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J.Chem.T echnol.Biotechnol. 1998,73, 414420

Catalyst Prepared byElectroless MethodCu/SiO2Ching-Yeh Shiau*& J. C. Tsai

Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei,Taiwan

(Received 26 January 1998; accepted 5 August 1998)

Abstract: catalysts prepared by an electroless deposition method wereCu/SiO2

investigated and compared with those by an impregnation method. Copper con-tents varied from 5% to 15% and was used as support. All catalysts wereSiO

2characterized by BET, DSC, SEM and TPR and tested by ann-butanol dehydro-genation reaction for activities and stabilities. BET analysis showed that thecatalysts prepared by the two methods present larger average pore size and lesssurface area than those of the fresh indicating that smaller pores may getSiO

2,

blocked during the course of preparation. This blockage is more severe in theimpregnation method. SEM photos showed that the electroless method producessmaller copper crystals than the impregnated method. The reaction activity wasfound to be in the order of the calcined electroless copper catalyst [ the freshelectroless copper catalyst[ impregnated copper catalyst. 1998 Society of(Chemical Industry

J.Chem.T echnol.Biotechnol.73, 414420 (1998)

Key words: copper catalyst; electroless plating; impregnation; n-butanolSiO2

;dehydrogenation

INTRODUCTION

Copper-based catalysts are widely used in many indus-

trial reactions, especially for dehydrogenation reactions.

Church and Joshi1and Franckaerts and Froment2indi-cated that a CuCoCr catalyst had good activity for

ethanol dehydrogenation. Pepe et al.3 studied the dehy-drogenation of isopropanol and found that the reaction

rate increased linearly with the exposed copper surface

area of the supported catalysts. Doca and Segal4h7usedCr-, Mn-, Fe- and Ni-promoted copper catalysts to

investigate the kinetics of low aliphatic alcoholic

dehydrogenation in the temperature range of(C2C

4)

200280C by a chromatographic pulse technique. They

found that the fresh copper catalyst was very active, but

its activity decreased rapidly with pulse number. If the

promoters Cr and Mn were added into the catalysts, the

activity of the catalysts remained fairly constant for a

* To whom correspondence should be addressed.Contract/grant sponsor : National Science Council of the

Republic of China; Contract/grant number: NSC84-2214-E011-005.

longer time due to the formation of a Cu-oxide junc-

tion. Prasad et al.8 and Tu et al.9 studied the role ofchromia in a copper catalyst for the dehydrogenation of

ethanol; the addition of chromia improved dispersion of

copper on the support and helped to prevent the cata-

lyst from sintering. Sivarajet al.10 found that CuZnOAl catalysts prepared by a depositionprecipitation

method had high selectivity for the dehydrogenation of

cyclohexanol to cyclohexanone. Lin et al .11 used a

CuZnO catalyst to investigate the oxidative dehydro-genation of cyclohexanol to cyclohexanone. Sivaraj et

al.12 examined the selectivity dependence on the acidityof supported copper catalysts prepared using the urea

hydrolysis procedure in the hydrogenation of cyclo-

hexanol. Shiau and Liaw13 found that a CuBa catalystwas potentially attractive for the dehydrogenation ofn-

butanol to butyraldehyde. Shiau and Chen14 also foundthat a CuCr catalyst was quite eective for the ethanol

dehydrogenation reaction. Grift et al .15 studied theeect of preparation procedure on the reduction behav-

ior of silica-supported copper catalysts. They found that

the dispersion of copper strongly depended on the prep-

aration methods and the conditions used.

4141998 Society of Chemical Industry. J.Chem.T echnol.Biotechnol. 0268-2575/98/$17.50. Printed in Great Britain(

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Cu/SiO2

catalyst prepared by electroless method 415

Traditionally, copper catalysts are prepared by either

impregnation methods or precipitation methods.

Recently, electroless deposition method has been

adopted in the preparation of copper catalysts. Chang

and Saleque16h19 used this method to prepare a coppercatalyst on for the dehydrogenation reactionsAl

2O3

and found that the catalysts prepared by the electrolessmethod were better than those prepared by the conven-

tional methods. Shiau and Tsai20 also found similarresults for the dehydrogenation reaction of n-butanol

when using catalysts prepared by the electro-Cu/Al2

O3

less method. In this study, the electroless deposition

method was used to prepare copper catalysts for the

dehydrogenation of n-butanol. was used asSiO2

support. All the catalysts prepared by the electroless

method were compared with the catalysts prepared by

the impregnation method.

EXPERIMENTAL

Catalyst preparation

Electroless method

The electroless method is an oxidationreduction

chemical deposition reaction, which can deposit certain

metals on a substrate without an external electrical

source. In this study was used as substrate. BeforeSiO2

electroless deposition, was rstly treated withSiO2

dilute acid solution to remove any fats and oils. The

clean was then treated with palladium chlorideSiO

2solution for activation. At this stage, palladium servedas seeds for catalytic nucleating centers. The activated

was nally contacted with copper solution forSiO2

copper plating. In the copper solution, formaldehyde

was added as reducing agent for the oxidation

reduction reaction. The plating bath was maintained at

70C and the pH was varied from 11 to 13. The plated

was then ltered and washed with distilled water,SiO2

then dried at 110C for 24 h. The copper content was

controlled by the plating solution concentration as well

as the plating time. The plated copper catalysts can be

directly used as the plated copper is present as copper

atoms instead of copper oxide. However, some freshelectroless copper catalysts were also calcined at 450C

for 3 h to study the calcination eect.

Impregnation method

Catalysts were prepared by putting support into aSiO2

copper nitrate solution container for 30 min impregna-

tion. The container was then placed in an isothermal

water bath to vaporize most of water. The bath tem-

perature was maintained at 70C. The soaked paste was

then dried at 110C and calcined, if necessary, at 450C

for 3 h.

Six catalysts were prepared, namely, I05, I10, I15,

E05, E10 and E15 in which I denotes impregnation

method, E denotes electroless method and the numbers

represent the copper content in the catalyst as a per-

centage. The copper content was determined by atomic

absorption spectrometry. The catalysts were character-

ized by BET, DSC, SEM and TPR analyses.

n-Butanol reaction

The catalyst activity data were obtained by carrying out

the dehydrogenation reaction ofn-butanol in a contin-

uous ow type reactor with a xed catalyst bed under

atmospheric pressure. The reactor was made of a Pyrex

tube with 136 mm inner diameter, equipped with a

thermocouple well along the central axis. A known

amount of catalyst was loaded in the reactor. Pure n-

butanol was fed into the reactor by a metering pump.

The reaction temperature was set at 270C. All connect-

ing gas lines and valves were wrapped with heating tape

to prevent possible condensation. The compositions ofinlet and outlet streams were determined chromato-

graphically using a column loaded with Porapak Q.

The experiments were conducted under conditions free

of external mass transfer and internal diusion resist-

ances.

RESULTS AND DISCUSSION

Catalyst characterization

Table 1 shows the specic surface areas and the meanpore sizes for the six types of catalysts measured by the

BET method. Fresh was also included for refer-SiO2

ence. As can be seen from this table, all the catalysts

have less surface area and larger mean pore size than

the fresh and the catalysts prepared by the elec-SiO2

,

troless method exhibit a larger surface area and smaller

mean pore size than all the impregnated catalysts.

Moreover, the surface area increases and the mean pore

size decreases with increasing copper loading for the

electroless catalysts, but vice versa for the impregnated

catalysts. All this information indicates that the impreg-

nation method will block some small pores and this

TABLE 1

BET Surface Analysis

Catalyst Surface area Pore size

(m2 g~1) (A )

SiO2 2988 2113

I05 2552 2430

I10 2415 2562

I15 2347 2664

E05 2644 2385

E10 2712 2324

E15 2785 2253

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416 C.-Y. Shiau, J. C . T sai

Fig. 1. Pore distribution for impregnated catalysts.

blockage will become more severe with increasing

copper loading, but the blockage phenomenon in the

electroless method is much less. These blockage pheno-

mena can also be seen from the pore distribution

curves, as shown in Figs 1 and 2. Figure 1 is the pore

distribution for the impregnation method and Fig. 2 for

the electroless method. It is clearly seen from Fig. 1 that

the specic pore volume was sharply decreased when

loading copper metal onto the support by the impreg-

nation method and the curves are slightly right-shiftingwhen the copper loading increases, indicating that more

smaller pores are blocked when increasing copper load-

ings. In contrast, the curves for the electroless method,

as shown in Fig. 2, are slightly left-shifting when the

Fig. 2. Pore distribution for electroless catalysts.

copper loading increases. This is due to the fact that

copper was more uniformly plated on the wall of the

pores by the electroless method. Expect for those ne

pores which became blocked, the pore size of the non-

blocked pores therefore becomes smaller when copper

loading increases.

Apart from the BET surface area, the copper particlesize also plays an important role in the catalysts activ-

ity. Figures 3 and 4 are the SEM photos of the I15 cata-

lyst and the fresh E15 catalyst, respectively. It is seen

from these two gures that the electroless method pro-

duces quite small ball-like copper catalysts whereas the

impregnated methods forms much larger needle-like

ones. Thus, the crystal type is quite dierent in the two

preparation methods and the copper crystal size pre-

pared by the electroless method is much smaller than

that prepared by the impregnation method. Figure 5 is

the SEM photo of calcined E15 catalyst. Comparing

Figs 3 and 5 shows that even the calcined E15 catalystgives smaller crystals than the I15 catalyst.

Figure 6 and 7 are the TPR proles of the six cata-

lysts. The TPR experiments were conducted in a xed

bed reactor from room temperature to 500C at a con-

Fig. 3. SEM photo of I15 catalyst.

Fig. 4. SEM photo of E15 catalyst.

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Cu/SiO2

catalyst prepared by electroless method 417

Fig. 5. SEM photo of E15 catalyst with calcination.

stant rate of 10C min~1. A mixture stream of H2

/Ar

(25%/75%) was introduced at 30 cm3 min~1 to reduce

the calcined catalyst sample. The effluent stream wasanalyzed for hydrogen by a thermal conductivity detec-

tor after removal of moisture by a molecular sieve trap.

For both preparation methods; the TPR of each cata-

lyst exhibited only one peak. This peak is attributed to

the reaction:

CuO]H2]Cu]H

2O

Both gures show that larger copper loadings have

larger hydrogen consumption. However, comparing the

two gures indicates that the reduction pattern is slight-

ly dierent for the two types of catalysts. Firstly, the

peak maxima of the impregnated catalysts are about

50C higher than those of the electroless catalysts. Sec-

Fig. 6. TPR spectra for impregnated catalysts.

Fig. 7. TPR spectra for electroless catalysts.

ondly, the TPR curves of the electroless catalysts are

much sharper and narrower than those of the impreg-

nated catalysts. Thirdly, as can be seen from Fig. 6,

there are no real peak maxima for the I05 and I10 cata-

lysts. These three points imply that the interaction

between copper and the support for the two prep-

aration methods are dierent and the electroless cata-

lysts are easier to get reduction.The DSC analysis traces, recorded in the temperature

range of room temperature up to 450C at a rate of

10C min~1 for the impregnated and the electrolesscatalysts are given in Figs 8 and 9 respectively. In Fig.

8, an endothermic peak was observed around 100C,

indicating the dehydration of the impregnated catalysts.

Starting from 230C to about 290C, a larger endo-

thermic peak was observed. This peak represents the

decomposition of copper salts and some kind of

bonding formed between copper and support. Higher

copper loadings give larger peaks. Above 300C, no

peaks were observed, indicating that the impregnatedcatalysts are quite stable from 300 to 450C. For the

electroless catalysts, as shown in Fig. 9, a similar endo-

thermic peak was observed around 100C followed by a

wide exothermic peak. The endothermic peak is the

vaporization of water inside the catalyst and the exo-

thermic peak represents the phase change of fresh elec-

troless copper to copper oxides. Again, higher copper

loadings present larger peaks. No endothermic peak at

around 250C was observed for the electroless catalysts,

indicating that the interaction between copper and

support for the electroless catalysts may be dierent

from that for the impregnation catalysts. This point

seems quite similar to the TPR result.

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418 C.-Y. Shiau, J. C . T sai

Fig. 8. DSC spectra for impregnated catalysts.

Catalyst activities

Dehydrogenation of n-butanol is used as the test reac-

tion for the catalysts activity. The catalysts loading was

04 g and time factor was 47 g-cat h gmole~1. Experi-mental results show that all the catalysts dehydrogenate

n-butanol into n-butyraldehyde and hydrogen. Only a

Fig. 9. DSC spectra for electroless catalysts.

Fig. 10. Reaction activity of 5% Cu catalysts.

trace amount of heavy compounds was detected.

Figures 1012 show the catalysts stabilities and activ-

ities for the n-butanol dehydrogenation reaction. The

calcined electroless copper catalysts are also included.

Comparing these three gures reveals three interesting

points. Firstly, higher copper loadings have better reac-

tion activities and the electroless copper catalysts

Fig. 11. Reaction activity of 10% Cu catalysts.

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Cu/SiO2

catalyst prepared by electroless method 419

Fig. 12. Reaction activity of 15% Cu catalysts.

present better performance for all copper loadings. Sec-

ondly, all the impregnated catalysts are deactivated sig-

nicantly, especially the I05 catalyst. In contrast, both

E10 and E15 are quite stable during an 8 h reaction

course. Thirdly, the calcined electroless copper catalysts

show much better reaction activities than the fresh elec-

troless copper catalysts. The higher activities of the cal-

TABLE 2

Carbon Content after Reaction

Catalyst Carbon content (wt%)

I05 632

I10 545

I15 498

E05 242

E10 114

E15 081

TABLE 3

Surface Area Change after Reaction

Catalyst BET surface area (m2 g~1)

Fresh Used % change

I05 2552 2222 [ 129I10 2415 2244 [ 71I15 2347 2274 [ 31E05 2644 2581 [ 24E10 2712 2685 [ 10

E15 2785 2734 [ 18

cined electroless copper catalysts may be attributed to

the interaction between copper and support during cal-

cination.

Catalyst deactivation

Coking and sintering problems which cause catalyst

deactivation were also investigated in this study. For

the coking problem, we used elemental analysis to

determine the weight % of carbon present in the cata-

lyst after an 8 h reaction at 270C, and for the sintering

problem we used the BET method to determine the

surface area change. Table 2 shows the result of elemen-

tal analysis which indicates that all the catalysts have

carbon deposition after undergoing the dehydroge-

nation reaction. The weight percentage of carbon on the

copper surface ranges from 081% to 632%. Table 2

also shows that after the dehydrogenation reaction thecatalysts prepared by the electroless method have much

less carbon deposition than the impregnated catalysts.

The amount of carbon deposition for the electroless

catalysts is much less than 40% of that for impregnated

ones. Table 3 compares the BET surface area between

the fresh and used catalysts. The fourth column in the

table is the percentage change of the surface area after

reaction. As can be seen from this result, the impreg-

nated catalysts have a signicant sintering phenomenon

while the degree of sintering is slight for the electroless

catalysts. The percentage decrease in surface area for

the electroless catalysts is about one-fth of that for the

impregnated catalysts. Tables 2 and 3 clearly indicatewhy the electroless catalysts show better stability and

activity than the impregnated catalysts do, as aforemen-

tioned in the reaction performance results.

CONCLUSIONS

(1) All the characterization results show that the elec-

troless deposition method provides more uniform

copper distribution than the impregnation method.

(2) Although the calcined electroless copper catalysts

have larger copper particles, they exhibit better reac-tion activities than the fresh electroless catalysts.

(3) The reaction activities are in the order of the cal-

cined electroless copper catalyst[ the fresh electro-

less copper catalyst[ the impregnated copper

catalysts.

ACKNOWLEDGEMENT

This work was supported by the National Science

Council of the Republic of China (NSC84-2214-E011-

005).

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420 C.-Y. Shiau, J. C . T sai

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