CN113398938A

CN113398938A - Methanol synthesis catalyst and preparation method thereof

Info

Publication number: CN113398938A
Application number: CN202110628924.6A
Authority: CN
Inventors: 赵天生; 周康; 贾红霞; 马清祥; 张建利; 高新华; 范素兵
Original assignee: Ningxia University
Current assignee: Ningxia University
Priority date: 2021-06-07
Filing date: 2021-06-07
Publication date: 2021-09-17

Abstract

The invention provides a methanol synthesis catalyst. The catalyst is prepared by a solid phase grinding method and can be used for methanol synthesis under the condition of low temperature. The method has the advantages of few preparation steps, no reduction before use, high methanol selectivity and contribution to solving the problems of more preparation steps, low methanol selectivity and the like of the catalyst in the prior art. The catalyst comprises copper, zinc oxide and zirconium oxide, wherein the mass content of the copper is 30-65%, the mass content of the zinc oxide is 10-30%, and the mass content of the zirconium oxide is 10-35%.

Description

Methanol synthesis catalyst and preparation method thereof

Technical Field

The invention belongs to the technical field of catalysts, and relates to a low-temperature methanol synthesis catalyst. In particular to CO/CO₂/H₂The raw material gas is used for synthesizing the copper-based catalyst for methanol.

Background

Methanol is used as basic chemical raw material, can be used for producing formate, dimethyl ether, olefin, aromatic hydrocarbon and the like, and can also be used as vehicle fuel, fuel cell raw material and the likeAngew. Chem. Int. Ed. 2013, 52, 104-107). The demand of methanol in China continuously rises. The industrial methanol synthesis is mainly carried out by Cu/ZnO/Al₂O₃Catalyst synthesis gas (CO/CO)₂/H₂) Is generated under high temperature (200 ℃ C.) and high pressure (5-10 MPa). The problems of low single-pass conversion rate of raw materials, strong water gas shift, easy sintering of the catalyst and the like exist. From CO/CO₂/H₂The preparation of methanol from raw material gas is a favorable reaction at low temperature, but a high-efficiency low-temperature catalyst needs to be developed.

Industrial methanol synthesis Cu/ZnO/Al₂O₃Cu in the catalyst is an active component, ZnO and Al₂O₃The catalyst is an electronic assistant and a structural assistant respectively, and the synergistic effect of the electronic assistant and the structural assistant is a key factor for the catalyst to exert activity. But the catalyst preparation is complicated and the activity is low. The preparation of Cu/ZnO catalyst by formic acid auxiliary grinding method has been reported, but the problems of low surface area and low methanol selectivity are needed to be solved. ZrO (ZrO)₂The acid-base property and the oxidation-reduction property are used for preparing the high-temperature copper-based catalyst for methanol synthesis (RSC Adv., 2017, 7，8709−8717）。Cu、ZrO₂The interaction between the two can promote the hydrogen overflow effect on the surface of the catalyst and improve the selectivity of methanol.

To control the greenhouse effect, CO is added₂Change to chemicals is of concern. The problem that the copper-based catalyst used in industry is applied to methanol synthesis under low temperature condition, the conversion rate of raw material gas and the selectivity of methanol are low, etc. (Chem. Rev., 2016, 116,3722– 3811) And more wastewater is generated in the preparation process. Therefore, the improvement of the activity of the copper-based methanol synthesis catalyst, the increase of the methanol selectivity, the energy conservation and the consumption reduction are the research focuses of the technicians in the field.

Disclosure of Invention

The invention aims to overcome the defects of complex preparation process, low methanol selectivity, higher byproduct content, difficult product utilization and the like of the existing Cu-based methanol synthesis catalyst, and provides a copper-based methanol catalyst for quickly synthesizing high dispersity, multiple active sites and high methanol selectivity and a preparation method thereof.

The catalyst provided by the invention does not need to undergo a reduction step, realizes self-reduction and catalyst motif self-assembly through formic acid decomposition, and has multiple active sites under a hydrogenation reaction atmosphere, so that the alcohol forming activity is effectively enhanced on a molecular level. Meanwhile, the formic acid plays a role in structure guiding and optimizing the structure of the catalyst. Copper species of Cu⁰、Cu₂O, etc. multi-valence state dispersed and stabilized in ZnO and ZrO₂On the primitive, the atom utilization rate can be exerted to the maximum extent. The catalytic activity shows that the selectivity of the synthesized methanol is high.

The method avoids a long preparation process, and the preparation can be completed within 18-22 h, namely the period can be shortened to complete within one day in the rapid preparation. And the operation process does not produce secondary pollutants such as wastewater and the like.

The present invention has been made in an intensive study for solving the above problems, and a series of experiments have been conducted to obtain CO and CO₂The best composition and preparation conditions of the methanol synthesis catalyst with high conversion rate and high methanol selectivity, thereby perfecting the invention.

The invention adopts a solid phase grinding method to prepare mesoporous Cu⁰-CuO-Cu₂O/ZnO@ZrO₂The catalyst has the specific technical scheme that: the specific surface area of the catalyst is 10-30 m²Per g, containing Cu⁰、CuO、Cu₂O, ZnO and ZrO₂Wherein the mass content of the copper species is 30-65%; the exposed Cu crystal planes are oriented as (111), (200), (220); ZrO (ZrO)₂Is in an amorphous state; the valence of Cu is 0, +1, + 2. The catalyst of the invention is Cu⁰-CuO-Cu₂O/ZnO@ZrO₂；Cu⁰Dispersed in ZrO by atoms₂The above step (1); cu relative to the total atomic number of Cu⁰10-40% of the total; cu₂O accounts for 1-20%; cu⁰、Cu₂The O-O interface is limited by a local electron environment, has coupling force and is stabilized at ZnO @ ZrO₂The above step (1); the electronic environment is generated by formic acid in situ induction; cu⁰、Cu₂O is generated by in-situ reduction of formic acid; in CO and CO₂Mixing and addingIn hydrogen atmosphere, the catalyst does not undergo a reduction step, and Cu is present at the active site⁰-CuO、Cu⁰-Cu₂O、Cu⁰-CuO-Cu₂O、Cu⁰-Cu₂O-ZnO、Cu⁰-Cu₂O-ZnO- ZrO₂、Cu⁰-CuO-Cu₂O-ZnO- ZrO₂。

The catalyst of the invention presents the accumulation morphology of spherical particles, ZnO and ZrO₂With respect to the m-stacking, expressed as @, ZnO @ ZrO₂Can coordinate with copper species to catalyze CO₂Hydrogenation to alcohols; ZnO content of 10-30 wt%, ZrO₂The mass content is 10-35%; ZrO (ZrO)₂Is in an amorphous state. The dispersion degree of copper in the catalyst is higher than 15 percent; the exposed Cu crystal planes are oriented as (111), (200), (220).

The preparation method of the methanol synthesis catalyst comprises the following steps:

(1) grinding nitrates of copper, zinc and zirconium for 10 min;

(2) adding formic acid, and continuously grinding for 10 min under the ultrasonic environment; the addition amount of formic acid is as follows according to molar ratio: HCOOH/(Cu)²⁺+Zr⁴⁺)=12～20；

(3) Vacuum drying at 120 ℃ and N₂Roasting for 1-3 h at 300-500 ℃ in the atmosphere, and passivating for 0.2-1 h by 1% oxygen. The passivated metal being oxidized, e.g. Cu⁰A CuO protective layer is formed on the surface.

In step (1), one or more of cerium, magnesium, iron, lanthanum, manganese elements may be simultaneously doped to improve copper species dispersion and catalytic activity. The prepared catalyst is presented as a multi-metal catalyst.

It is worth noting that: the roasting mode of the step (3) is as follows: heating the mixture from room temperature to 300-500 ℃ at the speed of 2 ℃/min, and calcining the mixture for 3 hours, wherein N is₂The flow rate is 30-50 mL/min; roasting to produce CO and H₂Reducing gas, copper species are reduced, and the catalyst metal elements self-assemble.

Procedure for evaluating the activity of the catalyst of the invention: the reaction is carried out in a batch slurry bed reactor (the internal volume is 100 mL), and the raw material gas comprises 25-35 percent of CO and CO₂(0-10%) and H₂(55～65 %) The solvent: 40 mL of ethanol, 1-4 g of catalyst, reaction temperature of 150 ℃, reaction pressure of 3-5 MPa, stirring speed of 850 r.p.m., and reaction time of 2-8 h.

Drawings

FIG. 1 is the phase of a sample of the catalyst of example 2. FIG. 2 is a scanning electron micrograph of example 2. FIG. 3 is a photoelectron spectrum of example 2.

Detailed Description

Example 1

Weighing 10.67 g Cu (NO)₃)₂‧3H₂O、4.38 g Zn(NO₃)₂‧6H₂O with 2.53 g Zr (NO)₃)₄‧5H₂Placing O in a mortar for grinding; 31.0 g of formic acid solution (88%) was added and the mixture was ground for about 10 min, starting to react and becoming slurry gradually as the raw materials were ground. Continuing to perform ultrasonic grinding for 10 min and stopping grinding; drying the product at 130 ℃ for 10 h in a tube furnace N₂Roasting for 3 h at the temperature of 400 ℃, cooling to room temperature and passivating for 3 h to obtain the finished catalyst. Evaluation of methanol Synthesis Activity: the raw material gas consists of 31.2 percent of CO and CO₂5.0%、H₂61.8 percent. The reaction temperature was 150 ℃ and the reaction pressure was 3 MPa, and the results are shown in Table 1.

Example 2

9.79 g of Cu (NO) was weighed₃)₂‧3H₂O、4.02 g Zn(NO₃)₂‧6H₂O with 4.64 g Zr (NO)₃)₄‧5H₂Placing O in a mortar for grinding; 32.30 g of formic acid solution (88%) was added and the mixture was ground for about 10 min, starting to react and becoming slurry gradually as the starting material was ground. Continuing to perform ultrasonic grinding for 10 min and stopping grinding; drying the product at 130 ℃ for 10 h in a tube furnace N₂Roasting for 3 h at the temperature of 400 ℃, cooling to room temperature and passivating for 3 h to obtain the finished catalyst. The methanol synthesis activity was evaluated in reference to example 1, and the results are shown in Table 1.

Example 3

Weigh 8.64 g Cu (NO)₃)₂‧3H₂O、3.55 g Zn(NO₃)₂‧6H₂O with 6.14 g Zr (NO)₃)₄‧5H₂Placing O in a mortar for grinding; 31.50 g formic acid solution (88%) was added and ground for about 10 min with no further grindingThe ground starting material started to react and became gradually slurry. Continuing to perform ultrasonic grinding for 10 min and stopping grinding; drying the product at 120 ℃ for 10 h in a tube furnace N₂Roasting for 3 h at the temperature of 400 ℃, cooling to room temperature and passivating for 3 h to obtain the finished catalyst. The methanol synthesis activity was evaluated in reference to example 1, and the results are shown in Table 1.

Example 4

9.78 g of Cu (NO) was weighed out₃)₂‧3H₂O、4.02 g Zn(NO₃)₂‧6H₂O、0.45 g Ce(NO₃)₄‧3H₂O with 4.01 g Zr (NO)₃)₄‧5H₂Placing O in a mortar for grinding; 27.6 g formic acid solution (88%) was added and ground for about 10 min. With continued grinding, the material started to react and became gradually slurried. Continuing to perform ultrasonic grinding for 10 min and stopping grinding; the product was dried at 120 ℃ for 10 h and placed in a tube furnace N₂Roasting for 3 h at the temperature of 400 ℃, cooling to room temperature, and passivating for 3 h to obtain the finished catalyst. The methanol synthesis activity was evaluated in reference to example 1, and the results are shown in Table 1.

Example 5

Catalyst preparation reference was made to example 2. The calcination temperature of the catalyst precursor is 300 ℃,

evaluation of methanol Synthesis Activity: see table 1 for results with reference to example 1.

Example 6

Catalyst preparation reference was made to example 2. The roasting temperature of the catalyst precursor is 500 ℃,

Fig. 1 shows that the X-ray characteristic diffraction peaks of the prepared catalyst samples at 2 θ = 43.4 °, 50.6 ° and 74.2 ° are assigned to the (111), (200) and (220) crystal planes of Cu, and the characteristic diffraction peaks at 2 θ = 31.8 °, 34.4 °, 36.3 °, 47.5 °, 56.6 °, 62.9 °, 67.9 ° and 72.5 ° are assigned to the (100), (002), (101), (102), (110), (103), (112), (004) crystal planes of ZnO. No occurrence of ZrO₂Characteristic diffraction peak, indicating ZrO₂Is in an amorphous state.

FIG. 3 is an X-ray photoelectron spectrum of example 2. Cu 2pThe electron binding energies in the spectrum are around 932.3 eV and 952.3 eVTwo peaks ascribed to Cu 2p _3/2And Cu 2 p _1/2. In addition, the Auger spectrum Cu LMM-XAES spectrum shows two peaks which are respectively positioned at 916.8 eV and 918.7 eV, and the Cu is shown in the catalyst⁰And Cu⁺Species co-exist.

Table 1 shows the methanol synthesis activity of the catalyst. ZrO of₂The content is increased, the catalytic activity is increased and then reduced, and the selectivity of the methanol is kept stable. The catalyst activity was highest when Zr addition was 26%. The catalyst has high activity, and the adsorption and activation performance of the catalyst on the feed gas is enhanced when the Zr content is high; and the dispersion of the active component Cu was promoted, corresponding to the catalyst prepared in example 2. By using N₂The dispersion degree of Cu in the catalyst of example 2 was determined by O-titration to be 17.6%, and the degree of Cu dispersion was good.

TABLE 1 Low temperature methanol Synthesis Activity of the catalysts

Examples	CO conversion (%)	CO₂Conversion (%)	CH₃OH selectivity (%)
				1	25.5	47.1	89.2
2	27.3	57.4	89.9
				3	27.2	47.7	88.4
4	22.3	52.0	91.3
				5	23.2	59.4	89.9
6	33.8	51.6	89.1

Claims

1. A methanol synthesis catalyst, characterized in that: the catalyst is Cu⁰-CuO-Cu₂O/ZnO@ZrO₂(ii) a Cu relative to the total atomic number of Cu⁰10-40% of the total; cu₂O accounts for 1-20%; cu⁰、Cu₂O at ZnO @ ZrO₂The above step (1); cu⁰、Cu₂O is generated by in-situ reduction of formic acid; in CO and CO₂In mixed hydrogenation atmosphere, the catalyst does not undergo a reduction step, and Cu exists at the site for promoting activity⁰-CuO、Cu⁰-Cu₂O、Cu⁰-CuO-Cu₂O、Cu⁰-Cu₂O-ZnO、Cu⁰-Cu₂O-ZnO-ZrO₂、Cu⁰-CuO-Cu₂O-ZnO-ZrO₂。

2. The methanol synthesis catalyst of claim 1, wherein the catalyst exhibits a spherical particle packing morphology, ZnO @ ZrO₂Can coordinate with copper species to catalyze CO₂Hydrogenation to alcohols; ZnO content of 10-30 wt%, ZrO₂The mass content is 10-35%; ZrO (ZrO)₂Is in an amorphous state.

3. A methanol synthesis catalyst as claimed in claim 1, characterized in that the degree of dispersion of copper in the catalyst is higher than 15%; the exposed Cu crystal planes are oriented as (111), (200), (220).

4. The methanol synthesis catalyst according to claim 1, characterized in that the catalyst preparation method comprises the steps of:

(1) grinding nitrates of copper, zinc and zirconium for 10 min;

(3) Vacuum drying at 130 ℃ for 10 h and N₂Roasting for 1-3 h at 300-500 ℃ in the atmosphere, and passivating for 1-3 h by 1% oxygen.

5. The methanol synthesis catalyst according to claim 4, wherein in step (1), one or more of cerium, magnesium, iron, lanthanum, manganese elements may be simultaneously incorporated to improve copper species dispersion and catalytic activity.