A palladium-based bimetallic nanocatalyst, a preparation method and application thereof

Abstract

The application provides a palladium-based bimetallic nanocatalyst and a preparation method and application thereof, and relates to the technical field of carbon dioxide hydrogenation catalyst preparation. The catalyst is prepared by a two-step reduction method, and comprises a TiO2 carrier and bimetallic nanoparticles loaded on the TiO2 carrier, wherein the bimetallic nanoparticles are composed of Pd and M, and M is one of Cu, Zn and Fe. The catalyst prepared by the method has high carbon dioxide conversion rate and high selectivity of low-carbon mixed alcohol in the reaction of preparing low-carbon mixed alcohol by carbon dioxide hydrogenation.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide hydrogenation catalyst preparation technology, and in particular to a palladium-based bimetallic nanocatalyst, its preparation method, and its application. Background Technology

[0002] With rapid industrialization, the excessive use of fossil fuels has led to the severe impact of carbon dioxide (CO2) emissions on human survival and social development. On average, tens of billions of tons of CO2 are emitted into the atmosphere annually, causing a rapid increase in atmospheric CO2 levels and posing a significant threat to ecosystems, such as global warming, glacial melting, and ocean acidification. Therefore, reducing CO2 emissions and ensuring sustainable development is of paramount importance. From a long-term perspective, converting carbon dioxide into high-value-added chemical products through chemical conversion (hydrogenation) can achieve a sustainable artificial carbon cycle. This is widely recognized as an effective, profitable, and promising solution, while also reducing dependence on fossil fuels. Currently, chemical products generated from the hydrogenation of carbon dioxide include carbon monoxide, methane, methanol, ethanol, and olefins.

[0003] Among them, low-carbon alcohols (methanol, ethanol, and propanol) have received considerable attention due to their high calorific value and wide range of applications. For example, methanol has a volumetric energy density of 15.6 MJ / L, about half that of diesel (38.6 MJ / L) and gasoline (34.2 MJ / L), and can be used as an additive or substitute for gasoline in internal combustion engines (ICE) to increase the octane rating. Compared with conventional gasoline ICE engines, methanol ICE engines emit significantly lower levels of hydrocarbons, nitrogen oxides, sulfur oxides, and particulate matter, making them a high-quality diesel fuel alternative and a suitable domestic fuel. Ethanol is considered an excellent fuel additive, disinfectant, and solvent, and is one of the most valuable chemical products for chemical synthesis, with substantial demand. Traditional ethanol synthesis methods include natural feedstock fermentation and ethylene hydration. With the continuous growth of the population, traditional production models can no longer meet the needs of production and daily life, thus urgently requiring the exploration of a low-consumption, large-scale ethanol production method to address practical demand. Therefore, utilizing carbon dioxide hydrogenation to convert into low-carbon alcohols is of significant practical importance as an effective way to mitigate the greenhouse effect.

[0004] Palladium is the most commonly used hydrogenation catalyst, with a hydrogen activation capacity far exceeding that of copper and other metal catalysts. It also possesses excellent stability and resistance to sintering and poisoning. Therefore, palladium-based supported catalysts are widely used in carbon dioxide hydrogenation research. Chinese patent CN101444731A discloses a palladium-zinc catalyst supported on carbon nanotubes. This catalyst, using carbon nanotube-based materials as promoters, is prepared via a co-precipitation method and applied to the carbon dioxide hydrogenation to methanol reaction. However, this catalyst limits the use of carbon nanotube-based materials as the support / promoter, making the preparation process complex, cumbersome, and costly. Chinese patent CN113083296A discloses a palladium / boron catalyst supported on zirconium oxide. This catalyst utilizes plasma-assisted catalysis technology to generate high-energy electrons and ions to bombard the catalyst surface, promoting the decomposition of the catalyst precursor, thereby obtaining the catalyst. However, the reaction products of this catalyst are mainly methane and carbon monoxide. Chinese patent CN113145113A discloses a palladium-doped metal oxide solid solution catalyst. The catalyst was prepared by co-precipitation using zinc zirconium oxide solid solution as a support. However, the catalyst had a low carbon dioxide conversion rate, and the liquid phase products were mainly methanol and carbon monoxide.

[0005] In summary, the main problems with palladium-based catalysts in current carbon dioxide hydrogenation reactions are low carbon dioxide conversion rates and the main products remaining methanol, methane, and carbon monoxide, with low selectivity for lower-carbon mixed alcohols. Therefore, developing novel palladium-based catalysts to achieve efficient carbon dioxide hydrogenation while simultaneously enabling controllable production of lower-carbon alcohols from methanol would broaden the application of palladium-based catalysts in carbon dioxide hydrogenation reactions and further increase the added value of reaction products. This not only has academic research value but also significant economic and practical benefits. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a catalyst for the hydrogenation of carbon dioxide to prepare low-carbon mixed alcohols, its preparation method, and its applications. The catalyst prepared using the method of this invention exhibits high carbon dioxide conversion and high selectivity for low-carbon mixed alcohols in the hydrogenation reaction.

[0007] One of the objectives of this invention is to provide a method for preparing palladium-based bimetallic nanocatalysts.

[0008] The second objective of this invention is to provide a palladium-based bimetallic nanocatalyst prepared by this method.

[0009] The third objective of this invention is to provide an application of this palladium-based bimetallic nanocatalyst.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0011] In a first aspect, the present invention provides a method for preparing palladium-based bimetallic nanocatalysts, comprising the following steps:

[0012] S1. Dissolve the TiO2 support and the metal M precursor in a solvent to obtain solution A. Based on the mass of the TiO2 support, the content of M ions is 1wt%-5wt%, and M is one of Cu, Zn, and Fe. Dissolve the reducing agent in water to obtain solution B. Add solution B dropwise to solution A and stir to obtain solution C.

[0013] S2. Dissolve the palladium precursor in a solvent to obtain solution D. Based on the mass of the TiO2 support, the palladium ion content is 0.5wt%-1wt%. Add solution D dropwise to solution C and stir to obtain a mixed solution.

[0014] S3. Wash and dry the obtained mixed solution to obtain palladium-based bimetallic nanocatalyst.

[0015] The catalyst of this invention is prepared by a two-step sequential reduction method. First, the metal M precursor is reduced to metal nanoparticles by a reducing agent and deposited on a titanium dioxide support. Then, the palladium precursor is further reduced to palladium nanoparticles to obtain a palladium-based bimetallic nanocatalyst.

[0016] Step S1:

[0017] There are no special restrictions on the source of TiO2 support; it can be purchased commercially or prepared by oneself according to methods known in the art.

[0018] In some embodiments, in step S1, the average particle size of the TiO2 support is 20-40 nm.

[0019] In some embodiments, when M is Cu in step S1, the copper precursor is one or more of copper nitrate, copper chloride, copper sulfate, copper acetylacetone, copper acetate, or their hydrates.

[0020] When M is Zn, the zinc precursor is one or more of zinc nitrate, zinc chloride, zinc sulfate, zinc acetate, or their hydrates;

[0021] When M is Fe, the iron precursor is one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric acetate, or their hydrates.

[0022] In some embodiments, in step S1, the solvent is one or more of deionized water, acetone, methanol, ethanol, and ethylene glycol.

[0023] In some embodiments, in step S1, the reducing agent is one or more of ascorbic acid, ammonia borane complex, diborane, ethylene glycol, sodium borohydride, potassium borohydride, and hydrazine hydrate.

[0024] The concentration of the reducing agent in solution B is 0.2–3 mol / L.

[0025] In some embodiments, in step S1, the molar ratio of the reducing agent to the total molar ratio of M ions and palladium ions is 20:1 to 10:1.

[0026] In some embodiments, in step S1, the dropping rate is 0.3 to 1 mL / min, the stirring speed is 500 to 1200 r / min, and the stirring time is 0.5 to 3 h.

[0027] Step S2:

[0028] In some embodiments, in step S2, the palladium precursor is one or more of palladium acetate, palladium chloride, palladium nitrate, palladium acetylacetone, and potassium tetrachloropalladate.

[0029] In some embodiments, in step S2, the solvent is one or more of deionized water, acetone, methanol, ethanol, and ethylene glycol.

[0030] In some embodiments, in step S2, the dropping rate is 0.3 to 1 mL / min, the stirring speed is 500 to 1200 r / min, and the stirring time is 0.5 to 3 h.

[0031] Step S3:

[0032] In some embodiments, in step S3, the washing method is to centrifuge and wash with deionized water and anhydrous ethanol 3 to 8 times respectively;

[0033] The drying temperature is 50–120℃, and the drying time is 12–24 hours.

[0034] Secondly, the present invention provides a palladium-based bimetallic nanocatalyst, which is prepared by the above preparation method. The palladium-based bimetallic nanocatalyst includes a TiO2 support and bimetallic nanoparticles supported on the TiO2 support, wherein the bimetallic nanoparticles have Pd and M as the bimetals, and M is one of Cu, Zn and Fe; the average particle size of the bimetallic nanoparticles is 3-10 nm.

[0035] Based on the mass of the TiO2 support, the loading of Pd is 0.5wt%-1wt%, and the loading of M is 1wt%-5wt%.

[0036] Thirdly, the present invention provides an application of the above-mentioned palladium-based bimetallic nanocatalyst in the preparation of low-carbon mixed alcohols by the catalytic reaction of carbon dioxide hydrogenation.

[0037] Preferably, the catalytic reaction is carried out in a high-pressure fixed-bed continuous flow reactor under the following conditions: reaction temperature of 200-400℃, reaction pressure of 2-8MPa, total space velocity of feed gas of 2000-7000mL / g / h, volume ratio of hydrogen to carbon dioxide of 4:1-1:1, and the low-carbon mixed alcohol is methanol, ethanol and propanol.

[0038] Preferably, the palladium-based bimetallic nanocatalyst needs to be reduced before use. The reduction atmosphere is hydrogen, the hydrogen space velocity is 6000-20000 mL / g / h, the reduction temperature is 200-400℃, and the reduction time is 2-6 h.

[0039] Technical effects:

[0040] (1) The palladium-based bimetallic catalysts prepared by the present invention include palladium copper, palladium zinc and palladium iron catalysts. The preparation method is simple, the operation process is convenient, and it has wide applicability.

[0041] (2) The palladium-based bimetallic catalyst prepared by the present invention has high activity and high atom utilization rate for carbon dioxide hydrogenation. By adjusting the type and ratio of palladium and the second metal, the distribution of low-carbon mixed alcohol products can be selectively controlled.

[0042] (3) The catalyst of the present invention adopts a two-step sequential reduction method. By depositing palladium atoms on the surface of the second metal, palladium can be highly dispersed and its surface electronic structure can be controlled. However, changing the reduction order will cause the second metal to cover the surface of palladium, thereby reducing the catalytic reaction activity. Therefore, the reduction order in the present invention is crucial for the preparation of high-performance catalysts.

[0043] (4) This invention utilizes the strong interaction between the metal support to achieve a high dispersion distribution of the second metal on the titanium dioxide support. Furthermore, using the highly dispersed second metal as a "dispersant," the high dispersion distribution of palladium atoms is achieved by regulating the reduction rate of palladium ions. This reduces the activation ability of palladium for hydrogen but enhances its desorption ability for carbon monoxide. Simultaneously, the synergistic effect between palladium and the second metal is beneficial for the activation of carbon dioxide and the regulation of reaction intermediates, promoting the coupling of intermediates and thus improving the conversion rate of carbon dioxide and the selectivity of low-carbon mixed alcohols. This represents a significant improvement compared to traditional palladium-based catalysts and copper-based catalysts.

[0044] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0045] Figure 1Dark-field image (STEM) of the PdCu / TiO2 catalyst prepared in Example 1. Detailed Implementation

[0046] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0047] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0048] Example 1: Preparation and Catalytic Performance Evaluation of Palladium-Copper Catalyst

[0049] 1 g of titanium dioxide P25 and 0.189 g of copper nitrate trihydrate (0.05 g Cu) were dissolved in 6 mL of deionized water and stirred until homogeneous. An excess sodium borohydride aqueous solution (2.2 mol / L) was slowly added dropwise to the above mixed solution and stirred for 1 h, wherein the molar ratio of sodium borohydride to the sum of palladium and copper ions was 10:1. 0.024 g of palladium nitrate dihydrate (0.01 g Pd) was weighed and dissolved in 2 mL of deionized water, and the palladium nitrate aqueous solution was further slowly added dropwise to the above solution and stirred for 1 h. The mixed solution was centrifuged and washed 5 times each with deionized water and ethanol, and then dried at 60 °C for 12 h to obtain catalyst powder. Based on the mass of titanium dioxide, the loading of palladium nanoparticles was 1 wt%, and the loading of copper nanoparticles was 5 wt%.

[0050] The morphology and composition of nanoparticles were observed using transmission electron microscopy (TEM) or high-resolution transmission electron microscopy (HRTEM). The particle size of nanoparticles in palladium-based catalysts was calculated by observing and statistically analyzing the particle size of the metal nanoparticles using TEM or HRTEM, and then taking the average value. Figure 1 As can be seen, the uniformly dispersed bright spots are palladium-copper active bimetallic nanoparticles, confirming that the catalyst structure is palladium-copper nanoparticles uniformly distributed on a TiO2 support. The average particle size of the palladium-copper active bimetallic nanoparticles is about 4 nm. The small particle size indicates that the nanoparticles have good dispersibility and no obvious agglomeration.

[0051] Then, the catalytic performance of carbon dioxide hydrogenation was tested. The test conditions were: 0.3g catalyst, compressed into tablets and sieved through a 20-40 mesh sieve. Before the reaction test, hydrogen pre-reduction treatment was performed at a space velocity of 8000 mL / g / h at 200℃ for 2 hours. After the temperature cooled to room temperature, the reaction performance was evaluated in a fixed-bed reactor at a reaction temperature of 250℃, a reaction pressure of 3 MPa, a total space velocity of 6000 mL / g / h, and a CO2 / H2 / N2 volume ratio of 24:72:4. The reaction performance test results are shown in Table 1.

[0052] Example 2: Preparation and Catalytic Performance Evaluation of Palladium-Zinc Catalyst

[0053] 1 g of titanium dioxide P25 and 0.182 g of zinc nitrate hexahydrate (0.04 g Zn) were dissolved in 6 mL of deionized water and stirred until homogeneous. An excess of sodium borohydride aqueous solution (concentration 1.76 mol / L) was slowly added dropwise to the above mixed solution and stirred for 1 h, wherein the molar ratio of sodium borohydride to the sum of palladium and zinc ions was 10:1. 0.024 g of palladium nitrate dihydrate (0.01 g Pd) was weighed and dissolved in 2 mL of deionized water, and the palladium nitrate aqueous solution was further slowly added dropwise to the above solution and stirred for 1 h. The mixed solution was centrifuged and washed 5 times each with deionized water and ethanol, and then dried at 60 °C for 12 h to obtain catalyst powder. Based on the mass of titanium dioxide, the loading of palladium nanoparticles was 1 wt%, and the loading of zinc nanoparticles was 4 wt%.

[0054] Then, the catalytic performance of carbon dioxide hydrogenation was tested. The test conditions were: 0.3g catalyst, compressed into tablets and sieved through a 20-40 mesh sieve. Before the reaction test, hydrogen pre-reduction treatment was performed at a space velocity of 8000 mL / g / h at 200℃ for 2 hours. After the temperature cooled to room temperature, the reaction performance was evaluated in a fixed-bed reactor at a reaction temperature of 250℃, a reaction pressure of 3 MPa, a total space velocity of 6000 mL / g / h, and a CO2 / H2 / N2 volume ratio of 24:72:4. The reaction performance test results are shown in Table 1.

[0055] Example 3: Preparation and Catalytic Performance Evaluation of Palladium-Iron Catalyst

[0056] 1 g of titanium dioxide P25 and 0.361 g of ferric nitrate nonahydrate (0.05 g Fe) were dissolved in 6 mL of deionized water and stirred until homogeneous. An excess sodium borohydride aqueous solution (concentration 2.47 mol / L) was slowly added dropwise to the above mixed solution and stirred for 1 h, wherein the molar ratio of sodium borohydride to the sum of palladium and iron ions was 10:1. 0.024 g of palladium nitrate dihydrate (0.01 g Pd) was weighed and dissolved in 2 mL of deionized water, and the palladium nitrate aqueous solution was further slowly added dropwise to the above solution and stirred for 1 h. The mixed solution was centrifuged and washed 5 times each with deionized water and ethanol, and then dried at 60 °C for 12 h to obtain catalyst powder. Based on the mass of titanium dioxide, the loading of palladium nanoparticles was 1 wt%, and the loading of iron nanoparticles was 5 wt%.

[0057] Then, the catalytic performance of carbon dioxide hydrogenation was tested. The test conditions were: 0.3g catalyst, compressed into tablets and sieved through a 20-40 mesh sieve. Before the reaction test, hydrogen pre-reduction treatment was performed at a space velocity of 8000 mL / g / h at 200℃ for 2 hours. After the temperature cooled to room temperature, the reaction performance was evaluated in a fixed-bed reactor at a reaction temperature of 250℃, a reaction pressure of 3 MPa, a total space velocity of 6000 mL / g / h, and a CO2 / H2 / N2 volume ratio of 24:72:4. The reaction performance test results are shown in Table 1.

[0058] Examples 1-3 prepared palladium-copper, palladium-zinc, and palladium-iron catalysts, respectively. In Example 1, copper was selected as the second metal, and a highly dispersed palladium-copper catalyst was successfully prepared via a two-step sequential reduction method under specific feed amounts and concentrations. In Example 2, zinc was selected as the second metal, and a highly dispersed palladium-zinc catalyst was successfully prepared via a two-step sequential reduction method under specific feed amounts and concentrations. In Example 3, iron was selected as the second metal, and a highly dispersed palladium-iron catalyst was successfully prepared via a two-step sequential reduction method under specific feed amounts and concentrations. The distribution of low-carbon mixed alcohol products obtained after catalytic reactions of carbon dioxide hydrogenation with different metals and palladium catalysts varied.

[0059] Comparative Example 1

[0060] 1 g of titanium dioxide P25 and 0.024 g of palladium nitrate dihydrate (0.01 g Pd) were dissolved in 6 mL of deionized water and stirred until homogeneous. An excess of sodium borohydride aqueous solution (0.23 mol / L) was slowly added dropwise to the above mixed solution and stirred for 1 h, wherein the molar ratio of sodium borohydride to palladium ions was 10:1. The solution was washed twice by centrifugation with water and ethanol, respectively, and dried at 60 °C for 12 h to obtain catalyst powder.

[0061] Then, the catalytic performance of carbon dioxide hydrogenation was tested. The test conditions were: 0.3g catalyst, compressed into tablets and sieved through a 20-40 mesh sieve. Before the reaction test, hydrogen pre-reduction treatment was performed at a space velocity of 8000 mL / g / h at 200℃ for 2 hours. After the temperature cooled to room temperature, the reaction performance was evaluated in a fixed-bed reactor at a reaction temperature of 250℃, a reaction pressure of 3 MPa, a total space velocity of 6000 mL / g / h, and a CO2 / H2 / N2 volume ratio of 24:72:4. The reaction performance test results are shown in Table 1.

[0062] Comparative Example 2

[0063] 1 g of titanium dioxide P25, 0.361 g of ferric nitrate nonahydrate (0.05 g Fe), and 0.024 g of palladium nitrate dihydrate (0.01 g Pd) were dissolved in 6 mL of deionized water and stirred until homogeneous. An excess of sodium borohydride aqueous solution (2.47 mol / L) was slowly added dropwise to the above mixed solution and stirred for 1 h, wherein the molar ratio of sodium borohydride to the sum of palladium and iron ions was 10:1. The solution was washed twice by centrifugation with water and ethanol, respectively, and dried at 60 °C for 12 h to obtain catalyst powder.

[0064] Then, the catalytic performance of carbon dioxide hydrogenation was tested. The test conditions were: 0.3g catalyst, compressed into tablets and sieved through a 20-40 mesh sieve. Before the reaction test, hydrogen pre-reduction treatment was performed at a space velocity of 8000 mL / g / h at 200℃ for 2 hours. After the temperature cooled to room temperature, the reaction performance was evaluated in a fixed-bed reactor at a reaction temperature of 250℃, a reaction pressure of 3 MPa, a total space velocity of 6000 mL / g / h, and a CO2 / H2 / N2 volume ratio of 24:72:4. The reaction performance test results are shown in Table 1.

[0065] Comparative Example 3

[0066] 1 g of titanium dioxide P25 and 0.024 g of palladium nitrate dihydrate (0.01 g Pd) were dissolved in 6 mL of deionized water and stirred until homogeneous. An excess of sodium borohydride aqueous solution (concentration 2.47 mol / L) was slowly added dropwise to the above mixed solution and stirred for 1 h, wherein the molar ratio of sodium borohydride to the sum of palladium and iron ions was 10:1. 0.361 g of ferric nitrate nonahydrate (0.05 g Fe) was weighed and dissolved in 2 mL of deionized water, and the ferric nitrate aqueous solution was further slowly added dropwise to the above solution and stirred for 1 h. The mixed solution was centrifuged and washed 5 times each with deionized water and ethanol, and then dried at 60 °C for 12 h to obtain catalyst powder. Based on the mass of titanium dioxide, the loading of palladium nanoparticles was 1 wt%, and the loading of iron nanoparticles was 5 wt%.

[0067] Then, the catalytic performance of carbon dioxide hydrogenation was tested. The test conditions were: 0.3g catalyst, compressed into tablets and sieved through a 20-40 mesh sieve. Before the reaction test, hydrogen pre-reduction treatment was performed at a space velocity of 8000 mL / g / h at 200℃ for 2 hours. After the temperature cooled to room temperature, the reaction performance was evaluated in a fixed-bed reactor at a reaction temperature of 250℃, a reaction pressure of 3 MPa, a total space velocity of 6000 mL / g / h, and a CO2 / H2 / N2 volume ratio of 24:72:4. The reaction performance test results are shown in Table 1. The calculation process for the CO2 conversion rate and the selectivity of each component is as follows:

[0068]

[0069] Among them, [CO2] inlet and [CO2] outlet These represent the molar concentrations of CO2 in the raw gas and the exhaust gas, respectively.

[0070]

[0071]

[0072]

[0073] Among them, [CO] and [C] i H x [C] i H x O y [ ] represents the molar concentration of CO, hydrocarbons, and alcohols, respectively.

[0074] Table 1. Catalyst activity evaluation results

[0075]

[0076] As shown in Table 1, the catalyst prepared by this invention can effectively achieve the technical effect of preparing low-carbon mixed alcohols by carbon dioxide hydrogenation. Taking Example 3 as an example, the conversion rate of carbon dioxide is 26%, and the total selectivity of low-carbon alcohols can reach 55%. Compared with Comparative Example 2, the catalytic performance is improved by nearly 7 times. This also shows that the catalyst prepared by the method of this invention can effectively control the product distribution of low-carbon mixed alcohols. In addition, after changing the reduction order (Comparative Example 3), the performance of the catalyst is significantly reduced compared with Example 3, which also proves the importance and uniqueness of the reduction order in this invention.

[0077] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a palladium-based bimetallic nanocatalyst, characterized in that, Includes the following steps: S1. Dissolve the TiO2 support and the metal M precursor in a solvent to obtain solution A. Based on the mass of the TiO2 support, the content of M ions is 1wt%-5wt%, and M is one of Cu, Zn, and Fe. Dissolve the reducing agent in water to obtain solution B. The concentration of the reducing agent in solution B is 0.2~3mol / L. Add solution B dropwise to solution A and stir to obtain solution C. S2. Dissolve the palladium precursor in a solvent to obtain solution D. Based on the mass of the TiO2 support, the palladium ion content is 0.5wt%-1wt%. Add solution D dropwise to solution C and stir to obtain a mixed solution. The molar ratio of the reducing agent to the total molar ratio of M ions and palladium ions is 20:1 to 10:

1. S3. Wash and dry the obtained mixed solution to obtain palladium-based bimetallic nanocatalyst.

2. The preparation method according to claim 1, characterized in that, In step S1, when M is Cu, the copper precursor is one or more of copper nitrate, copper chloride, copper sulfate, copper acetylacetone, copper acetate, or their hydrates. When M is Zn, the zinc precursor is one or more of zinc nitrate, zinc chloride, zinc sulfate, zinc acetate, or their hydrates; When M is Fe, the iron precursor is one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric acetate, or their hydrates.

3. The preparation method according to claim 1, characterized in that, In step S1, the reducing agent is one or more of ascorbic acid, ammonia borane complex, diborane, ethylene glycol, sodium borohydride, potassium borohydride, and hydrazine hydrate.

4. The preparation method according to claim 1, characterized in that, In step S1, the dropping rate is 0.3~1 mL / min, the stirring speed is 500~1200 r / min, and the stirring time is 0.5~3 h.

5. The preparation method according to claim 1, characterized in that, In step S2, the palladium precursor is one or more of palladium acetate, palladium chloride, palladium nitrate, palladium acetylacetone, and potassium tetrachloropalladate.

6. The preparation method according to claim 1, characterized in that, In step S2, the dropping rate is 0.3~1 mL / min, the stirring speed is 500~1200 r / min, and the stirring time is 0.5~3 h.

7. A palladium-based bimetallic nanocatalyst, characterized in that, The palladium-based bimetallic nanocatalyst is prepared by the preparation method according to any one of claims 1-6, comprising a TiO2 support and bimetallic nanoparticles supported on the TiO2 support, wherein the bimetallic nanoparticles are Pd and M, and M is one of Cu, Zn and Fe; the average particle size of the bimetallic nanoparticles is 3-10 nm. Based on the mass of the TiO2 support, the loading of Pd is 0.5wt%-1wt%, and the loading of M is 1wt%-5wt%.

8. The application of the palladium-based bimetallic nanocatalyst of claim 7 in the preparation of low-carbon mixed alcohols by the catalytic reaction of carbon dioxide hydrogenation, wherein the low-carbon mixed alcohols are methanol, ethanol and propanol.

9. The application according to claim 8, characterized in that, The catalytic reaction is carried out in a high-pressure fixed-bed continuous flow reactor under the following conditions: reaction temperature of 200-400°C, reaction pressure of 2-8 MPa, total space velocity of feed gas of 2000-7000 mL / g / h, and volume ratio of hydrogen to carbon dioxide of 4:1-1:

1.

10. The application according to claim 9, characterized in that, The palladium-based bimetallic nanocatalyst needs to be reduced before use. The reduction atmosphere is hydrogen, the hydrogen space velocity is 6000~20000mL / g / h, the reduction temperature is 200~400°C, and the reduction time is 2~6h.

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