4 catalyst after hydrogen reduction in Comparative Example 1. Detailed implementation manners

[0018] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0019] The first aspect of the present invention provides a Pd-Ag / g-C3N4 catalyst, which catalyst comprises a carrier and an active component supported on the carrier, the carrier is g-C3N4, and the active component comprises Pd and Ag; the particle size of the active component is 2-15 nm.

[0020] According to the present invention, preferably, the particle size of the active component is 2-5 nm.

[0021] In the present invention, the particle size of the catalyst is obtained by testing with a transmission electron microscope (TEM).

[0022] In the present invention, the g-C3N4 represents C3N4 having a graphitic phase structure.

[0023] According to the present invention, preferably, the Pd comprises Pd(0) and Pd(+2), wherein Pd(0) represents the chemical state of Pd is 0 valence, and Pd(+2) represents the chemical state of Pd is +2 valence; preferably, the molar ratio of Pd(0) to Pd(+2) is 0.3-2:1 (for example, 0.3:1, 0.5:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, and the ranges composed of any two of the above), more preferably 1-1.6:1.

[0024] In the present invention, the molar ratio of different valence states of Pd in the catalyst is obtained by testing with X-ray photoelectron spectroscopy (XPS).

[0025] According to the present invention, preferably, the XPS spectrum of the catalyst shows that Pd 3d has four characteristic peaks in the electron binding energy of 344-332 eV; more preferably, the XPS spectrum of the catalyst shows that Pd 3d 3 / 2It has two characteristic peaks at electron binding energies of 344 - 338 eV; the XPS spectrum of the catalyst shows Pd 3d 5 / 2 It has two characteristic peaks at electron binding energies of 338 - 332 eV.

[0026] According to the present invention, preferably, in the XPS spectrum of the catalyst, in order of decreasing electron binding energy, the two characteristic peaks at electron binding energies of 344 - 338 eV are respectively the Pd(+2)3d 3 / 2 characteristic peak and the Pd(0)3d 3 / 2 characteristic peak.

[0027] According to the present invention, preferably, in the XPS spectrum of the catalyst, in order of decreasing electron binding energy, the two characteristic peaks at electron binding energies of 338 - 332 eV are respectively the Pd(+2)3d 5 / 2 characteristic peak and the Pd(0)3d 5 / 2 characteristic peak.

[0028] According to the present invention, the amounts of the carrier and the active component in the catalyst can be selected within a relatively wide range. Preferably, relative to 100 g of the carrier, the content of Pd is 0.001 - 0.1 g, more preferably 0.01 - 0.1 g, further preferably 0.01 - 0.07 g, and even more preferably 0.01 - 0.035 g; the content of Ag is 0.001 - 0.1 g, more preferably 0.01 - 0.1 g, further preferably 0.03 - 0.1 g, and even more preferably 0.03 - 0.07 g. In the present invention, the content of the active component in the catalyst is calculated based on the feed amount.

[0029] According to the present invention, preferably, the specific surface area of the catalyst is 10 - 120 m 2 / g (for example, 10 m 2 / g, 20 m 2 / g, 30 m 2 / g, 40 m 2 / g, 50 m 2 / g, 60 m 2 / g, 70 m 2 / g, 80 m 2 / g, 90 m 2 / g, 100 m 2 / g, 110 m 2 / g, 120 m 2 / g, and the ranges formed by any two of the above), and more preferably 30 - 80 m 2 / g.

[0030] The second aspect of the present invention provides a method for preparing a Pd-Ag / g-C3N4 catalyst, which method comprises: loading an active component on a support, wherein the support is g-C3N4 and the active component comprises Pd and Ag.

[0031] The inventors of the present invention further found that when the active component is loaded by a photodeposition method, the conversion rate of alkynes and the selectivity of alkenes can be further improved. Preferably, the loading method is: contacting the active component precursor with the support under light irradiation conditions and in the presence of a sacrificial agent, wherein the active component precursor comprises a palladium precursor and a silver precursor, and the support is g-C3N4.

[0032] According to the present invention, preferably, the amount of the active component precursor used is such that in the resulting catalyst, relative to 100 g of the support, the content of Pd is 0.001 - 0.1 g, more preferably 0.01 - 0.1 g, further preferably 0.01 - 0.07 g, and even more preferably 0.01 - 0.035 g; the content of Ag is 0.001 - 0.1 g, more preferably 0.01 - 0.1 g, further preferably 0.03 - 0.1 g, and even more preferably 0.03 - 0.07 g.

[0033] According to the present invention, the palladium precursor is any substance capable of providing palladium element, such as a palladium salt. Preferably, the palladium precursor is at least one of palladium nitrate, palladium chloride, and palladium acetate. The palladium precursor may be palladium nitrate, palladium chloride, palladium acetate, etc.

[0034] According to the present invention, the silver precursor is any substance capable of providing silver element, such as a silver salt. Preferably, the silver precursor is silver nitrate and / or silver chloride. The silver precursor may be silver nitrate, silver chloride, etc.

[0035] According to the present invention, preferably, the specific surface area of the g-C3N4 is 10 - 120 m 2 / g (for example, 10 m 2 / g, 20 m 2 / g, 30 m 2 / g, 40 m 2 / g, 50 m 2 / g, 60 m 2 / g, 70 m 2 / g, 80 m 2 / g, 90 m 2 / g, 100 m 2 / g, 110 m 2 / g, 120 m 2 / g, and the ranges composed of any two of the above), more preferably 30 - 60 m 2 / g.

[0036] In the present invention, g-C3N4 can be directly purchased or prepared according to the methods in the literature. For example, it can be prepared as follows: in an air atmosphere, a nitrogen- and carbon-containing precursor is calcined at 400-700 °C for 2-10 h. Among them, the nitrogen- and carbon-containing precursor can be at least one of urea, dicyandiamide, melamine, and thiourea. The calcination temperature of the nitrogen- and carbon-containing precursor can be 500-650 °C, preferably 550-600 °C. The calcination time of the nitrogen- and carbon-containing precursor can be 4-10 h, preferably 4-6 h. In a particularly preferred case, the calcination conditions further include: heating to the calcination temperature at a heating rate of 5-15 °C / min, and then calcining at this temperature.

[0037] According to the present invention, in order to further improve the conversion rate of alkynes and the selectivity of olefins, preferably, the nitrogen- and carbon-containing precursor is urea. When urea is used as the nitrogen- and carbon-containing precursor, the selectivity of olefins can be further improved. The inventor speculates that this may be because the synthesis of C3N4 from urea is more conducive to forming a strong metal-support interaction with Pd and Ag, further improving the thermal stability of Pd-Ag particles, achieving a highly dispersed Pd-Ag active component, exposing more active metal Pd top-site active sites, being beneficial to the formation of ethylene molecules adsorbed by π bonds, and being more easily desorbed from the catalyst surface rather than further hydrogenated to ethane, thereby improving the ethylene selectivity of the catalyst.

[0038] According to the present invention, in order to promote the deposition of palladium and silver elements on the support and further improve the selectivity of ethylene, preferably, the light irradiation conditions include: the power of the light source is 100-400 W, the wavelength of the light source is 300-400 nm, more preferably 350-380 nm, further preferably 360-370 nm, and the light irradiation time is 0.5-6 h.

[0039] In the present invention, the power of the light source can be 100 W, 150 W, 200 W, 250 W, 280 W, 300 W, 320 W, 350 W, 400 W, and the range composed of any two of the above, preferably, the power of the light source is 280-350 W.

[0040] In the present invention, the light irradiation time can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 5 h, 6 h, and the range composed of any two of the above, preferably, the light irradiation time is 0.5-2 h.

[0041] According to the present invention, there is no particular limitation on the light intensity of the light irradiation. Generally, the light intensity of the light irradiation is 80-100 mw / cm 2 .

[0042] In the present invention, there is no particular limitation on the light source, which can be a light source commonly used in the preparation of catalysts by photodeposition. The light source can be a high-power density light strip (such as an LED light strip). In the present invention, the contact can be carried out in a conventional photoreaction device, for example, the fluidized photoreaction device in CN202211307358.X. The fluidized photoreaction device consists of a glass reactor and a high-power density light strip to form a photoreaction device, combined with a flow meter, a temperature control element, a circulation pump, and an electronic control, etc. Usually, the light source is wound around the outside of the glass reactor.

[0043] According to the present invention, the sacrificial agent can be a commonly used electron donor in the art, which can consume holes to avoid the recombination of photoelectrons and holes again, so that more photoelectrons are generated on the surface of the carrier. The sacrificial agent can be an alcohol sacrificial agent, an alkanolamine sacrificial agent (such as triethanolamine (TEOA)), a sulfite sacrificial agent, and an ascorbic acid sacrificial agent (AA acid). In order to promote the uniform deposition of palladium and silver elements on the carrier and further improve the selectivity of ethylene, preferably, the sacrificial agent is an alcohol with 1-5 carbon atoms, more preferably a monohydric alcohol with 1-5 carbon atoms (for example, methanol, ethanol, n-propanol, isopropanol, butanol, pentanol, etc.), and further preferably methanol.

[0044] According to the present invention, the dosage of the sacrificial agent can be selected within a relatively wide range. Preferably, relative to 100 g of the carrier, the total dosage of the sacrificial agent is 50-300 mL. In the present invention, relative to 100 g of the carrier, the total dosage of the sacrificial agent can be 50 mL, 100 mL, 150 mL, 200 mL, 250 mL, 300 mL, and the range composed of any two of the above, and more preferably 100-200 mL.

[0045] According to the present invention, there is no particular limitation on the way the active component precursor contacts the carrier, as long as the carrier can be suspended in the precursor solution for direct contact. For example, a mixture of the palladium precursor and the silver precursor directly contacts the carrier. Preferably, the palladium precursor and the silver precursor contact the carrier step by step. For example, first, the palladium precursor contacts the carrier to obtain Pd / g-C3N4, and then Pd / g-C3N4 contacts the silver precursor to obtain the Pd-Ag / g-C3N4 catalyst. Another example is that first, the silver precursor contacts the carrier to obtain Ag / g-C3N4, and then Ag / g-C3N4 contacts the silver precursor to obtain the Pd-Ag / g-C3N4 catalyst. More preferably, the contact method includes: first contacting the palladium precursor with the carrier to obtain Pd / g-C3N4, and then contacting Pd / g-C3N4 with the silver precursor to obtain the Pd-Ag / g-C3N4 catalyst. In the present invention, the temperature of the contact is not particularly limited and can be the temperature commonly used in the preparation of catalysts by photodeposition method. For example, the contact is carried out at room temperature (about 20 - 25 °C).

[0046] In the present invention, the palladium precursor and the silver precursor can be used in solid form or in solution form. Preferably, the palladium precursor and the silver precursor are prepared into (aqueous) solutions for standby; more preferably, the concentration of the palladium precursor in the palladium precursor solution in terms of Pd is 40 - 100 mg / mL, preferably 40 - 60 mg / mL. More preferably, the concentration of the silver precursor in the silver precursor solution in terms of Ag is 80 - 120 mg / mL.

[0047] According to the present invention, preferably, the contact method further includes: independently washing and drying the product of the first contact and the product of the second contact. Among them, washing can be carried out with water as long as the sacrificial agent and the active component precursor on the surface of the carrier can be removed. The drying conditions can include: the temperature is 60 - 120 °C, and the time is 4 - 12 h.

[0048] According to a preferred embodiment of the present invention, the method includes:

[0049] (1) Under light irradiation conditions, the first photodeposition solution is first contacted with the carrier and dried to obtain Pd / g-C3N4, wherein the first photodeposition solution is an aqueous solution containing a palladium salt and a sacrificial agent;

[0050] (2) Under light irradiation conditions, the second photodeposition solution is contacted with Pd / g-C3N4 and dried to obtain the Pd-Ag / g-C3N4 catalyst, wherein the second photodeposition solution is an aqueous solution containing a silver salt and a sacrificial agent.

[0051] According to a preferred embodiment of the present invention, in step (1), the preparation method of the first photo-deposition solution includes: mixing an aqueous solution of palladium salt with a sacrificial agent and water to obtain the first photo-deposition solution.

[0052] According to a preferred embodiment of the present invention, in step (1), relative to 100 g of the carrier, the dosage of the sacrificial agent is 90 - 120 mL. The volume ratio of the sacrificial agent to water can be 1:8 - 12.

[0053] According to a preferred embodiment of the present invention, in step (2), the preparation method of the second photo-deposition solution includes: mixing an aqueous solution of silver salt with a sacrificial agent and water to obtain the second photo-deposition solution.

[0054] According to a preferred embodiment of the present invention, in step (2), relative to 100 g of the carrier, the dosage of the sacrificial agent is 90 - 120 mL. The volume ratio of the sacrificial agent to water can be 1:8 - 12.

[0055] In the present invention, the loading method can also be other common loading methods in the art, for example, coating method, impregnation method, vapor deposition method, etc. For example, the loading method is: impregnating the active component precursor on the carrier by the impregnation method, and then performing calcination, wherein the active component precursor includes a palladium precursor and a silver precursor.

[0056] In the present invention, when preparing the catalyst by the impregnation method, the impregnation conditions can be the common impregnation conditions in the art. Preferably, the impregnation temperature is 15 - 40 °C, and the impregnation time is 0.5 - 4 h. More preferably, the process of preparing the catalyst by the impregnation method includes: (1) impregnating the carrier with an aqueous solution of palladium salt (the impregnation time is 0.5 - 2 h), and obtaining PdO x / g-C3N4 after drying and calcination; (2) impregnating PdO x / g-C3N4 with an aqueous solution of silver salt (the impregnation time is 0.5 - 2 h), and obtaining PdAgO x / g-C3N4 after drying and calcination. Preferably, the calcination conditions independently include: the temperature is 400 - 500 °C, and the time is 4 - 6 h. Preferably, the drying conditions independently include: the temperature is 100 - 140 °C, and the time is 10 - 15 h.

[0057] According to a particularly preferred embodiment of the present invention, the method includes:

[0058] (1) Putting urea into a muffle furnace, under an air atmosphere, heating it to 590 - 600 °C at a heating rate of 5 - 5.5 °C / min, and then calcining it at this temperature for 4 - 4.5 h to obtain g-C3N4.

[0059] (2) Add 10 - 10.5 g of g-C3N4, 100 - 105 mL of distilled water, 10 - 10.5 mL of methanol, and 70 - 72 μL of an aqueous Pd(NO3)2 solution (the concentration of Pd is 50 - 52 mg / mL) to the fluidized photoreaction system. After fully mixing to form a fluidized suspension, turn on a 290 - 300 W light source and control the light intensity to 95 - 100 mw / cm 2 . After irradiating for 1 - 1.2 h, take it out, rinse it several times with distilled water, and dry it at 60 - 70 °C for 10 - 12 h to obtain Pd / g-C3N4.

[0060] (3) Put the Pd / g-C3N4 obtained in step (2) into the photoreactor, add 100 - 105 mL of distilled water, 10 - 10.5 mL of methanol, and 70 - 72 μL of an aqueous AgNO3 solution (the concentration of Ag is 100 - 105 mg / mL). After fully mixing to form a fluidized suspension, turn on a 290 - 300 W light source and control the light intensity to 95 - 100 mw / cm 2 . After irradiating for 1 - 1.2 h, take it out, rinse it several times with distilled water, and dry it at 60 - 70 °C for 10 - 12 h to obtain the Pd-Ag / g-C3N4 catalyst.

[0061] The third aspect of the present invention provides the catalyst prepared by the method described above.

[0062] The fourth aspect of the present invention provides the application of the catalyst described above and / or the catalyst prepared by the method described above in alkyne hydrogenation.

[0063] According to the present invention, preferably, the alkyne is a C2 - C5 alkyne, such as acetylene, propyne, butyne, pentyne, etc. More preferably, the alkyne is acetylene.

[0064] The fifth aspect of the present invention provides a method for alkyne hydrogenation, which includes: performing a hydrogenation reaction on the alkyne in the raw material gas in the presence of the catalyst described above and / or the catalyst prepared by the method described above.

[0065] According to the present invention, preferably, the alkyne is a C2 - C5 alkyne, such as acetylene, propyne, butyne, pentyne, etc. More preferably, the alkyne is acetylene.

[0066] According to the present invention, preferably, the conditions for the hydrogenation reaction include: the temperature is 35 - 100 °C, preferably 60 - 90 °C, and more preferably 70 - 80 °C.

[0067] According to the present invention, preferably, the raw material gas is a C2 fraction. Among them, the source of the C2 fraction can be a mixture of hydrocarbons containing two carbon atoms separated from petroleum pyrolysis gas.

[0068] According to the present invention, preferably, the content of acetylene in the raw material gas is 0.2 - 2% by volume, for example, it can be 0.2% by volume, 0.4% by volume, 0.6% by volume, 1% by volume, 1.5% by volume, 2% by volume, and the ranges composed of any two of the above.

[0069] According to the present invention, preferably, the raw material gas further contains ethylene. More preferably, the content of ethylene in the raw material gas is 30 - 50% by volume, for example, it can be 30% by volume, 35% by volume, 40% by volume, 45% by volume, 50% by volume, and the ranges composed of any two of the above.

[0070] According to the present invention, preferably, the raw material gas further contains nitrogen. More preferably, the content of nitrogen in the raw material gas is 40 - 60% by volume, for example, it can be 40% by volume, 45% by volume, 50% by volume, 55% by volume, 60% by volume, and the ranges composed of any two of the above.

[0071] According to the present invention, preferably, the raw material gas further contains hydrogen. More preferably, the content of hydrogen in the raw material gas is 0.4 - 0.8% by volume, for example, it can be 0.4% by volume, 0.6% by volume, 0.8% by volume, and the ranges composed of any two of the above.

[0072] According to the present invention, preferably, the raw material gas further contains ethane. More preferably, the content of ethane in the raw material gas is 4 - 8% by volume.

[0073] According to the present invention, preferably, the pressure of the reaction is 0.1 - 2 MPa, more preferably 0.5 - 1.5 MPa. The pressure in the present invention is gauge pressure.

[0074] According to the present invention, preferably, the space velocity of the reaction is 3000 - 12000 h -1 and more preferably 4000 - 5000 h -1 .

[0075] The present invention will be described in detail below through examples. In the following examples,

[0076] room temperature is about 20 - 25 °C.

[0077] The wavelength of the light source is 365 nm.

[0078] Example 1

[0079] (1) Put 100 g of urea into a muffle furnace. Under an air atmosphere, heat it to 600 °C at a heating rate of 5 °C / min, and then calcine it at this temperature for 4 h to obtain g-C3N4 (denoted as carrier #1). The X-ray diffraction spectrum (XRD) of carrier #1 is as Figure 2As shown, it can be concluded from XRD analysis that the support #1 is C3N4 with a graphitic phase structure.

[0080] (2) Add 10 g of support #1, 100 mL of distilled water, 10 mL of methanol, and 70 μL of an aqueous Pd(NO3)2 solution (Pd concentration is 50 mg / mL) to the fluidized photoreaction system (as Figure 1 shown). After fully mixing to form a fluidized suspension, turn on a 300 W light source and control the light intensity to 100 mw / cm 2 . After taking it out after 1 h of light irradiation, rinse it several times with distilled water and then dry it at 60 °C for 12 h to obtain Pd / g-C3N4.

[0081] (3) Put the Pd / g-C3N4 obtained in step (2) into the photoreactor, add 100 mL of distilled water, 10 mL of methanol, and 70 μL of an aqueous AgNO3 solution (Ag concentration is 100 mg / mL), fully mix to form a fluidized suspension, then turn on a 300 W light source and control the light intensity to 100 mw / cm 2 . After taking it out after 1 h of light irradiation, rinse it several times with distilled water and then dry it at 60 °C for 12 h to obtain the Pd-Ag / g-C3N4 catalyst. Relative to 100 g of the said support, the content of Pd is 0.035 g and the content of Ag is 0.07 g.

[0082] The XPS diagram of the active component Pd 3d of the Pd-Ag / g-C3N4 catalyst in Example 1 is as Figure 3 shown. It can be seen from Figure 3 that Pd 3d 3 / 2 has two characteristic peaks in the electron binding energy range of 344 - 338 eV; Pd 3d 5 / 2 has two characteristic peaks in the electron binding energy range of 338 - 332 eV.

[0083] The TEM diagram of the Pd-Ag / g-C3N4 catalyst in Example 1 is as Figure 4 shown. It can be seen from Figure 4 that the active component Pd-Ag is evenly dispersed on the surface of the support, and the particle size of the active component Pd-Ag is relatively small.

[0084] Example 2

[0085] (1) Put 100 g of urea into a muffle furnace. Under an air atmosphere, heat it at a heating rate of 6 °C / min to 570 °C, and then calcine it at this temperature for 5 h to obtain g-C3N4 (denoted as support #2). After XRD analysis: Support #2 is C3N4 with a graphitic phase structure.

[0086] (2) In the fluidized photoreaction system (as Figure 110 g of support #1, 100 mL of distilled water, 12 mL of methanol, and 60 μL of an aqueous Pd(NO3)2 solution (Pd concentration: 50 mg / mL) were added to the one shown in the figure, and after being thoroughly mixed to form a fluidized suspension, a 300 W light source was turned on, and the light intensity was controlled to be 100 mw / cm 2 , and after taking it out after 1.5 h of light irradiation, it was rinsed several times with distilled water and then dried at 60 °C for 12 h to obtain Pd / g-C3N4.

[0087] (3) The Pd / g-C3N4 obtained in step (2) was placed in a photoreactor, and 100 mL of distilled water, 12 mL of methanol, and 60 μL of an aqueous AgNO3 solution (Ag concentration: 100 mg / mL) were added. After being thoroughly mixed to form a fluidized suspension, a 300 W light source was turned on, and the light intensity was controlled to be 100 mw / cm 2 , and after taking it out after 1.2 h of light irradiation, it was rinsed several times with distilled water and then dried at 60 °C for 12 h to obtain a Pd-Ag / g-C3N4 catalyst. With respect to 100 g of the said support, the content of Pd was 0.03 g and the content of Ag was 0.06 g.

[0088] Example 3

[0089] It was carried out according to the method of Example 1, except that in step (1), the temperature was raised to 500 °C at a heating rate of 5 °C / min, and then calcined at this temperature for 10 h. g-C3N4 (denoted as support #3) was obtained. By XRD analysis: Support #3 was C3N4 with a graphitic phase structure.

[0090] Example 4

[0091] It was carried out according to the method of Example 1, except that in step (1), urea was replaced with an equal weight of dicyandiamide, and the obtained g-C3N4 (denoted as support #4) was obtained. By XRD analysis: Support #4 was C3N4 with a graphitic phase structure.

[0092] Example 5

[0093] It was carried out according to the method of Example 1, except that in step (1), urea was replaced with an equal weight of thiourea, and the obtained g-C3N4 (denoted as support #5) was obtained. By XRD analysis: Support #5 was C3N4 with a graphitic phase structure.

[0094] Example 6

[0095] (1) Support #1 was prepared according to the method of Example 1.

[0096] (2) In a fluidized photoreaction system (such as Figure 110 g of carrier #1, 100 mL of distilled water, 10 mL of methanol, 70 μL of Pd(NO3)2 aqueous solution (Pd concentration is 50 mg / mL) and 70 μL of AgNO3 aqueous solution (Ag concentration is 100 mg / mL) were added to a flask (as shown in the figure), and after being fully mixed to form a fluidized suspension, a 300 W light source was turned on to an irradiation intensity of 100%. After irradiation for 1 hour, the flask was taken out, rinsed with distilled water several times, and dried at 60°C for 12 hours to obtain a Pd-Ag / g-C3N4 catalyst.

[0097] Example 7

[0098] The method of Example 1 is followed, except that the order of the Pd(NO3)2 aqueous solution in step (2) and the AgNO3 aqueous solution in step (3) is swapped; that is, the carrier is first contacted with the AgNO3 aqueous solution; and then contacted with the Pd(NO3)2 aqueous solution.

[0099] Example 8

[0100] (1) Prepare carrier #1 according to the method of Example 1.

[0101] (2) 10 g of carrier #1, 70 μL of Pd(NO3)2 aqueous solution (Pd concentration is 50 mg / mL) and 100 mL of deionized water were added to a flask, and carrier #1 was immersed at room temperature for 1 h. The solid was separated by filtration, dried at 120°C for 12 h, and then calcined at 450°C for 5 h to obtain oxidized PdO x / g-C3N4.

[0102] (3) Add the oxidized PdO obtained in step (2) into the flask. x / g-C3N4, 70μL of AgNO3 aqueous solution (Ag concentration is 100mg / mL) and 100mL of deionized water to make the oxidized PdO x / g-C3N4 was impregnated at room temperature for 1 h, and the solid was separated by filtration. The solid was dried at 120 °C for 12 h and then calcined at 450 °C for 5 h to obtain oxidized PdAgO x / g-C3N4.

[0103] Oxidized PdAgO x / g-C3N4 was reduced at 150°C for 2h under hydrogen atmosphere to obtain a reduced Pd-Ag / g-C3N4 catalyst. Relative to 100g of the carrier, the content of Pd was 0.035g, and the content of Ag was 0.07g.

[0104] The TEM image of the Pd-Ag / g-C3N4 catalyst after hydrogen reduction in Example 8 is as follows: Figure 5 As shown by Figure 5It can be seen that the dispersion effect of the active component Pd-Ag on the carrier surface is poor, and the particle size of the active component Pd-Ag is large.

[0105] Comparative Example 1

[0106] It was carried out according to the method of Example 8, except that carrier #1 was replaced with an equal weight of Al2O3 to obtain Pd-Ag / Al2O3.

[0107] The TEM image of the Pd-Ag / Al2O3 catalyst after hydrogen reduction in Comparative Example 1 is as Figure 6 shown, and from Figure 6 it can be seen that the dispersion effect of the active component Pd-Ag on the carrier surface is poor, and the particle size of the active component Pd-Ag is large.

[0108] Test Example 1

[0109] The catalysts prepared in the above examples and comparative examples were characterized, and the characterization results are shown in Table 1.

[0110] The specific surface areas of the carrier and the catalyst were obtained by BET test.

[0111] The particle size of the active component (Pd-Ag) in the catalyst was obtained by transmission electron microscopy (TEM) test.

[0112] The chemical valence state of Pd on the catalyst surface was determined by X-ray photoelectron spectroscopy (XPS), and the Pd 3d orbital was tested. "The XPS test was carried out using a photoelectron spectrometer from Thermo Scientific, USA, and the X-ray excitation source was AI Ka (photon energy of 1486.6 eV). After the scanned XPS spectrum was calibrated with the standard carbon spectrum position (284.5 eV), the final spectrum was obtained by fitting and peak splitting with CasaXPS software.

[0113] Table 1

[0114]

[0115] It can be seen from Table 1 that, compared with Comparative Example 1, under the condition of the same active component loading amount, the particle size of the active component in the catalyst prepared by the photo-deposition method of the present invention is smaller and the specific surface area is larger, which can provide more active sites for the reaction.

[0116] Test Example 2

[0117] The catalysts prepared in the examples and the hydrogen-reduced catalysts prepared in the comparative examples were used for the selective hydrogenation of C2 to remove acetylene. The reaction conditions were as follows: 5 mL of the catalyst was loaded into a tubular reactor, and after being sealed with ceramic balls filled above and below, it was fixed in a tubular heating furnace. After purging with nitrogen at room temperature, the feed gas (0.6% hydrogen, 6.0% ethane, 0.4% acetylene, 44% ethylene, 49% nitrogen) was introduced, and the gas hourly space velocity was 4000 h -1 , the reaction pressure was 1.0 MPa, the reaction temperatures were 60 °C, 70 °C, and 80 °C. The composition at the reactor outlet was measured using gas chromatography, and the acetylene (C2H2) conversion rate (Formula 1) and ethylene (C2H4) selectivity (Formula 2) of the above catalysts at different temperatures were calculated, and the performance of the above catalysts for the selective hydrogenation of C2 to remove acetylene could be evaluated. The results are shown in Table 2.

[0118] C2H2 conversion rate (C%) = (C2H2) 进 -(C2H2) 出 / (C2H2) 进 ×100% (Formula 1)

[0119] C2H4 selectivity (S%) = (C2H4) 出 -(C2H4) 进 / (C2H2) 进 -(C2H2) 出 ×100% (Formula 2)

[0120] Among them, (C2H2) in the above formulas 进 , (C2H2) 出 , (C2H4) 出 , and (C2H4) all have the unit of mol.

[0121] Table 2

[0122]

[0123] As can be seen from Table 2, compared with the comparative example, the catalyst of the present invention has higher ethylene selectivity at lower temperatures (60 - 70 °C); preferably, the catalysts of Examples 1 - 3 of the present invention have higher ethylene selectivity at low temperatures; more preferably, Examples 1 - 2 of the present invention simultaneously have higher acetylene conversion rate and higher ethylene selectivity.

[0124] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A Pd-Ag / g-C3N4 catalyst, characterized in that, The catalyst comprises a support and an active component supported on the support, the support being g-C3N4, and the active component comprising Pd and Ag; the particle size of the active component is 2-15 nm, preferably 2-5 nm.

2. The catalyst according to claim 1, wherein, The Pd comprises Pd(0) and Pd(+2), where Pd(0) represents that the chemical state of Pd is 0 valence, and Pd(+2) represents that the chemical state of Pd is +2 valence; preferably, the molar ratio of Pd(0) to Pd(+2) is 0.3-2:1, more preferably 1-1.6:1; and / or, relative to 100 g of the support, the content of Pd is 0.001-0.1 g, preferably 0.01-0.1 g, and the content of Ag is 0.001-0.1 g, preferably 0.01-0.1 g.

3. The catalyst according to claim 1, wherein The specific surface area of the catalyst is 10-120 m 2 / g, preferably 30-80 m 2 / g.

4. A method for preparing a Pd-Ag / g-C3N4 catalyst, characterized in that, The method comprises: loading an active component on a support, where the support is g-C3N4 and the active component comprises Pd and Ag.

5. The method according to claim 4, wherein, The loading method is: contacting an active component precursor with the support under light conditions and in the presence of a sacrificial agent, where the active component precursor comprises a palladium precursor and a silver precursor; alternatively, the loading method is: impregnating the support with an active component precursor by an impregnation method and then performing calcination, where the active component precursor comprises a palladium precursor and a silver precursor.

6. The method according to claim 5, wherein, The amount of the active component precursor used is such that in the resulting catalyst, relative to 100 g of the support, the content of Pd is 0.001-0.1 g, preferably 0.01-0.1 g, and the content of Ag is 0.001-0.1 g, preferably 0.01-0.1 g; and / or, the palladium precursor is at least one of palladium nitrate, palladium chloride, and palladium acetate; and / or, the silver precursor is silver nitrate and / or silver chloride; and / or, the specific surface area of the g-C3N4 is 10-120 m 2 / g, preferably 30-60 m 2 / g.

7. The method according to claim 5, wherein The light conditions include: the power of the light source is 100-400 W, the wavelength of the light source is 300-400 nm, preferably 350-380 nm, and the light irradiation time is 0.5-6 h.

8. The method according to claim 5, wherein The sacrificial agent is an alcohol having 1-5 carbon atoms, preferably a monohydric alcohol having 1-5 carbon atoms, more preferably methanol; and / or, relative to 100 g of the support, the total amount of the sacrificial agent used is 50-300 mL.

9. The method according to claim 5, wherein, The contacting method includes: first contacting the palladium precursor with the support to obtain Pd / g-C3N4, and then contacting Pd / g-C3N4 with the silver precursor to obtain a Pd-Ag / g-C3N4 catalyst.

10. A catalyst prepared by the method according to any one of claims 5-9.

11. Use of the catalyst according to any one of claims 1-3 and 10 and / or the catalyst prepared by the method according to any one of claims 4-8 in alkyne hydrogenation, preferably in acetylene selective hydrogenation.

12. A method for hydrogenating alkynes in a raw material gas, characterized in that, The method comprises: carrying out a hydrogenation reaction on the alkyne in the feed gas in the presence of the catalyst according to any one of claims 1-3 and 10 and / or the catalyst prepared by the method according to any one of claims 4-9; Preferably, the alkyne is acetylene; Preferably, the conditions for the hydrogenation reaction include: a temperature of 35 - 100 °C, preferably 60 - 90 °C, more preferably 70 - 80 °C.

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