WO2017190553A1

WO2017190553A1 - Transition metal nanoparticle catalyst with dual confinement structure and application thereof for catalysis in selective hydrogenation reaction of dimethyl terephthalate

Info

Publication number: WO2017190553A1
Application number: PCT/CN2017/076444
Authority: WO
Inventors: 张法智; 杨志祥; 樊启宁
Original assignee: 北京化工大学
Priority date: 2016-05-06
Filing date: 2017-03-13
Publication date: 2017-11-09
Also published as: CN105964258A

Abstract

The invention discloses a method for preparing a transition metal nanoparticle catalyst with a dual confinement structure and an application thereof for catalysis in selective hydrogenation reaction of dimethyl terephthalate. The preparation method of the catalyst comprises: synthesizing a laminate of a hydrotalcite-like precursor containing transition metal and aluminium ions, and then preparing the transition metal nanoparticle catalyst with the dual confinement structure through reduction. The catalyst structure is characterized in that the transition metal nanoparticles are embedded sequentially in a double shell, which is comprised of an aluminium doped transition metal oxide shell and an amorphous aluminum oxide shell, so that a dual confinement structure of the nanometer metal particle is formed. With the catalyst, conversion rate of dimethyl terephthalate is improved, and selectivity and reaction stability of dimethyl 1,4-cyclohexanedicarboxylate is substantially improved.

Description

Transition metal nanoparticle catalyst with double confinement structure and its application for catalytic hydrogenation of dimethyl terephthalate

Technical field

The invention belongs to the technical field of catalyst preparation, in particular to a method for controlling reduction and preparation of a hydrotalcite-like precursor, wherein a metal nanoparticle is sequentially embedded in a double shell of a metal oxide and an amorphous alumina to form a transition metal having a double confinement structure. Nanoparticle catalysts and their use in catalyzing the selective hydrogenation of dimethyl terephthalate.

Background technique

The industrial hydrogenation of dimethyl terephthalate to produce dimethyl 1,4-cyclohexanedicarboxylate mainly uses a supported noble metal Pd, Ru or Rh-based catalyst. However, noble metal catalysts have higher hydrogenation activity and selectivity, but their process conditions are more demanding, and their price is relatively expensive, which is not conducive to the further development of industrialization. Therefore, the focus of current research is mostly on the use of non-precious metals, mainly using transition metal Ni instead of precious metals. On the other hand, the conventional preparation of supported catalysts mostly adopts the impregnation method, which is simple in preparation and low in process cost. However, the impregnation method is easy to cause metal particle agglomeration to grow due to factors such as solvation effect in the preparation of the supported catalyst. The prepared catalyst active component has poor dispersion, resulting in poor reactivity and service life of the catalyst.

LDHs are compounds formed by the orderly assembly of interlayer anions and positively charged layers. The chemical composition is generally as follows: [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ [A ^n- ] _x/n · yH ₂ O, wherein M ²⁺ and M ³⁺ are divalent and trivalent metal cations, respectively, on the host layer; A ^n- is an interlayer anion; x is M ³⁺ /(M ²⁺ The molar ratio of +M ³⁺ ); y is the number of water molecules in the interlayer. The LDHs have the characteristics of tunable denaturation of the metal ion composition of the main layer, the charge density of the main layer and its variability, the variability of the type and amount of intercalated anion, the variability of the intra-layer space, and the variability of the interaction between the host and the guest. Such structural features make LDHs a meaningful platform for the development of new catalysts, catalyst precursors and catalyst supports with variable structure and properties. With LDHs as the precursor, the metal oxide catalyst materials can be obtained by calcination under certain conditions (temperature, time). The structure of such materials is good and the catalytic activity sites are relatively uniform. However, on the basis of such materials, the active metal nanoparticles prepared by the heat treatment under a reducing atmosphere are large, the interaction force between the metal and the substrate is weak, and the reactivity is still limited. Moreover, in the reduction process, the oxide reduction is difficult, and the degree of reduction of Ni metal is reduced.

Summary of the invention

It is an object of the present invention to provide a process for the simple preparation of a transition metal nanoparticle catalyst having a dual confinement structure and the use of the catalyst for the selective hydrogenation of dimethyl terephthalate.

The invention firstly synthesizes a hydrotalcite-like precursor containing a transition metal and an aluminum ion in a laminate, and then obtains a transition metal nanoparticle catalyst having a double confinement structure by reduction. The structure of the catalyst is characterized in that the transition metal nanoparticles are sequentially embedded in the double-shell of the aluminum-doped transition metal oxide and the amorphous alumina to form a double-limited nano metal particle structure. The catalyst is applied to the selective hydrogenation reaction of dimethyl terephthalate, which can effectively improve the conversion rate, selectivity and stability of the reaction.

The double-domain structure transition metal nanoparticle catalyst of the invention has the following structure: the transition metal nanoparticles are limited in the aluminum-doped transition metal oxide shell layer, and the outermost part is composed of amorphous alumina. The shell structure forms a double-limited nano metal particle structure; the catalyst is a black powdery substance having a single particle diameter of 4-8 nm; and the total loading of the transition metal is 60-66 wt% based on the total mass of the catalyst.

The preparation method of the double-domain structure transition metal nanoparticle catalyst of the invention is as follows:

A. The hydrotalcite precursor is dried at 60-100 ° C for 24-36 h, then calcined in a muffle furnace at 300-700 ° C for 2-8 h in an air atmosphere, and the heating rate is 2-10 ° C / min to obtain aluminum doping. Miscellaneous transition metal oxides;

B. The aluminum-doped transition metal oxide is placed in an atmosphere furnace, heat-treated at 300-700 ° C for 0.5-6 h under a hydrogen atmosphere, the heating rate is 2-10 ° C / min; the hydrogen flow rate is 30-80 mL / min, the reaction is completed The transition metal nanoparticle catalyst with double confinement structure is obtained.

The preparation method of the double-domain-structured transition metal nanoparticle catalyst of the invention is as follows: the hydrotalcite precursor is placed in an atmosphere furnace, heat-treated at 300-700 ° C for 0.5-6 h under a hydrogen atmosphere, and the heating rate is 2-10. °C/min; hydrogen flow rate is 30-80mL / min, after the reaction is completed, the transition metal nanoparticle catalyst with double confinement structure is obtained.

The divalent metal ions in the laminate of the hydrotalcite precursor are selected from transition metal ions, and the trivalent metal ions are aluminum ions.

The transition metal ion is one or more of Ni ²⁺ , Co ²⁺ , Cu ²⁺ , Fe ²⁺ .

The double-domain-structured transition metal nanoparticle catalyst prepared by the above method catalyzes the selective hydrogenation of dimethyl terephthalate. The catalytic process conditions are: dimethyl terephthalate is 0.5-2.5 g, the amount of transition metal nanoparticle catalyst with double confinement structure is 0.15-0.5 g, solvent is 80-100 mL, reaction temperature is 80-130 ° C, hydrogen The pressure is 2-8 MPa and the reaction time is 3-6 h.

The solvent is selected from one or more of isopropanol, ethanol, and ethyl acetate.

The invention adopts the method of controlled reduction of hydrotalcite precursor to prepare a transition nano metal nanoparticle catalyst with double confinement structure, the two oxide shell structures make the dispersion of the transition metal more uniform, and the interaction between the transition metal and the carrier is stronger. It prevents the loss of sintering and transition metals and provides the reactive sites for the reaction. The catalyst not only improves the conversion rate of dimethyl terephthalate, but also greatly improves the selectivity of dimethyl 1,4-cyclohexanedicarboxylate, and has outstanding reaction stability, thereby improving the hydrogenation reaction. performance. The conversion rate of the selective hydrogenation reaction of dimethyl terephthalate was 99.9% and the selectivity was 93.3% under the conditions of 90 ° C, 6 MPa hydrogen pressure and 4:1 reactant/catalyst. Moreover, the catalyst preparation process does not require the use of an organic solvent or an additive, and the method is simple and environmentally friendly. The catalyst can also be used in the reaction of pyrolysis gasoline for selective hydrogenation, methane reforming, and hydrogenation of CO and CO _{2 to} produce low carbon hydrocarbons and alcohols.

DRAWINGS

1 is a powder X-ray diffraction pattern (a), a Fourier transform infrared pattern (b), a thermogravimetric thermal analysis pattern (c), and a scanning electron microscope image (d) of Ni ₂ Al-LDHs prepared in Example 1. .

2 is an XRD pattern of R600 prepared in Example 1 and a C400R600 sample prepared in Example 2.

3 is a photograph of a high-resolution transmission electron microscope of R400 (a), R600 (b) prepared in Example 1, and C400R400 (c), C400R600 (d) prepared in Example 2, and corresponding particle size distribution maps (based on each Sample 150 particles calculated).

4 is a bright field diagram (a), a dark field diagram (b) of a transition metal nanoparticle catalyst R600 sample of the double-domain structure in Example 1, and a dark field after adding an energy scatter spectrum accessory. Field map (c), Ni element distribution (d), aluminum element distribution (e), and NiAl element distribution (f).

detailed description

Example 1

A. 19.2 g of Ni(NO ₃ ) ₂ ·6H ₂ O, 12.4 g of Al(NO ₃ ) ₂ ·9H ₂ O was added to 150 mL of deionized water, and ultrasonically dissolved to obtain a mixed salt solution; 6.3 g of hydrogen peroxide was added; Sodium and 7.0 g of sodium carbonate were added to 150 mL of deionized water, and ultrasonically dissolved to obtain a mixed alkali solution; 150 mL of deionized water was placed in a 500 mL three-necked flask, and then the mixed alkali solution was gradually dropped to a pH of 10, and then mixed at the same time. The salt solution was kept at pH 10; after the addition was completed, the obtained slurry was transferred to a 250 mL Teflon autoclave, crystallized at 130 ° C for 24 h, filtered, washed with deionized water and filtered to pH 7. Finally, it was dried at 70 ° C for 24 h to obtain a highly dispersed hydrotalcite precursor, which was recorded as Ni ₂ Al-LDHs (XRD, FT-IR, TG-DTA spectrum and SEM image shown in Figure 1);

B. The high-dispersion hydrotalcite precursor Ni ₂ Al-LDHs prepared in step A was placed in a high-temperature atmosphere furnace, and H _{2 having a} purity of 99.999% was introduced at a flow rate of 60 mL/min, and the temperature in the furnace was increased to 400 ° C, respectively. And at 600 ° C, the heating rate is 5 ° C / min, held for 5 h, and then naturally cooled to room temperature, to obtain a double-domain structure of transition metal nanoparticle catalysts are recorded as Ni / NiAlO _x / AlO _x (R400) and Ni / NiAlO _x /AlO _x (R600) sample (XRD pattern is shown in Figure 2).

The obtained Ni ₂ Al-LDHs precursors were characterized by XRD, FTIR, TG-DTA and SEM. The results are shown in Fig. 1. It can be seen from the figure that the layered structure of hydrotalcite-like structure is obtained, and the overall structure of the material is uniform and uniform, Ni _{2 The} precursor of Al-LDHs is a hexagonal plate-like structure of several tens of nanometers, and the overall thickness is only a dozen nanometers.

The double-domain-structured transition metal nanoparticle catalyst prepared above has a composition structure in which nickel nanoparticles are bounded in an aluminum-doped nickel oxide shell layer, and the outermost layer is a shell structure composed of amorphous alumina. Double-limited nano metal particle structure; the catalyst is a black powdery substance with a single particle size of 4-8 nm; and the total loading of nickel is 65 wt% based on the total mass of the catalyst.

Example 2

The hydrotalcite precursor prepared in the step A of Example 1 was placed in a muffle furnace, air-fired, the furnace temperature was raised to 400 ° C, the heating rate was 5 ° C / min, held for 5 h, and then naturally cooled to room temperature; Then placed in a high-temperature atmosphere furnace, and passed H ₂ with a purity of 99.999%, the flow rate was 60mL/min, respectively increased the furnace temperature to 400 ° C and 600 ° C, the heating rate was 5 ° C / min, held for 5 h, then naturally cooled At room temperature, the transition metal nanoparticle catalysts with double confinement structure were recorded as Ni/NiAlO _x /AlO _x (C400R400) and Ni/NiAlO _x /AlO _x (C400R600) samples (see Figure 2 for XRD pattern).

The R600 obtained in Example 1 and the C400R600 sample material obtained in Example 2 were characterized by XRD. The results are shown in Fig. 2. It can be seen from Fig. 2 that the R600 sample obtained is stronger than the C400R600 sample, and the characteristic peak of Ni is stronger. The degree of reduction is higher, and the characteristic peak of NiO is relatively flat. In the C400R600 sample, NiO still accounts for the majority of the total phase composition.

The R400 and R600 obtained in Example 1 and the C400R400 and C400R600 sample materials obtained in Example 2 were subjected to HRETEM characterization. The results are shown in Fig. 3. As can be seen from Fig. 3, the 3.0-5.0 nm particle size of the obtained R400 sample accounted for 86. %, while the 4.0-6.0 nm particles in the C400R400 sample accounted for 90%. In the R600 sample Particles larger than 5.5-7.5 nm accounted for 85%, while particles of 9.0-12.0 nm in the C400R600 sample accounted for 83%.

The obtained nano-metal particle catalyst Ni/NiAlO _x /AlO _x obtained by double-domain structure was characterized by Cs-corrected STEM. The results are shown in Fig. 4. It can be seen from Fig. 4 that the size of the obtained nanoparticles is mostly 4-7 nm. Between the Ni elements are mainly distributed in the central region of the nanoparticles, and the Al elements are mainly distributed at the edges of the particles and at the junctions of some of the voids. It shows that the obtained nanoparticles have higher dispersion, smaller particle size and uniform shape, especially the nano metal particle catalyst Ni/NiAlO _x /AlO _x which forms a double confinement structure.

Example 3

A. 19.2 g of Co(NO ₃ ) ₂ ·6H ₂ O, 12.4 g of Al(NO ₃ ) ₂ ·9H ₂ O was added to 150 mL of deionized water, and ultrasonically dissolved to obtain a mixed salt solution; 6.3 g of hydr Sodium and 7.0 g of sodium carbonate were added to 150 mL of deionized water, and ultrasonically dissolved to obtain a mixed alkali solution; 150 mL of deionized water was placed in a 500 mL three-necked flask, and then the mixed alkali solution was gradually dropped to a pH of 10, and then mixed at the same time. The salt solution was kept at pH 10; after the addition was completed, the obtained slurry was transferred to a 250 mL Teflon autoclave, crystallized at 130 ° C for 24 h, filtered, washed with deionized water and filtered to pH 7. Finally, drying at 70 ° C for 24 h, to obtain a highly dispersed hydrotalcite precursor, denoted as Co ₂ Al-LDHs;

B. The high-dispersion hydrotalcite precursor Co ₂ Al-LDHs prepared in the step A is placed in a high-temperature atmosphere furnace, and H _{2 having a} purity of 99.999% is passed, the flow rate is 60 mL/min, and the temperature in the furnace is raised to 300 ° C. The heating rate was 5 ° C / min, held for 5 h, and then naturally cooled to room temperature, to obtain a double-domain structure of transition metal nanoparticle catalyst, denoted as Co / CoAlO _x / AlO _x .

The double-domain-structured transition metal nanoparticle catalyst prepared above has a composition structure in which cobalt nanoparticles are confined in an aluminum-doped cobalt oxide shell layer, and the outermost layer is a shell structure composed of amorphous alumina. The double-limited nano metal particle structure; the catalyst is a black powdery substance having a single particle diameter of 4-8 nm; and the total loading of cobalt is 65 wt% based on the total mass of the catalyst.

Example 4

A. 19.5 g of Cu(NO ₃ ) ₂ ·6H ₂ O, 12.4 g of Al(NO ₃ ) ₂ ·9H ₂ O was added to 150 mL of deionized water, and ultrasonically dissolved to obtain a mixed salt solution; 6.3 g of hydr Sodium and 7.0 g of sodium carbonate were added to 150 mL of deionized water, and ultrasonically dissolved to obtain a mixed alkali solution; 150 mL of deionized water was placed in a 500 mL three-necked flask, and then the mixed alkali solution was gradually dropped to a pH of 10, and then mixed at the same time. The salt solution was kept at pH 10; after the addition was completed, the obtained slurry was transferred to a 250 mL Teflon autoclave, crystallized at 130 ° C for 24 h, filtered, washed with deionized water and filtered to pH 7. Finally, drying at 70 ° C for 24 h, to obtain a highly dispersed hydrotalcite precursor, denoted as Cu ₂ Al-LDHs;

B. The high-dispersion hydrotalcite precursor Cu ₂ Al-LDHs prepared in the step A is placed in a high-temperature atmosphere furnace, and H _{2 having a} purity of 99.999% is introduced, the flow rate is 60 mL/min, and the temperature in the furnace is raised to 700 ° C. The heating rate was 5 ° C / min, held for 5 h, and then naturally cooled to room temperature, to obtain a double-domain structure of the transition metal nanoparticle catalyst, denoted as Cu / CuAlO _x / AlO _x .

The double-domain-structured transition metal nanoparticle catalyst prepared above has a composition structure in which copper nanoparticles are bounded in an aluminum-doped copper oxide shell layer, and the outermost layer is a shell structure composed of amorphous alumina. Double-domain nano metal particle structure; the catalyst is a black powdery substance with a single particle diameter of 4-8 nm; and the total loading of copper is 65 wt% based on the total mass of the catalyst.

Example 5

A. 26.7 g of Fe(NO ₃ ) ₂ ·9H ₂ O, 12.4 g of Al(NO ₃ ) ₂ ·9H ₂ O was added to 150 mL of deionized water, and ultrasonically dissolved to obtain a mixed salt solution; 6.3 g of hydr Sodium and 7.0 g of sodium carbonate were added to 150 mL of deionized water, and ultrasonically dissolved to obtain a mixed alkali solution; 150 mL of deionized water was placed in a 500 mL three-necked flask, and then the mixed alkali solution was gradually dropped to a pH of 10, and then mixed at the same time. The salt solution was kept at pH 10; after the addition was completed, the obtained slurry was transferred to a 250 mL Teflon autoclave, crystallized at 130 ° C for 24 h, filtered, washed with deionized water and filtered to pH 7. Finally, drying at 70 ° C for 24 h, to obtain a highly dispersed hydrotalcite precursor, denoted as Fe ₂ Al-LDHs;

B. The high-dispersion hydrotalcite precursor Fe ₂ Al-LDHs prepared in step A was placed in a high-temperature atmosphere furnace, and H _{2 having a} purity of 99.999% was introduced at a flow rate of 60 mL/min, and the temperature in the furnace was increased to 500 ° C, respectively. The heating rate was 5 ° C / min, held for 5 h, and then naturally cooled to room temperature to obtain a double-domain structure of the transition metal nanoparticle catalyst, denoted as Fe / FeAlO _x / AlO _x .

The double-domain-structured transition metal nanoparticle catalyst prepared above has a composition structure in which iron nanoparticles are bounded in an aluminum-doped iron oxide shell layer, and the outermost layer is a shell structure composed of amorphous alumina. The double-limited nano metal particle structure; the catalyst is a black powdery substance, the single particle diameter is 4-8 nm; and the total loading of iron is 65 wt% based on the total mass of the catalyst.

Application example 1

0.25 g of the catalyst sample prepared in Example 1 and Example 2 was placed in a 300 mL high temperature autoclave, 1.0 g of dimethyl terephthalate reactant was added, and 80 mL of isopropanol was added as a solvent; The second N ₂ was refilled and discharged 3 times of H ₂ , and finally the hydrogen pressure was maintained at 6 MPa, the reaction temperature was set to 90 ° C, stirring was started, and the time was recorded. When the reaction time was 4 h, the stirring and heating apparatus were stopped, and after waiting for cooling to room temperature, the liquid in the autoclave was taken to obtain a reaction product. The reaction product was analyzed by gas chromatography (the reaction results are shown in Table 1). Table 1 is a table showing the conversion and selectivity data for the catalytic hydrogenation of dimethyl terephthalate in R400, R600, C400R400, C400R600 and commercial 65% Ni-based catalyst samples in Example 1.

Table 1

According to the preparation method provided by the invention, the nano metal particle catalyst Ni/NiAlO _x /AlO _x prepared by the double confinement structure is particularly suitable for the selective hydrogenation reaction of dimethyl terephthalate. Compared with R400 and C400R400, C400R600 and Commercial Ni catalyst samples, the results are shown in Table 1:

1) It can be seen from Table 1 that the nano metal particle catalyst R600 sample of the double confinement structure has the highest conversion rate of 99.9% for the dimethyl terephthalate reactant.

2) It can be seen from Table 1 that the conversion rate of the sample calcined prior to air is lower than that of the directly reduced sample, only 30.3% for C400R400 and 79.8% for C400R600. And as can be seen from Figure 3, R400 has a smaller particle size than C400R400, and R600 and C400R600 have larger particle sizes. This indicates that the catalyst prepared by the direct reduction method has a stronger interaction between the metal and the substrate, and the metal active site is more temperature, so that the activity is improved at the same degree of reduction.

3) It can be seen from Table 1 that the sample R400 reduced at a lower temperature has a smaller particle size than the R600 sample (Fig. 3), but the conversion rate is significantly lower than that of the latter, and it is known that the double confinement structure has a higher The degree of reduction and the interaction between the metal and the substrate lead to higher catalytic activity.

4) It can be seen from Table 1 that the obtained nano-metal particle catalyst with double-domain structure has much higher activity for hydrogenated terephthalate than commercial catalyst, and the conversion rate of commercial catalyst is only 32.2%.

5) It can be seen from Table 1 that the influence of each sample on the conversion rate of the reaction is not obvious, and the influence on the reactivity is obvious.

Claims

A double-domain-constrained transition metal nanoparticle catalyst characterized in that the composition of the transition metal nanoparticles is limited to an aluminum-doped transition metal oxide shell layer, and the outermost layer is composed of amorphous alumina. The shell structure forms a double-limited nano metal particle structure; the catalyst is a black powdery substance having a single particle diameter of 4-8 nm; and the total loading of the transition metal is 60-66 wt% based on the total mass of the catalyst.
A method for preparing a transition metal nanoparticle catalyst with double confinement structure, characterized in that the specific operation steps are as follows:

A. The hydrotalcite precursor is dried at 60-100 ° C for 24-36 h, then calcined in a muffle furnace at 300-700 ° C for 2-8 h in an air atmosphere, and the heating rate is 2-10 ° C / min to obtain aluminum doping. Miscellaneous transition metal oxides;

B. The aluminum-doped transition metal oxide is placed in an atmosphere furnace, heat-treated at 300-700 ° C for 0.5-6 h under a hydrogen atmosphere, the heating rate is 2-10 ° C / min; the hydrogen flow rate is 30-80 mL / min, the reaction is completed The transition metal nanoparticle catalyst with double confinement structure is obtained.
The invention discloses a preparation method of a transition metal nanoparticle catalyst with double confinement structure, characterized in that the specific operating condition is: placing the hydrotalcite precursor in an atmosphere furnace, heat-treating at 300-700 ° C for 0.5-6 h under a hydrogen atmosphere, The heating rate is 2-10 ° C / min; the hydrogen flow rate is 30-80 mL / min, after the reaction is completed, the transition metal nanoparticle catalyst with double confinement structure is obtained.
The preparation method according to claim 2 or 3, wherein the divalent metal ions in the laminate of the hydrotalcite precursor are selected from transition metal ions, and the trivalent metal ions are aluminum ions.
The preparation method according to claim 4, wherein the transition metal ion is one or more of Ni 2+ , Co 2+ , Cu 2+ , and Fe 2+ .
The use of the double-domain-structured transition metal nanoparticle catalyst prepared by the method according to claim 2 or 3 to catalyze the selective hydrogenation of dimethyl terephthalate.
The use according to claim 6, wherein the reaction condition of the double-domain-structured transition metal nanoparticle catalyst for catalyzing the selective hydrogenation of dimethyl terephthalate is: dimethyl terephthalate is The amount of the transition metal nanoparticle catalyst of 0.5-2.5 g, double-domain structure is 0.15-0.5 g, the solvent is 80-100 mL, the reaction temperature is 80-130 ° C, the hydrogen pressure is 2-8 MPa, and the reaction time is 3-6 h.
The use according to claim 7, wherein the solvent is one or more selected from the group consisting of isopropyl alcohol, ethanol, and ethyl acetate.