CN114632538A

CN114632538A - Pd/Ce-F/MCM-48 catalyst and preparation method and application thereof

Info

Publication number: CN114632538A
Application number: CN202210338228.6A
Authority: CN
Inventors: 崔艳红; 王彦宏; 汪颖军; 孙鹏; 所艳华; 张微; 卢志涛
Original assignee: Northeast Petroleum University; Heilongjiang Bayi Agricultural University
Current assignee: Northeast Petroleum University; Heilongjiang Bayi Agricultural University
Priority date: 2022-04-01
Filing date: 2022-04-01
Publication date: 2022-06-17
Anticipated expiration: 2042-04-01
Also published as: CN114632538B

Abstract

The invention discloses a Ce-F/MCM-48 mesoporous material and a Pd catalyst taking the mesoporous material as a carrier. The invention utilizes an NaF and Ce in-situ doping hydrothermal synthesis method to synthesize Ce-F/MCM-48, and adopts an impregnation method to prepare the Pd/Ce-F/MCM-48 bimetallic catalyst taking Ce-F/MCM-48 as a carrier Pd for loading. The catalytic performance of the catalyst for n-heptane isomerization reaction was examined. The results show that: the molecular sieve prepared by adding NaF doping has the advantages of increased specific surface area and pore volume, uniform pore size distribution and moderate acidity. The optimal loading amount of the noble metal Pd is 0.4 percent by mass, the reaction temperature is 280 ℃, the catalytic performance is relatively stable when the reaction time is 120min, the conversion rate of n-heptane isomerization is 79.7 percent, and the selectivity of iso-heptane is 91.5 percent. Is expected to become an important catalyst for n-heptane hydroisomerization.

Description

Pd/Ce-F/MCM-48 catalyst, and preparation method and application thereof

Technical Field

The invention belongs to the technical field of catalysts, and particularly relates to a Pd/Ce-F/MCM-48 catalyst, and a preparation method and application thereof.

Background

Upgrading of the quality of the catalytic gasoline is a main problem which must be faced and solved in the coming years of China. The conversion of straight-chain alkane into branched-chain alkane is the most important means for ensuring the octane number of gasoline. Heptane isomerization catalyst preparation is also of great interest. Currently, the supported metal catalyst is mostly prepared for the heptane isomerization catalyst. The property of the carrier has a great influence on the catalyst, and in the preparation of the carrier material, scientists of Mobil corporation in the early 90 th 20 th century reported the synthesis of M41S [ Beck J S, Vartuli J C, Roth W J, et al.A new family of molecular sieves prepared with liquid crystals [ J ] J.J.chem.sol, 1992,114(27):10834-10843 ] mesoporous molecular sieves, MCM-48 is a member of M41S series, and the material has a double-helix three-dimensional pore structure and good transmission performance, and is expected to be applied in the field of catalysis.

However, as MCM-48 silicon-oxygen tetrahedron is a charge balance system, the pure silicon mesoporous molecular sieve has few lattice defects in the framework, low surface acid center concentration and no catalytic oxidation reaction capability, and can not be directly used as a catalyst generally, the mesoporous molecular sieve needs to be functionally modified, the most modification method is to carry out heteroatomic reaction aiming at different catalytic reactions, and the other important carrier modification method is to introduce anions into the molecular sieve framework.

Disclosure of Invention

It is an object of the present invention to provide an anion-doped mesoporous material with a high degree of order.

The anion-doped mesoporous material (Ce-F-MCM-48) with high order degree provided by the invention takes CTAB as a template, NaF and Ce (NO)₃)·6H₂O is an additive reagent, TEOS (tetraethyl orthosilicate) is a silicon source, and the catalyst is prepared by a hydrothermal synthesis method under an alkaline condition.

Wherein, in the initial reaction system, n (TEOS), n (CTAB), n (Ce), n (NaF) and NaF are respectively 1.0:0.65:0.02 (0-0.15), but the dosage of NaF is not 0. Specifically, n (TEOS): n (CTAB): n (Ce): n (NaF): 1.0:0.65:0.02:0.05 or 1.0:0.65:0.02:0.10 or 1.0:0.65:0.02: 0.15.

Further, the alkaline condition can be provided by NaOH, in the initial reaction system, n (TEOS): n (CTAB): n (H)₂O, n (NaOH), n (Ce), n (NaF) 1.0:0.65:62:0.5, (0.01-0.05) 0-0.15, but NaF is not used in an amount of 0. Specifically, n (TEOS) n (CTAB) n (H)₂O):n(NaOH):n(Ce):n(NaF)＝1.0:0.65:62:0.5:0.02:0.10。

The hydrothermal synthesis method comprises the following hydrothermal conditions: and transferring the initial gel prepared from the reaction mixture into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and putting the reaction kettle into a drying oven for crystallization at a constant temperature of 100-140 ℃ for 12-108 h, specifically for crystallization at a constant temperature of 110 ℃ for 72 h.

After the hydrothermal synthesis method is finished, the method also comprises the steps of drying and roasting the product.

The drying conditions are as follows: drying for 4-24 h at 70-100 ℃ on an electric hot plate, and drying for 4-12 h in a drying box at 105-120 ℃.

The roasting conditions can be as follows: and roasting the dried product in a resistance furnace at 300-800 ℃ for 2-10 h, specifically at 550 ℃ for 6 h.

The specific preparation method of the anion-doped mesoporous material with high order degree comprises the following steps:

firstly, NaOH is dissolved in deionized water and stirred evenly, and NaF and Ce (NO) are added in sequence₃)·6H₂Stirring for 15-60 min by using O, adding CTAB into the mixture for multiple times in a small amount under the condition of heating in a water bath at 35-45 ℃, and stirring for 60-180 min, wherein the solution is transparent; then gradually and intermittently adding TEOS into the solution, continuously stirring for 30-180 min, wherein the molar ratio of the raw materials of the reaction mixture is n (TEOS), n (CTAB), n (H)₂O, n (NaOH), n (Ce), n (NaF) 1.0:0.65:62:0.5, (0.01-0.05) 0-0.15; transferring the prepared initial gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and putting the initial gel into a drying oven for constant-temperature crystallization at 100-140 ℃ for 12-108 hours; washing and filtering the product; drying for 4-24 h at 70-100 ℃ on an electric hot plate, drying for 4-12 h in a drying box at 105-120 ℃, and roasting for 2-10 h in a resistance furnace at 300-800 ℃, so as to obtain a sample labeled as Ce-F/MCM-48-x.

Another object of the present invention is to provide a catalyst supporting a metal active component and a method for preparing the same.

The active component of the catalyst loaded with the metal active component is noble metal palladium, and the carrier is the mesoporous material Ce-F/MCM-48; the catalyst is Pd-Ce-F/MCM-48; the supported amount (mass fraction) of Pd in the catalyst is 0-0.5% (excluding 0).

The catalyst loaded with the metal active component is prepared by adopting an impregnation method and comprises the following steps:

dissolving Pd in deionized water, and then immersing the prepared Ce-F/MCM-48-x in the deionized water; ultrasonic dispersing, standing at room temperature for more than 6h, drying and roasting to obtain the Pd supported catalyst which is recorded as Pd-Ce-F/MCM-48.

In the method, the ultrasonic dispersion condition can be 40-80 ℃ for 10-120 min;

in the above method, the drying specifically comprises: drying the electric hot plate for 4 to 24 hours at 70 to 100 ℃, and drying the electric hot plate for 4 to 12 hours in a drying oven at 105 to 120 ℃.

In the method, the roasting condition is that roasting is carried out for 2-10 h at 300-400 ℃, and specifically roasting can be carried out for 4h at 400 DEG C

It is a further object of the present invention to provide the use of the above catalyst supporting a metal active component.

The application is that the catalyst is used for catalyzing isomerization of n-heptane.

The invention also provides a method for catalyzing the isomerization of the n-heptane.

The method for catalyzing the isomerization of the n-heptane provided by the invention takes the Pd-Ce-F/MCM-48 as a catalyst to catalyze the isomerization of the n-heptane; the reaction conditions are as follows: the reaction temperature is 220-360 ℃ (preferably 260-320 ℃, and more preferably 280-300 ℃); the reaction time is 60-240 min (preferably 100-200 min, more preferably 120-150 min).

Preferably, the optimal load of the noble metal Pd in the Pd-Ce-F/MCM-48 is 0.4 percent by mass, the reaction temperature is 280 ℃, and the catalytic performance is relatively stable when the reaction time is 120 min.

The Pd-Ce-F/MCM-48 catalyst needs to be activated before being used, and the activation conditions are as follows: activating for 1-5 h under the conditions of 1.0MPa of pressure and 300-400 ℃ in a hydrogen atmosphere.

Further, in the isomerization process, the hydrogen flow rate is 10-50 mL/min, and the weight hourly space velocity is 3.5-8.0 h^-1。

Compared with the prior art, the invention has the following technical effects:

firstly, the invention synthesizes a new mesoporous material, NaF is a good structural auxiliary agent, and the application is characterized in that the ratio of n (Ce): n (Si) doping amount is under the condition of 0.02 mol ratio, and the optimal n (F) is determined by regulating and controlling the proportion of fluorine silicon raw materials: the molar ratio of n to (Si) is 0.10, and a hydrothermal method is adopted to successfully synthesize the highly ordered F/Ce-MCM-48 mesoporous material. F compared to MCM-48 and Ce-MCM-48^-1After the introduction, the specific surface area and the pore volume of the Ce/F-MCM-48 are increased (see table 1), and as can be seen from figure 6, the pore size distribution range is narrower, the Ce/F-MCM-48 is composed of a large number of mesopores with uniform pore sizes, the pore size distribution tends to be uniform (figure 6), the range of the capacity of the carrier to elements is wide (see table 2), and the acid amount and the acid strength are enhanced (figure 7).

TABLE 1 structural parameters of catalyst samples

TABLE 2 elemental data for Ce-MCM-48 catalyst

Theoretical and measured values of elemental compositions of the prepared Ce-MCM-48 mesoporous material and 0.4% Pd-Ce (f) -MCM-48-x (x ═ 0, 0.10) catalyst are given in table 2. According to the molar ratio of the raw materials of the reaction mixture of n (TEOS), n (CTAB), n (H)₂O, n (NaOH), n (NaF) 1.0, 0.65, 62, 0.5, 0.02, x (x) 0, 0.10). As can be seen from Table 2, F is introduced^-1The actual load rate of the F element in the later Ce (F) -MCM-48-0.10 molecular sieve is 63.3 percent, the actual load rate of the first metal Ce is slightly reduced to 95.5 percent, which shows that the F is doped^-1The first metal is not peeled off. The actual load ratios of Pd, F and Ce in the Pd-impregnated 0.4% Pd-Ce-F/MCM-48-0.10 catalyst are respectively 97.2%, 63.1% and 94%; with the impregnation of Pd, the F, Ce content was unaffected and no flaking occurred. The range of capacities of the illustrative carriers is wide.

TABLE 3 surface acidity of the catalyst

FIG. 7 shows NH of MCM-48, Ce-MCM-48 and Ce/F-MCM-48₃The TPD curve, it can be analyzed from fig. 7 and table 3 that the acid content of the mesoporous material is increased, the acid strength is increased, the acid content of MCM-48 is almost zero, and the acid content of the MCM-48 mesoporous material is increased after rare earth Ce is introduced. Introduction of F^-1The acid content is increased.

Secondly, the catalyst which loads noble metal palladium on the mesoporous material is not reported in documents before, and after Pd is loaded by an impregnation method, a high-quality catalyst new material Pd-Ce-F/MCM-48 with good palladium metal dispersity and high sustainable doping amount is obtained.

Thirdly, the application also focuses on the catalytic performance of the catalyst. The catalyst catalytic performance is particularly inspected on a micro reaction device by taking the n-heptane isomerization reaction as a probe. The result shows that the optimal loading amount of the noble metal Pd is 0.4 percent by mass, the reaction temperature is 280 ℃, the reaction time is 120min, the catalytic performance is relatively stable, the conversion rate of n-heptane isomerization is 79.7 percent, and the selectivity of iso-heptane is 91.5 percent. A molecular sieve material is constructed, the octane number of gasoline is improved by alkane isomerization, and the molecular sieve material has important application prospect along with the enhancement of energy conservation, emission reduction and environmental protection awareness.

Drawings

FIG. 1 is a small angle XRD diffractogram of the Ce-F/MCM-48 mesoporous material of example 1.

FIG. 2 is a small angle XRD diffractogram of the mesoporous material Pd-/Ce-F/MCM-48 of example 2.

FIG. 3 is a scanning electron micrograph of Ce-F/MCM-48 of example 1.

FIG. 4 is a wide angle XRD diffractogram of Pd-Ce-F/MCM-48 of example 2.

FIG. 5 is a transmission electron micrograph of Ce-F/MCM-48 of example 1.

FIG. 6 is a graph of the pore size distribution of Ce-F/MCM-48 of example 1.

FIG. 7 is NH of Ce-F/MCM-48 of example 1₃-TPD map.

FIG. 8 is a transmission electron micrograph of Pd-F/Ce-MCM-48 of example 2.

FIG. 9 is a transmission electron micrograph of the fluorine-undoped 0.4% Pd-Ce-MCM-48 of comparative example 1.

FIG. 10 is a bar graph of x% Pd-Ce-F/MCM-48 catalyst performance with Pd content in example 3.

FIG. 11 is a bar graph of the performance of the 0.4% Pd-Ce-F/MCM-48 catalyst in example 3 as a function of reaction temperature.

FIG. 12 is a bar graph of the performance of the 0.4% Pd-Ce-F/MCM-48 catalyst of example 3 as a function of reaction time.

Detailed Description

The present invention will be further illustrated with reference to the following specific examples, but the present invention is not limited to the following examples. The method is a conventional method unless otherwise specified. The starting materials are commercially available from the open literature unless otherwise specified.

Example 1 preparation of anion-doped mesoporous Material with high degree of order Ce-F/MCM-48

Using CTAB as template, NaF and Ce (NO)₃)·6H₂O is an additive reagent, and is prepared by a hydrothermal synthesis method under an alkaline condition.

Firstly, NaOH is dissolved in deionized water and stirred evenly, and NaF and Ce (NO) are added in sequence₃)·6H₂Stirring for 30min, adding CTAB into the mixture for 90min while heating in 35 deg.C water bath, stirring to obtain transparent solution, adding TEOS into the solution dropwise and intermittently with 3mL plastic pipette, and stirring for 60min₂O, n (NaOH), n (Ce), n (NaF) 1.0:0.65:62:0.5:0.02: 0.10. The prepared initial gel is transferred into a stainless steel reaction kettle with a polytetrafluoroethylene lining and is put into a drying oven for crystallization for 72 hours at the constant temperature of 110 ℃. The product is washed by water and filtered. Drying on an electric hot plate at 90 ℃ for 6h, drying in a drying oven at 105 ℃ for 5h, and roasting in a resistance furnace at 550 ℃ for 6 h. The sample obtained is designated Ce-F/MCM-48-x, x represents the molar ratio of the raw materials of the reaction mixture n (TEOS): n (NaF).

Example 2 preparation of a catalyst supporting a Metal active component

The active component of the catalyst loaded with the metal active component is noble metal palladium, and the carrier is the mesoporous material Ce-F/MCM-48 prepared in the embodiment 1; the catalyst is Pd-Ce-F/MCM-48.

The catalyst was prepared by impregnation with a Pd loading (mass fraction) of 0.4%. Pd was dissolved in a porcelain crucible of deionized water, and then Ce-F/MCM-48-0.10 was immersed therein. Ultrasonic dispersing at 50 deg.C for 20 min. Standing at room temperature for more than 6h, drying on an electric hot plate at 90 ℃ for 4h, drying in a drying oven at 105 ℃ for 5h, and calcining at 400 ℃ for 4h to obtain the Pd-supported catalyst, which is recorded as 0.4% Pd-Ce-F/MCM-48.

Comparative example 1 preparation of a non-fluorine-doped 0.4% Pd-Ce-MCM-48 catalyst

A fluorine-free 0.4% Pd-Ce-MCM-48 catalyst was prepared according to the procedure of example 2, except that the support was prepared essentially as in example 1, except that NaF was not added.

Example 3, evaluation of catalytic reaction Performance of 0.4% Pd-Ce-F/MCM-48 for catalyzing isomerization of n-heptane

And the catalytic reaction performance evaluation is carried out on a fixed bed micro reaction device, and the prepared catalyst is subjected to tabletting and screening to obtain 60-80-mesh particles for later use. The loading was 0.3g, and the mixture was mixed with quartz sand and placed in a reaction tube having an inner diameter of 6 mm. The catalyst is activated for 4 hours under the conditions of 1.0MPa of pressure and 300 ℃ in the hydrogen atmosphere before reaction, and then cooled to 220-360 ℃ for modulation. The reaction evaluation process condition is pressure n-C₇Flow rate 6.0mL/H, n-H₂The flow rate is 30mL/min, the MHSV is 7.6h^-1. And (5) starting sampling after stabilizing for 30min, and performing on-line analysis on the composition of a product by using a gas chromatograph FID detector after the product is separated by a chromatographic column.

In the embodiment, the relationship between the performance of the 0.4% Pd-Ce-F/MCM-48 catalyst and the reaction temperature is investigated (the rest conditions are consistent, the hydrogen flow rate is 10-50 mL/min, and the weight hourly space velocity is 3.5-8.0 h in the isomerization process^-1. ) The histogram of the 0.4% Pd-Ce-F/MCM-48 catalyst performance as a function of reaction temperature is shown in FIG. 11. As can be seen from fig. 11, as the reaction temperature increased, the conversion rate increased and the selectivity decreased continuously. Although n-heptane isomerization is a slightly exothermic reaction, if the reaction temperature is too low, the overall reaction rate is too slow, and above all, conversion results are not desirable. It is therefore necessary to raise the reaction temperature to a temperature which is so endothermic that the cracking reaction is promoted, so that the optimum reaction temperature is 280 ℃.

In the embodiment, the relationship between the performance of the 0.4% Pd-Ce-F/MCM-48 catalyst and the reaction time is investigated (the rest conditions are consistent, the hydrogen flow rate is 10-50 mL/min, and the weight hourly space velocity is 3.5-8.0 h^-1. ) The 0.4% Pd-Ce-F/MCM-48 catalyst performance as a function of reaction time is shown in the bar graph of FIG. 12. As can be seen from fig. 12, the n-heptane conversion and the isomerization selectivity increased with the increase of the reaction time and then decreased with the increase of the reaction time within 120min, because some carbon deposition occurred on the active center of the flower catalyst with the progress of the reaction, resulting in the decrease of the conversion. The deactivation may be caused by collapse of the pores, which are formedThe catalyst loses activity due to structural blockage, loss of acid sites and the like. When the reaction temperature was 280 ℃ and the reaction time was 120min, the maximum yield of isoheptane was 72.9% and the optimum binding point was obtained for conversion and selectivity. The conversion rate and the selectivity are both better.

This example also examined the catalytic performance of different Pd loading (0% -0.5%) catalysts. The x% Pd-Ce-F/MCM-48 catalyst performance is shown in the histogram of Pd content in FIG. 10. As can be seen from FIG. 10, the conversion and selectivity of n-heptane were the lowest when the catalyst contained no Pd, indicating that Ce (F) -MCM-48 exhibited weak catalytic activity without Pd loading. As the ratio of n (Pd)/n (Si) is gradually increased from 0.1% to 0.5%, the activity of xPd-Ce (F) -MCM-48 for catalyzing the isomerization of n-heptane is increased and then decreased. When x is 0.4%, the n-heptane conversion of 0.4% Pd-ce (f) -MCM-48 is 79.7% and the iso-heptane selectivity is 91.5%. This is because the activity center is a palladium atom existing in a low-valent coordination state when the supported amount of palladium in the catalyst is small, the activity and the reusability are good, and when the supported amount of Pd is gradually increased, there is aggregation of metallic Pd particles in addition to the atomic palladium. When the Pd content is 0.5%, excessive metals are accumulated, and the activity is poor. Thus, to obtain a good heptane isomerization catalyst, excellent carrier properties, state of active component, auxiliary agent F^-1Is crucial. The Pd content was therefore chosen to be 0.4%.

The results show that the optimal loading amount of the noble metal Pd is 0.4 percent by mass, the reaction temperature is 280 ℃, the reaction time is 120min, the catalytic performance is relatively stable, the conversion rate of n-heptane isomerization is 79.7 percent, and the selectivity of iso-heptane is 91.5 percent. A molecular sieve material is constructed, the octane number of gasoline is improved by alkane isomerization, and the molecular sieve material has important application prospect along with the enhancement of energy conservation, emission reduction and environmental protection awareness.

Claims

1. A process for preparing the anionic doped mesoporous material from CTAB as template, NaF and Ce (NO)₃)·6H₂O is an additive reagent, TEOS (ethyl silicate) is a silicon source, and the compound is prepared by a hydrothermal synthesis method under an alkaline condition; the mesoporesThe material is designated Ce-F/MCM-48.

2. The method of claim 1, wherein: in the initial reaction system, n (TEOS), n (CTAB), n (Ce), n (NaF) and (NaF) are respectively 1.0:0.65:0.02 (0-0.15), but the dosage of NaF is not 0;

further, the alkaline condition is provided by NaOH, in the initial reaction system, n (TEOS): n (CTAB): n (H)₂O, n (NaOH), n (Ce), n (NaF) (1.0: 0.65:62: 0.5) (0.01-0.05) and (0-0.15), but the amount of NaF is not 0.

3. The production method according to claim 1 or 2, characterized in that: the hydrothermal synthesis method comprises the following hydrothermal conditions: transferring the initial gel prepared from the reaction mixture into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and putting the reaction kettle into a drying oven for crystallization at a constant temperature of 100-140 ℃ for 12-108 hours;

after the hydrothermal synthesis method is finished, the method also comprises the steps of drying and roasting the product;

the drying conditions are as follows: drying for 4-24 h at 70-100 ℃ on an electric hot plate, and drying for 4-12 h in a drying box at 105-120 ℃;

the roasting conditions are as follows: and roasting the dried product in a resistance furnace for 2-10 h at the temperature of 300-800 ℃.

4. The production method according to any one of claims 1 to 3, characterized in that: the preparation method specifically comprises the following steps: firstly, NaOH is dissolved in deionized water and stirred evenly, and NaF and Ce (NO) are added in sequence₃)·6H₂Stirring for 15-60 min by using O, adding CTAB into the mixture for multiple times in a small amount under the condition of heating in a water bath at 35-45 ℃, and stirring for 60-180 min, wherein the solution is transparent; gradually and intermittently adding TEOS into the solution dropwise and continuously stirring for 30-180 min; transferring the prepared initial gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and putting the initial gel into a drying oven for constant-temperature crystallization at 100-140 ℃ for 12-108 hours; washing and filtering the product; drying for 4-24 h at 70-100 ℃ on an electric hot plate, drying for 4-12 h in a drying box at 105-120 ℃, and roasting for 2-10 h at 300-800 ℃ in a resistance furnace to obtain the product.

5. The anion-doped mesoporous material prepared by the method of any one of claims 1 to 4.

6. A catalyst carrying a metal active component, wherein the active component is noble metal palladium, and the carrier is the mesoporous material of claim 6; the load amount (mass fraction) of Pd in the catalyst is 0-0.5%, but 0 is not included.

7. A method for preparing a catalyst loaded with metal active components as claimed in claim 6, which is prepared by an impregnation method, comprising the following steps: dissolving Pd in deionized water, and then immersing the mesoporous material of claim 5 therein; and (3) carrying out ultrasonic dispersion, standing for more than 6h at room temperature, drying and roasting to obtain the catalyst loaded with the metal active component.

8. The method of claim 7, wherein:

the ultrasonic dispersion condition is that ultrasonic dispersion is carried out for 10-120 min at 40-80 ℃;

the drying specifically comprises the following steps: drying the electric hot plate for 4 to 24 hours at 70 to 90 ℃, and drying the electric hot plate for 4 to 12 hours in a drying oven at 105 to 120 ℃;

the roasting condition is that roasting is carried out for 2-10 hours at 300-400 ℃.

9. Use of the metal active component-supporting catalyst of claim 6 for catalyzing the isomerization of n-heptane.

10. A method for catalyzing isomerization of n-heptane, which comprises catalyzing isomerization of n-heptane with the metal active component-supporting catalyst of claim 6; the reaction conditions are as follows: the reaction temperature is 220-260 ℃; the reaction time is 60-240 min.