Photocatalyst for catalyzing high-efficiency conversion of carboxylic acid to long-chain alkane, preparation method and application thereof

Abstract

The application belongs to the field of catalysts, and relates to a photocatalyst for catalyzing high-efficiency conversion of carboxylic acid into long-chain alkane as well as a preparation method and application thereof. The photocatalyst takes titanium dioxide as a carrier, takes Ag with a particle size of 0.3-1 nm as an active component, and the proportion of the active component in the photocatalyst is 0.1wt%-1wt%, the amount is less, and the cost is lower. When the photocatalyst is used for catalyzing conversion of carboxylic acid into alkane, the conversion rates of various carboxylic acids can all reach more than 97%, and C5-C20 alkane has high yield and selectivity.

Description

Technical Field

[0001] This invention belongs to the field of catalysts, and relates to photocatalysts for the efficient conversion of carboxylic acids into long-chain alkanes, their preparation methods, and applications. Background Technology

[0002] Biodiesel refers to a renewable diesel fuel produced from oilseed crops such as soybeans, rapeseed, cotton, and palm oil, wild oil plants, aquatic plants such as engineered microalgae, animal fats, and waste cooking oil through transesterification or thermochemical processes. It can replace petrochemical diesel, and its main component is C5-C20 alkanes. C5-C20 alkanes can not only be used as the main component of biodiesel and jet fuel, but also as feedstock for the production of olefins and aromatics. To achieve sustainable development, existing technologies utilize fatty acids to replace non-renewable fossil resources in the production of C5-C20 alkanes.

[0003] Currently, the main methods for producing C5-C20 alkanes from fatty acids include transesterification, thermochemical conversion, hydrogenation, and photocatalysis. Among these, photocatalysis is favored by scientists due to its mild reaction conditions and low energy consumption. Photocatalytic production of C5-C20 alkanes from fatty acids widely utilizes noble metal catalysts. These catalysts possess excellent catalytic activity and low-temperature, atmospheric-pressure activity. The noble metals used mainly include Pt, Pd, and Au, but their content is generally high, and the yield of long-chain alkanes is low. For example, in Chinese patent literature with publication number CN111233603 A and publication date June 5, 2020, titanium dioxide is used as a support, and noble metals Pt, Pd, Au, Ag, and Ru are used as active components. When 1 wt% Ag is used as the active component, the yield of long-chain alkanes is only 68%. Furthermore, free radicals in the photocatalytic conversion of carboxylic acids to alkanes tend to form chain-extended products through C-C radical coupling, and the selectivity for C5-C20 alkanes is typically below 50%. Summary of the Invention

[0004] This invention provides a photocatalyst for the efficient conversion of carboxylic acids to long-chain alkanes, its preparation method, and its application. The aim is to reduce the cost of existing photocatalysts for the conversion of C5-C20 carboxylic acids to C5-C20 alkanes and to improve the selectivity of C5-C20 alkanes.

[0005] To achieve the above-mentioned objectives, this invention uses titanium dioxide as a carrier and Ag as an active component to prepare a photocatalyst for catalyzing the decarboxylation of carboxylic acids to produce alkanes. This photocatalyst can greatly improve the yield and selectivity of alkanes, and is particularly suitable for the production of long-chain alkanes, namely C5 to C20 alkanes.

[0006] The first aspect of this invention provides a photocatalyst for catalyzing the conversion of carboxylic acids to alkanes, comprising:

[0007] The carrier is titanium dioxide;

[0008] The active component, namely Ag, is uniformly dispersed in the carrier and has a particle size of 0.3–1 nm.

[0009] The average particle size of the photocatalyst is 1 μm;

[0010] The proportion of the active component in the photocatalyst is X, where 0.1wt% ≤ X ≤ 1wt%.

[0011] In any embodiment of the present invention, the photocatalyst is used to catalyze the conversion of C5-C20 carboxylic acids into C5-C20 alkanes; more specifically, the photocatalyst is used to catalyze the conversion of C5-C20 saturated fatty acids into C5-C20 alkanes.

[0012] In any embodiment of the present invention, the proportion of the active component in the photocatalyst is X, where 0.25 wt% ≤ X ≤ 1.0 wt%. Further, 0.25 wt% ≤ X ≤ 0.50 wt%. Even further, X is 0.25 wt%.

[0013] A second aspect of the present invention provides a method for preparing the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acids to alkanes, comprising the following steps:

[0014] Add a titanium source dropwise to acetic acid, then add a soluble precursor of Ag, and stir at room temperature until the solution turns white to obtain a precursor solution;

[0015] The precursor fluid was kept at 120–150°C for 10–30 hours, cooled naturally, centrifuged, and the white precipitate was collected, washed, dried and pulverized.

[0016] The pulverized material was fully calcined in an oxygen-containing atmosphere at 400–650°C. After the calcined product was cooled to room temperature, it was fully reduced in a hydrogen-containing atmosphere at 350–500°C to obtain the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acids to alkanes.

[0017] In some embodiments of the present invention, the titanium source is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, and tetramethyl titanate.

[0018] A third aspect of the present invention provides another method for preparing the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acids to alkanes, comprising the following steps:

[0019] TiO2 nanoparticles were dispersed in deionized water to obtain a TiO2 suspension;

[0020] Add a soluble precursor of Ag to the TiO2 suspension, mix thoroughly, dry, and pulverize.

[0021] The pulverized material was fully calcined in an oxygen-containing atmosphere at 400–650°C. After the calcined product was cooled to room temperature, it was fully reduced in a hydrogen-containing atmosphere at 350–500°C to obtain the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acids to alkanes.

[0022] In some embodiments of the present invention, the soluble precursor of Ag is silver nitrate or silver ammonia solution.

[0023] In some embodiments of the present invention, the oxygen-containing atmosphere is air; the hydrogen-containing atmosphere is hydrogen.

[0024] The fourth aspect of the present invention provides the application of the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acids into alkanes in the production of alkanes, preferably, the alkanes are C5 to C20 alkanes, and preferably, the production of alkanes is a step in the production of biodiesel.

[0025] The fifth aspect of this invention provides a method for photocatalytic production of alkanes from carboxylic acids, comprising the following steps:

[0026] Carboxylic acid, the aforementioned photocatalyst used to catalyze the conversion of carboxylic acid to alkanes, and an organic solvent are placed in a photoreactor;

[0027] The reaction was carried out under stirring at room temperature, in an oxygen-free atmosphere, and under ultraviolet light to obtain alkanes.

[0028] In this invention, the carboxylic acid is a fatty acid; preferably, the carboxylic acid is a saturated fatty acid; more preferably, the carboxylic acid is a C5-C20 saturated fatty acid used to prepare C5-C20 alkanes; in some embodiments of this invention, the carboxylic acid is one or more of stearic acid, palmitic acid, arachidic acid, myristic acid, and lauric acid.

[0029] In some embodiments of the present invention, the oxygen-free atmosphere is one of hydrogen, nitrogen, an inert gas, hydrogen-containing nitrogen, or hydrogen-containing inert gas; and / or, the pressure is 0.1–4 MPa. Preferably, it is a hydrogen atmosphere, and the pressure is preferably 0.2–4 MPa.

[0030] In some embodiments of the present invention, the photoreactor is purged with hydrogen gas before ultraviolet light irradiation and the hydrogen gas pressure inside the photoreactor is controlled to be 0.1 to 4 MPa.

[0031] In some embodiments of the present invention, the organic solvent is a C8-C16 alkane or acetonitrile; and / or, the ultraviolet light is an LED light source with a power of 10-40W.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] 1. The noble metal supported on the photocatalyst of the present invention for catalyzing the conversion of carboxylic acids to alkanes is Ag, and the Ag content is very low, which reduces the cost compared with existing photocatalysts for catalyzing the conversion of carboxylic acids to alkanes.

[0034] 2. The photocatalyst of this invention for catalyzing the conversion of carboxylic acids into alkanes can increase the conversion rate of five common fatty acids to over 97% under normal temperature and pressure reaction conditions, with the yield of the corresponding target alkanes all greater than 78% and high selectivity for the target alkanes. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 Scanning electron microscope images of Ag / TiO2 catalysts; where (a) Ag / TiO2-1; (b) Ag / TiO2-2; (c) Ag / TiO2-3; (d) Ag / TiO2-4.

[0037] Figure 2 EDS elemental distribution and analysis diagram of Ag / TiO2-3, from left to right: Ag, Ti, O elements.

[0038] Figure 3 XRD pattern of Ag / TiO2 catalyst.

[0039] Figure 4 Example 1 shows the stearic acid conversion activity of the catalyst prepared in Example 1, where (a) stearic acid conversion and heptadecane selectivity; and (b) stearic acid conversion and heptadecane selectivity at different reaction times and in different atmospheres.

[0040] Figure 5 : Fatty acid conversion activity diagram of Ag / TiO2-3.

[0041] Figure 6 Example 2: Stearic acid conversion activity diagram of the catalyst prepared in Example 2.

[0042] Figure 7 Example 3 shows the stearic acid conversion activity of the catalyst prepared in Example 3.

[0043] Figure 8 Stearic acid conversion activity diagram of catalysts loaded with different active components.

[0044] Figure 9(a) Photocurrent (It) of Ag / TiO2; (b) Impedance (EIS) diagram of Ag / TiO2. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0046] For simplicity, this document only explicitly discloses certain numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range. Similarly, any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit, combined with any other point or individual value, or combined with other lower or upper limits to form an unspecified range.

[0047] It should be noted that, in the description herein, unless otherwise stated, "above" and "below" include the number itself, and "multiple" in "one or more" means two or more. Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0048] In the description of this specification, the references to terms such as "any embodiment / mode," "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0049] In the description of this invention, the term "conversion rate" refers to the percentage of a reactant that is converted during the reaction relative to the initial amount of that reactant. For example:

[0050]

[0051] In the description of this invention, the term "yield" refers to the ratio of the amount of reactant converted into the desired product to the initial amount of that reactant, for example:

[0052]

[0053] In the description of this invention, the term "selectivity" refers to the ratio of the amount of reactant in the system converted into the desired product to the total amount of that reactant converted in all reactions, for example:

[0054]

[0055] Heptadecane yield = stearic acid conversion × heptadecane selectivity.

[0056] The above description of the invention is not intended to describe every disclosed embodiment or implementation of the invention. Exemplary embodiments are described in more detail below. These embodiments can be used in various combinations. In each example, the listing is merely representative and should not be construed as exhaustive.

[0057] As described in the background section, the precious metal catalysts widely used in the photocatalytic production of biodiesel from fatty acids in the prior art generally have high precious metal content and low yields of long-chain alkanes. Chinese patent document CN116217333A, published on June 6, 2023, discloses a method for obtaining olefins from various carboxylic acids under light irradiation. This method uses a catalyst supported by a mixture of rutile and anatase phase titanium dioxide in a weight ratio of 3:1, with Au, Rh, or Pd as the supported active components, and the content of the active components is relatively high. This catalyst can prepare olefins from carboxylic acids, but it does not disclose its ability to prepare alkanes from carboxylic acids.

[0058] Chinese patent document CN111233603 A, published on June 5, 2020, discloses a method for preparing alkanes by hydrogenation photocatalytic decarboxylation of fatty acids. This method involves mixing fatty acids, a catalyst, and a solvent, placing the mixture in a quartz reactor, replacing the atmosphere in the reactor with hydrogen, sealing it, and stirring to induce a hydrogenation reaction without light. Then, an external light source is applied to induce a decarboxylation reaction to generate alkanes. The catalysts used in this method often employ noble metals as the active component; however, when 1 wt% Ag is used as the active component, the yield of long-chain alkanes is only 68%.

[0059] The inventors discovered that a photocatalyst using titanium dioxide as a support, Ag with a particle size of 0.3–1 nm as the active component, and a loading of 0.1 wt%–1 wt% exhibits high selectivity for C5–C20 alkanes and a yield greater than 70% when photocatalyzing the conversion of carboxylic acids to alkanes. In particular, when the Ag content is 0.25 wt%–1.0 wt%, the selectivity for C5–C20 alkanes reaches over 95%, and the yield exceeds 85%. Especially when the Ag content is 0.25 wt%, both the selectivity and yield of C5–C20 alkanes reach their highest levels, significantly reducing costs compared to existing catalysts.

[0060] Current technology suggests that the principle of photocatalytic conversion of carboxylic acids to alkanes is as follows:

[0061] R-CH2CH2COOH→R-CH2CH2COO - +H + (1)

[0062]

[0063] H + +e - →H · (3)

[0064] H · +H · →H2 (4)

[0065]

[0066]

[0067]

[0068]

[0069] In this process, free radicals tend to couple through C-C radicals to form chain-extended products with more than 20 C atoms, and the selectivity for C5-C20 alkanes is usually less than 50%.

[0070] The photocatalyst of this invention uses titanium dioxide as a support and Ag as the active component. Titanium dioxide generates photocurrent under ultraviolet light irradiation, exhibiting excellent photogenerated charge transfer and separation efficiency, which is beneficial for reducing H+ to H· and promoting the coupling of alkyl radicals and H· to form alkanes. This photocatalyst inhibits free radical oligomerization. It can convert carboxylic acids to alkanes in both hydrogen and nitrogen atmospheres, especially at room temperature and pressure in a hydrogen atmosphere, where the selectivity for C5-C20 alkanes reaches as high as 97%. Furthermore, this photocatalyst only requires ≤1 wt% of the active component Ag, resulting in very low cost.

[0071] Photocatalyst

[0072] The photocatalyst provided by this invention for catalyzing the conversion of carboxylic acids to alkanes comprises:

[0073] The carrier is titanium dioxide;

[0074] The active component, namely Ag, is uniformly dispersed in the carrier and has a particle size of 0.3–1 nm.

[0075] The average particle size of the photocatalyst is 1 μm;

[0076] The proportion of the active component in the photocatalyst is X, where 0.1wt% ≤ X ≤ 1wt%.

[0077] The photocatalyst has an average particle size of 1 μm and is loaded with Ag with a particle size of 0.3–1 nm. When the loading is 0.1 wt%–1 wt%, the yield of carboxylic acid to alkanes by hydrogenation deoxygenation can reach more than 70%, and the conversion rate of alkanes can reach more than 95%, which reduces the cost compared with existing catalysts.

[0078] In some embodiments of the present invention, the photocatalyst is urchin-shaped, which further increases the specific surface area, thereby improving its catalytic activity and increasing the conversion rate of alkanes.

[0079] In this invention, the proportion of the active component Ag in the photocatalyst is X, where 0.25 wt% ≤ X ≤ 1.0 wt%. Within this range, the alkane yield can be controlled to be greater than 80%, ensuring a high C5-C20 alkane yield (>78%) and a carboxylic acid conversion rate at room temperature and pressure (>97%). Further, with 0.25 wt% ≤ X ≤ 0.50 wt%, the cost of the photocatalyst is further reduced without affecting the yield and selectivity of C5-C20 alkanes. Even further, with X at 0.25 wt%, the cost of the catalyst is further reduced, while the yield and selectivity of C5-C20 alkanes reach their maximum. Optionally, the proportion of Ag in the photocatalyst includes, but is not limited to, 0.10 wt%, 0.20 wt%, 0.25 wt%, 0.30 wt%, 0.40 wt%, 0.50 wt%, 0.60 wt%, 0.70 wt%, 0.80 wt%, 0.90 wt%, and 1.0 wt%.

[0080] In some embodiments of the present invention, the titanium dioxide is anatase titanium dioxide or rutile titanium dioxide.

[0081] Preparation method

[0082] This invention provides a method for preparing the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acids to alkanes, comprising the following steps:

[0083] Add a titanium source dropwise to acetic acid, then add a soluble precursor of Ag, and stir at room temperature until the solution turns white to obtain a precursor solution;

[0084] The precursor fluid was kept at 120–150°C for 10–30 hours, cooled naturally, centrifuged, and the white precipitate was collected, washed, dried and pulverized.

[0085] The pulverized material was fully calcined in an oxygen-containing atmosphere at 400–650°C. After the calcined product was cooled to room temperature, it was fully reduced in a hydrogen-containing atmosphere at 350–500°C to obtain the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acids to alkanes.

[0086] This method loads the active component onto the support simultaneously with the formation of anatase phase titanium dioxide. This allows for more uniform dispersion of the active component on the support and high utilization of the soluble precursor of the active component. The pulverized material is fully calcined in an aerobic atmosphere at 400–650°C, obtaining oxides of the active component along with the anatase phase titanium dioxide. After cooling to room temperature, the calcined product is subjected to full reduction in a hydrogen-containing atmosphere at 350–500°C, which reduces the oxide of the active component to the zero-valent metal of the active component. This method starts from readily available raw materials, avoids intermediate separation, and involves continuous multi-step reactions, reducing synthesis time and cost. The steps are simple and easy to operate.

[0087] In some embodiments of the present invention, the titanium source is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, and tetramethyl titanate. These titanium sources can form a white precipitate, i.e., an amorphous titanium dioxide sol, in the presence of acetic acid. During this process, the titanium dioxide sol can maximize the adsorption and encapsulation of the soluble precursors of the active component, thereby fully utilizing the soluble precursors of the active component.

[0088] This invention provides another method for preparing the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acids to alkanes, comprising the following steps:

[0089] TiO2 nanoparticles were dispersed in deionized water to obtain a TiO2 suspension;

[0090] Add a soluble precursor of Ag to the TiO2 suspension, mix thoroughly, dry, and pulverize.

[0091] The pulverized material was fully calcined in an oxygen-containing atmosphere at 400–650°C. After the calcined product was cooled to room temperature, it was fully reduced in a hydrogen-containing atmosphere at 350–500°C to obtain the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acids to alkanes.

[0092] This method utilizes self-made or commercially available TiO2 nanoparticles to prepare photocatalysts. It only requires dissolving a soluble precursor of Ag in water and impregnating it onto TiO2 nanoparticles, then drying and sequentially calcining and reducing to obtain the photocatalyst. The method is simple and easy to operate.

[0093] The soluble precursor of Ag used in the above two methods is silver nitrate or silver ammonia solution.

[0094] The calcination and reduction in the two methods described above can employ the same means. In some embodiments, for simplicity, air is chosen as the oxygen-containing atmosphere and hydrogen as the hydrogen-containing atmosphere, but this should not be considered a limitation on the oxygen-containing and hydrogen-containing atmospheres of this invention. Those skilled in the art may also choose an inert gas mixed with oxygen or nitrogen mixed with oxygen as the oxygen-containing atmosphere, and an inert gas mixed with hydrogen or nitrogen mixed with hydrogen as the hydrogen-containing atmosphere.

[0095] In both methods above, the purpose of pulverization is to ensure more complete calcination and reduction of the photocatalyst, without limiting the particle size of the pulverized material. The pulverized material shows no significant changes before and after calcination or reduction.

[0096] application

[0097] This invention applies the aforementioned photocatalyst used for catalyzing the conversion of carboxylic acids to alkanes to catalyze the conversion of carboxylic acids to alkanes, particularly for catalyzing the hydrodeoxygenation of C5-C20 saturated fatty acids to produce C5-C20 alkanes. This application can be a step in the production of biodiesel. For example, when producing biodiesel using a mixture of C5-C20 saturated fatty acids and oils, the C5-C20 saturated fatty acids are first catalyzed to produce C5-C20 alkanes through hydrodeoxygenation, and then the oils are catalyzed to form long-chain alkanes; or the oils are first catalyzed to form long-chain alkanes, and then the C5-C20 saturated fatty acids are catalyzed to produce C5-C20 alkanes through hydrodeoxygenation.

[0098] Photocatalytic method for producing alkanes from carboxylic acids

[0099] The present invention uses the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acid to alkanes to catalyze the conversion of carboxylic acid to alkanes. The provided method for photocatalytic production of alkanes from carboxylic acid includes: placing carboxylic acid, the above-mentioned photocatalyst for catalyzing the conversion of carboxylic acid to alkanes, and an organic solvent in a photoreactor; stirring and reacting under ambient temperature, an oxygen-free atmosphere, and ultraviolet light irradiation to obtain alkanes.

[0100] This photocatalytic method for producing alkanes from carboxylic acids can rapidly produce alkanes at room temperature with high yield and selectivity.

[0101] In this invention, the carboxylic acid is a fatty acid; preferably, the carboxylic acid is a saturated fatty acid; more preferably, the carboxylic acid is a C5-C20 saturated fatty acid. This method is used to prepare C5-C20 alkanes with high yield and selectivity. In some embodiments of this invention, the carboxylic acid is one or more of stearic acid, palmitic acid, arachidic acid, myristic acid, and lauric acid. These carboxylic acids, in the presence of the above photocatalyst, can be converted to C5-C20 alkanes with extremely high selectivity and high yield.

[0102] In some embodiments of the present invention, the oxygen-free atmosphere is one of hydrogen, nitrogen, an inert gas, hydrogen-containing nitrogen, or hydrogen-containing inert gas; and / or, the pressure is 0.1–4 MPa. Preferably, a hydrogen atmosphere is used, and the pressure is preferably 0.2–4 MPa. Preferably, the photoreactor is purged with hydrogen before ultraviolet irradiation, and the hydrogen pressure inside the photoreactor is controlled to be 0.1–4 MPa. Hydrogen pressure can be between 0.1 and 4 MPa; the reaction can be carried out at atmospheric pressure (0.1 MPa) or high pressure (0.2–4 MPa). A high carboxylic acid conversion rate (>97%) can be ensured at room temperature and pressure, and the conversion rate will be even higher at high pressure.

[0103] In some embodiments of the present invention, the organic solvent used in the above-described photocatalytic method for producing alkanes from carboxylic acids is a C8-C16 alkane or acetonitrile. The ultraviolet light is provided by an LED light source with a power of 10-40W; preferably, the ultraviolet light is provided by an LED light source with a center wavelength of 365nm and a power of 40W.

[0104] Example

[0105] The following are embodiments of the present invention. These embodiments are exemplary and only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. The anatase phase titanium dioxide used in this invention can be commercially available anatase phase titanium dioxide, or it can be prepared by the following method: Preparation method of anatase phase titanium dioxide: Add 30 mL of acetic acid to a 50 mL polytetrafluoroethylene container, add 100 μL of deionized water; then add 1 mL of tetrabutyl titanate, stir at room temperature for about 2 hours until the solution turns white, transfer the polytetrafluoroethylene container to a stainless steel autoclave, maintain at 140°C for 24 hours, and then allow it to cool naturally in air. Centrifuge, collect the white precipitate, wash thoroughly with ethanol and water, and then dry at 60°C for 3 hours. The dried product was then placed in a muffle furnace and calcined completely at 650°C for 3 hours. The resulting calcined product was anatase titanium dioxide.

[0106] Example 1: One-pot preparation of Ag / TiO2 catalyst

[0107] 30 mL of acetic acid was added to a 50 mL polytetrafluoroethylene (PTFE) container, followed by the addition of 1 mL of tetrabutyl titanate and AgNO3. The mixture was stirred at room temperature for approximately 2 hours until the solution turned white. The PTFE container was then transferred to a stainless steel autoclave and kept at 140 °C for 24 hours, followed by natural cooling in air. The white precipitate was collected by centrifugation, thoroughly washed with ethanol and water, and then dried at 60 °C for 3 hours. The dried product was then calcined completely at 650 °C for 3 hours in a muffle furnace. After cooling to room temperature, the sample was placed in a hydrogen atmosphere and heated to 500 °C at a heating rate of 1 °C / min. Reduction was then carried out at 500 °C in a hydrogen atmosphere for 5 hours to obtain the Ag / TiO2 catalyst.

[0108] Depending on the amount of AgNO3 added, Ag / TiO2 catalysts with Ag mass fractions of 0 wt%, 0.05 wt%, 0.10 wt%, 0.25 wt%, 0.50 wt%, 1.0 wt%, and 2 wt% were obtained and named TiO2, Ag / TiO2-1, Ag / TiO2-2, Ag / TiO2-3, Ag / TiO2-4, Ag / TiO2-5, and Ag / TiO2-6, respectively.

[0109] Example 2: Preparation of Ag / TiO2-A catalyst by impregnation-calcination method

[0110] 1. Commercially available anatase phase titanium dioxide nanoparticles were dispersed in deionized water to obtain a TiO2 suspension; each TiO2 suspension consisted of 30 mL of deionized water and 1 g of support. Different masses of AgNO3 powder were added to each TiO2 suspension according to the mass fraction of Ag in the Ag / TiO2 catalyst: 0 wt%, 0.05 wt%, 0.10 wt%, 0.25 wt%, 0.50 wt%, 1.0 wt%, and 2 wt%, and mixed thoroughly to obtain a slurry.

[0111] 2. The above slurry was stirred overnight in the dark at ambient temperature, and then dried at 100.5°C for 12 hours. The obtained solid was crushed in a quartz boat to obtain Ag / TiO2 powder.

[0112] 3. The Ag / TiO2 powder was first calcined in a muffle furnace at 400℃ for 4 hours, then cooled to room temperature at a cooling rate of 10℃ / min. It was then placed in a hydrogen atmosphere and heated to 500℃ at a heating rate of 1℃ / min, and maintained at 500℃ for reduction for 5 hours to obtain the Ag / TiO2 catalyst. Ag / TiO2 catalysts with Ag mass fractions of 0wt%, 0.05wt%, 0.10wt%, 0.25wt%, 0.50wt%, 1.0wt%, and 2wt% were named TiO2-A, Ag / TiO2-A1, Ag / TiO2-A2, Ag / TiO2-A3, Ag / TiO2-A4, Ag / TiO2-A5, and Ag / TiO2-A6, respectively.

[0113] Example 3: Preparation of Ag / TiO2-R catalyst by impregnation-calcination method

[0114] 1. Commercially available rutile titanium dioxide nanoparticles were dispersed in deionized water to obtain a TiO2 suspension; each TiO2 suspension consisted of 30 mL of deionized water and 1 g of support. Different masses of AgNO3 powder were added to each TiO2 suspension according to the mass fraction of Ag in the Ag / TiO2 catalyst: 0 wt%, 0.05 wt%, 0.10 wt%, 0.25 wt%, 0.50 wt%, 1.0 wt%, and 2 wt%, and the mixture was stirred evenly to obtain a slurry.

[0115] 2. The above slurry was stirred overnight in the dark at ambient temperature, and then dried at 100.5°C for 12 hours. The obtained solid was crushed in a quartz boat to obtain Ag / TiO2 powder.

[0116] 3. The Ag / TiO2 powder was first calcined in a muffle furnace at 400℃ for 4 hours, then cooled to room temperature at a cooling rate of 10℃ / min. It was then placed in a hydrogen atmosphere and heated to 500℃ at a heating rate of 1℃ / min, and maintained at 500℃ for reduction for 5 hours to obtain the Ag / TiO2 catalyst. Ag / TiO2 catalysts with Ag mass fractions of 0wt%, 0.05wt%, 0.10wt%, 0.25wt%, 0.50wt%, 1.0wt%, and 2wt% were named TiO2-R, Ag / TiO2-R1, Ag / TiO2-R2, Ag / TiO2-R3, Ag / TiO2-R4, Ag / TiO2-R5, and Ag / TiO2-R6, respectively.

[0117] Example 4: Preparation of 0.25 wt% platinum-based titanium dioxide catalyst (0.25 wt% Pt / TiO2)

[0118] 1. Commercially available anatase phase titanium dioxide nanoparticles were dispersed in deionized water to obtain a TiO2 suspension; each TiO2 suspension consisted of 30 mL of deionized water and 1 g of support. H2PtCl6 powder was added to the TiO2 suspension at a mass fraction of 0.25 wt% of Pt in the Pt / TiO2 catalyst, and the mixture was stirred evenly to obtain a slurry.

[0119] 2. The above slurry was stirred overnight in the dark at ambient temperature, and then dried at 100.5°C for 12 hours. The obtained solid was crushed in a quartz boat to obtain Pt / TiO2 powder.

[0120] 3. The Pt / TiO2 powder was first placed in a muffle furnace and calcined at 400°C in air for 4 hours. Then it was cooled to room temperature at a cooling rate of 10°C / min. Next, it was placed in a hydrogen atmosphere and heated to 350°C at a heating rate of 1°C / min. The temperature was maintained at 350°C for 4 hours to obtain the Pt / TiO2 catalyst, named 0.25wt%Pt / TiO2.

[0121] Example 5: Preparation of 0.25 wt% gold-based titanium dioxide catalyst (0.25 wt% Au / TiO2)

[0122] 1. Commercially available anatase phase titanium dioxide nanoparticles were dispersed in deionized water to obtain a TiO2 suspension; each TiO2 suspension consisted of 30 mL of deionized water and 1 g of support. H2AuCl6 powder was added to the TiO2 suspension at a mass fraction of 0.25 wt% of Au in the Au / TiO2 catalyst, and the mixture was stirred evenly to obtain a slurry.

[0123] 2. The above slurry was stirred overnight in the dark at ambient temperature, and then dried at 100.5°C for 12 hours. The obtained solid was crushed in a quartz boat to obtain Au / TiO2 powder.

[0124] 3. The Au / TiO2 powder was first placed in a muffle furnace and calcined at 400°C in air for 4 hours. Then it was cooled to room temperature at a cooling rate of 10°C / min. Next, it was placed in a hydrogen atmosphere and heated to 350°C at a heating rate of 1°C / min. The temperature was maintained at 350°C for 4 hours to obtain the Au / TiO2 catalyst, named 0.25wt% Au / TiO2.

[0125] Example 6: Preparation of 0.25 wt% ruthenium-based titanium dioxide catalyst (0.25 wt% Ru / TiO2)

[0126] 1. Commercially available anatase phase titanium dioxide nanoparticles were dispersed in deionized water to obtain a TiO2 suspension; each TiO2 suspension consisted of 30 mL of deionized water and 1 g of support. RuCl3 powder was added to the TiO2 suspension at a mass fraction of 0.25 wt% for Ru in the Ru / TiO2 catalyst, and the mixture was stirred evenly to obtain a slurry.

[0127] 2. The above slurry was stirred overnight in the dark at ambient temperature, and then dried at 100.5°C for 12 hours. The obtained solid was crushed in a quartz boat to obtain Ru / TiO2 powder.

[0128] 3. The Ru / TiO2 powder was first placed in a muffle furnace and calcined at 400°C in air for 4 hours. Then it was cooled to room temperature at a cooling rate of 10°C / min. Next, it was placed in a hydrogen atmosphere and heated to 350°C at a heating rate of 1°C / min. The temperature was maintained at 350°C for 4 hours to obtain the Ru / TiO2 catalyst, which was named 0.25wt%Ru / TiO2.

[0129] test:

[0130] Morphology of Ag / TiO2 catalyst:

[0131] The Ag / TiO2 catalyst prepared in Example 1 was subjected to electron microscopy scanning. Figure 1 The scanning electron microscope image shown indicates that Ag / TiO2-3 appears urchin-like. Figure 1 c), the average particle size of Ag / TiO2-3 is about 1 μm, while that of Ag / TiO2-1 is... Figure 1 a) Ag / TiO2-2( Figure 1 b) and Ag / TiO2-4 ( Figure 1 The average particle size of d) is similar to that of Ag / TiO2-3.

[0132] Elemental analysis of Ag / TiO2 catalyst:

[0133] The Ag, Ti, and O elements in the Ag / TiO2-3 prepared in Example 1 were detected using energy-dispersive X-ray spectroscopy (EDS). Figure 2 The scanning electron microscope images shown indicate that the Ti and O elements in the Ag / TiO2-3 catalyst are uniformly distributed, and highly dispersed and uniformly loaded Ag can be seen on the Ag / TiO2-3 surface, with Ag particle size of 0.3-1 nm.

[0134] Crystallization analysis of Ag / TiO2 catalyst:

[0135] The crystallinity of the Ag / TiO2 catalyst prepared in Example 1 was determined using X-ray powder diffraction (XRD). Figure 3 The X-ray powder diffraction patterns shown indicate that the four catalysts, Ag / TiO2-1, Ag / TiO2-2, Ag / TiO2-3, and Ag / TiO2-4, are all anatase phases. Ag / TiO2-1 has the highest crystallinity. As the Ag content increases, some Ag enters the TiO2 lattice, leading to a gradual decrease in crystallinity. Figure 3 The absence of Ag diffraction peaks indicates that metallic Ag is highly dispersed in the anatase phase of titanium dioxide.

[0136] Stearic acid conversion activity test of Ag / TiO2 catalyst:

[0137] The stearic acid conversion activity of TiO2, Ag / TiO2-1, Ag / TiO2-2, Ag / TiO2-3, Ag / TiO2-4, Ag / TiO2-5, and Ag / TiO2-6 prepared in Example 1 was tested. The test conditions were as follows: 30 mg of stearic acid, 20 mg of a single photocatalyst, and 10 mL of acetonitrile were placed in a stainless steel photoreactor; the stainless steel photoreactor was purged five times with H2 or N2 and pressurized to a pressure of 0.1 MPa. When the temperature reached 28°C, the stainless steel photoreactor was irradiated with an LED light source (center wavelength 365 nm, power 40 W), the stirring rate was 1000 rpm, and the reaction time was 2 h.

[0138] like Figure 4 The stearic acid conversion activity demonstrated shows that when Ag / TiO2-3 and Ag / TiO2-4 are used as photocatalysts, the stearic acid conversion rate reaches over 95%, and the stearic acid conversion rate using Ag / TiO2-1 as the photocatalyst is significantly higher than that using TiO2 as the photocatalyst. Figure 4 As shown in (a), the Ag / TiO2 yield of the present invention with an Ag loading of 0.25wt% to 1wt% can reach over 80%, and the stearic acid conversion rate is over 95%, exhibiting extremely high catalytic activity. Figure 4 As shown in (b), compared with the N2 atmosphere, the yield of Ag / TiO2-3 catalyzing the conversion of stearic acid to heptadecane in the H2 atmosphere is greatly improved, indicating that the H2 atmosphere significantly affects the adsorption and decarboxylation of acid.

[0139] Activity of Ag / TiO2 catalyst for the conversion of different fatty acids:

[0140] The conversion activity of five fatty acids (stearic acid, palmitic acid, arachidic acid, myristic acid, and lauric acid) in the Ag / TiO2-3 prepared in Example 1 was tested. The test conditions were as follows: 30 mg of each fatty acid, 20 mg of photocatalyst, and 10 mL of acetonitrile were placed in a stainless steel photoreactor; the stainless steel photoreactor was purged five times with H2 and pressurized to a hydrogen pressure of 0.1 MPa. When the temperature reached 28°C, the stainless steel photoreactor was irradiated with an LED light source (center wavelength 365 nm, power 40 W), the stirring rate was 1000 rpm, and the reaction time was 2 h.

[0141] like Figure 5 As shown, the conversion rates of all five fatty acids reached over 97%, and the yields were all greater than 78%, indicating that Ag / TiO2-3 has excellent fatty acid catalytic activity and is suitable for various fatty acid decarboxylation reactions. The conversion rate of stearic acid catalyzed by Ag / TiO2-3 was 97.66%, with a yield of 84.12%; the conversion rate of palmitic acid catalyzed by Ag / TiO2-3 was 97.02%, with a yield of 83.24%; the conversion rate of arachidic acid catalyzed by Ag / TiO2-3 was 98.92%, with a yield of 78.27%; the conversion rate of myristic acid catalyzed by Ag / TiO2-3 was 98.79%, with a yield of 79.48%; and the conversion rate of lauric acid catalyzed by Ag / TiO2-3 was 98.94%, with a yield of 79.81%.

[0142] Stearic acid conversion activity of Ag / TiO2-A catalyst:

[0143] The stearic acid conversion activity of the photocatalysts TiO2-A, Ag / TiO2-A1, Ag / TiO2-A2, Ag / TiO2-A3, Ag / TiO2-A4, Ag / TiO2-A5, and Ag / TiO2-A6 prepared in Example 2 was tested. The test conditions were as follows: 30 mg of stearic acid, 20 mg of each photocatalyst, and 10 mL of acetonitrile were placed in a stainless steel photoreactor. The stainless steel photoreactor was purged five times with H2 and pressurized to a hydrogen pressure of 0.1 MPa. When the temperature reached 28°C, the stainless steel photoreactor was irradiated with an LED light source (center wavelength 365 nm, power 40 W), the stirring rate was 1000 rpm, and the reaction time was 2 h.

[0144] like Figure 6As shown, when Ag / TiO2-A3 and Ag / TiO2-A4 are used as photocatalysts, the conversion rate of stearic acid reaches over 95%. The stearic acid conversion rate of Ag / TiO2-A1 as a photocatalyst is much higher than that of TiO2-A. Ag / TiO2-A3 achieves high stearic acid conversion and heptadecane selectivity with a heptadecane selectivity of over 87% at a relatively low metal loading.

[0145] Stearic acid conversion activity of Ag / TiO2-R catalyst:

[0146] The stearic acid conversion activity of the photocatalysts TiO2-R, Ag / TiO2-R1, Ag / TiO2-R2, Ag / TiO2-R3, Ag / TiO2-R4, Ag / TiO2-R5, and Ag / TiO2-R6 prepared in Example 3 was tested. The test conditions were as follows: 30 mg of stearic acid, 20 mg of each photocatalyst, and 10 mL of acetonitrile were placed in a stainless steel photoreactor. The stainless steel photoreactor was purged five times with H2 and pressurized to a hydrogen pressure of 0.1 MPa. When the temperature reached 28°C, the stainless steel photoreactor was irradiated with an LED light source (center wavelength 365 nm, power 40 W), the stirring rate was 1000 rpm, and the reaction time was 2 h.

[0147] like Figure 7 As shown, when Ag / TiO2-R3 and Ag / TiO2-R4 are used as photocatalysts, the conversion rate of stearic acid reaches over 95%. The stearic acid conversion rate of Ag / TiO2-R1 as a photocatalyst is much higher than that of TiO2-R. Ag / TiO2-R3 achieves high stearic acid conversion and heptadecane selectivity with a heptadecane selectivity of over 87% at a relatively low metal loading.

[0148] Stearic acid conversion activity of catalysts supported on different metals:

[0149] The stearic acid conversion activity of Ag / TiO2-3 prepared in Example 1, Pt / TiO2 prepared in Example 4, and Au / TiO2 prepared in Example 5 was tested. The test conditions were as follows: 30 mg of stearic acid, 20 mg of a single photocatalyst, and 10 mL of acetonitrile were placed in a stainless steel photoreactor; the stainless steel photoreactor was purged five times with H2 and pressurized to a hydrogen pressure of 0.1 MPa. When the temperature reached 28°C, the stainless steel photoreactor was irradiated with an LED light source (center wavelength 365 nm, power 40 W), the stirring rate was 1000 rpm, and the reaction time was 2 h.

[0150] like Figure 8As shown, compared with catalysts loaded with other noble metals, Ag / TiO2-3 has the highest yield of heptadecane under the same reaction conditions. Among them, the yield of 0.25wt% Ru / TiO2 is 55.42%, the yield of heptadecane of 0.25wt% Pt / TiO2 is 72.21%, the yield of heptadecane of 0.25wt% Au / TiO2 is 71.04%, and the yield of heptadecane of 0.25wt% Ag / TiO2 is 84.12%, indicating that Au / TiO2 has excellent photocatalytic activity.

[0151] Photocurrent and impedance tests:

[0152] Ag / TiO2-1, Ag / TiO2-2, Ag / TiO2-3, and Ag / TiO2-4 (each 10 mg) prepared in Example 1 were respectively dispersed in ethanol (1 mL), and then Nafion solution (30 μL) was added, and ultrasonic treatment was carried out for 30 minutes to form a uniform suspension. 200 μL of the suspension was dropped on ITO (indium tin oxide) glass, and after drying at room temperature, photoelectric tests were carried out. An electrochemical workstation (CHI660E) and a three-electrode quartz cell system (counter electrode: Pt electrode; reference electrode: Ag / AgCl; working electrode: ITO) were used to test the photochemical properties.

[0153] Using 0.5M Na2SO4 solution as the electrolyte and xenon lamp as the light source, the I-t and EIS of Ag / TiO2-1, Ag / TiO2-2, Ag / TiO2-3, and Ag / TiO2-4 were measured to study the efficiency of photogenerated charge separation and transfer. Compared with other catalysts, Ag / TiO2-3 showed the strongest photocurrent intensity ( Figure 9 a), indicating that the transfer and separation efficiency of interfacial electrons is higher and the recombination at the catalyst interface is smaller. The EIS curve is as Figure 9 shown in b. The EIS trends of the 4 catalysts are as follows: Ag / TiO2-3 < Ag / TiO2-4 < Ag / TiO2-2 < Ag / TiO2-1, which is consistent with the trend of photocurrent. The above results show that Ag / TiO2-3 exhibits excellent photogenerated charge transfer and separation efficiency, which is beneficial to reducing H+ to H· and promoting the coupling of alkyl radicals and H· atoms to generate alkanes.

[0154] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A photocatalyst for catalyzing the conversion of carboxylic acids to alkanes, characterized in that, The photocatalyst is in the shape of sea urchin, comprising: a carrier, which is titanium dioxide; an active component, which is Ag, uniformly dispersed in the carrier, with a particle size of 0.3-1 nm; the average particle size of the photocatalyst is 1 μm; the proportion of the active component in the photocatalyst is X, 0.25 wt%≤X≤0.5 wt%; the preparation method of the photocatalyst for catalyzing the conversion of carboxylic acid into alkane, comprising the following steps: adding a titanium source into acetic acid, then adding a soluble precursor of the active component, stirring at room temperature until the solution becomes white, obtaining a precursor solution; keeping the precursor solution at 120-150 ℃ for 10-30 hours, centrifuging after natural cooling, collecting the white precipitate, drying after washing and crushing; fully calcining the crushed product in an oxygen-containing atmosphere at 400-650 ℃, fully reducing the calcined product at 350-500 ℃ in a hydrogen-containing atmosphere after cooling to room temperature, obtaining the photocatalyst for catalyzing the conversion of carboxylic acid into alkane.

2. A process for the preparation of a photocatalyst for catalyzing the conversion of carboxylic acids into alkanes according to claim 1, characterized in that, comprising the following steps: adding a titanium source into acetic acid, then adding a soluble precursor of the active component, stirring at room temperature until the solution becomes white, obtaining a precursor solution; keeping the precursor solution at 120-150 ℃ for 10-30 hours, centrifuging after natural cooling, collecting the white precipitate, drying after washing and crushing; fully calcining the crushed product in an oxygen-containing atmosphere at 400-650 ℃, fully reducing the calcined product at 350-500 ℃ in a hydrogen-containing atmosphere after cooling to room temperature, obtaining the photocatalyst for catalyzing the conversion of carboxylic acid into alkane of claim 1.

3. The preparation method of the photocatalyst for catalyzing the conversion of carboxylic acid into alkane according to claim 2, characterized in that: the soluble precursor of the active component is silver nitrate or silver ammine solution.

4. The application of the photocatalyst for catalyzing the conversion of carboxylic acid into alkane of claim 1 in the production of alkane.

5. A method for photocatalytic production of alkanes from carboxylic acids, characterized by, comprising the following steps: placing carboxylic acid, the photocatalyst for catalyzing the conversion of carboxylic acid into alkane of claim 1 and an organic solvent in a photo reactor; stirring and reacting under normal temperature, oxygen-free atmosphere and ultraviolet light irradiation, obtaining alkane.

6. The method of producing alkane by photocatalyzing carboxylic acid according to claim 5, characterized in that: the oxygen-free atmosphere is one of hydrogen, nitrogen, inert gas, hydrogen-containing nitrogen and hydrogen-containing inert gas; and / or, the gas pressure is 0.1-4 MPa.

7. The method of producing alkane by photocatalyzing carboxylic acid according to claim 5, characterized in that: the carboxylic acid comprises one or more of stearic acid, palmitic acid, arachidic acid and myristic acid.

8. The method of producing alkane by photocatalyzing carboxylic acid according to claim 5, characterized in that: The organic solvent is C8-C 16 alkane or acetonitrile; and / or, the ultraviolet light uses an LED light source with a power of 10-40 W.

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