Study on Alumina-Supported Cobalt–Nickel Oxide Catalyst for Synthesis of Acetonitrile from Ethanol

Catal Lett (2011) 141:168–177 DOI 10.1007/s10562-010-0468-z

Cheng Feng • Yuecheng Zhang • Yining Zhang • Yanlong Wen • Jiquan Zhao

Received: 2 July 2010 / Accepted: 8 October 2010 / Published online: 26 October 2010 Ó Springer Science+Business Media, LLC 2010

Abstract A new alumina-supported cobalt–nickel oxide 1 Introduction catalyst for the synthesis of acetonitrile from ethanol and ammonia was prepared by coprecipitation-kneading Acetonitrile is an important fine chemical product which has method. The parameters influencing the reaction were been widely used as the synthetic intermediate for pharma- studied thoroughly and an optimized process, which is ceutical, agricultural, and functional material chemicals [1]. running the reaction at 380 °C under atmospheric pressure It also used as a general purpose solvent for many com- while keeping the ammonia/alcohol molar ratio of 5 and pounds and movable phase in high-performance liquid GHSV of 1,163 h-1, was obtained. Under the optimized chromatographic analysis. Currently, it is mainly produced conditions the catalyst reached its best performance when as a by-product during the propylene ammoxidation process being on stream for 40 h, at which the yield of acetonitrile to acrylonitrile [2, 3]. With the increasing demand, it is dif- was 92.6%. Then the selectivity to acetonitrile decreased ficult to meet the need in the future to obtain acetonitrile only gradually but the yield of acetonitrile always remained from the production of acrylonitrile. Furthermore, the pro- higher than 81% within 720 h. The samples of the fresh and duction of acetonitrile as a by-product of acrylonitrile has the used catalyst were characterized by XRD, XPS, TEM, disadvantages of concomitance of toxic hydrogen cyanide

EDX and N2 adsorption–desorption analysis. The results and difficulty in separation of the crude product [4]. There- revealed that carbon deposition and formation of metal fore, it is important to develop a green and advanced process carbides from the active species in the catalytic runs led to to produce acetonitrile. Many methods have been reported to the deterioration of the catalyst. synthesize acetonitrile from other chemical substances up till now. The raw materials include carbon monoxide [5–8], Keywords Cobalt–nickel oxide Á Catalyst Á Acetonitrile Á methane or other hydrocarbon compounds [9–14], ethanol Ethanol Á Deterioration Á Metal carbides [15–21] and acetic acid [22, 23]. Among all the raw materials ethanol becomes the first choice because it can provide a process which avoids the concomitance of high toxic hydrogen cyanide and gives high quality acetonitrile. Two approaches so-called amination-dehygrogenation [20, 21] and ammoxidation of ethanol [15–20] can be employed to the transfer of ethanol to acetonitrile. However, only the former can meet the need of avoiding formation of high toxic & C. Feng Á Y. Zhang Á Y. Zhang Á Y. Wen Á J. Zhao ( ) hydrogen cyanide. In 1960s, Kryukov et al. [24] first reported School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, the conversion of alcohols to acetonitriles by amination- People’s Republic of China dehygrogenation process over a fused iron catalyst. Since e-mail: [email protected] then, several catalysts have been reported to transfer ethanol to acetonitrile [4, 20, 25]. But all the catalysts suffer from a C. Feng College of Science, Agriculture University of Hebei, disadvantage of either a high ammonia/ethanol ratio Baoding 071001, People’s Republic of China dependence [20] or low acetonitrile selectivity [4]. Besides, 123 Study on Alumina-Supported Cobalt–Nickel Oxide Catalyst 169 no clear information about the lifetime and structures of the of the samples were recorded with a Rigaku D/max 2500 catalysts was mentioned in any of the reports. X-ray diffractometer using Cu Ka radiation (40 kV, 150 Recently, we prepared an alumina-supported cobalt– mA) in the range 2h = 10°–90°. X-ray photoelectron nickel oxide catalyst for the amination-dehygrogenation of spectroscopy (XPS) was performed with a PHI 1600 ethanol to acetonitrile by kneading method. The catalyst spectroscope using Mg Ka X-ray source for excitation. showed high catalytic activity, good selectivity and long Transmission electron micrographs (TEM) were obtained lifetime [21]. However, the catalyst was fragile during the on a JEOL 100CX-II instrument equipped with an energy course of regeneration for further investigation. For dispersive X-ray (EDX) detector (Oxford Instruments) at improving the mechanical strength of the catalyst, we used an accelerating voltage of 200 kV. Specimens for TEM coprecipitation-kneading method instead of kneading analysis were prepared by ultrasonic dispersion in n-buta- method to prepare a new alumina-supported cobalt–nickel nol where a drop of the resultant suspension was evapo- oxide catalyst. The catalyst also showed high activity, good rated on a lacey-carbon/Cu grid. The surface area, total selectivity to acetonitrile and long lifetime as that prepared pore volume and pore size distribution of the samples were by kneading method, but had good mechanical strength in measured at 77 K by nitrogen adsorption using a catalytic runs. Therefore, we characterized the catalyst Micromeritics ASAP 2020 Surface Area and Porosity thoroughly to explore the deterioration reasons of the new Analyzer. The crushing strength of the catalyst was mea- catalyst in catalytic runs. Herein, we present the results of sured on a ZQJ-II particle strength tester produced by the study. Dalian Intelligent Tester Plant. The applied force and idle stroke velocity were automatically set on 5 N/s and 1 mm/s, respectively. 2 Experimental Section The IR spectra of adsorbed pyridine were recorded using a Thermo Nicliet Nicolet Nexus 470 spectrometer equip-

2.1 Catalyst Preparation ped with a heatable and evacuatable IR cell with CaF2 windows, connected to a gas dosing-evacuating system. All the chemicals were reagent grade. The alumina-sup- The powdered samples were pressed into self-supporting ported cobalt–nickel oxide catalyst was prepared by wafers with a diameter of 20 mm and a weight of 50 mg. coprecipitation-kneading method as the following proce- Prior to analysis, all samples were pretreated at 400 °C for 5 dures. 44.4 g of Co(NO3)2Á6H2O and 6.7 g of Ni(NO3)2Á 1 h, under high vacuum conditions (5 9 10 Pa), followed 6H2O were dissolved in 302.6 g of distilled water, then into by cooling to 200 °C. Then, pyridine was adsorbed at this this solution was dropped 20% (w/w) sodium carbonate temperature for 15 min. The physisorbed pyridine was solution under vigorous stirring at 60 °C until the pH removed by evacuating during 1 h at 200 °C, under high reached 8. The reaction mixture was submitted to an aging vacuum conditions (5 9 105 Pa). Then the infrared spectra treatment at 80 °C for 0.5 h while maintained the pH of 8. were recorded. The resulting mixture was filtered and the solid separated was washed with distilled water until the pH of the filtrate 2.3 Catalytic Experiments reached 7 to remove the excess of sodium completely. Afterwards, the resulting solid was dried and pulverized to Catalytic tests were carried out in a continuous fixed-bed obtain a black powder finally. The black powder was mixed reactor. 30.0 mL of the catalyst sample was loaded into a with 34.7 g of c-Al2O3 pretreated with about 10 mL of 1% reactor (i.d. = 12 mm; length = 1,100 mm), which created diluted nitric acid. The mixture was kneaded for 3 h in a a catalyst zone of 100 mm. The temperature in the catalyst kneader and the resulting kneaded material was then pro- zone was kept constant and measured using a thermocouple cessed in an extruder to obtain extrudates in a diameter of located in the center of the catalyst bed. The ethanol (95%) 2 mm and length of 2.5 mm. The extrudates were superfi- was dosed into the reactor at a speed of 7.0 mL/h by a cially dried at 120 °C for 12 h, and then calcined at 550 °C syringe pump and the flux of ammonia was regulated by a for 4 h. The contents of Co and Ni were determined by PID cascade controller (STP 220 mL/min). The liquid inductively coupled plasma (ICP) spectroscopy. products were separated from a gas–liquid separator and analyzed by a gas chromatograph equipped with a 30 m of 2.2 Catalyst Characterization PEG-20M capillary column and a thermal conductivity

detector (TCD) with H2 as carrier gas. The exhaust (H2, For determining the metal content, the sample was ﬁrst NH3,C2H4 et al.) was analyzed by the same gas chro- dissolved in concentrated HNO3 and HF, and then the matograph with N2 as carrier gas. The components of the metal content of the solution was analyzed by a T.J.A. ICP- mixture were identiﬁed by a HP5971 MS equipped with a 9000(N?M) type ICP-AES instrument. The XRD patterns 30 m of PEG-20M capillary column. 123 170 C. Feng et al.

2.4 Regeneration Procedure 100

Regeneration of the used catalyst sample for further catalytic evaluation was carried out by continuously blowing 80 conversion of ethanol air (STP 250 mL/min) into the ﬁxed-bed at 470 °C for 5 h selectivity of acetonitrile on-line. selectivity of butyronitrile 60 selectivity of ethylene selectivity of pyridine base selectivity of higher boiling 20 3 Results and Discussion components

10 3.1 Catalytic Activity Test Conversion/selectivity (%) 0 The mechanical strength of the catalyst was evaluated by 340 360 380 400 420 440 measuring the crushing strength of the catalyst. The new Reaction temperature (centigrade) catalyst had a crushing strength of 20 N/mm higher than that (13 N/mm) of the previously reported catalyst prepared Fig. 1 The effect of reaction temperature on the performance of the by kneading method [21]. The result indicated that the catalyst. Reaction conditions: NH3/C2H5OH molar ratio = 5, GHSV = 1,163 h-1, pressure = 1 atm. The data were obtained at catalyst had good mechanical strength as we expected. The the time when the catalyst was on stream for 40 h increase of the mechanical strength of the catalyst can be attributed to the difference of the precursors between the conversion of ethanol increased with the increasing of two catalysts. For the catalyst prepared by coprecipitation- temperature from 340 to 380 °C, and reached 100% at kneading method, the cobalt and nickel nitrates were 380 °C, and then maintained constant at the temperatures transferred to their basic cobalt carbonates in the copre- higher than 380 °C. However, the selectivity of acetonitrile cipitation process, therefore, the actual precursor was basic reached its maximum of 92.6% at 380 °C and then cobalt and nickel carbonates. The decomposition behaviors decreased significantly with the temperature increasing. As of nitrates and basic carbonates are different in calcination, shown in Fig. 1, the selectivity of high boiling point which led to the difference in matrix between the two compounds increased sharply from 0.02% at 380 °Cto catalysts. 20.9% at 420 °C. Other components had no significant The catalytic performance of the catalyst on the ami- change with the reaction temperature increase. Therefore, nation-dehygrogenation of ethanol to acetonitrile was tes- the decrease of the selectivity of acetonitrile can be mainly ted after the strength measurement. First the catalytic test attributed to the formation of high boiling point compounds was run under the optimized conditions used in the previ- at high temperature. ous catalyst that are running the reaction at 420 °C under Besides acetonitrile and high boiling point compounds, the ammonia/ethanol ratio of 5 [21]. However, the yield of the condensed components also included pyridine bases acetonitrile was not good as we expected. Only about 70% and butyronitrile. It is a general phenomenon that pyridine of yield of acetonitrile was received, which was much bases are concomitant in the synthesis of acetonitrile from lower than that catalyzed by the previous one. For probing ethanol [26] or acetaldehyde [27]. However, it is interest- into the reasons causing the low yield of acetonitrile, we ing that butyronitrile was detected with a selectivity as high analyzed the reaction mixture preciously by means of GC- as 7.6% at 340 °C in the reaction mixture. Moreover, little MS combined with distillation. It was found that the ethylamine was observed in the mixture, which was dif- mixture was composed of pyridines, ethylene, butyronitrile ferent from hydroamination of ethanol on Co/SiO2 [28] and and high boiling point compounds besides acetonitrile. The other catalysts [29]. The facts indicated that not the for- results indicated that the reaction parameters could have mation of ethylamine but the dehydrogenation of ethanol to strong effects on the selectivity of acetonitrile. Therefore, acetaldehyde was the first step in the synthesis of aceto- the effects of reaction parameters on the performance of the nitrile from ethanol and ammonia catalyzed by the catalyst catalyst were studied thoroughly. Because initial experi- here. Once the generation of acetaldehyde, it acted as the mental results had showed that the catalyst reached its best starting material to give acetonitrile, pyridine bases and performance when it was on stream for 40 h, all the opti- butyronitrile through a series of reactions. A proposed mized parameters were determined at this moment in the mechanism for the formations of the compounds is shown subsequent experiments. in Scheme 1. The acetonitrile was generated as the path- The influence of reaction temperature on the catalytic way described in our previous report [21] and the forma- performance of the catalyst was first investigated and the tion of pyridines was similar to the mechanism given by results are shown in Fig. 1. It can be seen that the others [30–32]. The formation of butyronitrile is in need of 123 Study on Alumina-Supported Cobalt–Nickel Oxide Catalyst 171 describing in detail. The butyronitrile was formed as fol- weakened the acidity of the catalyst, which brought down lows. First, two molecules of acetaldehyde from the the condensation of acetaldehyde with ammonia to imine dehydrogenation of ethanol underwent aldol condensation being a key step in the formation of acetonitrile as shown in on the acid sites of the catalyst to give crotonaldehyde. Scheme 1. After the crotonaldehyde molecules were formed, there IR measurements of adsorbed pyridine were applied to will be two possible pathways (A and B) as shown in determine the acidity of the fresh catalyst and the results Scheme 1 to afford butyronitrile. In path A, crotonalde- are shown in Fig. 3. Two peaks at 1,545 and 1,450 cm-1 hyde condensed with ammonia to generate the intermediate are appeared in the figure. In view of no species with imine which underwent dehydrogenation to give crotonit- carbon–oxygen bond absorbing in the same region is rile and hydrogen intermediately. The hydrogen generated present in the fresh catalyst due to the calcination in the from the dehydrogenation of the imine in situ hydrogenated catalyst preparation processes, the peaks can be attributed the carbon–carbon double bond in the crotonitrile molecule to the characteristic absorptions of pyridine molecules generating butyronitrile. In path B, hydrogenation first took adsorbed on the Brønsted and Lewis acid centers of the place on crotonaldehyde to give butyroaldehyde, then the catalyst, respectively [33–35]. Therefore, it can be con- butyroaldehyde condensed with ammonia followed by cluded that high concentration of ammonia led to more dehydrogenation to give butyronitrile. ammonia molecules adsorbed on the acid centers of the The influence of ammonia/alcohol molar ratio on the catalyst and then slowed down the reaction rate in the catalytic reaction was also investigated and the results are catalytic runs. presented in Fig. 2. It was found that when the ammonia/ For a given reaction that is run in a fixed-bed reactor, alcohol molar ratio increased from 2 to 5, meanwhile the gas hourly space velocity (GHSV) is another very temperature was kept at 380 °C and the pressure was important parameter that one must consider. Therefore, 1 atm, the conversion of ethanol was always maintained the catalytic performance of the alumina-supported around 100%, but the selectivity of acetonitrile increased cobalt–nickel oxide catalyst was evaluated under different from 76.5 to 92.6%. Figure 2 clearly shows that high GHSV. The results are shown in Fig. 4. It was found that content of ammonia could prevent the formation of the when the GHSV was increased from 379 to 1,163 h-1, high boiling point compounds, which led to the increase of the conversion of ethanol was kept at 100% but the the selectivity of acetonitrile. Of course it is not to say that selectivity of acetonitrile increased from 75.9% to its we can increase the ammonia/alcohol molar ratio unlimit- maximum of 92.6%, and then both of them decreased in edly for increasing the selectivity of acetonitrile. When the some degree with the increase of GHSV. It was also ammonia/alcohol molar ratio was higher than 5, both the observed that low GHSV was in favor of the formation of conversion of ethanol and selectivity of acetonitrile had high boiling point compounds due to long detention time tendencies of decrease. The reason may be that the excess of materials on the catalyst leading to oligomerization or ammonia diluted the concentration of ethanol and also coking.

Scheme 1 The possible H2 mechanisms for the synthesis of H CCH H3C CNH2 H2O 2 2 H2 acetonitrile and the formation of OH H2 NH3 H2O H2 butyronitrile C H OH CH CHO C NH H C C NH H C CN 2 5 3 H C 2 3 3 3 H H acid CH3CHO

CH3CHCH2CHO OH NH H2O 3

H3CCC CHO B H H A H2O

CH CH CH CHO H3CCC C N 3 2 2 H2 H H

NH3

CH3CH2CH2CN H2O

123 172 C. Feng et al.

100 100

80 80 conversion of ethanol conversion of ethanol selectivity of acetonitrile selectivity of acetonitrile selectivity of butyronitrile selectivity of butyronitrile 60 selectivity of ethylene 60 selectivity of ethylene selectivity of pyridine base selectivity of pyridine base selectivity of higher boiling 20 selectivity of higher boiling 10 components components

Conversion/selectivity (%) 10 Conversion/selectivity/yield (%) 0 0 400 600 800 1000 1200 1400 1600 1800 23456 -1 Ammonia/alcohol (molar ratio) GHSV (h )

Fig. 2 The effect of molar ratio of ammonia to alcohol on catalytic Fig. 4 The effect of GHSV on catalytic performance of the catalyst. performance of the catalyst. Reaction conditions: T = 380 °C, Reaction conditions: T = 380 °C, NH3/C2H5OH molar ratio = 5, GHSV = 1,163 h-1, pressure = 1 atm. The data were obtained at pressure = 1 atm. The data were obtained at the time when the the time when the catalyst was on stream for 40 h catalyst was on stream for 40 h

12 conditions the yield of acetonitrile reached 92.6% at the moment that the catalyst was on stream for 40 h. The above 10 results indicate that the new catalyst can afford an identical yield of acetonitrile at a lower reaction temperature com- 8 pared with the previous one [21].

6 1545 cm-1 3.2 Lifetime Test

Transmittance (%) Initial study showed that the new catalyst prepared by coprecipitation-kneading method is an effective one for 2 the amination-dehygrogenation of ethanol to acetonitrile. 1450 cm-1 Subsequently, its lifetime and regeneration were investi- 0 gated and the results are shown in Fig. 5. It can be seen 1700 1650 1600 1550 1500 1450 1400 1350 1300 Wavenumber (cm-1) that the conversion of ethanol was 100% initially and maintained with the reaction time extension. However, the Fig. 3 IR spectrum of the pyridine absorbed on the fresh catalyst selectivity of acetonitrile decreased gradually and dropped to 81.3% from its maximum of 92.6% after the catalyst The pressure effect was also investigated within the had been run for 720 h. The catalyst was regenerated on- range of atmospheric pressure to 0.3 MPa in the reaction. It line similar to the procedures reported by others [36–38] was noted that the selectivity of acetonitrile decreased and the reaction was run once again. The curve repre- monotonically with increasing the pressure. In addition, the senting the changing of the selectivity of acetonitrile with amination-dehygrogenation of ethanol to acetonitrile is an the running time of the regenerated catalyst almost entropy increasing process, so increasing pressure is superposed with that of the fresh one, which indicated unfavorable for the formation of acetonitrile. Therefore, that the catalyst was regenerated on-line successfully. We the reasonable pressure in the reaction was atmospheric can speculate that the main reason leading to the decrease pressure. of selectivity of acetonitrile is the deposition of carbon From the study of parameter effects on the amination- from coking which prevents the contact of reactants with dehygrogenation of ethanol to acetonitrile, we obtained an the active centers of the catalyst. This was conﬁrmed by optimized process for synthesizing acetonitrile over the the TEM analysis and will be discussed in the charac- alumina-supported cobalt–nickel oxide catalyst, which is terization section. All results indicated that the new alu- running the reaction at 380 °C under atmospheric pressure mina-supported cobalt–nickel oxide catalyst performed while keeping the ammonia/alcohol molar ratio of 5 and excellently and will be suitable for application in large GHSV of 1,163 h-1, respectively. At the optimized scale.

123 Study on Alumina-Supported Cobalt–Nickel Oxide Catalyst 173

105 # + a b # Co3O4 + Al O 100 2 3 % HOPG 0 # & Co 95 # # # * CoO # # + + # # d 90 & # #

Regeneration + % + + % # & # & c 85 # + & * # # + + 80 # & * # + b Conversion/Selectivity % 75 Conversion of ethanol # # # # + Selectivity of acetonitrile # # + # a 70 # 0 200 400 600 800 1000 1200 1400

Reaction time (h) 20 40 60 80 Two-Theta (degree) Fig. 5 The ethanol conversion and the acetonitrile selectivity as functions of reaction time. (a) The process of reaction on the fresh Fig. 6 XRD patterns of the catalyst. (a) Fresh; (b) run for 40 h; catalyst, (b) the process of reaction on the regenerated catalyst. (c) run for 720 h; (d) Regenerated Reaction conditions: T = 380 °C, NH3/C2H5OH molar ratio = 5, GHSV = 1,163 h-1, pressure = 1 atm

two new species indicated that some of the Co3O4 was The new alumina-supported cobalt–nickel oxides cata- transformed to CoO and Co0 after the catalyst was on lyst showed good performance over the previous one in the stream for 40 h. According to lifetime test (Fig. 5), the aspect that the reaction can be run at lower temperature. highest yield of acetonitrile was found after the catalyst However, compared to the previous one [21] the new cat- was on stream for 40 h. Therefore, it may be concluded that alyst must be on stream for about 40 h then could reach its CoO and Co0 are active species of the catalyst too and are optimum state (see Fig. 5 and Ref. [21]). It is hard to say more active than Co3O4. We can speculate that Co3O4 as why the two catalysts exhibited so obvious difference in the only active species catalyzed imine dehydrogenation to their catalytic properties. The only possible reason is that acetonitrile and hydrogen in the beginning. Then Co3O4 0 cobalt nitrate and nickel nitrate were transferred to their was transformed to Co by the H2 generated in situ grad- corresponding basic carbonates during the coprecipitation, ually. Once the generation of Co0, it accelerated the imine which might cause slight differences between the two dehydrogenation leading to the increase of the selectivity catalysts in matrix structure and crystalline phase of cata- of acetonitrile. High temperature could largely shorten the 0 lytic active species during calcination processes due to transformation time of Co3O4 to Co , therefore, the different decomposition behaviors of the nitrates and induction period was not observed in the previous com- carbonates. munication [21]. Comparing the pattern of the sample run for 720 h with 3.3 Catalyst Characterization that of the one run for 40 h, the peaks representing the CoO crystalline phase were intensively weakened and the ones For elucidating the active species and deterioration mech- representing the Co0 crystalline phase strengthened, dem- anism of the catalyst in the catalytic run, the catalyst was onstrating that most of CoO was transformed to Co0. ﬁrst characterized by XRD. Figure 6 shows the diffraction Meanwhile, an additional peak attributed to the highly patterns of the samples of the fresh, run for 40 h, run for oriented pyrolytic graphite (HOPG) [36, 41] appeared, 720 h and regenerated catalyst. The patterns of the fresh indicating the growth of HOPG around the catalyst similar catalyst revealed that the fresh catalyst had a Co3O4 crys- to the carbon deposition on the active sites in the ethyl- talline phase same as that of the previous one reported by benzene dehydrogenation [36] and CO2/CH4 reforming us recently [21]. The sharpness of the XRD peaks indicated reaction processes [42], which led to the decrease of the higher crystallinity of Co3O4 in the fresh catalyst. After selectivity to acetonitrile. After regeneration, the deposed 0 the catalyst was run for 40 h, the peaks of the Co3O4 carbon was removed and the Co was oxidized to Co3O4 crystalline phase in the XRD patterns were intensively again, therefore, the regenerated catalyst displayed the weakened and some of which were not detectable. Mean- same behavior as the fresh one (Fig. 5). while, several new peaks attributed to the CoO [39] and Besides the peaks in the patterns discussed above, two 0 Co [40] were observed. The appearance of the peaks of the peaks at 45.7° and 66.4° corresponding to those of c-Al2O3

123 174 C. Feng et al.

[40] were also found. However, no phase associated with of the used catalyst also displayed a much lower C 1s the nickel was identiﬁed, which indicated that the content binding energy at 281.4 eV. The smaller binding energy of of the Ni or the crystalline related to Ni in the catalyst was C 1s in the used catalyst indicated that the carbon had too small to be detected. The regenerated catalyst displayed combined with Co or Ni in the catalytic runs [45–48]. diffraction patterns identical to those of the fresh one, Therefore, it may be concluded that the formation of metal 0 indicating the transformation of Co to Co3O4 and removal carbides in the catalytic runs is another reason for the of carbon by combustion during the regeneration process, decrease of selectivity to acetonitrile of the catalyst. The therefore, showed catalytic performance same as that of the binding energy of Ni in the catalyst was detected near fresh one. 854.7 eV, indicating that nickel was present as NiO [49]in The XPS technique is much more sensitive than XRD the fresh and regenerated catalysts. However, the binding for the analysis of surface oxides. Therefore, the surface energy of Ni in the used catalyst was about 851.5 eV, compositions of the fresh, used and regenerated samples indicating that nickel was present as Ni0. The metal content were determined by XPS. Figure 7 shows the analysis of the fresh catalyst was analyzed by ICP-AES mentioned results. Both the fresh and regenerated samples showed that above. The results showed the mass content of Co and Ni the binding energy of Co 2p was 779.77 eV, indicating that was 20.75 and 3.12%, respectively. the Co was present as Co3O4 [43]. For the used sample, The morphological features of the fresh, used and after a curve-ﬁtting procedure was applied, the binding regenerated samples of the alumina-supported cobalt– energy of 777.33 eV was observed clearly, which indicated nickel oxide catalyst can be assessed from the TEM the presence of metal cobalt [44]. This result is in agree- images as shown in Fig. 8. In all the samples the dark ment with the XRD analysis above. Figure 7 also shows portions attributed to Co3O4 particles were seen in the the presence of the binding energy of C 1s. All the samples TEM images and dispersed on the surface of the c-Al2O3 had a C 1s binding energy around 284 eV derived from the with diameters of 20–30 nm. Besides, in the used catalyst carbon contamination in the analysis. However, the sample partial Co3O4 particles were surrounded by the carbon as

Fig. 7 XPS patterns of the Co 2p C 1s 3.5 catalysts. (a) Fresh; (b) used; Energy: 281.401 (c) regenerated 2.0 Energy: 779.767 3.0 Energy: 284.050 2.5

Energy: 777.570 c Energy: 780.531 2.0 c C/S C/S 1.5 Energy: 284.350 Energy: 779.766 b 1.5 Energy: 284.500 1.0 b

a 0.5 a

0.0 810 800 790 780 770 760 292 290 288 286 284 282 280 278 276 Binding energy (eV) Binding energy (eV)

× 10 4 Co2p Ni 2p 1.95 Pos. Sep. %Area b 777.33 0.00 55.68 Energy: 854.800 1.9 780.31 2.98 44.32 c 1.6 1.85 Energy: 851.456 b 1.8 c/s C/S

Energy: 854.750 1.75 1.4 a 1.7

1.65 784 782 780 778 776 774 890 880 870 860 850 840 Binding Energy (eV) Binding energy (eV)

123 Study on Alumina-Supported Cobalt–Nickel Oxide Catalyst 175

Fig. 8 TEM micrographs of a b a fresh, b, c used, d regenerated samples and e EDX spectra on points 1–3 1

c d

e Al O

Co Co C Cu Ni 3 Co O Co Ni Cu Al C 2 C Co Co O Al Ni Cu 1

012345678910 Energy (KeV) shown in the top left corner of Fig. 8b, and carbon-coated conﬁrmed that deterioration of the alumina-supported cobalt nanocapsules were observed in Fig. 8c. These were cobalt–nickel oxide catalyst was mainly caused by the supported by the EDX analysis (Fig. 8e); element C was growth of carbon around cobalt oxide concluded from the mainly detected at the bright point 1 and Co and O were XRD analysis. In addition, the Co3O4 particle size of the mainly present at the dark point 2 as well as Al and O regenerated sample (30 nm) was larger than those of the were mainly found at point 3 by EDS analysis(Fig. 8e). fresh and used catalyst samples (20 nm), indicating that The carbon deposition phenomena were also observed in cobalt oxide was partly sintered during the regeneration the literatures [43, 50, 51]. TEM analysis directly process.

123 176 C. Feng et al.

0.06 Table 1 summarizes textural properties of the alumina- Pore Diameter: 8.3176 Pore Diameter: 8.3956 supported cobalt–nickel oxide catalyst. Compared to the fresh catalyst, the used catalyst possessed a relatively large Pore Diameter: 7.2842 surface area (197.79 m2/g), a small pore volume (0.50 cm3/ g) and pore diameter (8.93 nm). The drop in the pore 0.04 nm) · /g volume could be the result that a certain amount of carbon 3 was deposited in the pores of the catalyst in the catalytic runs. Table 1 also demonstrates that regenerated catalyst had a lower surface area and pore volume than those of the 0.02 dV/dD (cm fresh one, which can be explained by the fact that the cobalt oxide was partly sintered during the regeneration a b c process, as detected by TEM investigation. There was a strange phenomenon that the surface area of 0.00 010010 100 0 10 100 0 10 the used catalyst was larger than that of the fresh one and Pore Diameter (nm) could be recovered after regeneration. Based on the XRD, XPS and TEM results, it could be concluded that the Fig. 10 Pore size distribution curves as a function of pore diameter. increase of the surface area was brought about by the (a) Fresh; (b) used; (c) regenerated deposition of activated carbon with large surface area on the framework of the catalyst [51, 52]. In order to sample occurred with no bulge while the fresh and regen- strengthen this inference, the porous structure of the cata- erated ones occurred with it, indicating that structural lyst was further analyzed. The adsorption–desorption iso- properties of the used catalyst were similar to the type H4 therms are show in Fig. 9. All the samples displayed type hysteretic loop, which was a indicative of highly micro- IV isotherms. In addition, the hysteretic loop of the used porosity with slit-like pores as the characteristic of activated carbon [53]. A pore size distribution of the catalyst was determined using the BJH desorption method too Table 1 Textural properties of the alumina-supported cobalt–nickel (Fig. 10). The major differences between the fresh and oxide catalysts determined by N2 adsorption–desorption analysis a 2 -1 b 3 -1 c used samples were the decrease of the maximum distri- SBET (m g )V(cm g )dp (nm) bution of pore diameter and the increase of micropores in Fresh 176.63 0.52 10.30 the used catalyst, which indicated that many micropores as Used 197.79 0.50 8.93 the feature of activated carbon [54, 55], were formed Regenerated 164.67 0.49 10.67 during the catalytic runs. These results conﬁrmed further that porous carbon deposition took place during the reac- a BET surface area tion process. b BJH cumulative desorption pore volume c Mean pore diameter = 4 V/SBET 4 Conclusions

550 The alumina-supported cobalt–nickel oxide catalyst for 500 desorption catalytic amination of alcohol to acetonitrile prepared by 450 adsorption coprecipitation-kneading method showed high mechanical /g STP) 3 400 strength compared to the one prepared by kneading method 350 reported previously. The parameters which effect on the 300 c performances of the catalyst were studied thoroughly and 250 an optimized process for synthesizing acetonitrile from 200 b ethanol and ammonia over the catalyst was obtained. Under 150 the optimized conditions the catalyst can last for 720 h to

Quantity Adsorbed (cm 100 afford acetonitrile with a yield higher than 81%. The cat- 50 a alytic performance can be recovered on-line by flowing of air into the catalyst bed at 470 °C. The reasons leading to 0.0 0.2 0.4 0.6 0.8 1.0 the deterioration of the catalyst were studied through the Relative Pressure (P/P0) characterization of the catalysts by means of XRD, XPS, TEM, EDX and N adsorption–desorption techniques. Fig. 9 Adsorption–desorption isotherms of the catalyst. (a) Fresh; 2 (b) used; (c) regenerated Characterization results revealed that the deterioration of 123 Study on Alumina-Supported Cobalt–Nickel Oxide Catalyst 177 the catalyst was attributed to the carbon deposition on the 24. Kryukov YB, Bashkirov AN, Zakirov NS, Novak FL (1966) Dokl catalyst and the formation of metal carbides from the active Akad Nauk SSSR 170:852 25. Pan WX (1992) CN Patent 1,062,303, Tsinghua University species in the catalytic run. 26. Kulkarni SJ, Ramachandra Rao R, Subrahmanyam M, Rama Rao AV (1994) Appl Catal A 113:1 Acknowledgments We thank the financial support by the National 27. Kumar RJ, Joshi PN, Chapekar GM (2005) WO Patent Natural Science Foundation of China (Grant no. 20976034) and the 2,005,000,816A, Council of Scientific and Industrial Research, Natural Science Foundation for Young Scientists of Hebei Province, Jubilant Organosys Ltd China (Grant no. B2009000009) and Guide Project for the Devel- 28. Rausch AK, van Steen E, Roessner F (2008) J Catal 253:111 opment of Science and Technology of Hebei Province, China (Grant 29. Neylon MK, Bej SK, Bennett CA, Thompson LT (2002) Appl no. 072156136). Catal A 232:13 30. Higashio YS, Shoji T (2004) Appl Catal A 260:251 31. Ramachandra Rao R, Srinivas N, Kulkarni SJ, Subrahmanyam M, References Raghavan KV (1997) Appl Catal A 161:L37 32. Jin F, Cui YG, Li YD (2008) Appl Catal A 350:71 33. Volckmar CE, Bron M, Bentrup U, Martin A, Claus P (2009) J 1. 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