Preparation method of high-dispersity transition metal catalyst

Abstract

The invention discloses a preparation method of a high-dispersity transition metal catalyst, which specifically comprises the following steps: step 1, taking 2.09 ml of chloroplatinic acid hexahydrate solution, adding into a cerium-titanium mixing agent, and stirring for 4 hours; step 2, adding 0.5 g of urea, and stirring for 1 hour by using a magnetic stirrer to obtain a mixed solution; 3, 100 ml of the mixed solution is taken and put into a reaction kettle, the reaction kettle is placed in a drying oven to be dried, and a reaction kettle product is obtained; 4, washing the reaction kettle product, and drying in a drying oven to obtain a catalyst semi-finished product; 5, roasting the catalyst semi-finished product in a muffle furnace to obtain a finished product catalyst; the invention relates to the technical field of catalysts. According to the preparation method of the high-dispersity transition metal catalyst, cerium nitrate hexahydrate, tetrabutyl titanate, a chloroplatinic acid hexahydrate solution and urea are used as raw materials to prepare the metal catalyst, and the metal catalyst has the advantage of high dispersity, is also beneficial to hydrogenation reaction and has the advantages of being green and environmentally friendly.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a method for preparing a highly dispersed transition metal catalyst. Background Art

[0002] With the development of catalytic science, high selectivity of target products has become particularly important. α, β-unsaturated aldehydes / ketones (cinnamaldehyde, citral, furfural and crotonaldehyde, etc.) are important chemical raw materials and intermediates. The target product α, β-unsaturated alcohol obtained by selective hydrogenation is an important raw material and reaction intermediate in the production of spices, medicines and other fine chemical products, and is widely used in organic synthesis. Since its structure contains both C=C and C=O bonds, the selective hydrogenation of C=O has a more important significance in many studies. On the one hand, the industrial value of the product obtained by hydrogenation of the C=O bond is much higher than that of the product obtained by hydrogenation of the C=C bond; on the other hand, from a thermodynamic point of view, the bond energy of the C=C bond is equal to 615KJ / mol, and the bond energy of the C=O bond is equal to 715KJ / mol. Especially in the case of conjugation, it is relatively difficult to hydrogenate the C=O bond without destroying the C=C bond. Due to the complexity of the hydrogenation system, the activity of the catalyst and the selectivity of the product will be affected by many factors. At the same time, the competitive adsorption, dissociation, hydrogenation and other aspects of the material are very important. Therefore, the preparation research of high-activity and high-selectivity catalytic hydrogenation catalysts is of great significance both in theory and in practical industrial applications.

[0003] Generally, α,β-unsaturated aldehydes are directly reduced by lithium aluminum tetrahydride or sodium borohydride to obtain α,β-unsaturated alcohols, or α,β-unsaturated aldehydes are reduced by using aluminum isopropoxide as a hydrogen source through a hydrogen transfer method to obtain α,β-unsaturated alcohols with a higher yield. However, due to the high preparation cost and high reaction conditions, the product after the reaction is difficult to separate from the reducing agent and the solvent, and a lot of three wastes are generated. Generally, 20-50kg of wastes are generated for every 1kg of unsaturated alcohol produced, which is not conducive to the requirements of green chemistry and sustainable development of environmental protection. The solid catalyst itself and the product are easier to separate, and the cost is controllable. Using it for catalytic hydrogenation of α,β-unsaturated aldehydes meets the requirements of atom economy and green chemistry. Therefore, a preparation method of a highly dispersed transition metal catalyst is proposed. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a method for preparing a highly dispersed transition metal catalyst, which solves the problems raised in the above background technology.

[0005] To achieve the above objectives, the present invention is implemented by the following technical scheme: a method for preparing a highly dispersed transition metal catalyst, specifically comprising the following steps:

[0006] Step 1: Take 2.09 ml of chloroplatinic acid hexahydrate solution, add it to the cerium-titanium mixture, and stir for 4 hours;

[0007] Step 2: Add 0.5 g of urea and stir with a magnetic stirrer for 1 h to obtain a mixed solution;

[0008] Step 3: Take 100 ml of the mixed solution into a reactor, place the reactor in an oven for drying, and obtain the reactor product;

[0009] Step 4: After washing the product of the reaction kettle, put it into an oven for drying to obtain a semi-finished catalyst;

[0010] Step 5: Place the semi-finished catalyst in a muffle furnace for calcination to obtain a finished catalyst.

[0011] The present invention is further configured as follows: the concentration of the hexahydrate chloroplatinic acid solution in the step 1 is 1 g / 100 mL.

[0012] The present invention is further configured as follows: the cerium-titanium mixture in step one comprises cerium nitrate hexahydrate and tetrabutyl titanate.

[0013] The present invention is further configured as follows: the molar ratio of the cerium nitrate hexahydrate to tetrabutyl titanate includes: 1:1, 1:2, 1:3, 2:3 and 7:3.

[0014] The present invention is further configured as follows: the oven temperature in step three is 120° C., and the drying time is 10 hours.

[0015] The present invention is further configured as follows: the method of washing the reaction kettle product in step 4 comprises:

[0016] Add the product of the reactor into a centrifuge tube, add deionized water, wash it in a centrifuge, remove the supernatant, and repeat 3-5 times;

[0017] Add ethanol to the centrifuge tube, wash it using a centrifuge, remove the supernatant, and repeat 3-5 times to complete the washing of the reactor product.

[0018] The present invention is further configured as follows: the method of washing the reaction kettle product in step 4 comprises:

[0019] Add the product of the reactor into a centrifuge tube, add deionized water, wash it in a centrifuge, remove the supernatant, and repeat 3-5 times;

[0020] Add ethanol to the centrifuge tube, wash it using a centrifuge, remove the supernatant, and repeat 3-5 times to complete the washing of the reactor product.

[0021] The present invention is further configured as follows: in the step five, the catalyst semi-finished product is placed in a muffle furnace for calcination at a temperature of 400° C., and the heating rate is 5° C. / min.

[0022] The present invention provides a method for preparing a highly dispersed transition metal catalyst, which has the following beneficial effects:

[0023] The present invention uses cerium nitrate hexahydrate, tetrabutyl titanate, chloroplatinic acid hexahydrate solution and urea as raw materials to prepare a metal catalyst, which has the advantages of high dispersibility, is conducive to the hydrogenation reaction, and has the advantages of being green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the preparation process of the present invention;

[0025] Figure 2 This is a schematic diagram of the X-ray diffraction test results in an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram of the hydrogen desorption test results in an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of the infrared spectrum characterization results of pyridine in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0029] See also Figure 1-4 , the embodiment of the present invention provides the following technical solutions:

[0030] Embodiment 1: A method for preparing a highly dispersed transition metal catalyst, comprising the following steps:

[0031] Step 1: dilute 1g of chloroplatinic acid hexahydrate (H2PtCl6·6H2O) with distilled water into a 100mL volumetric flask, weigh 2.09ml of chloroplatinic acid hexahydrate solution, add cerium nitrate hexahydrate Ce(NO3)3·6H2O and tetrabutyl titanate C with a cerium-titanium molar ratio of 1:1, 16 H 36 O4Ti, stirred for 4 h, so that cerium ions and titanium ions were adsorbed on platinum;

[0032] Step 2: Add 0.5 g of urea and stir with a magnetic stirrer for 1 h to obtain a mixed solution;

[0033] Step 3: Take 100 ml of the mixed solution into a reaction kettle, place the reaction kettle in an oven, and dry it at 120° C. for 10 h to obtain the reaction kettle product;

[0034] Step 4: Add the product of the reactor to a centrifuge tube, add deionized water, wash it with a centrifuge, remove the supernatant, repeat 3-5 times, add ethanol to the centrifuge tube, wash it with a centrifuge, remove the supernatant, repeat 3-5 times, and after washing the product of the reactor, put it in an oven and dry it at 70° C. for 10 hours to obtain a semi-finished catalyst;

[0035] Step 5: Place the semi-finished catalyst in a muffle furnace and calcine it at a temperature of 400°C with a heating rate of 5°C / min to obtain the finished catalyst Pt / CeO2-TiO2, i.e. Pt-1Ce / 1TiO2.

[0036] The loading amount of Pt is 1 wt%.

[0037] Example 2: The finished catalyst was prepared on the basis of Example 1, except that cerium nitrate hexahydrate Ce(NO3)3·6H2O and tetrabutyl titanate C with a molar ratio of cerium to titanium of 1:2 were added to the hexahydrate chloroplatinic acid solution. 16 H 36 O4Ti.

[0038] Finally, the finished catalyst Pt / CeO2-TiO2, namely Pt-1Ce / 2TiO2, is obtained.

[0039] Example 3: The finished catalyst was prepared on the basis of Example 1, except that cerium nitrate hexahydrate Ce(NO3)3·6H2O and tetrabutyl titanate C with a molar ratio of cerium to titanium of 1:3 were added to the hexahydrate chloroplatinic acid solution. 16 H 36 O4Ti.

[0040] Finally, the finished catalyst Pt / CeO2-TiO2, namely Pt-1Ce / 3TiO2, is obtained.

[0041] Example 4: The finished catalyst was prepared on the basis of Example 1, except that cerium nitrate hexahydrate Ce(NO3)3·6H2O and tetrabutyl titanate C with a molar ratio of cerium to titanium of 2:3 were added to the hexahydrate chloroplatinic acid solution. 16 H 36 O4Ti.

[0042] Finally, the finished catalyst Pt / CeO2-TiO2, namely Pt-2Ce / 3TiO 22 .

[0043] Example 5: The finished catalyst was prepared on the basis of Example 1, except that cerium nitrate hexahydrate Ce(NO3)3·6H2O and tetrabutyl titanate C with a molar ratio of cerium to titanium of 7:3 were added to the hexahydrate chloroplatinic acid solution.16 H 36 O4Ti.

[0044] Finally, the finished catalyst Pt / CeO2-TiO2, namely Pt-7Ce / 3TiO2, is obtained.

[0045] After obtaining finished catalysts with different cerium-titanium molar ratios according to the above examples, catalysts Pt-TiO2 and Pt-Ce were introduced to conduct comparative tests:

[0046] The results of the X-ray diffraction test are shown in the attached Figure 2 As shown in the figure, a is Pt-Ce, b is Pt-7Ce / 3TiO2, c is Pt-1Ce / 1TiO2, d is Pt-2Ce / 3TiO2, e is Pt-1Ce / 2TiO2, f is Pt-1Ce / 3TiO2, and g is Pt-TiO2. It can be seen that only the typical anatase TiO22 (JCPDS#21-1272) characteristic peak appears in the Pt-TiO2 catalyst. With the increase of Ce content, the intensity of this characteristic peak decreases significantly. When Ce:Ti is less than 1:2, the Ce-rich sample is mainly composed of monoclinic Ce2TiO5 (JCPDS PDF#49-1606) and TiO2. With the increase of Ce:Ti molar ratio to 2:3, the Pt-2Ce / 3TiO2 catalyst has multiple diffraction peaks in the range of 10-20°, which are attributed to TiO2 (JCPDS PDF#49-1606). PDF#46-1238) and Ti3O5 (JCPDS PDF#49-1606), and the intensity of the diffraction peak weakened with the further increase of Ce content. When the molar ratio of Ce:Ti is greater than 1, the typical characteristic peaks of cubic cerium oxide phase (c-CeO2, JCPDS#43-1002) appear. These phenomena indicate that CeO2 and TiOx can be highly dispersed at an appropriate Ce / Ti molar ratio. In all Pt-xCe / yTiO2 catalysts, Ce substances enter the TiO2 lattice to form Ce2TiO5 solid solution. In addition, no Pt diffraction peaks (2θ=39.8°, 46.2°) were found in all catalysts, indicating that the Pt loading is low and the dispersion is high.

[0047] The results of the hydrogen desorption test are shown in the attached Figure 3As shown, a is Pt-Ce, b is Pt-7Ce / 3TiO2, c is Pt-1Ce / 1TiO2, d is Pt-2Ce / 3TiO2, e is Pt-1Ce / 2TiO2, f is Pt-1Ce / 3TiO2, and g is Pt-TiO2. Compared with Pt-TiO2, all catalysts have a strong desorption peak of H2 near 550℃. It is worth noting that in the presence of Ce in the catalyst, the release zone of hydrogen moves to a higher temperature, and the desorption peak area of ​​H2 gradually increases. When Ce:Ti When the molar ratio exceeds 2:3, the desorption peak area of ​​H2 begins to decrease, and the desorption peak of H2 gradually moves toward the low temperature direction, indicating that the introduction of an appropriate amount of Ce is beneficial to enhancing the adsorption of H2. Excessive addition of Ce will inhibit the adsorption of H2, resulting in reduced catalytic activity. The H2 desorption peak area of ​​the Pt / 2CeO2-3TiO2 catalyst is the largest and the desorption temperature is the highest, indicating that the increase in Ce content makes the precious metal Pt stronger in binding with the CeO2-TiO2 composite oxide carrier, which is extremely beneficial for the adsorption of hydrogen, and can better activate H2 and improve the reaction activity.

[0048] In order to further explore the type of acid centers on the catalyst surface, the catalysts Pt-TiO2 and Pt-2Ce / 3TiO2 were characterized by pyridine infrared spectroscopy. Figure 4 As shown in the spectrum, the band is at 1440cm -1 The characteristic peak is attributed to the interaction between pyridine and L acid in the sample or hydrogen bonding. The band is at 1470 cm -1 The absorption peak at 1580 cm corresponds to the result of the interaction between pyridine molecules and B acid and L acid. -1 The absorption peak at can be attributed to the formation of pyridine molecules adsorbed on Lewis acidic sites. Compared with Pt-TiO2, the intensities of L acid and B acid peaks in Pt-2Ce / 3TiO2 are enhanced, especially L acid. The corresponding L / B acid ratio at room temperature was calculated by the molar extinction coefficient method, which increased from 7.98 to 9.27; when the temperature was 100℃, the L / B acid ratio increased from 6.68 to 7.09, indicating that the surface of the prepared catalyst Pt-2Ce / 3TiO2 mainly exists in the form of Lewis acidic sites, and the Lewis acid centers on the catalyst surface are conducive to the hydrogenation reaction.

[0049] In order to characterize the morphology of the catalyst and the size of Pt nanoparticles, the catalysts Pt-TiO2 and Pt-2Ce / 3TiO2 were characterized by TEM. It was found that the active components of the two catalysts were dispersed in clusters more evenly on the surface of the carrier, with less agglomeration. The active components were dispersed in clusters more evenly on the surface of the carrier. The addition of Ce species can significantly improve the dispersion of the active species, so that the active components have a higher dispersion on the surface of the carrier, and Pt, Ti and Ce metals are evenly distributed. In particular, Pt particles show higher dispersibility due to their low content and small particle size.

[0050] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a highly dispersed transition metal catalyst, characterized in that: The specific steps include: Step 1: Take 2.09 ml of chloroplatinic acid hexahydrate solution, add it to the cerium-titanium mixture, and stir for 4 hours; Step 2: Add 0.5 g of urea and stir with a magnetic stirrer for 1 h to obtain a mixed solution; Step 3: Take 100 ml of the mixed solution into a reactor, place the reactor in an oven for drying, and obtain the reactor product; Step 4: After washing the product of the reactor, put it into an oven for drying to obtain a semi-finished catalyst; Step 5: Place the semi-finished catalyst in a muffle furnace and calcine to obtain the finished catalyst Pt / CeO2-TiO2.

2. The method for preparing a highly dispersed transition metal catalyst according to claim 1, characterized in that: The concentration of the chloroplatinic acid hexahydrate solution in the step 1 is 1 g / 100 mL.

3. The method for preparing a highly dispersed transition metal catalyst according to claim 1, characterized in that: The cerium-titanium mixture in step 1 includes cerium nitrate hexahydrate and tetrabutyl titanate.

4. The method for preparing a highly dispersed transition metal catalyst according to claim 3, characterized in that: The molar ratio of the cerium nitrate hexahydrate to tetrabutyl titanate includes: 1:1, 1:2, 1:3, 2:3 and 7:

3.

5. The method for preparing a highly dispersed transition metal catalyst according to claim 1, characterized in that: The oven temperature in step 3 is 120° C. and the drying time is 10 h.

6. The method for preparing a highly dispersed transition metal catalyst according to claim 1, characterized in that: The method for washing the reaction kettle product in step 4 includes: Add the product of the reactor into a centrifuge tube, add deionized water, wash it in a centrifuge, remove the supernatant, and repeat 3-5 times; Add ethanol to the centrifuge tube, wash it using a centrifuge, remove the supernatant, and repeat 3-5 times to complete the washing of the reactor product.

7. The method for preparing a highly dispersed transition metal catalyst according to claim 1, characterized in that: The oven temperature in step 4 is 70° C. and the drying time is 10 h.

8. The method for preparing a highly dispersed transition metal catalyst according to claim 1, characterized in that: In the step 5, the semi-finished catalyst is placed in a muffle furnace and calcined at a temperature of 400° C., and the heating rate is 5° C. / min.

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