Active Impregnation Method for Copper Foam as Catalyst Support for

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Kinetics, Catalysis, and Reaction Engineering

Active Impregnation Method for Copper Foam as Catalyst Support for Methanol Steam Reforming for Hydrogen Production Tianqing Zheng, Wei Zhou, Yu Gao, Wei Yu, Yangxu Liu, Chenying Zhang, Congcong Zheng, Shaolong Wan, Jingdong Lin, and Jianhua Xiang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05241 • Publication Date (Web): 25 Feb 2019 Downloaded from http://pubs.acs.org on February 27, 2019

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Industrial & Engineering Chemistry Research

Copper foam surface (traditional impregnation)

Micro-CT diagram of axial center (traditional impregnation)

Copper foam surface (active impregnation)

Micro-CT diagram of axial center (active impregnation)

Schematic diagram of active impregnation device for copper foam as catalyst support

Distribution of catalyst loaded on the copper foam using different impregnation methods

ACS Paragon Plus Environment

Reaction performance of microreactor for hydrogen production under 320℃ reaction temperature for different catalyst loading methods

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Active Impregnation Method for Copper Foam as Catalyst Support for Methanol Steam Reforming for Hydrogen Production Tianqing Zheng a, Wei Zhou a,*, Yu Gao b, Wei Yu a, Yangxu Liu a, Chenying Zhang a, Congcong Zheng c, Shaolong Wan c, Jingdong Lin c, Jianhua Xiang d a Department

of Mechanical & Electrical Engineering, Xiamen University, Xiamen 361005, China

b School c College d School

of Mechatronics Engineering, Foshan University, Foshan 528000, China

of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China

of Mechanical and Electric Engineering, Guangzhou University, Guangzhou 510006, China

*Corresponding

author. Tel., 86-592-2188698; Fax: 86-592-2186383

E-mail address: [email protected] (Wei Zhou).

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Abstract: In order to realize uniformly loading catalyst on copper foam, a new device was designed to drive catalyst precursor solution to flow into the inner pore structures of copper foam by changing driving pressure and flow rate. The three-dimensional models of copper foam loaded with catalyst using different impregnation methods were reconstructed by Micro-CT. The catalyst loading distribution was studied by Micro-CT and SEM. Moreover, methanol steam reforming reaction performance of microreactor with copper foam loaded with catalyst using different methods was compared and analyzed. The results showed that the best loading performance of copper foam was obtained when driving pressure and flow rate of catalyst precursor solution were 0.102 MPa and 0.3 L/min, respectively. Compared with traditional impregnation method, copper foam using active impregnation method exhibited more uniform distribution of catalyst and better reaction performance for hydrogen production. This work provides a feasible method to optimize catalyst loading process. Keywords: Methanol steam reforming; Hydrogen production; Copper foam; Active impregnation method; Micro-CT

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1. Introduction Methanol steam reforming reaction is one of the most promising hydrogen production technologies, because of its advantages such as low reforming temperature, low energy consumption, easy storage and transportation, convenient feeding, and safety.1 Compared with conventional reactor, because of its characteristics of microchannel structure and small channel size, microreactor offers the advantages such as high surface-to-volume ratio, intensified heat and mass transfer, rapid and direct amplification, as well as high safety. Especially, the microreactor can use methanol as fuel to produce hydrogen, which can provide reliable on-line hydrogen source for fuel cells by using methanol steam reforming reaction. Therefore, the microreactor for hydrogen production has received considerable attentions from researchers at home and abroad.2-5 In the previous work, the microreactor technology and catalyst for methanol steam reforming for hydrogen production have been extensively studied including relevant researches such as structural design, manufacturing method of microreactor, and new catalyst support, catalyst performance and so on.6-22 In the structural design of the microreactor, many kinds of microreactors such as a plate–fin microreactor, cube–post microreactor, annular microreactor, and cylindrical microreactor have been developed.6-10 For the manufacturing method of microreactor, some technologies such as milling, special process, and microelectromechanical systems (MEMSs) have been developed to fabricate straight channels, serpentine channels, spiral channels, etc..11-14

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Nomenclature Variables m

volume fraction of CO in reformate gas, %

n

volume fraction of CO2 in reformate gas, %

Vinjection injection velocity of the mixture of methanol and water, mL/h Vreformate gas injection velocity of reformate gas, mL/min XCH3OH

methanol conversion, %

Abbreviations MEMSs Micro-CT PPI SEM

microelectromechanical systems micro computed tomography

pores per inch scanning electron microscope

For different catalyst supports, porous metal materials used as the catalyst support in microreactors have also been examined. Foam technology, solid-phase sintering technology, and liquid-phase sintering technology have been developed to fabricate the porous metal materials and have been successfully used as catalyst support in ammonia decomposition and hydrogen production by methanol.15-18 As for the catalyst, the effect of catalyst element composition, additive of auxiliaries, preparation method, and reaction conditions on catalyst performance have been studied deeply.19-22 The several types of catalysts of Cu series, Cr-Zn series and noble metals (such as Pd and Pt) with different activities have been obtained. Moreover, the optimum preparation method and reaction conditions of catalyst have been gained.

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To date, some catalyst loading methods have been developed for loading catalyst on microchannels or porous supports by impregnation, chemical and physical vapor deposition. The common methods such as precipitation, impregnation, combustion, sol-gel have mainly been used in loading process of catalyst.23-26 However, the impregnation method is mainly used to load catalyst on the porous catalyst support such as copper foam.27-29 When the impregnation method is used, the catalyst support loads the solution with catalyst components by impregnation, then dries in the oven. The impregnation-drying process is repeated until that the required loading amount of catalyst is loaded on the catalyst support. Owing to the dense porous structure of copper foam, the precursor solution of catalyst is difficult to flow into the inner pore structures of copper foam to be loaded on each position of catalyst support. Moreover, the traditional impregnation method can not solve the problem of flow difficulty. Hence, the distribution of loaded catalyst is non-uniform when traditional impregnation method is used. As we know, the more uniform distribution of the catalyst loaded on copper foam leads to more larger surface area of the catalyst. Subsequently, the more contacting opportunity between the reactants and catalyst can be obtained, which is of the benefit to achieve the better methanol reforming reaction performance for hydrogen production. In fact, the uniformity of catalyst loading distribution has been studied by a few scholars.30-32 For example, Lee et al. adjusted the pH value and aging time of catalyst precursor solution in the impregnation process, achieving more uniform distribution of loaded catalyst and smaller catalyst particles, improving the catalytic activity of

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catalyst.31 Allahyari et al. employed the ultrasound-assisted co-precipitation method to prepare Cu/ZnO/Al2O3 catalysts. It was found that the catalyst prepared by acetate presented better dispersion, smaller particle size, and larger specific surface area, as well as better catalytic activity, compared with nitrate.32 Although some research works involving the design, manufacturing, catalyst support, and catalyst performance for methanol steam reforming microreactor for hydrogen production have been conducted. However, the study of the loading method about uniform distribution of catalyst loaded on the porous catalyst support of methanol steam reforming for hydrogen production has not been reported in previous literatures. Here, an active impregnation method and relevant device for copper foam as catalyst support were firstly designed, and then the catalyst loading performance under different loading parameters was studied. Compared with traditional impregnation method, the catalyst loading distribution of the copper foam as catalyst support using active impregnation method was analyzed in detail using micro computed tomography (Micro-CT) and scanning electron microscope (SEM). Moreover, the methanol steam reforming reaction performance of mircroreactor for hydrogen production using copper foam as catalyst support which had been loaded with catalyst using different loading methods was compared and discussed.

2. Experimental 2.1. Design of active loading method and device According to the previous literature.4,6,33 the traditional impregnation method employed for loading catalyst on the copper foam as catalyst support usually raises

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some problems. Because of the dense porous structure of copper foam, the catalyst precursor solution is difficult to flow into the inner pore structures of copper foam using normal pressure conditions. Moreover, with the operation of impregnation and drying continuing, much smaller pore size of the copper foam loaded with catalyst is obtained. In this way, the precursor solution is more difficult to flow into the copper foam. Figure 1 shows the schematic diagram of technical principle of active impregnation method for copper foam as catalyst support. Compressed air was used to control the driving pressure and flow rate of catalyst precursor solution to drive the precursor solution to flow into copper foam, to make the copper foam actively impregnate the precursor solution. The red solid line and dotted line indicate the flow direction of catalyst precursor solution. Compressed air Catalyst precursor solution

Compressed air Liquid storage vessel

Impregnation vessel Reaction support of copper foam

Air tube

Figure 1. Schematic diagram of technical principle of active impregnation method for copper foam as catalyst support

Figure 2 shows the active loading process of catalyst for copper foam as catalyst support. The catalyst precursor solution which consisted of Cu(NO3)2, Zn(NO3)2, Al(NO3)3 and Zr(NO3)4 solution was in an impregnation vessel.12 A copper foam was placed in the impregnation vessel, and impregnated precursor solution using active impregnation method. Then the copper foam which had loaded the precursor solution Page 7 of 28


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was placed in an oven for 30 minutes under 130℃ drying temperature. Subsequently, the operations of active impregnation and drying were repeated until the desired amount of catalyst was loaded on copper foam. In order to examine and control the amount of the catalyst loaded on the copper foam, the copper foam loaded with the precursor solution was weighed.

The 1th impregnation

The 1th drying

The 2th impregnation

The Nth drying

The 2th drying

The Nth impregnation

Figure 2. Schematic diagram of active loading process of catalyst for copper foam as catalyst support

Figure 3 shows the schematic diagram of active impregnation device for copper foam as catalyst support. The active impregnation device was composed of air compressor, air cylinder, impregnation vessel and liquid storage vessel. For working principle of the active impregnation device, with the descending of air cylinder, seal sheet on main body of seal vessel and upper cover of seal vessel were tightly bonded to seal the vessel. Subsequently, the compressed air was supplied into the seal vessel by an air compressor. The catalyst precursor solution flowed between an impregnation vessel and an liquid storage vessel under the pressure action

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of compressed air. The flow rate of precursor solution was controlled by a speed regulator and a flowmeter. The driving pressure of the precursor solution was controlled by a precision pressure regulator and a pressure sensor, and the flow direction of the precursor solution could be changed by using a 3-way valve.

Copper foam

Air cylinder

Liquid storage vessel Impregnation vessel

Upper cover of seal vessel

3-way valve Flowmeter

Pressure sensor Main body of seal vessel

Precision pressure regulator

Air compressor

Figure 3. Schematic diagram of active impregnation device for copper foam as catalyst support

2.2. Loading parameters optimization of active impregnation method The amount of the catalyst loaded on copper foam was used as an index to evaluate the loading performance of impregnation method. Meanwhile, the copper foam with 110 PPI porosity, 6 mm in thickness and 40 mm in outer diameter Page 9 of 28


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(Purchased from Jia Yi Sheng Company, Jiangsu, China) was used as catalyst support to be loaded with catalyst using the active impregnation method. The amount of the catalyst loaded on copper foam under different driving pressures was compared in the condition of 0.5 L/min flow rate of precursor solution. Additionally, the amount of the catalyst loaded on copper foam under different flow rates of precursor solution was compared in the condition of 0.102 MPa driving pressure of precursor solution. 2.3. Investigation of catalyst distribution and loading strength In order to attain the information of catalyst loading distribution of copper foam, Micro-CT (XTV160H, X-TEK Company, British)34-36 was used to reconstruct the three-dimensional model of the copper foam which had been loaded with 1.2-g catalyst, and showed the information of catalyst loading distribution on each axial cross-section in the reconstructed model. In the reconstructed 3D model, green part was catalyst, while yellow and black part was copper. Moreover，SEM (JSM-IT5000, JEOL Company, Japan) was also used to study the catalyst loading distribution of the copper foam. The loading strength of catalyst loaded on the copper foam using different impregnation methods was also studied by using a peristaltic pump to drive air to blow the copper foam on the condition of 2.5 L/min flow rate. The mass difference between the catalyst loaded on copper foam before air blowing and the copper foam after air blowing was used as an index for evaluating catalyst loading strength. The smaller mass difference indicated the better catalyst loading strength. Figure 4 shows the schematic diagram of the testing process of catalyst loading strength for copper Page 10 of 28



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foam. The copper foam loaded with catalyst was weighed by electronic balance, and was then blew by a peristaltic pump. Subsequently, the copper foam was weighed again. Peristaltic pump Microreactor

Weigh

Air blow

Weigh

Figure 4. Schematic diagram of the testing process of catalyst loading strength for copper foam

2.4. Performance test of microreactor for hydrogen production Thermocouple Heating cartridges

Inlet tube

Copper foam

Evaporation chamber

Reforming chamber

Outlet tube

Figure 5. Structural design of methanol steam reforming microreactor for hydrogen production

Figure 5 shows the structural design of methanol steam reforming microreactor for hydrogen production. The microreactor consisted of an evaporation chamber, a

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reforming chamber, a copper foam as catalyst support, heating rod, and thermocouple and so on. The copper foam was loaded with a Cu/Zn/Al/Zr catalyst by above active impregnation method. The mixture of methanol and water as reactant was evaporated into gas in an evaporation chamber. Then, reactant gas happened to conduct the methanol steam reaction with the catalyst loaded on copper foam to produce hydrogen in a reforming chamber.37-39 CH 3 OH  H 2 O  3H 2  CO 2 , CH 3 OH  CO  2 H 2 , CO  H 2 O  CO 2  H 2 ,

（1）

H 298 C  49.4 KJ / mol

（2）

H 298 C  92.0 KJ / mol

（3）

H 298 C  41.1 KJ / mol

N2 Mass flowmeter

Computer

Gas chromatograph Electronic soaping flowmeter

H2

Microreactor Precise injection pump

Drying tube Condensing tube

Thermostat Figure 6. Schematic diagram of testing system of methanol steam reforming microreactor for hydrogen production

Eq. (1) is the algebraic summation of Eqs. (2), (3). Eq. (2) represents the

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methanol decomposition. Eq. (3) represents a water–gas shift reaction. The dominant products in reformate gas are H2 and CO2, while a small percentage of CO is also produced. Figure 6 shows the schematic diagram of testing system of methanol steam reforming microreactor for hydrogen production. The testing system was mainly composed of mass flowmeter, precise injection pump,thermostats, condensing cube, drying cube, electric soaping flowmeter, computer, and gas chromatograph. The mixture of methanol and water (at a mole ratio of 1:1.3) was injected into the microreactor by means of a precise injection pump. The injection velocity of mixture of methanol and water was controlled by a precise injection pump. The amount of catalyst loaded on copper foam was changed by active impregnation method of catalyst. The methanol steam reforming temperature was adjusted by heating cartridges, thermocouples, and thermostats. Unreacted methanol and steam were separated from reacted hydrogen-rich gas by a condensing tube and drying tube. The flow rate of reformate gas was measured by a soaping flowmeter. The volume fractions of CO, CO2, and H2 in reformate gas were analyzed by a gas chromatograph. Eq. (4) is the empirical formulas for methanol conversion. In this formulas, 273 represented Kelvin temperature (K) at 0℃, coefficient between Vinjection (mL/h) and Vreformate

1 60 gas

represented the conversion (mL/min), 22400 represented

volume (mL) of 1 mole gas at a temperature of 0℃ (273 K) and standard atmospheric pressure, and

1 64

represented the mole quantity of methanol in 1 mL mixture of

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methanol and water. In this study, the Kelvin environmental temperature of methanol steam reforming was 298 K.

X CH 3OH 

Vreformate gas * ( m  n) 1 1 273 Vinjection * * * * 22400 60 64 K

(4)

The copper foam was loaded with 1.2-g catalyst using traditional and active impregnation method. The reaction performance of microreactor with copper foam for hydrogen production was studied under different injection velocities in the condition of 320℃ reaction temperature.6,26,40

3. Results and discussion 3.1. Loading parameters for maximum catalyst loading amount The maximum catalyst loading amount of copper foam as catalyst support was studied by changing the driving pressure and flow rate of catalyst precursor solution. 3.1.1. Driving pressure Figure 7 shows the amount of catalyst loaded on copper foam under different driving pressures. It is clear that the maximum amount of catalyst loaded on copper foam was obtained under the condition of 0.102 MPa driving pressure. The driving pressure could provide the power for the flow of catalyst precursor solution. Moreover, the same amount of the catalyst could be loaded on the copper foam using one time active impregnation process with different driving pressures. However, larger driving pressure gave rise to reduce the loading strength of catalyst, so the catalyst loaded on the copper foam was easy to happen to fall off from copper foam.41 Page 14 of 28



Thus, with 0.102 MPa driving pressure, the maximum amount of catalyst loaded on copper foam was obtained in the tested range of driving pressure.

Amount of catalyst (g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3

0.102

0.204

0.408

0.816

1.632

1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3

0.1 0.2 0.4 0.8 1.6 Driving pressure of catalyst precursor solution (Mpa) Figure 7. Amount of catalyst loaded on copper foam under different driving pressures

3.1.2. Flow rate Figure 8 shows the amount of catalyst loaded on copper foam under different flow rates. It is found that the larger amount of catalyst loaded on copper foam was obtained in the condition of 0.1 L/min and 0.3 L/min flow rate. However, when the 8.1 L/min flow rate was employed, the least amount of catalyst was emerged in the tested range of flow rate. In order to reduce the operation time of the active impregnation process, 0.3 L/min was recommended to select as the optimum flow rate. With different flow rate of precursor solution, the binding force of catalyst loaded on copper foam could be affected. The catalyst was easy to shed from the surface of copper foam with larger flow rate of precursor solution.41 Therefore, the larger amount of catalyst loaded on copper foam was obtained in the condition of 0.3 L/min flow rate.

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Amount of catalyst (g)

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1.3

1.3

1.2

1.2

1.1

1.1

1.0

1.0

0.9

0.9

0.8

0.8

0.7

0.7

0.6

0.6

0.5 0.4

0.3

0.1

0.9

2.7

0.5

8.1

0.1 0.5 1 5 10 Flow rate of catalyst precursor solution (L/min)

0.4

Figure 8. Amount of catalyst loaded on copper foam under different flow rates

3.2. Catalyst distribution and loading strength The distribution of catalyst loaded on copper foam using different impregnation methods was studied by using Micro-CT and SEM. Moreover, the loading strength of catalyst loaded on copper foam was studied by using a peristaltic pump to drive air to blow the copper foam. 3.2.1. Catalyst loading operation Table 1. Catalyst loading operation parameters of different loading methods Operation parameters

Catalyst

Number of impregnation

Number of drying

loading amount

operation

operation

Traditional impregnation

1.2-g

5

5

Active impregnation

1.2-g

6

6

Loading method

Table 1 shows the catalyst loading operation parameters of different loading methods. For traditional impregnation method, the impregnation and drying operation was repeated five times for loading 1.2-g catalyst on the copper foam. However, for

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active impregnation method, six times were done . 3.2.2. Catalyst distribution

Traditional impregnation

a

b

Active impregnation

c

d

Figure 9. Distribution of catalyst loaded on the copper foam using different impregnation methods. Traditional impregnation : (a) optical image of surface of catalyst-loaded copper foam; (b) Micro-CT diagram of catalyst-loaded ofthe middle of thickness. Active impregnation: (c) optical image of surface of catalyst-loaded copper foam; (d) Micro-CT diagram of catalyst-loaded of the middle of thickness.

Figure 9 shows distribution of catalyst loaded on the copper foam using different impregnation methods. It is found that the non-uniform distribution of catalyst (green part) was observed on the surface and in the middle of the copper foam using traditional impregnation method, as shown in Figure 9.a and b. Moreover, the much difference of green part between the surface and the middle of the copper foam was Page 17 of 28


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observed. However, the uniform green part was found on the surface and in the middle of thickness of the copper foam using active impregnation method, as shown in Figure 9.c and d. Furthermore, the little difference of green part between the surface and the middle of the copper foam using active impregnation method was found. Thus, the uniform distribution of catalyst loaded on the copper foam could be obtained using active impregnation method . Figure 10 shows the SEM micrograph and EDX elemental analysis of copper foam loaded with catalyst using different impregnation methods. Using the traditional impregnation method, it is found that the catalyst was easy to be accumulated on the surface of copper foam to cover the pore structure, as shown in Figure 10.a and b. However, the CuZnAlZr catalyst is uniformly loaded on surface of copper foam using the active impregnation method, as shown in Figure 10.d and e. Moreover, the EDX elemental analysis of the CuZnAlZr catalyst is shown in Figure 10.c. and f. Furthermore, the size of catalyst particles obtained by active impregnation method mostly concentrates in 7.2 mm, however that by traditional impregnation method mostly concentrates in 10 mm, as shown in Figure 10.c. and f. We speculate that the catalyst precursor solution could easily flow into the inner pore structures of copper foam with help of the pressure using the active impregnation method. The distribution uniformity of catalyst loaded on copper foam was enhanced comparing with traditional impregnation method. According to the SEM micrograph and EDX as well as the Micro-CT results, we conclude that the catalyst was uniformly loaded on the surface of copper foam using the active impregnation method. Page 18 of 28



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b

a

200um

500um

c

Mass%

20um

d

e

500um

f

200um

Mass%

20um

Figure 10. SEM micrograph and EDX elemental analysis of copper foam loaded with catalyst using different impregnation methods. Traditional impregnation: (a) ×25; (b) ×85; (c)EDX elemental analysis. Active impregnation: (d) ×25; (e) ×85; (f) EDX elemental analysis.

3.2.3. Catalyst loading strength Figure 11 shows the mass of catalyst loaded on copper foam under different Page 19 of 28


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blowing times. With the blowing time increasing, the basically same mass of catalyst was kept on the copper foam using different impregnation methods under 2.5 L/min blowing rate. These results may be attributed to that the better binding strength between catalyst and copper foam was generated, whether traditional or active impregnation method was used to load catalyst on copper foam. 1.25 Mass of loaded catalyst (g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Traditional impregnation Active impregnation

1.25

1.20

1.20

1.15

1.15

1.10

1.10

1.05

1.05 0

10 Blowing time (min)

30

Figure 11. Mass of catalyst loaded on copper foam under different blowing times

3.3. Reaction performance of microreactor for hydrogen production Figure 12 shows the reaction performance of microreactor for hydrogen production under 320℃ reaction temperature for different catalyst loading methods. Compared with traditional impregnation method, much higher methanol conversion of microreactor was obtained for using active impregnation method as catalyst loading method. Moreover, higher methanol conversion difference was observed in the low flow rate of reactants. For example, when the injection velocity of reactants was 6 mL/h, the methanol conversion difference could be increased by 7.5%. However, when the injection velocity of reactants was 22 mL/h, the methanol conversion difference could be 3.6%. With the help of active impregnation device, the precursor solution can easily flow into the inner pore structures of copper foam. Therefore, the uniform distribution of catalyst loaded on copper foam was obtained. In this way, the Page 20 of 28



larger total surface area of the catalyst is produced to offer much more contacting opportunity between the reactants and catalyst, resulting in the better methanol steam reforming reaction performance of microreactor. 42-44

Methanol conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Traditional impregnation Active impregnation

100

100

80

80

60

60

40

40

20

20

0

6

10 14 18 Injection velocity (mL/h)

22

0

Figure 12. Reaction performance of microreactor for hydrogen production under 320℃ reaction temperature for different catalyst loading methods

4. Conclusions To solve the non-uniform distribution of catalyst loaded on copper foam as catalyst support using traditional impregnation method, an active impregnation method of catalyst for copper foam was proposed and relevant experiments were done. The main conclusions could be drawn as follows: (1) Larger driving pressure and flow rate of catalyst precursor solution gave rise to reduce the loading strength of catalyst, so the catalyst loaded on the copper foam was easy to happen to fall off from copper foam. However, the flow of the precursor solution needed a certain driving force and flow rate. Thus, when 0.102 MPa and 0.3 L/min were selected as the driving pressure and the flow rate of the precursor solution, the better loading performance of catalyst for copper foam was attained. (2) Compared with traditional impregnation, the uniform distribution of catalyst loaded on the copper foam was observed in the different locations of the copper foam

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loaded with catalyst using active impregnation, based on the Micro-CT and SEM results. It can be concluded that the uniform distribution of catalyst loaded on the copper foam using active impregnation method was obtained. (3) With different injection velocities and 320℃ reaction temperature, the microreactor with copper foam which had been loaded with catalyst using the active impregnation method presented the larger methanol conversion compared with traditional impregnation method. Our proposed active impregnation method can improve the uniform distribution of catalyst, which have broad application prospect in the microreactor for hydrogen production.

Acknowledgments This work was supported by the Guangdong Natural Science Funds for Distinguished Young Scholars (No.2016A030306032) and the Natural Science Foundation of Fujian Province of China (No.2017J06015). In addition, the supports from the Fundamental Research Funds for Central Universities, Xiamen University (Nos. 20720160079 and 2072062009) are also acknowledged.

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Active Impregnation Method for Copper Foam as Catalyst Support for

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