Sulfolene Hydrogenation over an Amorphous Ni−B Alloy Catalyst on

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Sulfolene Hydrogenation over an Amorphous Ni-B Alloy Catalyst on MgO Shaohui Ge, Zhijie Wu, Minghui Zhang,* Wei Li, and Keyi Tao Institute of New Catalytic Materials Science, Department of Materials Chemistry, College of Chemistry, Nankai UniVersity, Tianjin 300071, P. R. China

The catalytic hydrogenations of sulfolene to sulfolane over different supported amorphous Ni-B alloy catalysts and Raney nickel catalysts were performed in a batch reactor under pressurized conditions. The deposition of amorphous Ni-B particles (average Ni-B particle size ) 40.5 nm) on MgO was carried out by a silvercatalyzed electroless plating technique. The influence of significant variables, such as the plating temperature and content of potassium borohydride, was investigated in the preparation. The silver and Ni-B loadings in the catalyst were varied as well. The catalysts were characterized by X-ray powder diffraction (XRD), inductively coupled plasma (ICP) spectrometry, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and N2 physisorption. The load of nickel on MgO increases with the plating temperature, use of potassium borohydride, and loading of silver. The best Ni-B/MgO catalyst showed a remarkably superior catalytic activity to that of the Ni-B/TiO2 or Raney nickel catalyst, and the difference is ascribed to the nature of amorphous structure and the characteristics of amorphous Ni-B particles on MgO. Introduction The hydrogenation of sulfolene to sulfolane is of great industrial importance because sulfolane is widely used as a solvent for both extraction and reaction.1 Generally, the sulfolene is obtained from the Diels-Alder reaction of 1,3-butadiene and sulfur dioxide and thus contains a small quantity of sulfur dioxide, by which the catalysts are deactivated quickly after hydrogenation.2-9 Mostly, the hydrogenation is carried out over Raney nickel catalysts in the liquid phase at elevated hydrogen pressures, and the sulfolene should be treated by ammonia or amine to control the amount of sulfur dioxide and enhance the quality of the sulfolane obtained. However, the typical Raney nickel catalysts have shown many serious disadvantages, such as short lifetimes due to sulfur poisoning10,11 and environmental pollution caused by alkaline leaching during their preparation. Therefore, it is highly desirable to develop environmentally benign catalysts with excellent activities in the hydrogenation of sulfolene. Although most of the catalytic hydrogenation studies to date have involved Raney nickel or noble metal systems, other catalysts have also been considered.12-20 A recent hydrogenation study showed that supported nickel-metalloid amorphous alloy catalysts exhibit extremely high catalytic activities and selectivities in various hydrogenation processes.12-18 In our previous work, two types of nickel-based amorphous alloy catalysts, a Ni-P (B) amorphous alloy catalyst obtained by chemical reduction and a supported amorphous Ni-B alloy obtained via chemical deposition, were investigated in the sulfolene hydrogenation reaction.19,20 However, the hydrogenation activities of both catalysts were not as good as that of Raney nickel at industrial conditions. Moreover, during the impregnation of nickel ions on the support and the reduction of nickel ions by potassium borohydride, there are many ions, such as nickel ions and borate, in the residual solution, resulting in environmental pollution and waste. Alternatively, such problems can be avoided by using the electroless plating technique for the recycling of the plating solution.21-23 To overcome the shortcomings of these * To whom correspondence should be addressed. Fax: +86-22-23507730. Tel: +86-22-2350-7730. E-mail: [email protected].

catalysts while retaining their attractive characteristics, we introduced a novel silver-catalyzed electroless plating technique for the preparation of supported amorphous alloy catalysts.24,25 Electroless plating is a process involving the selective reduction of nickel ions at the surface of a catalytic substrate immersed in an aqueous solution of nickel ions, with continuous deposition on the substrate through the autocatalytic action of the deposit itself. For the silver-catalyzed electroless plating process, the plating solution consists of nickel sulfate, ethylenediamine, sodium hydroxide, and potassium borohydride without a stabilizer. In a typical experiment, the support, loaded with a small amount of silver (generally 0.2 wt %) is transferred to the plating solution, and the silver catalyzes the plating. During the plating, nickel nuclei are formed on the surface by the catalysis of silver in the initial stage; then a mass of Ni-B particles is deposited on the support through the autocatalysis of nickel nuclei. Finally, a large number of amorphous porous Ni-B particles are homogeneously distributed on the support. Within the current work, we focused on the precipitation of Ni-B on MgO instead of TiO2 for economy. The silver was plated on the support as reported previously,26 and the optimal conditions for the preparation of the supported amorphous NiB/MgO catalysts, such as the plating temperature, silver loading, and potassium borohydride content in the plating solution, were investigated. Experimental Section Catalyst Preparation. MgO powers (800 mesh, SBET ) 3.7 m2/g), nickel sulfate (NiSO4‚6H2O), silver nitrite (AgNO3), potassium borohydride (KBH4), ethylenediamine (H2NCH2CH2NH2), sodium hydroxide (NaOH), and ethanol were of reagent grade and were used as received. Ag/MgO was synthesized as a reference compound,24,26 and the load of silver on the support was controlled at 0.025-0.20 wt %. Deionized water with a resistivity greater than 18.2 MΩ‚cm, obtained from a Milli-Q purification system (Millipore, Bedford, MA), was used in sample preparation, in rinsing of the glassware, and in the experimental setup. Deposition of electroless Ni-B on the Ag/MgO support was performed by transferring the supports in a basic borohydride

10.1021/ie0512542 CCC: $33.50 © 2006 American Chemical Society Published on Web 02/23/2006

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bath of the following compositions: nickel sulfate, 12.0 g/L; potassium borohydride, 5.5 g/L; ethylenediamine, 10 g/L; and sodium hydroxide, amount needed to maintain the desirable pH value (ca. 13.4-13.5). Six 250-mL round-bottomed reaction flasks containing plating solution for electroless Ni-B deposition were mounted in a Carousel 6 Place Reaction Station (Radleys, U.K.). The variation of temperature at plating was less than 1 K from the set point. The plating conditions were as follows: pH, 13.4-13.5; temperature, 308-333 K; and plating time, 10-30 min. The pH value of the plating solution was adjusted to between 13.4 and 13.5 by addition of NaOH, and the plating solution was then heated to 318 K. The pretreated support (Ag/MgO) was transferred into the plating solution. After 12 min, the plating had finished, and the black precipitates (Ni-B/MgO-1) in the solution were washed thoroughly with deionized water until the pH value reached 7, after which they were washed with ethanol and stored in ethanol. In optimization experiments, the plating temperature, loading of silver on the support, and content of potassium borohydride in the plating solution were varied. For comparison, Ni-B/TiO2 was synthesized by silvercatalyzed electroless plating under the same condition as NiB/MgO-1. The theoretical loading of nickel on the support is controlled at 20 wt %. Catalyst Characterization. The structures of the as-prepared catalysts were measured by X-ray powder diffraction (XRD) using a D/MAX-2500 X-ray diffractometer with Cu KR radiation (λ e 1.54056 Å) at a scanning rate of 0.02°/s in 2θ ranging from 10° to 80°. The chemical compositions of these Ni-B alloys were analyzed by inductively coupled plasma (ICP) spectrometric analysis on an IRIS Intrepid spectrometer. The particle size was determined by high-resolution transmission electron microscopy (HRTEM, JEOL-2010 FEF instrument, with a TOPCON 022B microscope operated at 200 keV). Samples were supported on copper grids with holey carbon films by dipping the grids in the sample powder and shaking off the excess. Several bright-field TEM images of different portions of the sample were obtained at magnifications up to 400 000. At least 1000 particles were employed to determine the average particle size. Selected-area electron diffraction (SAED) patterns were recorded on a JEOL-2010 FEF instrument operated at 80 kV (with a beam size of ∼40 nm) to analyze the crystallinity. The surface morphology and the diffusion of Ni-B particles on the supports were observed by scanning electronic microscopy (SEM) performed on a LEO 1530VP instrument. The surface area was measured by the BET method by N2 adsorption at 77 K on an automatic surface area and pore size analyzer (Autosorb-1-MP 1530VP). Prior to analysis, the samples were degassed at 373 K for 2.0 h. The nickel surface area was determined by the hydrodesulfurization of 3-methylthiophene in the liquid phase.27-29 Experimental Setup. The sulfolene hydrogenation experiments were performed in a 100-mL high-pressure stainless autoclave. The catalytic activity of the inner wall of the reactor could be neglected, as found by experiments. The reaction was carried out at 600 rpm using a volume of liquid of 30.0 mL of deionized water, 30.0 g of sulfolene, and 0.3 g of catalyst. The hydrogen pressure in all experiments was 2.5 MPa. The possibility of diffusional limitations during the catalytic tests was investigated following procedures described elsewhere.30 Experiments were carried out at different stirring velocities in the range of 100-1000 rpm. The constancy of the activity and selectivity above 450 rpm ensured that external diffusional limitations were absent at the rotation speed selected

Table 1. Compositions of Supported Amorphous Ni-B Alloys sample Ni-B/MgO-1 Ni-B/TiO2 Raney nickel

Ni loading (wt %)

composition (at. %)

SBET (m2/g)

SNi (m2/g)

conversion (%)

14.83 14.89

Ni75.1B24.9 Ni65.9B34.1

26.3 28.4

6.5 5.6

80.1 63.5 64.5

(600 rpm). On the other hand, to ensure that the catalytic results were not influenced by intraparticle mass-transfer limitations, the catalysts were crushed to 800 mesh. Then, several runs using the crushed catalyst were carried out. In every case, the conversion and selectivity values obtained were the same as those for the catalyst that had not been crushed. Hence, it can be accepted that internal diffusional limitations were absent at the operating conditions of this work. The hydrogenation was carried out at 318 K for 2.0 h. The products were analyzed by gas chromatography with flame ionization detection (FID), from which the conversion of sulfolene was obtained. Results and Discussion Generally, the amorphous alloys obtained by electroless plating have been widely used as effective anticorrosive materials,31 and recent studies have shown that highly dispersed Ni-B particles or Ni-B films from electroless plating on support can catalyze many reactions.23,32 Up to now, the supported Ni-B nanoparticles are considered to be active catalysts for hydrocarbon hydrogenation.33 In this study, the sulfolene hydrogenation reaction was investigated over supported Ni-B/MgO catalysts obtained by silver-catalyzed electroless plating under different conditions. Table 1 shows the bulk compositions of as-prepared supported Ni-B alloy catalysts determined by ICP analysis. The Ni loading in Ni-B/ MgO-1 is lower than the theoretical value, because some nickel ions remained in the solution as complexes with ethylenediamine. It was found that the Ni/B mole ratio of Ni-B/TiO2 is maintained at 2/1, but the ratio changes to 3/1 in Ni-B/MgO. As it has been demonstrated that the reduction mechanism of potassium borohydride varies under different conditions;34-37 here, we also found that the support can influence the composition of supported Ni-B catalysts. In fact, the MgO in the plating solution could change to Mg(OH)2 partly as a result of the

Figure 1. XRD patterns of different samples: (a) MgO, (b) Ni-B/TiO2, (c) Ni-B/MgO, (d) crystalline Ni-B/MgO at 773 K in N2 flow for 2.0 h. The peaks of Ni are designated by [, and the peaks of Mg(OH)2 are designated by ].

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Figure 2. (a) TEM image of Ni-B/MgO-1. (b) HRTEM image of Ni-B/MgO-1. (c) Particle size distribution. (d) EDS of Ni-B/MgO-1.

reaction between MgO and NaOH (Figure 1). On the other hand, the results of sulfolene hydrogenation suggest that the supported Ni-B/MgO catalyst shows a much higher hydrogenation activity than Ni-B/TiO2 and Raney Ni catalyst (Table 1). Figure 1 shows the XRD patterns of amorphous samples and the MgO support. Generally speaking, the present study indicates that the amorphous Ni-B alloy shows a broad peak around 2θ e 45° in the XRD patterns, with the complete absence of any sharp crystalline peaks. In comparison to the XRD patterns of the MgO support (Figure 1a), Ni-B/MgO-1 (Figure 1c) demonstrates the presence of Mg(OH)2. For the supported Ni-B catalysts, Ni-B/MgO-1 presents an obvious broad peak at around 2θ e 45°(subtracting the peaks due to MgO), suggesting an amorphous structure of Ni and B. Moreover, the XRD pattern of the crystalline sample (Figure 1d) presents three peaks due to crystalline nickel, indicating the loading of nickel on the support. TEM was used to characterize the nature of the Ni-B particles on MgO. Figure 2a indicates that the Ni-B particles are spherical and mainly situated on the outer surface of the supports. It is obvious that the particles present a flowlike shape with pores, consistent with that of Ni-B/TiO2.26 The SAED patterns (inset of Figure 2a) exhibit only diffuse Debye rings rather than distinct dots, verifying the amorphous nature of Ni-B on the supports (inset at the top of Figure 2b).38 After crystallization, the SAED pattern shows many distinct dots (inset

at the bottom of Figure 2b). The HRTEM image of Ni-B particle in the Ni-B/MgO-1 catalyst (Figure 2b) indicates that the particles present pores of 2.0-nm diameter, wider than those in Ni-B/TiO2 (1.0-1.5 nm). It is clear that the nature of the Ni-B particles varies over different supports. Figure 2a suggests that the Ni-B particles in Ni-B/MgO-1 are homogeneously dispersed in size and exhibit an average particle size of 40.5 nm (from Figure 2c). Although the particle size distribution ranges from 36 to 45 nm, the majority of the Ni-B particles fall within the range of 39-43 nm. Figure 2d suggests the presence of elements in Ni-B/MgO as determined by energy dispersive X-ray spectroscopy (EDS). The TEM characterization clearly demonstrates that the particle sizes of the Ni-B particles are due to the preparation method rather than support. However, the composition of Ni-B particles changes with the supports, as indicated in Table 1. In our view, the change might be associated with the different characteristics of the SternGrahame electrical double layer between support and plating.39-41 Figure 3 shows SEM images of Ni-B/MgO-1. Figure 3a suggests the diffusion of Ni-B particles on the MgO; a large number of Ni-B particles (white dots confirmed by EDX and Figure 3b) are located on MgO, and the sizes of Ni-B particles are homogeneous. Figure 3b shows a magnified image of Figure 3a. It is clear that the size and dispersion of Ni-B particles are homogeneous. Unlike traditional electroless plating of nickel on bulk substrates, the silver-catalyzed electroless plating was

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Figure 4. Plots of conversion of sulfolene and loading of nickel vs loading of silver.

Figure 3. SEM morphologies of Ni-B/MgO catalysts: (a) Ni-B/MgO1, (b) magnified image of Ni-B/MgO-1. Table 2. Compositions of Supported Amorphous Ni-B Alloys Obtained at Different Plating Temperatures samplea

temperature (K)

plating time (min)

Ni loading (wt %)

conversion (%)

Ni-B/MgO-1 Ni-B/MgO-2 Ni-B/MgO-3 Ni-B/MgO-4 Ni-B/MgO-5 Ni-B/MgO-6

318 308 313 323 328 333

12 40 20 12 12 12

14.83 7.67 8.23 14.85 14.86 14.90

80.1 49.6 56.2 80.6 80.5 80.6

a

Plating solution decomposes at 338 K.

carried out on powder supports with visible defects such as pores, pits, and cracks.22,40 Therefore, it is indispensable to tailor the powder support with homogeneously distributed passivation regions on the supports, to obtain homogeneously dispersed Ni-B nanoparticles on the supports. Figure 3 clearly demonstrates that the defects on the support are uniform for Ni-B deposition during the plating, because of the interaction between plating solution and MgO (shown in Figure 1). To optimize the preparation of Ni-B/MgO, the reaction temperature, content of potassium borohydride in the plating solution, and loading of silver on the support were investigated. Table 2 shows the influence of the plating temperature on the nature of Ni-B/MgO. As the plating solution would decompose at 338 K, the plating was carried out from 308 to 333 K. The results indicate that the plating time and the loading of nickel on the support were dependent on the plating temperature, when the plating was carried out at 308-318 K. The plating reaction is controlled by dynamics and thermodynamics from 308 to 318

Figure 5. Plots of conversion of sulfolene and loading of nickel vs B/Ni mole ratio in the plating solution.

K. However, it was found that the loading of nickel and the plating time are almost constant with changing plating temperature, when the temperature was controlled from 318 to 333 K. It seems that the plating reaction was dependent on the thermodynamics. Alternatively, the equilibrium of the metal salt and complex control the electroless nickel plating. Table 2 suggests that the change of Ni loading results in the various catalytic activities in the hydrogenation of sulfolene. It is obvious that the catalytic activity increases with the plating temperature from 308 to 318 K, because of the increased loading of nickel. However, the activity changed little when the loading of nickel was kept at 14.8-14.9 wt % from 318 to 333 K. In the present work, the influence of potassium borohydride in the preparation of supported Ni-B/MgO catalyst was investigated. Figures 4 and 5 show the influence of the loading of silver on the support and the content of potassium borohydride on the catalytic activities of catalysts, respectively. With increasing loading of silver on MgO, the loading of nickel increases, accompanying with the improvement of the catalytic activities (Figure 4). It has been demonstrated that the silver could catalyze the plating at lower temperature. The plot of the relation between the loading of silver on the support and the catalytic activity of the catalyst suggests that the optimal amount of plating catalyst (silver) is 0.20 wt % on the support. This clearly indicates that the amount of Ni-B particles on the support is controlled by dynamics at a certain temperature, which seems to indicate that the plating is dependent on the initial

Ind. Eng. Chem. Res., Vol. 45, No. 7, 2006 2233 Table 3. Compositions of Supported Amorphous Ni-B Catalysts Prepared with Different Contents of Potassium Borohydride in the Plating Solution sample

B/Ni mole ratio

Ni-B/MgO-1 Ni-B/MgO-7 Ni-B/MgO-8 Ni-B/MgO-9 Ni-B/MgO-10 Ni-B/MgO-11

0.25 0.5 1.0 1.5 2.0 3.0

composition (at. %) Ni75.1B24.9 Ni74.6B25.4 Ni74.5B25.5 Ni74.1B25.9 Ni74.6B25.4 Ni74.0B26.0

amorphous structure yes yes yes yes yes yes

rate of reaction. On the other hand, Figure 5 indicates that the amount of potassium borohydride determines the reducing efficiency of nickel ions. Generally, the best B/Ni mole ratio in the plating solution is 1/1.31 Use of more potassium borohydride should result in the presence of superfluous boron oxides. However, the Figure 4 suggests that the loading of nickel is mainly affected by the use of potassium borohydride in the plating solution. Moreover, Table 3 shows that the composition and amorphous structure of Ni-B particles change little with varying amounts of potassium borohydride. When the B/Ni mole ratio was increased to 1.5/1, the loading of nickel was kept at about 14.85 wt % with different contents of potassium borohydride in the plating solution. As the composition and loading of Ni-B particles change little, the excess boron should be present as borate in the plating solution, when the amount of potassium borohydride is increased to 1.5/1 (B/Ni mole ratio). Figure 5 shows that the catalytic activity increases with the loading of nickel and that the optimal B/Ni mole ratio in the plating solution is 1.5/1. Table 1 shows the conversions of sulfolene over Ni-B/MgO1, Ni-B/TiO2, and Raney nickel catalysts. From these results, one can see that the Ni-B/TiO2 catalyst exhibits the same catalytic capability as the Raney nickel. As has been demonstrated frequently, the high activity of supported amorphous Ni-B alloy catalyst, the same as and even higher than that of Raney nickel, is mainly due to the unique combination of small particle size and a short-range-ordered and long-range-disordered structure.20,31 The as-prepared supported amorphous Ni-B alloy catalyst with a higher loading of nickel (>10 wt %) shows excellent catalytic activity. For the supported Ni-B alloy catalyst obtained from silver-catalyzed electroless plating, we find that the supported amorphous Ni-B/MgO catalyst shows catalytic activity superior to that of the supported Ni-B/TiO2 catalyst. SNi of Ni-B/MgO is higher than that of Ni-B/TiO2, which leads to the greater exposure of active nickel on the surface of support. We have investigated the process of silvercatalyzed electroless plating Ni-B on TiO2. The process of plating consists of two steps: the nucleation stage and the growth stage. The nucleation stage lasts about 12 min, and the plating lasts about 35 min during the plating Ni-B on TiO2 at 318 K. However, the plating time of Ni-B/MgO is much shorter (12 min). Yin et al. reported a theoretical expression for the nickel deposition rate by investigating the Stern-Grahame electrical double layer.40,41 In addition, the different surface natures of the support,39 MgO, and TiO2, should show different plating frontiers (the inner Helmholtz plane). This further work is a current focus of our research. Conclusions Supported amorphous Ni-B/MgO catalysts obtained from silver-catalyzed electroless plating show the highest activity in the hydrogenation of sulfolene to sulfolane. The factors accounting for the superior catalytic activity of Ni-B/MgO were,

on one hand, the amorphous nature of Ni-B on MgO, on which 40.5-nm amorphous Ni-B particles were located. On the other hand, the effect of MgO promoted the characteristics of the Ni-B particles, the homogeneous distribution of Ni-B particles on the support, and the high SNi value. The conditions applied during the preparation of supported Ni-B/MgO catalyst, such as the plating temperature, silver loading on the support, and potassium borohydride content were investigated. Economically and effectively, these conditions should be controlled according to the actual loading of nickel on the support. Acknowledgment The present work was partly supported by NSF of China (20403009 and 20233030), Key Project of Chinese Ministry of Education (105045), and Open Foundation of State Key Laboratory of Heavy Oil Processing. Literature Cited (1) Choi, Y. J.; Cho, K. W.; Cho, B. W.; Yeo, Y.-K. Optimization of the sulfolane extraction plant based on modeling and simulation. Ind. Eng. Chem. Res. 2002, 41 (22), 5504. (2) Middlebrook, J. T. Hydrogenation of sulfolenes to sulfolanes. U.S. Patent 3,152,144, 1964. (3) Nash, M. E. Use of a solvent for hydrogenation of sulfolene to sulfolane. U.S. Patent 5,030,737, 1991. (4) Huxley, E. E. Conversion of sulfolene to sulfolane in the presence of a tertiary amine. U.S. Patent 3,928,385, 1975. (5) Johnson, M. M. Catalytic hydrogenation of sulfolenes. U.S. Patent 4,558,138, 1985. (6) Kornilova, V. P.; Sukhareva, T. S. Effect of additives on the activity and stability of Raney nickel catalysts for sulfolene hydrogenation. USSR, Katal. ProtesessoV Polucheniyai PreVrashcheniya Sernist. Soedin., NoVosibirsk 1979, 66. (7) Mahan, J. E.; Fauske, S. C. Hydrogenating sulfolenes to sulfolanes. U.S. Patent 2,578,565, 1948. (8) Sapozhnikova, E. A.; Masagutov, R. M.; Talipoy, G. Sh. Hydrogenation of 3-sulfolene on a modified Raney nickel catalyst. USSR, Katal. Pererab. UgleVodorodn. Syr′ya 1970, 4, 115. (9) Gorbenko, Yu. R.; Lange, S. A.; Evdokimova, Zh. A.; Aleksandrova, T. P.; Avdeeva, L. B. Hydrogenation of sulfolene in the presence of a Raney nickel catalyst. SalaVatskii Neftekhim. Komb., SalaVat, USSR, Nefterkhimiya 1972, 12 (3), 392. (10) Mashkina, A. V.; Khramov, A. V.; Khim, S. S. Catalytic hydrogenation of sulfolene. Soderzhashch. Neft. Nefteprod., Akad. Nauk SSSR, Bashkirsk. Filial 1964, 6, 308. (11) Sultanov, A. S.; Sapozhnikova, E. A. Hydrogenation of sulfolene over Raney nickel in isopropyl alcohol. USSR. Katal. Pererab. UgleVodorod. Syr′ya 1971, 5, 183. (12) Smith, G. V.; Brower, W. E. Amorphous alloy catalysts. Proc. Int Congr. Catal., 7th, Tokyo 1980, 355. (13) Molnar, S.; Smith, G. V.; Bartok, M. New catalytic materials from amorphous metal alloys. AdV. Catal. 1989, 36 (2), 329. (14) Wonterghem, J. V. Formation of ultrafine amorphous alloy by reduction in aqueous solution, Nature. 1986, 322, 622. (15) Baiker, A. Metallic glasses in heterogeneous catalysis. J. Chem. Soc., Faraday Discuss. 1989, 87, 239. (16) Chen, Y. Chemical preparation and characterization of metalmetalloid ultrafine amorphous alloy particles. Catal. Today 1998, 44, 3. (17) Deng, J. F.; Li, H. X.; Wang, W. J. Progress in design of new amorphous alloy catalysts. Catal. Today 1999, 51, 113. (18) Deng, J. F. Supported metal-metalloid amorphous alloy as hydrogenation catalysts. Curr. Top. Catal. 1999, 2, 1. (19) Ma, Y. F.; Li, W.; Zhang, M. H.; Zhou, Y.; Tao, K. Y. Preparation and catalytic properties of amorphous alloys in hydrogenation of sulfolene. Appl. Catal. A 2003, 243, 215. (20) Wang, L. J.; Li, W.; Zhang, M. H.; Tao, K. Y. The interactions between the NiB amorphous alloy and TiO2 support in the NiB/TiO2 amorphous catalysts. Appl. Catal. A 2004, 259, 185. (21) Sankara Narayanan, T. S. N.; Seshadri, S. K. Formation and characterization of borohydride reduced electroless nickel deposits. J. Alloys Compds. 2004, 365, 197.

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ReceiVed for reView November 12, 2005 ReVised manuscript receiVed January 3, 2006 Accepted January 27, 2006 IE0512542