8866
Ind. Eng. Chem. Res. 2006, 45, 8866-8873
Effect of Additive (W, Mo, and Ru) on Ni-B Amorphous Alloy Catalyst in Hydrogenation of p-Chloronitrobenzene Liang-Fu Chen and Yu-Wen Chen* Department of Chemical and Materials Engineering, Institute of Materials Science and Engineering, National Central UniVersity, Chung-Li 320 Taiwan
A series of W-, Ru-, and Mo-promoted Ni-B amorphous nanocatalysts were prepared by chemical reduction of the precursors of promoters, respectively, and nickel acetate with sodium borohydride in methanol/water (1:1) solution. The catalysts were characterized by X-ray diffraction, nitrogen sorption, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy. With a specific concentration of promoter, the particles of the Ni-B catalysts became smaller. The catalysts also demonstrated higher thermal resistance, protecting the amorphous structure from high-temperature treatment. The correlation of the catalytic performance to both the structural and the electronic characteristics was discussed. W6+ and Mo6+ cations were not reduced by NaBH4. They formed oxides or hydroxides since the preparation solutions were basic. They acted as spacers and prevented Ni-B from sintering and agglomeration. Ru3+ could be reduced by NaBH4 to Ru metal. Ru is also a catalyst for this reaction. The promoted Ni-B catalysts were proved to be effective during the hydrogenation of p-chloronitrobenzene in this study for enhancing the thermal stability and the catalytic activity. Mo and W additives not only served the role of spacer to increase the dispersion of active sites and protect the amorphous structure, but also changed the composition of Ni-B catalyst, which caused the increase of amorphous B in Ni-B catalysts. With the increase of concentration of boron, the coordination number of Ni reduced, showing that the Ni active sites became more highly unsaturated. For hydrogenation of p-chloronitrobenzene, these promoted catalysts exhibited higher activities than unpromoted catalyst and Raney nickel. The catalysts also exhibited high selectivity to p-chloroaniline. Mo-Ni-B showed the highest activity. Introduction Aromatic haloamines are important intermediates in the chemistry of herbicides, dyes, drugs, and pesticides. The traditional synthesis routes are usually harmful for the environment. The best choice seems to be that the synthesis of haloamines is done from the selective hydrogenation of the corresponding halonitroaromatics over metal catalysts. However, the process is difficult because of extensive dehalogenation.1 The reaction routes involved in hydrogenation of p-chloronitrobenzene (p-CNB) are shown in Scheme 1.2 With a variety of catalysts (e.g., Pt, Pd, Ni, Rh), hydrogenation of halonitroaromatics to the corresponding haloanilines is always accompanied by some dehalogenation reaction.3 Depending on the halogen and its position relative to the nitro group in the aromatic system, dehalogenation can vary from negligible to 100%. In the process, it is desirable to achieve selective hydrogenation to p-chloroaniline (p-CAN) without dehalogenation. Its selectivity depends on the catalyst and the reaction conditions. It is generally known that a dehalogenation reaction and a reduction of the nitro group occur simultaneously. Furthermore, hydrogen chloride produced from the dehalogenation contributes to the corrosion of the reactor. To achieve high yields of haloanilines, many approaches have been developed by either dedicated preparation of the catalysts (alloying, controlling the metal particle dispersion and metalsupport interaction, etc.) or the use of specific additives (promoters, inhibitors).4-7 Figueras et al.3 investigated the catalytic hydrogenation of p-CNB to p-CAN over a series of ruthenium catalysts of widely varying dispersions and on * To whom correspondence should be addressed. E-mail: ywchen@ cc.ncu.edu.tw. Tel.: 886-3-4227151, ext 34203. Fax: 886-3-4252296.
supported bimetallics RuM (M ) Sn, Pb, Ge). Liu et al.8 reported the metal complex effect on the selective hydrogenation of m- and p-CNB over poly(vinylpyrrolidone) (PVP) stabilized Pt colloidal catalysts. Zheng et al.9 have reported the effect of rare earths on the hydrogenation properties of p-CNB over polymer-anchored platinum catalysts. They10 also have reported the influence of rare earths (Ce, Sm, Nd, La, and Pr) on the hydrogenation properties of chloronitrobenzene over Pt/ZrO2 catalyst. However, the cost of precious metal catalysts is too high in practice for the industry. Nanosized Ni-B catalysts have been reported to have excellent performance for the hydrogenation of p-CNB to p-CAN.11,12 Catalyst particles on a nanosize scale exhibited distinctive electronic and catalytic properties that differed from those in bulk. The nanocatalysts have more surface atoms and a higher concentration of highly coordinated unsaturated sites. Their unique isotropic structural and chemical properties have attracted extensive interest. However, only limited endeavors have been devoted to the synthesis of nanosized Ni-B particles.13-22 Nanosized Ni catalyst modified with boron has been reported to be a good catalyst for hydrogenation of nitrobenzene and furfural.23-27 The catalytic properties depend much on the preparation method and synthesis conditions.28,29 Many studies have been made on the catalytic properties of Ni-B catalysts.30-36 Metal catalysts containing boron species, generally called metal borides, have been studied extensively in some reactions.37-40 Metal boride catalysts have a simple preparation by reduction of metal salts with borohydride and excellent activity and selectivity for many hydrogenation reactions.41 These amorphous Ni-B particles were characterized by EXAFS as a structure with long-range disorder and short-range ordering, and with a size range of 10-50 nm by transmission electron
10.1021/ie060751v CCC: $33.50 © 2006 American Chemical Society Published on Web 11/29/2006
Ind. Eng. Chem. Res., Vol. 45, No. 26, 2006 8867 Scheme 1
microscopy. It has been reported that, with a small addition of lanthanum as a promoter of Ni-B catalysts, the catalytic activity and thermal stability were improved.12,42,43 For some other hydrogenation reactions, Ni-B catalysts with metal oxides serving as promoters have some improvements in catalytic performance for activity, selectivity, and thermal stability. Ceria has been used as an additive for Ni-B catalysts for the hydrogenation of furfural. Cerium, which is in the form of cerium oxides (CeO2), not only accelerates the reaction rate but also gets an elevation of the crystallization temperature.44 Chromia has been added into Ni-B catalysts for the hydrogenation of 2-ethylanthraquinone (2-eAQ) and became the form of chromium oxide in the catalysts. The oxide plays a role of support that enhances the dispersion of the active sites and acts as a Lewis adsorption site, which lowers the π*CO orbital of the reactant, favoring a carbonyl group bounded configuration.45 Tungsten, which has been doped into Ni-Co-B catalyst for the hydrogenation of benzene, reduces the formation of nickel oxides. In other words, more nickel in the elemental state was found.46 Cobalt has been added to Ni-B catalysts for the hydrogenation of acetonitrile and caused borate in the Ni-B catalysts to increase with the amount of the promoter. The activity and selectivity of metal boride can be altered significantly by varying the amount of metal-associated boron. Of the two kinds of boron species (boride and borate) present in colloids prepared by NaBH4 reduction, it was verified that only borate had a significant effect on the hydrogenation of o-CNB, while boride performed as a spectator.29,47-49 There are also some metal alloy catalysts with promoters showing excellent catalytic properties for some hydrogenations. Molybdenum as a promoter has been studied for the hydrogenation of furfural over Cu-B catalysts. Molybdenum was in the oxide form acting as the role of support.50 It has been reported51 that chromium and tungsten served as promoters for the hydrogenation of glucose over Cu-B catalysts. The formation of oxides enriched the catalytic activity with the mechanism of Lewis adsorption sites. Tungsten oxide, however, has better catalytic performances than chromium oxide because the W4+ species was more electropositive and had stronger affinity for oxygen of carbonyl group than the Cr3+ species. Molybdenum and tungsten have also been used as additives for Ru metal alloy catalysts.52 These additives have been used in the hydrogenation of o-chloronitrobenzene over the catalyst of ruthenium stabilized by polymer, denoted as PVP-Ru. PVPRu, compared to other noble metals, such as platinum and palladium, is less active but has much higher selectivity.52 However, the effect of Mo, W, and Ru additives on the catalytic properties of Ni-B catalyst in the hydrogenation of p-CNB has
not been studied. Recently, Yan et al.53 reported that Ni-Fe-P is an active catalyst for liquid-phase hydrogenation of m- and p-CNB. The objective of this study was to elucidate the effect of these additives on the catalytic properties of nanosized Ni-B catalyst in the hydrogenation of p-CNB. Experimental Section Materials. Nickel acetate and p-CNB were obtained from Acros. Ammonium heptamolybdate was obtained from Wako. Ammonium metatungstate was obtained from Aldrich. Ruthenium trichloride was obtained from Kojundo Chemical Laboratory. Sodium borohydride (NaBH4, >98%) was obtained from Lancaster. High purity hydrogen gas (>99.99% from Air Product) was used without further purification. Raney nickel catalyst was obtained from Merck. Methanol was from Showa. Water was double-distilled and demineralized. Catalyst Preparation. Promoted Ni-B catalysts were prepared by a chemical reduction method using NaBH4 as the reducing agent. Nickel acetate was used as the precursor. The metal salt promoter, such as ammonium heptamolybdate, ammonium metatungstate, or ruthenium trichloride, was added to the aqueous solution of nickel acetate. The promoter/Ni weight ratio was 1:9 in each case. A solution of NaBH4 with a concentration of 1 M was used as the reducing agent. This solution was added drop by drop to the solution of nickel salt (0.1 M) at 25 °C with vigorous stirring. To ensure full reduction of nickel, excess amount of NaBH4 in a B/Ni atomic ratio of 3:1 was used. The solvent was methanol in water with a volume ratio of 1:1. High purity nitrogen (99.9999%) was flowed through the reactor. Nitrogen was used as the sheltering gas in the experiment to prevent oxidation by the dissolved oxygen in water. The black precipitate was formed immediately. The precipitate was washed thoroughly, first with deionized water at least three times to remove the soluble boron species and K+ or Na+ ions which may act as a poison for nickel,12 and then with a 99.5% methanol at least 2 times. The resulting samples were soaked in absolute methanol before characterization. Characterization. X-ray diffraction (XRD) measurements were taken using a Siemens D500 powder diffractometer with Cu KR radiation (40 kV, 30 mA). The sample was scanned over the range 20-60° 2θ at a rate of 0.05 deg s-1 to identify the crystalline structure. Each sample for XRD was prepared as a thin layer on a sample holder. BET surface areas were obtained by physisorption of nitrogen at -197 °C using a Micromeritics 2010 instrument. Prior to measurement, the samples were degassed to 0.1 Pa at 120 °C.
8868
Ind. Eng. Chem. Res., Vol. 45, No. 26, 2006
The surface areas were calculated in a relative pressure range 0.05 < p/p0 < 0.2 assuming a cross-sectional area of 0.162 nm2 for the N2 molecule. The morphologies of the samples were determined by transmission electron microscopy (TEM) performed on a Jeol JEM-1200 EX II electron microscope operated at 160 kV. A powder specimen was dispersed in absolute methanol and sonicated for 20 min. One drop of the suspension was deposited on a specimen grid coated with a holely carbon film (300#) (Ted Pella Inc.) and dried in a vacuum over night. The average size and size distribution of each specimen were evaluated from about 300 randomly selected particles. Differential scanning calorimetry (DSC) was conducted under a nitrogen (99.99%) atmosphere on a Perkin-Elmer DSC7 instrument. The DSC experiment was carried out on samples in the temperature range of 50-560 °C at a rate of 10 °C min-1. The compositions and oxidation states of catalysts were examined by X-ray photoelectron spectroscopy (XPS) using a Perkin-Elmer PHI-1600 instrument. Mg KR radiation was used to excite photoelectrons, which were analyzed with the analyzer, operated at 150 eV pass energy. The nanoparticles were first pressed into a 10 mm × 10 mm disk in absolute ethanol to avoid contamination by air. The sample was fixed on a special sample holder, which was then placed in a vacuum chamber. The base pressure in the analyzing chamber was maintained on the order of 10-7 mbar. The spectrometer was operated at 23.5 eV pass energy. The binding energy of XPS was corrected by argon (Ar 2p3/2 ) 242.0 eV) in order to facilitate the comparisons of the values among the catalysts and the standard compounds. The surface compositions of the samples were determined from the peak areas of the corresponding lines using a Shirley type background and empirical cross section factor for XPS. Hydrogenation Reaction. The catalysts were tested for the liquid-phase hydrogenation of p-CNB to p-CAN. A fresh, asprepared catalyst was used in each reaction run. All the experiments were carried out in a cylindrical stirred-tank reactor (Parr Instrument Model 4842) with 160 mL capacity. A fourbladed pitched impeller was placed for effective agitation, and the agitator was connected to an electric motor with variable speed up to 700 rpm. A pressure transmitter and an automatic temperature controller were also provided. The gases were supplied from cylinders and introduced to the base of the reactor; another tube served as sampling tube for the liquid phase. The concentration of p-CNB was 0.2 M, and the pressure of hydrogen was 1.2 MPa. Methanol was used as the reaction medium in this study. In a previous paper,12 one of the authors reported that methanol is a better reaction medium than ethanol for this reaction. The reactor was charged with 2 mmol of Ni catalyst and 2.52 g of p-CNB in 80 mL of reaction medium (methanol). Air was flushed out of the reactor with hydrogen at room temperature, and hydrogen was then fed into the reactor. When the designated temperature was reached, hydrogen was fed to the predetermined pressure (time zero) that was maintained throughout the reaction; the stirring speed was fixed at 500 rpm. During the run, samples were withdrawn periodically (10 min) and analyzed by gas chromatography. A gas chromatograph equipped with a flame ionization detector and a 3 m × 1/8 in. (1 in. ) 2.54 cm) stainless steel column packed with 5% OV-101 on Chromsorb WAW-DMSC (80-100 mesh) was used for sample analysis. The experiments have been repeated twice at least. The reproducibility was within 98%.
Figure 1. XRD patterns of the (a) Ni-B, (b) Mo-Ni-B, (c) Ru-Ni-B, and (d) W-Ni-B catalysts.
Figure 2. DSC curves of the samples.
Results and Discussion The XRD patterns of the fresh Ni-B and promoted Ni-B catalysts are shown in Figure 1. The XRD patterns of MoNi-B and W-Ni-B catalysts reveal that the samples were present in a typical amorphous structure12,16 similar to that found in the fresh Ni-B amorphous alloy. Comparing with the specific broad peak around 45° 2θ in Ni-B catalyst, the intensities of XRD peaks of Mo-Ni-B and W-Ni-B are slightly intense, but still showing amorphous structure (no long-range order). There are many peaks appearing in the XRD pattern of the RuNi-B sample, showing the intrinsic peaks of ruthenium metal. No intense characteristic peaks of nickel are observed. Meanwhile, it can be observed, from the DSC curves of Ni-B and metal-promoted Ni-B catalysts in Figure 2, that all of the samples kept amorphous structure below 420 K. It should be noted that the reaction temperature was below 393 K. In other words, during the hydrogenation reaction of p-CNB, all of the metal-promoted Ni-B catalysts were of amorphous structure. It has been reported that the specific amorphous structure of Ni-B catalyst is beneficial for the activity of hydrogenation.48 As shown in Figure 2, the XRD peaks of crystallization of Ni-B catalyst are observed at 593 K, but they are not observed on the promoted samples. This demonstrates that the promoters could suppress the crystallization and enhance the thermal stability of Ni-B catalyst. In the DSC curve of Mo-Ni-B sample, there is an exothermic peak upon increasing the temperature to 420 K, which could be attributed to the decomposition of metal salts on Ni-B catalyst. There are some differences in thermal properties between Ni-B and promoted
Ind. Eng. Chem. Res., Vol. 45, No. 26, 2006 8869 Table 1. Structural Characteristics and Catalytic Properties of the Catalysts catalyst
composition (at. %)
XNi-Ba
BET surface area (m2‚g-1)
particle sizeb (nm)
activityc [mol of p-CNB (g of catalyst)-1 s-1] × 106
W-Ni-B Ru-Ni-B Mo-Ni-B Ni-B Raney nickel
Ni83B17 Ni83B17 Ni85B15 Ni91B9
0.51 0.52 0.50 0.59
24.2 7.5 20.9 19.2 1.5
27.9 89.9 32.3 35.1 449.4
52.3 30.5 86.4 19.5 8.7d
b c aX Ni-B means mole fraction of Ni-B in catalyst sample. Particle size was calculated from surface area. Reaction conditions: T ) 373 K; reaction solvent, methanol. d At 393 K.
Figure 3. TEM images of the (a) Ni-B, (b) Mo-Ni-B, (c) Ru-Ni-B, and (d) W-Ni-B catalysts.
Ni-B catalyst as shown in the DSC curves in Figure 2. The promoted Ni-B catalysts retained the amorphous structure and improved the thermal resistance of the catalysts. Table 1 shows the structural characteristics and catalytic properties of the as-prepared catalysts. The particles of the catalysts are spherical and nonporous, and the average particle size can be calculated by dh (nm) ) [6/(SBETF)](103), where SBET is the surface area and F is the density of a particle using the
value of 8.9 g‚cm-3 (the density of nickel).12 Table 1 shows that Ni-B had a larger surface area after addition of W and Mo, but the increase in surface area is very limited. However, the TEM images of W-Ni-B and Mo-Ni-B in Figure 3 did not show clear black circles like the Ni-B sample but more tiny ashy spots around the vast black area, revealing that much smaller particles were formed upon the addition of W and Mo in Ni-B catalysts. It should be noted that the average particle
8870
Ind. Eng. Chem. Res., Vol. 45, No. 26, 2006
Figure 4. XPS spectra of (a) Ni 2p, (b) Mo 3d, and (c) B 1s levels of Ni-B and Mo-Ni-B catalysts.
sizes were overestimated for the uncalcined samples because the catalysts were pretreated at 393 K for 24 h before nitrogen sorption measurements, which would cause metal aggregation and/or sintering to some extent. This is also the reason nitrogen sorption measurements gave particle sizes different from those in TEM observations. Nevertheless, both measurements show that promoted Ni-B catalysts had nanosized particles. It was reported41,50 that Mo and W promoters were present in the form of metal oxides, which could be confirmed by the XPS spectra of Mo 3d level and W 4f level in Figures 4 and 5, respectively. Mo and W were in the structure of oxide or hydroxide because the specific peaks at the binding energies of 232.5 and 32.5 eV, respectively, are observed. Since the
Figure 5. XPS spectra of (a) Ni 2p, (b) W 4f, and (c) B 1s levels of Ni-B and W-Ni-B catalysts.
preparation solution was basic, hydroxide was formed. During the drying process, some hydroxides may convert to oxides. The oxides or hydroxide would serve as a spacer preventing the catalyst particles from aggregation, resulting in larger surface area and smaller particles after promotion.41,45,50 This is also part of the reason for high thermal stability of the catalyst. However, as shown in Table 1, the surface area of Ru-Ni-B sample was exceptionally low in comparison with the other promoted Ni-B catalysts. From the XPS spectra of the Ru 3d level in Figure 6b, there is a distinct peak around the binding
Ind. Eng. Chem. Res., Vol. 45, No. 26, 2006 8871
Figure 7. Hydrogenation reaction of Ni-B and promoted Ni-B catalysts at 373 K.
Figure 6. XPS spectra of (a) Ni 2p, (b) Ru 3d, and (c) B 1s levels of Ni-B and Ru-Ni-B catalysts.
energy of 285 eV, which is assigned to Ru metal. This is not surprising because Ru3+ can be reduced by NaBH4 and bimetallic Ru-Ni-B is formed. Figure 7 shows that all of the promoted catalysts in this study had big improvements in the catalytic activity of hydrogenation of p-CNB. The hydrogenation activities of the promoted catalysts are also listed in Table 1. The activities of promoted catalysts increased at least 1.5-fold compared to the nonpromoted Ni-B catalyst, and they were much greater than that of Raney nickel. The surface compositions calculated from XPS data are listed in Table 1. The compositions of promoted Ni-B
samples showed limited differences compared with the unpromoted Ni-B sample. There are two categories in the effects of additives: Mo and W are one group, and Ru is the other. From the XPS spectra of Mo 3d level and W 4f level in Figures 4 and 5, respectively, Mo and W were present in the form of oxides or hydroxides, which played the role of spacer. These metal oxide/hydroxides not only protected the amorphous structure of the catalyst, which was beneficial for the activity of hydrogenation, but also enhanced the dispersion of active sites. Meanwhile, the electropositive ions in the oxides/hydroxides would act as Lewis adsorption sites, with the p-CNB molecule being adsorbed via the donation of a lone electron pair from the oxygen of the nitro group. This bonding polarized the NdO bond, which was favorable for a nucleophilic attack on the nitrogen atom by hydrogen adsorbed on the neighboring Ni active sites.6,12,51,53 It is known6,12,53 that the rate-determining step of this type of reaction is a nucleophilic attack of hydride ion, produced by dissociative adsorption of H2 molecule on the metal surface, on the nitrogen atom of the nitro group. Therefore, electronwithdrawing and electron-donating effects on the substituent would have a strong influence on the hydrogenation of p-CNB. According to this mechanism, Mo additive would be superior to W for the reason that Mo formed the oxide of MoO3 and W formed the oxide of WO2. The Mo additive exhibited a stronger promoting effect than the W additive, since Mo6+ species are more electropositive and in turn had a stronger affinity for oxygen of the nitro group than W4+ species.41 For the catalytic activity of the Ru-Ni-B, from the XPS spectra of Ru 3d in Figure 5b, Ru was not similar to Mo or W in forming oxides. It is in the form of a metal. Ruthenium itself is also active for the hydrogenation of p-CNB. However, the catalytic activity in the hydrogenation of p-CNB over Ru-Ni-B catalyst was not as good as those on Mo-Ni-B and W-Ni-B. It was reported that PVP-Ru as the catalyst for the hydrogenation of o-CNB had high selectivity but low activity.52 Ru itself has a lower activity than Ni. Recently, Yan et al.53 reported that NiFe-P is an active catalyst for liquid-phase hydrogenation of m- and p-CNB. The promoting effect of the Fe dopant could be attributed to both a dispersing effect that resulted in the higher stability and the electron donation of the metallic Fe to the metallic Ni that was favorable to hydrogenation. Our results are in accord with their conclusion. The XPS spectra of B 1s level was also an index of the catalytic activity of amorphous Ni-B catalyst. As one could
8872
Ind. Eng. Chem. Res., Vol. 45, No. 26, 2006
observe, from the XPS spectra of B 1s level in Figures 4-6, the peaks of B and B2O3 became intense, demonstrating that there were more amorphous B and B2O3 species in the promoted catalysts, compared with the unpromoted Ni-B catalyst. There are three independent reactions when borohydride is used as reducing agent to prepare metal-boron particles: (1) the hydrolysis of borohydride, (2) the reduction of metal ion, and (3) the reduction of metalloid.32 The three reactions are -
-
BH4 + 2H2O f BO2 + 4H2 BH4- + 2M2+ + 2H2O f 2M + BO2- + 4H+ + 2H2 -
-
BH4 + H2O f B + OH + 2.5H2
(1) (2) (3)
The fact of increasing B2O3 concentration in promoted samples indicated that the hydrolysis of borohydride and the reduction of metal ion were accelerated because these two reactions dominate the amount of B2O3.45 The reduction of metalloid contributed to the quantity of amorphous B since the reaction rate was pushed ahead by promoters. From the XPS spectra of Ni 2p level in Figures 4-6, there was evidence that the reduction of metal ion was encouraged for the peaks of metallic Ni in each case being stronger than unpromoted Ni-B catalyst. In other words, the concentrations of Ni and B increased, indicating that more Ni-B catalysts were produced in the presence of additives. However, the degree of advancement of amorphous B was much more obvious than that of metallic Ni, which proved that the content of B in the Ni-B catalyst increased after promotion, as shown in Table 1. It was reported that the rise of B content in Ni-B catalyst would boost the thermal stability and affect the catalytic activity by decreasing the coordination number of Ni with the increase of XB, showing that the Ni active sites became more highly unsaturated at high XB.48 Based on the shift of the peak of metallic Ni, the promoted samples were more electropositive than the unpromoted one. In other words, there were fewer electrons on the active sites. Nevertheless, the shift of binding energy is one of the factors that influence the catalytic activity of the catalyst. The variation of the binding energy of Ni was not very clearly observed due to its relatively bigger size and larger atomic mass compared to the B atom. At the same time, there was another important effect of activity showing that the peak area was larger than that of the original Ni-B catalyst, proving more active sites detected in the catalyst sample. Conclusion Mo-, W-, and Ru-promoted Ni-B catalysts were proved to be effective for hydrogenation of p-CNB in this study by enhancing the thermal stability and the catalytic activity. W6+ and Mo6+ cations were not reduced by NaBH4. They formed oxides or hydroxides since the preparation solutions were basic. They acted as spacers and prevented Ni-B from sintering and agglomeration. Ru3+ could be reduced by NaBH4 to Ru metal. Ru is also a catalyst for this reaction. Mo-Ni-B demonstrated the highest activity among all the catalysts. Mo and W additives not only served as the role of spacer to increase the dispersion of active sites and protect the amorphous structure, but also changed the composition of Ni-B catalyst, which caused the rise of boron content in Ni-B catalysts. With the increase of concentration of boron, the coordination number of Ni was reduced, showing that the Ni active sites became more highly unsaturated at higher concentrations of boron. There would also
be more active sites but fewer electrons on them after promotion. For hydrogenation of p-CNB, these promoted catalysts exhibited higher activities than unpromoted catalyst and Raney nickel. The catalysts also exhibited high selectivity to p-CAN. MoNi-B showed the highest activity. Acknowledgment This research was supported by the Ministry of Economic Affairs, Taiwan, Republic of China, under Contract No. 93EC-17-A-09-S1-022. Literature Cited (1) Baltzly, R.; Phillips, A. P. The Catalytic Hydrogenolysis of Halogen Compounds. J. Am. Chem. Soc. 1946, 68, 261-265. (2) Yu, Z.; Liao, S.; Xu, Y.; Yang, B.; Yu, D. A Remarkable Synergic Effect of Polymer-anchored Bimetallic Palladium-Ruthenium Catalysts in the Selective Hydrogenation of p-Chloronitrobenzene. J. Chem. Soc., Chem. Commun. 1995, 1155-1156. (3) Tijani, A.; Coq, B.; Figue´ras, F. Hydrogenation of para-Chloronitrobenzene over Supported Ruthenium-based Catalysts. Appl. Catal. 1991, 76, 255-266. (4) Coq, B.; Tijani, A.; Figue´ras, F. Pathways and the Role of Solvent in the Hydrogenation of Chloronitrobenzenes. J. Mol. Catal. 1992, 71, 317333. (5) Coq, B.; Tijani, A.; Figue´ras, F. Particle Size Effect on the Kinetics of p-Chloronitrobenzene Hydrogenation over Platinum/Alumina Catalysts. J. Mol. Catal. 1991, 68, 331-345. (6) Coq, B.; Tijani, A.; Dutartre, R.; Figue´ras, F. Influence of Support and Metallic Precursor on the Hydrogenation of p-Chloronitrobenzene over Supported Platinum Catalysts. J. Mol. Catal. 1993, 79, 253-264. (7) Greenfield, H.; Dovell, F. S. Metal Sulfide Catalysts for Hydrogenation of Halonitrobenzenes to Haloanilines. J. Org. Chem. 1967, 32, 36703671. (8) Tu, W.; Liu, H.; Tang, Y. The Metal Complex Effect on the Selective Hydrogenation of m- and p-Chloronitrobenzene over PVP-stabilized Platinum Colloidal Catalysts. J. Mol. Catal. A: Chem. 2000, 159, 115120. (9) Han, X.; Zhou, R.; Zheng, X.; Jiang, H. Effect of Rare Earths on the Hydrogenation Properties of p-Chloronitrobenzene over Polymeranchored Platinum Catalysts. J. Mol. Catal. A: Chem. 2003, 193, 103108. (10) Han, X.; Zhou, R.; Laia, G.; Yue, B.; Zheng, X. Influence of Rare Earth (Ce, Sm, Nd, La, and Pr) on the Hydrogenation Properties of Chloronitrobenzene over Pt/ZrO2 catalyst. Catal. Lett. 2003, 89, 255-259. (11) Liu, Y. C.; Huang, C. Y.; Chen, Y. W. Liquid-Phase Selective Hydrogenation of p-Chloronitrobenzene on Ni-P-B Nanocatalysts. Ind. Eng. Chem. Res. 2006, 45, 62-69. (12) Liu, Y. C.; Chen, Y. W. Hydrogenation of p-Chloronitrobenzene on La-promoted NiB Nanometal Catalysts. Ind. Eng. Chem. Res. 2006, 45, 2973-2980. (13) Schlesinger, H. I.; Brown, H. C.; Finholt, A. E.; Gilbreat, J. R.; Hoeksta, H. R.; Hyde, E. K. Sodium Borohydride, Its Hydrolysis and its Use as a Reducing Agent and in the Generation of Hydrogen. J. Am. Chem. Soc. 1953, 75, 215-219. (14) Raymond, P.; Buisson, P.; Joseph, N. Catalytic Activity of Nickel Borides. Ind. Eng. Chem. 1952, 44 (5), 1006-1010. (15) Brown, H. C.; Brown, C. A. The Reaction of Sodium Borohydride with Nickel Acetate in Ethanol SolutionsA Highly Selective Nickel Hydrogenation Catalyst. J. Am. Chem. Soc. 1963, 85, 1003-1005. (16) Lee, S. P.; Chen, Y. W. Catalytic Properties of Ni-B and Ni-P Ultrafine Materials. J. Chem. Technol. Biotechnol. 2000, 75, 1073-1079. (17) Rei, M. H.; Sheu, L. L.; Chen, Y. Z. Nickel Boride Catalysts in Organic Synthesis. Appl. Catal. 1986, 23, 281-290. (18) Chen, Y. Z.; Sheu, L. L.; Rei, M. H. Nickel Boride Catalyst in Organic SynthesissThe Effects of Promoters on Nickel Borides for Hydrogenation Reactions. J. Chin. Chem. Soc. 1989, 36, 67-72. (19) Deng, J. F.; Yang, J.; Sheng, S.; Chen, H.; Xiong, G. The Study of Ultrafine Ni-B and Ni-P Amorphous Alloy Powders as Catalysts. J. Catal. 1994, 150, 434-438. (20) Li, H.; Li, H. X.; Dai, W. L.; Wang, W.; Fang, Z.; Deng, J. F. XPS Studies on Surface Electronic Characteristics of Ni-B and Ni-P Amorphous Alloy and Its Correlation on Their Catalytic Properties. Appl. Surf. Sci. 1999, 152, 25-34.
Ind. Eng. Chem. Res., Vol. 45, No. 26, 2006 8873 (21) Fang, Z. G.; Shen, B. R.; Lu, J.; Fan, K. N.; Deng, J. F. DFT Study of Electron Transfer Between B and Ni in Ni-B Amorphous Alloy. Acta Chim. Sin. 1999, 57, 894-900. (22) Yu, Z. B.; Qiao, M. H.; Li, H. X.; Deng, J. F. Preparation of Amorphous Ni-Co-B Alloys and the Effect of Cobalt on Their Hydrogenation Activity. Appl. Catal., A: Gen. 1997, 163, 1-13. (23) Yao, H. C.; Emmett, P. H. Kinetics of Liquid Phase Hydrogenation. IV. Hydrogenation of Nitrocompounds over Raney Nickel and Nickel Powder Catalysts. J. Am. Chem. Soc. 1962, 84, 1086-1091. (24) Ma, A.; Lu, W.; Min, E. U.S. Patent 6,051,528, 2000. (25) Seo, G.; Chon, H. J. Hydrogenation of Furfural over Coppercontaining Catalysts. J. Catal. 1981, 67, 424-429. (26) Liu, I. H.; Chang, C. Y.; Liu, S. C.; Chang, I. C.; Shih, S. M. Absorption Removal of Sulfur Dioxide by Falling Water Droplets in the Presence of Inert Solid Particles. Atmos. EnViron. 1994, 28, 3409-3415. (27) Li, C.; Chen, Y.; Wang, W. J. Nitrobenzene Hydrogenation over Aluminum Borate-supported Platinum Catalyst. Appl. Catal., A: Gen. 1994, 119, 185-194. (28) Shen, J.; Hu, Z.; Zhang, Q.; Zhang, L.; Chen, Y. Investigation of Ni-P-B Ultrafine Amorphous Alloy Particles Produced by Chemical Reduction. J. Appl. Phys. 1992, 71, 5217-5221. (29) Lee, S. P.; Chen, Y. W. Effects of Preparation on the Catalytic Properties of Ni-P-B Ultrafine Materials. Ind. Eng. Chem. Res. 2001, 40, 1495-1499. (30) Baiker, A. Metallic Glasses in Heterogeneous Catalysis. Faraday Discuss. 1989, 87, 239-251. (31) Deng, J. F.; Li, H.; Wang, W. J. Progress in Design of New Amorphous Alloy Catalysts. Catal. Today 1999, 51, 113-125. (32) Chen, Y. Chemical Preparation and Characterization of MetalMetalloid Ultrafine Amorphous Alloy Particles. Catal. Today 1998, 44, 3-16. (33) Yoshida, S.; Yamashita, H.; Funabiki, T.; Yonezawa, T. Hydrogenation of Olefins over Amorphous Ni-P and Ni-B Alloys Prepared by the Rapid Quenching Method. J. Chem. Soc., Chem. Commun. 1982, 964965. (34) Yoshida, S.; Yamashita, H.; Funabiki, T.; Yonezawa, T. Catalysis by Amorphous Metal Alloys. Part 1.sHydrogenation of Olefins over Amorphous Ni-P and Ni-B. J. Chem. Soc., Faraday Trans. 1 1984, 80, 1435-1446. (35) Yamashita, H.; Funabiki, T.; Yoshida, S. Structural Modification Towards Metastable States and Catalytic Activity of an Amorphous Ni-B Alloy. J. Chem. Soc., Chem. Commun. 1984, 868-869. (36) Yamashita, H.; Yoshikawa, M.; Funabiki, T.; Yoshida, S. Catalysis by Amorphous Metal Alloys. Part 2.sEffects of Oxygen Pretreatment on the Catalytic Activity of Amorphous and Crystallised Ni-P Alloys. J. Chem. Soc., Faraday Trans. 1 1985, 81, 2485-2493. (37) Wade, R. C. Catalyzed Reductions of Organofunctional Groups with Sodium Borohydride. J. Mol. Catal. 1983, 18, 273-297. (38) Midland, M. M.; Lee, P. E. Efficient Asymmetric Reduction of Acyl Cyanides with B-3-pinanyl 9-BBN (Alpine-Borane). J. Org. Chem. 1985, 50, 3237-3289. (39) Hutchinson, C. R.; Heckendorf, A. H.; Straughn, J. L.; Daddona, P. E.; Cane, D. E. Biosynthesis of Camptothecin. 3. Definition of
Strictosamide as the Penultimate Biosynthetic Precursor Assisted by Carbon13 and Deuterium NMR Spectroscopy. J. Am. Chem. Soc. 1979, 101, 33583369. (40) Osby, J. O.; Heinzman, S. W.; Ganem, B. Studies on the Mechanism of Transition-metal-assisted Sodium Borohydride and Lithium Aluminum Hydride Reductions. J. Am. Chem. Soc. 1986, 108, 67-72. (41) Li, H. X.; Li, H.; Wang, M. Glucose Hydrogenation over Promoted Co-B Amorphous Alloy Catalysts. Appl. Catal., A: Gen. 2001, 207, 129137. (42) Shen, J.; Hu, Z.; Zhang, Q.; Zhang, L.; Chen, Y. Investigation of Ni-P-B Ultrafine Amorphous Alloy Particles Produced by Chemical Reduction. J. Appl. Phys. 1992, 71, 5217-5221. (43) Hou, Y.; Wang, F.; He, S.; Han, Z.; Mi, W.; Wu, E.; Min, E. Liquid Phase Hydrogenation of 2-Ethylanthraquinone over La-doped Ni-B Amorphous Alloy Catalysts. Mater. Lett. 2004, 58, 1267-1271. (44) Li, H.; Zhang, S.; Luo, H. A Ce-promoted Ni-B Amorphous Alloy Catalyst (Ni-Ce-B) for Liquid-phase Furfural Hydrogenation to Furfural Alcohol. Mater. Lett. 2004, 58, 2741-2746. (45) Fang, J.; Chen, X.; Liu, B.; Yan, S.; Qiao, M.; Li, H.; He, H. Liquidphase Chemoselective Hydrogenation of 2-Ethylanthraquinone over Chromium-modified Nanosized Amorphous Ni-B Catalysts. J. Catal. 2005, 229, 97-104. (46) Dai, W. L.; Qiao, M. H.; Deng, J. F. XPS Studies on a Novel Amorphous Ni-Co-W-B Alloy Powder. Appl. Surf. Sci. 1997, 120, 119-124. (47) Li, H.; Wu, Y.; Zhang, J.; Dai, W.; Qiao, M. Liquid-phase Acetonitrile Hydrogenation to Ethylamine over a Highly Active and Selective Ni-Co-B Amorphous Alloy Catalyst. Appl. Catal., A: Gen. 2004, 275, 199-206. (48) Li, H.; Li, H.; Dai, W.; Qiao, M. Preparation of the Ni-B Amorphous Alloys with Variable Boron Content and Its Correlation to the Hydrogenation Activity. Appl. Catal., A: Gen. 2003, 238, 119-130. (49) Okamoto, Y.; Nitta, Y.; Imanaka, T.; Teranishi, S. Surface Characterization of Nickel Boride and Nickel Phosphide Catalysts by X-ray Photoelectron Spectroscopy (Part I). J. Chem. Soc., Faraday Trans. 1 1979, 175, 2027-2039. (50) Chen, X.; Li, H.; Luo, H.; Qiao, M. Liquid-phase Hydrogenation of Furfural to Furfural Alcohol over Mo-doped Co-B Amorphous Alloy Catalysts. Appl. Catal., A: Gen. 2002, 233, 13-20. (51) Li, H.; Li, H.; Wang, M. Glucose Hydrogenation over Promoted Co-B Amorphous Alloy Catalysts. Appl. Catal., A: Gen. 2001, 207, 129137. (52) Yu, W. W.; Liu, H. Singular Modification Effects of Metal Cations and Metal Complex Ions on the Catalytic Properties of Metal Colloidal Nanocatalysts. J. Mol. Catal. A: Chem. 2006, 243, 120-141. (53) Yan, X.; Sun, J.; Wang, Y. Yang, J. A Fe-promoted Ni-P Amorphous Alloy Catalyst (Ni-Fe-P) for Liquid Phase Hydrogenation of m- and p-Chloronitrobenzene. J. Mol. Catal. A: Chem. 2006, 252, 17-22.
ReceiVed for reView June 12, 2006 ReVised manuscript receiVed September 29, 2006 Accepted October 13, 2006 IE060751V
