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Ind. Eng. Chem. Res. 1997, 36, 2080-2086
Electroless-Plated Cu/Al2O3 Catalysts Prepared with Different Chelating Agents and Their Activity on the Dehydrogenation of 2-Butanol Hsin-Fu Chang* and Chin-Fu Yang Department of Chemical Engineering, Feng Chia University, Taichung, Taiwan 407, Republic of China
The properties of the electroless Cu/Al2O3 catalyst prepared by the electroless plating technique depend upon the kind of chelating agents in the preparation process. In this study, two various chelating agents, ethylenediaminetetraacetic acid (EDTA) and triethanolamine (TEA), were individually used to prepare seven Cu/γ-Al2O3 catalysts of different copper contents, 8.44-24.56 wt % by EDTA and 7.09-25.92 wt % by TEA. Dehydrogenation of 2-butanol was used as a model reaction to test the activities of these catalysts. The dispersion of copper particle on the γ-Al2O3 support and the crystalline phase of the catalyst were characterized by scanning electron micrography (SEM) and X-ray diffraction (XRD), respectively. The copper surface area and the acidity of the catalyst were determined by the decomposition of nitrous oxide (N2O) and the chemisorption of ammonia (NH3), respectively, using the volumetric method. The experimental results showed that the dehydrogenation rate of 2-butanol increased with increasing temperature and the number of exposed copper atoms. The dehydration reaction competed with the dehydrogenation reaction only at higher temperatures and catalysts with higher acidity. Among these two series of catalysts, copper dispersed homogeneously over the γ-Al2O3 support by using EDTA as the chelating agent, resulting in a higher surface area and a higher dehydrogenation rate; however, bulky copper clusters aggregated on the γ-Al2O3 support by using TEA as the chelating agent, displaying a lower surface area and a lower dehydrogenation rate. Introduction High-dispersive supported copper catalysts have been widely used in the dehydrogenation of alcohols to ketones and aldehydes. Extensive studies on the catalytic activity of copper catalysts influenced by the variation of surface morphology and metal-support interaction due to different preparation methods have gained great attention in recent years (Sivaraj and Kanta Rao, 1988; Strohmeier et al., 1985). In the chemical process industry, catalysts with high activity, selectivity, and long life are essential. To meet these requirements, catalysts should possess a large and thermostable active surface area. Friedman and Freeman (1978) studied the interaction of cupric ions with γ-Al2O3 support for the catalysts prepared by the impregnation method. They were physically characterized by means of EXAFS, XRD, ESR, ESCA, and optical spectroscopy to develop a coherent description of the phases present and cation site distribution in the virgin and aged catalysts. Robinson and Mol (1988) characterized copper/alumina catalyst prepared by the dry impregnation method and found that the structure and activity of Cu/Al2O3 methanol synthesis catalysts are clearly influenced by the calcination temperature and the copper loading. They also concluded that a high copper dispersion has a negative effect on the catalytic activity of copper sites. Generally, the impregnation or precipitation method is used to prepare supported metal catalysts. At higher degrees of loading, evaporation of solvent or precipitation is required to deposit the active material on a support. As a consequence, these methods may not give a catalyst with uniform distribution of active material on the support (Sivaraj and Kanta Rao, 1988). Electroless plating has been studied by many workers from * Corresponding author. Fax: (+886-4) 4515517. S0888-5885(96)00341-7 CCC: $14.00
the chemical or electrochemical viewpoint and reviewed in several articles (El-Raghy and Abo-Salama, 1979; Kikuchi et al., 1986). Due to the redox mechanism of the electrochemical reaction, it is expected to give a uniform distribution of active material on the support with better physical and chemical properties. Over the past 3 decades, the applications of electroless copper plating techniques have been mainly on the fabrications of electronic parts, computer parts, printed circuit boards, etc. No attempts have been made to use this technique to develop high-dispersive supported copper catalysts. In our previous study, the results showed that the catalysts prepared by the electroless plating technique have higher dispersion and a more even spread of copper of on the alumina surface than the catalysts prepared by the impregnation method and the precipitation method (Chang and Saleque, 1993). An activity test also showed that the electroless-plated copper catalyst has a better dehydrogenation ability than the catalysts prepared by other methods. Although the electroless copper plating technique has been thoroughly studied and successfully applied in the electrochemical industry in the past 30 years, the new attempt to use this technique to prepare Cu/Al2O3 catalysts still has some equivocal points which have not been extensively acknowledged. In this present paper, two chelating agents, ethylenediaminetetraacetic acid (EDTA) and triethanolamine (TEA), were used in the electroless plating process to prepare Cu/Al2O3 catalysts of different copper loadings. EDTA is the most common chelating agent used in the electroless copper plating bath, and TEA is known to have a faster plating rate than any others do (Kondo et al., 1990). We tried to investigate the effects of chelating agents on the surface morphology and dispersion of copper on the alumina substrate and on the dehydrogenation activity of 2-butanol. © 1997 American Chemical Society
Ind. Eng. Chem. Res., Vol. 36, No. 6, 1997 2081 Table 1. Electroless Copper Plating Baths and Operating Conditions concentrations
Figure 1. Pretreatment process of electroless copper plating.
Experimental Section Catalyst Preparation. Electroless copper deposition refers to the chemical deposition of copper on a conductive, semiconductive, or nonconductive substrate in the absence of an external electric current. Generally, palladium is used as a seeding or a catalyzing agent to provide catalytic nucleating centers on the substrate and, thereafter, deposition the copper atoms by treating the catalyzed surface with a copper salt plus a reducing agent (Amelio et al., 1987). Copper is deposited on the substrate surface via the oxidation-reduction reaction mechanism. The copper ion in electroless copper plating solution may diffuse into the particle pore and adsorb at the nucleating centers of the alumina surface; then, the formaldehyde reduces the copper ion to metallic copper, and the deposition reaction continues further autocatalytically (Shipley, 1961). The electroless copper plating in this study is based on EDTA or TEA as the chelating agent with formaldehyde (HCHO) as the reducing agent. γ-Al2O3 (Merck), having particle sizes of 80-100 µm, was used as the substrate for the electroless plating process. In order to activate the surface of the substrate, a sequence of pretreatment steps illustrated in Figure 1 is conducted. Electroless plating is a catalytic process. The activation step provides active palladium nuclei on the substrate surface to perform the catalytic reaction (Shu et al., 1993). Reactants such as formaldehyde can be chemisorbed and activated on these catalytic metallic sites and further react with preadsorbed copper ions, leading to autocatalytic copper deposition. It is believed
components
EDTA bath
TEA bath
CuSO4‚5H2O EDTA‚4Na TEA HCHO pyridine 2,2-dipyridine K4[Fe(CN)6]‚3H2O temp, °C time, min pH
0.04 M 0.08 M
0.06 M
0.08 M 5 ppm
70 30 12.5
0.18 M 0.22 M 10 ppm 20 ppm 70 5 12.5
that the reduced copper atoms further deposit along the growing copper particles, resulting in the formation of larger dense particles which cover the substrate surface. The main purpose of pretreatment is to remove the adsorbed hydrocarbons and to provide palladium nucleating centers on the surface of the alumina. The pretreated alumina was transferred into the chemical copper plating solution. The chemical copper plating solution was prepared according to Table 1. The plated alumina was separated by filtration and then washed several times with distilled water. The clean plated alumina, i.e., catalyst, was dried at 110 °C for 24 h. The Cu/Al2O3 catalysts of varying composition were prepared by changing the volume of the chemical copper plating solution. Copper Surface Area and Acidity Determination. The evaluation of the free metal surface area in the copper-containing catalyst is usually made through the oxidation of the surface copper atom with N2O (Giamello et al., 1984; Evans et al., 1983; Chinchen et al., 1987). The decomposition of nitrous oxide molecules on the copper surface produces chemisorbed oxygen atoms, which generates gas-phase nitrogen according to the reaction
N2O(g) + 2Cu(s) f N2(g) + (Cu-O-Cu)(s) where s denotes a surface phase. The copper surface area and acidity of the catalysts in this study were measured by the volumetric chemisorption method using nitrous oxide and ammonia, respectively (Chang et al., 1994). For each measurement, correctly weighed catalyst (ca. 2 g) was loaded in the sample cell. Before evacuation, the catalyst was reduced at 523 K for 12 h with sufficient hydrogen flow. The main purpose of the reduction is to reduce the surface copper oxide which may be formed by the reaction with atmospheric oxygen. Continuous degassing was carried out at a temperature of 673 K and a pressure not exceeding 10-3 Torr for 3 h. After the catalyst cooled to the adsorption temperature, the nitrous oxide decomposition and the ammonia adsorption were carried out at 368 and 448 K, respectively. The copper surface area was determined using the following equation:
2nNa S ) 10-6 [m2/g of catalyst] 1.7 × 1019 where n is the amount of N2O (µmol/g of catalyst) decomposed, 1.7 × 1019 is the number of copper atoms per squared meter of copper surface, and Na is the Avogadro constant. The acidity of the copper catalyst
2082 Ind. Eng. Chem. Res., Vol. 36, No. 6, 1997 Table 2. Catalyst Content, BET Surface, Copper Surface Area, Acidity, Dispersion, and Crystallite Diameter of Various Catalysts surface area m2/g of catalyst
crystallite diameter, Å
catalyst
copper loading, wt %
BET
Cu
acidity, µmol/g of catalyst
dispersion, %
dBa
dCb
EDTA-1 EDTA-2 EDTA-3 EDTA-4 EDTA-5 EDTA-6 EDTA-7 TEA-1 TEA-2 TEA-3 TEA-4 TEA-5 TEA-6 TEA-7
8.44 13.36 14.46 16.52 19.17 22.92 24.56 7.09 11.40 12.56 17.49 21.38 22.96 25.92
155.33 142.53 140.11 136.65 126.98 101.23 92.38 132.51 125.97 124.14 113.18 107.46 101.50 99.38
7.025 8.88 9.25 9.68 9.43 8.63 8.01 4.06 4.25 4.35 4.61 4.82 4.91 5.09
220.50 200.16 184.75 171.59 159.69 155.55 152.90 265.80 260.87 256.32 248.37 244.51 240.12 238.95
14.94 11.93 11.48 10.52 8.83 6.76 5.85 10.28 6.69 6.22 4.73 4.05 3.84 3.52
207 205 209 200 198 199 189 428 251 389 165 147 158 233
81 101 105 114 136 178 205 117 180 193 254 297 313 341
a
Calculated from Scherrer’s equation using X-ray diffraction data. b Calculated from N2O decomposition data.
can be directly determined by the amount of NH3 (µmol/g of catalyst) adsorbed. Dehydrogenation of 2-Butanol and Activity Measurement. The dehydrogenation reactions were carried out in a microreactor operating under normal atmospheric pressure. A diagram of the microreactor and related apparatus can be found elsewhere (Saleque, 1993). For each run, about 0.5 g of catalyst was loaded into a Pyrex glass reactor and reduced at 523 K for 12 h with sufficient hydrogen flow. The activities were measured at different temperatures in the range 473573 K on the reduced catalysts, maintaining the reactant flow rate at 10.93 mL/h (WHSV ) 17.64 h-1). The products were analyzed by an on-line gas chromatography (Shimadzu 14A) with a flame ionization detector. The activity of the catalyst has been expressed as conversion of 2-butanol, X, and the turnover frequency, TOF. Both variables are related taking into account the amount of active copper present in the reaction medium:
X [1/s] TOF ) 4.17 × 10-3 LD where L and D are the copper loading (wt %) and copper dispersion (%), respectively. Results and Discussion Characterization of Catalysts. The copper content, BET surface area, copper surface area, acidity (µmol of NH3/g of catalyst), dispersion (%), and diameter of the copper crystallites of each catalyst, prepared with different chelating agents, are given in Table 2. The copper content varied from 8.44 to 24.56 wt % for EDTA series and 7.09-25.92 wt % for the TEA series. The BET surface area of the catalyst was gradually decreased for both the EDTA and TEA series, indicating that some copper crystallites might block the micropores of the support and reduce the BET surface area. The deposition rate of electroless copper plating relies upon the complexing capability of the chelating agent (Donahue et al., 1980). The plating rate for the TEA system was reported 20 times faster than the rate observed for the EDTA system (Kondo et al., 1990). In the present study, the preparation of Cu/Al2O3 catalysts with TEA took 5 min to complete the plating process, while with EDTA it required 30 min. Figure 2 shows the surface structure of the support and copper-plated catalysts. The existence of foreign material on the original untreated alumina support is
shown in Figure 2a. After being etched with alkali metal and acid, the foreign material on the surface was completely removed and the surface became clean as shown in Figure 2b. Definitely, the alkali metal and acid cleaning caused some corrosion. The copper deposited on the surface using different chelating agents can be clearly observed as shown in parts c-h of Figure 2. For the EDTA series, at low copper content, the copper particle was relatively small and uniformly distributed on the surface of the alumina support as shown in Figure 2d. As copper loading increased, the density of the copper particles increased, and finally, almost all of the surface was coated with copper as shown in Figure 2c. As the copper loading exceeded 20 wt %, the copper-coated the whole substrate surface and some of the copper particles were deposited on the coated surface. The copper particles on the coated layer were bulkier than the particles of the first layer, and some clusters of copper agglomerates appeared, as shown in Figure 2e. For the TEA series, even at low copper loading, the copper particles aggregated to bulkier clusters, which can be easily seen even at low magnification (1000×, Figure 2f). There were some alumina surface that remained unplated. Parts g and h of Figure 2 show that at higher copper loading, in addition to small crystallite, evenly spreaded, threedimensional bulkier copper clusters irregularly sat on the alumina support. Since agglomeration of small crystallites forms bulky clusters by reducing each exposing surface, the copper surface area of the TEA series is always smaller than that of the EDTA series as evidenced in Table 2 and Figure 3. In Figure 3 is shown the copper surface area variation with respect to copper loading for both chelate systems. For the EDTA series, the copper surface area gradually increased with loading up to ca. 16 wt % Cu and declined with further copper deposition. At the beginning of the electroless plating, the copper surface area was proportional to the number of sparsely distributed fine copper crystallites, which increased with copper loading. Up to a certain loading, the copper crystallites finally covered the whole substrate surface and formed a thin film that caused the exposed copper atoms to maximize. Further copper loading resulted in clusters of copper agglomerates blocking the micropores of the support and consequently reducing the exposed copper atoms. Sivaraj and Kanta Rao (1988) also demonstrated that the copper surface area increases with copper loading to a
Ind. Eng. Chem. Res., Vol. 36, No. 6, 1997 2083
Figure 2. SEM images of alumina and Cu/Al2O3 catalysts: (a) raw alumina; (b) Al2O3-etched acid and alkali metal; (c) EDTA-1; (d) EDTA-4; (e) EDTA-6; (f) TEA-1; (g) TEA-6; (h) TEA-7.
certain value and that further increasing the loading causes reduction of it. However, for the TEA series, the copper surface area linearly increased with loading at a slower rate, and no maximum appeared. This is because the number of small crystallites is independent of copper loading for the TEA series and the increase in copper surface area is mainly contributed from the increase of the number three-dimensional copper clusters.
Figure 4 shows the X-ray diffraction pattern of the raw, treated, and copper-plated alumina of the TEA series. The X-ray diffraction for the EDTA series can be found elsewhere (Chang et al., 1996), and we observed that the dependence of the XRD pattern on copper chelates is negligible. Figure 4b represents the XRD of the treated alumina which was obtained after being etched by alkali metal and acid and after undesirable materials such as fats, oils, and others were
2084 Ind. Eng. Chem. Res., Vol. 36, No. 6, 1997
Figure 5. Effect of copper loading on the relative acidity of the catalysts. Figure 3. Dependence of copper surface area on copper loading of the catalyst.
crystal, and peaks for the other two major planes are not observed. The intensity of the (111) plane increased with copper loading. This phenomenon may be explained by the mechanism of electroless copper plating. The copper ion adsorbs at the active sites of the palladium on the surface of the support, and the formaldehyde reduces it to metallic copper (Shipley, 1961). Thus, at low copper loading, the crystallinity of the deposited copper may be low or the growth of the crystal was not completed. In Figure 4e, two new peaks appeared at 2θ ) 50.6° and 74.5°, but the intensities of these three peaks were relatively low, when compared with parts f-h of Figure 4. At high copper loading, the deposited copper was highly crystalline in nature as shown in parts g-i of Figure 4. This phenomenon was also observed by Friedman and Freeman (1978). Applying the method of X-ray line broadening, the mean crystallite diameter dB can be calculated from Scherrer’s equation:
dB ) Kλ/B cos θ where λ is the X-ray wavelength, K is Scherrer’s constant, and B is the angular width expressed in radians. The mean crystallite diameter dB is listed in Table 2. Table 2 also shows the dependence of acidity on loading. The acidity of bare alumina, not shown in the table, is 345 µmol of NH3/g. The acidity decreased more markedly with copper loading for the EDTA series than it for the TEA series. It is clear that a good portion of the reduction in acidity may account for the reduction in the weight percent of alumina in the finished catalyst by the addition of copper. In order to avoid this dilution effect, we propose the relative acidity to explain the extent of reduction in acidity as a result of copper deposition. The relative acidity of catalyst with a copper loading L (wt %) is defined as Figure 4. X-ray diffraction patterns of alumina and Cu/Al2O3 catalysts: (a) raw alumina; (b) Al2O3-etched acid and alkali metal; (c) TEA-1; (d) TEA-2; (e) TEA-3; (f) TEA-4; (g) TEA-5; (h) TEA-6; (i) TEA-7.
removed, indicating that the structure of alumina remained unchanged. Comparison of parts a and b of Figure 4 provides the information that the alkali metal and acid cleaning had no effect on the structure of alumina. After electroless copper plating started, Figure 4c showed that there is one small new peak at 2θ ) 43.2° which is due to the (111) plane of the copper
relative acidity )
acidity of catalyst (1 - L)345
which relates the acidities of a copper/alumina catalyst and a bare alumina support. Figure 5 illustrates the effect of copper loading on the relative acidity of the catalysts. Since the copper catalysts plated with EDTA resulted in smaller crystallites and were spread more uniformly than the catalysts plated with TEA, the acid sites could be reduced more effectively for the EDTA series. In the process of electroless plating, the substrate surface was available for copper deposition and
Ind. Eng. Chem. Res., Vol. 36, No. 6, 1997 2085 Table 3. Dependence of the Selectivity (%) to Butene on Temperature of the EDTA and TEA Series Catalysts catalysts
200 °C
220 °C
240 °C
260 °C
280 °C
300 °C
γ-Al2O3a EDTA-1 EDTA-2 EDTA-3 EDTA-4 EDTA-5 EDTA-6 EDTA-7 TEA-1 TEA-2 TEA-3 TEA-4 TEA-5 TEA-6 TEA-7
0.04 0.18 0.55 0.25 0.41 1.01 0.19 0.17 1.07 0.86 0.87 1.04 0.94 0.51 0.49
0.10 0.31 1.64 0.89 1.20 1.88 0.29 0.30 1.89 1.17 1.17 0.97 1.70 0.43 1.06
0.51 0.79 4.67 3.28 3.95 3.24 0.67 0.72 3.97 2.83 2.48 2.22 3.50 1.26 3.04
1.63 3.55 10.80 9.19 10.54 7.55 1.81 1.88 8.51 5.57 5.44 4.42 7.89 4.40 7.51
8.23 11.12 17.80 19.20 21.67 15.86 4.88 5.44 17.51 10.87 12.49 9.31 15.93 16.50 16.01
15.18 23.24 39.33 35.72 38.58 27.53 11.15 11.09 30.89 18.80 23.79 15.99 23.58 28.58 25.67
a
Yield (%) of butene ) conversion × selectivity to butene.
Figure 6. Dependence of the rate of dehydrogenation of 2-butanol on the exposed copper atoms: (a) EDTA series; (b) TEA series. Symbols: (b) 200 °C; (3) 220 °C; (1) 240 °C; (0) 260 °C.
the copper atoms gradually shielded the acid site of the alumina; therefore, the acidity reduced as the copper loading increased. During the electroless copper plating, the copper ion was chelated with EDTA or TEA to prevent the precipitation of Cu(OH)2, and the SO42from CuSO4 can be easily washed from the catalyst. It was difficult to diffuse the Cu-EDTA or Cu-TEA complex deeply into the small micropores due to the bulkiness of the complex, and the fast electroless plating reaction induced insufficient plating on the walls of the small micropores, which left a fraction of the micropores unplated and the acidity of the catalysts was not sufficiently reduced. Conversely, Sivaraj et al. (1990) demonstrated that the acidity can be significantly reduced when catalysts are prepared by the precipitation method; the unchelated copper ions can easily diffuse into small micropores of alumina before the precipitation and shields relatively more acid sites of alumina. Dehydrogenation of 2-Butanol. The rate of dehydrogenation of 2-butanol increased with increasing temperatures as well as the number of exposed copper atoms, as shown in Figure 6. At higher temperatures, conversions appeared to become nearly independent of copper loading for both the EDTA and the TEA series. Both methyl ethyl ketone (MEK) and butene are obtained, and the selectivities to butene at various temperatures are listed in Table 3. Bare γ-Al2O3 shows no dehydrogenation capability, and its dehydration ability expressed in yield of butene is also listed in Table 3. It is clear that the dehydration of 2-butanol became markedly high at higher temperatures. The dehydration reaction is mainly contributed from the acidic sites of alumina (Sivaraj et al., 1990). It is an exothermic reaction which can compete with the dehydrogenation reaction only at a higher temperature. Figure 7 shows the variation of TOF with respect to copper dispersion to understand the inherent activity of an active site. The
Figure 7. Effect of dispersion on TOF: (a) EDTA series; (b) TEA series. Symbols: (b) 200 °C; (3) 220 °C; (1) 240 °C; (0) 260 °C; (9) 280 °C; (4) 300 °C.
TOF depends on the copper dispersion for both series, and the TOF of the TEA series catalysts is always higher than that of the EDTA series catalysts. This may indicate that the dehydrogenation of 2-butanol over Cu/Al2O3 catalyst is a slightly structure-sensitive reaction and the possibility of the interaction between the copper metal and alumina support may exist. Conclusions In this study, we used two chelating agents, EDTA and TEA, to prepare electroless Cu/Al2O3 catalysts of different copper loadings to study the effects of the complexing capability on the properties of the catalyst. According to the observation of SEM images and the results of chemisorption data, we conclude that the complexing capability of chelating agent dominates the particle size of the copper crystallites and, therefore, the copper dispersion on the alumina support. The experi-
2086 Ind. Eng. Chem. Res., Vol. 36, No. 6, 1997
mental results showed that the plating rate of the TEA system is much higher than that of the EDTA system. The Cu-TEA chelate enhanced the formation of bulky copper clusters occurring even at low copper loading. The catalysts prepared by Cu-EDTA chelates had smaller copper crystallites, higher copper dispersion, and higher activity than those prepared by Cu-TEA chelates. The acidity of the catalyst could be reduced more effectively for the EDTA series. The activity test of dehydrogenation of 2-butanol showed that the activity is directly proportional to the number of exposed copper atoms. The dehydration reaction becomes apparent only at higher temperatures and catalysts with higher acidity. Acknowledgment We thank the National Science Council of the Republic of China for financial support of the experimental work (Grant No. NSC85-2214-E-035-005). Literature Cited Amelio, W. J.; Bartolotta, P. G.; Markovich, V.; Parsons, R. E. Copper Plating Bath and Improved Stability. UP4655833, 1987. Chang, H. F.; Saleque, M. A. Dependence of Selectivity on the Preparation Method of Copper/R-Alumina Catalysts in the Dehydrogenation of Cyclohexanol. Appl. Catal. A 1993, 103, 233. Chang, H. F.; Saleque, M. A.; Hsu, W. S.; Lin, W. H. Effect of Acidity and Copper Surface Area of the Cu/Al2O3 Catalyst Prepared by Electroless Plating Procedure on Dehydrogenation Reactions. J. Mol. Catal. 1994, 94, 242. Chang, H. F.; Saleque, M. A.; Hsu, W. S.; Lin, W. H. Characterization and Dehydrogenation Activity of Cu/Al2O3 Catalysts Prepared by Electroless Plating Technique. J. Mol. Catal. A 1996, 109, 249. Chinchen, G. C.; Hay, C. M.; Vanderwell, H. D.; Waugh, K. C. The Measurement of Copper Surface Areas by Reactive Frontal Chromatography. J. Catal. 1987, 103, 79. Donahue, F. M.; Wong, K. L. M.; Bhalla, R. Kinetics of Electroless Copper Plating. IV. Empirical Rate Law for H2CO-EDTA Baths. J. Electrochem. Soc. 1980, 127, 2340. El-Raghy, S. M.; Abo-Salama, A. A. The Electrochemistry of Electroless Deposition of Copper. J. Electrochem. Soc. 1979, 126, 171.
Evans, J. W.; Casey, P. S.; Wainwright, M. S.; Trimm, D. L.; Cant, N. W. Hydrogenolysis of Alkyl Formates over a Copper Chromite Catalyst. Appl. Catal. 1983, 7, 31. Friedman, R. M.; Freeman, J. J. Characterization of Cu/Al2O3 Catalysts. J. Catal. 1978, 55, 10. Giamello, E.; Fubin, B.; Lauro, P.; Bossi, A. A Microcalorimetric Method for the Evaluation of Copper Surface Area in Cu-ZnO Catalyst. J. Catal. 1984, 87, 443. Kikuchi, H.; Tomizama, A.; Oka, H. Electroless Plating Solution. UP4563217, 1986. Kondo, K.; Ishikawa, J.; Takenaka, O.; Matsubara, T.; Irie, M. Electroless Copper Plating in the Presence of Excess Triethanol Amine. J. Electrochem. Soc. 1990, 137, 1859. Robinson, W. R. A. M.; Mol, J. C. Characterization and Catalytic Activity of Copper/Alumina Methanol Synthesis Catalysts. Appl. Catal. 1988, 44, 165. Saleque, M. A. The Study of Dehydrogenation of Cyclohexanol on the Electroless Plated Copper Catalysts. Master’s Thesis, Department of Chemical Engineering, Feng Chia University, 1993. Shipley, C. R., Jr. Method of Electroless Deposition on a Substrate and Catalyst Solution Therefore. UP3011920, 1961. Shu, J.; Grandjean, B. P. A.; Ghali, E.; Kaliaguine, S. Autocatalytic Effect in Electroless Deposition of Palladium. J. Electrochem. Soc. 1993, 140, 3175. Sivaraj, C.; Kanta Rao, P. Characterization of Copper/Alumina Catalysts Prepared by Deposition-Precipitation Using Area Hydrolysis. I. Nitrous Oxide Decomposition and Reaction of Ethanol. Appl. Catal. 1988, 45, 103. Sivaraj, C.; Srinivas, S. T.; Nageshwar Rao, V.; Kanta Rao, P. Selectivity Dependence on the Acidity of Copper-Alumina Catalysts in the Dehydrogenation of Cyclohexanol. J. Mol. Catal. 1990, 60, L23. Strohmeier, B. R.; Leyden, D. E.; Field, R. S.; Hercules, D. M. Surface Spectroscopic Characterization of Cu/Al2O3 Catalysts. J. Catal. 1985, 94, 514.
Received for review June 17, 1996 Revised manuscript received October 18, 1996 Accepted February 18, 1997X IE960341E
X Abstract published in Advance ACS Abstracts, April 1, 1997.
