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γ-alumina catalysts from recycled Ni for hydrotreating reactions
Applied Catalysis A: General 292 (2005) 113–117 www.elsevier.com/locate/apcata
Preparation of ZnNiMo/g-alumina catalysts from recycled Ni for hydrotreating reactions Carlos F. Linares a,*, Julio Lo´pez a, Adriana Scaffidi b, Carlos E. Scott b a
Laboratorio de Cata´lisis y Metales de Transicio´n, Facultad de Ciencias y Tecnologı´a, Departamento de Quı´mica, Universidad de Carabobo, Valencia Edo Carabobo, Apartado Postal 3336, Venezuela b Centro de Cata´lisis, Petro´leo y Petroquı´mica, Universidad Central de VenezuelaFacultad de Ciencias, Apartado 47102, Los Chaguaramos, Caracas, Venezuela Received 25 November 2004; received in revised form 19 May 2005; accepted 23 May 2005 Available online 18 July 2005
Abstract Ni, recovered from Ni–Cd cellular phone batteries, was used in the preparation of ZnNiMo/Al2O3 catalysts. The catalysts were characterized by temperature programmed reductions (TPR), surface area determinations (BET) and chemical analysis. Vanadyl octaethyl porphyrin (VOOEP) hydrodeporphyrinization (HDP) and thiophene hydrodesulfurization (HDS) were used as catalytic tests. It was found that the addition of Zn increases the ratio between octahedral and tetrahedral Mo in ZnMo and ZnNiMo catalysts, and that Ni addition lowers the reduction temperature of Mo species. Both results induce a positive synergetic effect for HDP and HDS reactions. An activity maximum was found for the catalyst with a Zn/(Zn + Ni) atomic ratio equal to 0.29, for both reactions. Finally, the use of a possible pollutant (Ni–Cd batteries) to produce a catalyst to eliminate contaminants in fuels was shown to be feasible. # 2005 Elsevier B.V. All rights reserved. Keywords: Ni–Zn–Mo Catalysts; Ni–Cd batteries; HDP; Tiophene HDS
1. Introduction Cellular phones is a rapidly growing marked in many countries, and they are widely used nowadays. Cell phone batteries are of many different kinds, but the more commons are the Ni–Cd ones. Their use imposed an important problem for some countries, since few of them are able to recycle this kind of disposed batteries, and the metals they contain are highly pollutant, so it is imperative to find practical uses for the metals in these materials [1], for example finding ways of recycling them, in order to avoid the ecological problems associated with their disposal. Thus, it has been determined that in the Venezuelan state of Carabobo, the amount of Ni and Cd in cellular phone batteries thrown away can be as much as 500 and 700 Kg per year, respectively [2]. Besides, there has been an increase in the need of cleaner fuels due to more stringent environmental legislations across * Corresponding author. Tel.: +58 241 8678805; fax: +58 241 8678805. E-mail address: [email protected] (C.F. Linares). 0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2005.05.013
the world [3,4]. Hence, much efforts has been spent in research and development of new hydrotreating catalysts [5,6], capable of more effectively diminishing the amount of toxic heteroatom in oils, in particular in heavy crude oils, since the reserve of light crude are becoming less abundant [3]. It is then clear that new catalysts more active and selective for treating heavier petroleum fractions are needed. Adding a third metal (such as Cr, V, Ti, Zr, Sn or Zn), to conventional Co(Ni)–Mo(W) catalysts, has been used as a way of improving catalyst activity and selectivity [7]. Some of them are said to have an electronic effect, while others, like Zn or Mg [8–10], are proposed to have a geometric effect. It has been proposed that the latter can substitute Co2+, in CoMo/ Al2O3 catalysts, thus diminishing the amount of tetrahedral Co (as cobalt aluminate), which is inactive in hydrotreating (HDT) reactions. However, no many papers have dealt with the characterization of such catalysts. Thus, Fierro et al. [9] reported that Zn, in ZnO–CoO– MoO3/Al2O3, increases the activity and stability of such catalysts, for the HDS of dibenzothiophene, and that the
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activity is maximum for the catalysts with an atomic Zn/ (Zn + Co) ratio of 0.48. The present work explores the use of Ni recycled from cellular phone batteries in the preparation of Zn–Ni–Mo catalysts for hydrotreatment. Hydrodesulphurization of thiophene (HDS) and hydrodeporphyrinization (HDP) of vanadyl octaethyl porphyrin (VOOEP) were used as catalytic tests.
2. Experimental Ni was recovered by manually separating the black particles (Ni) from the white ones (Cd) from previously opened Ni–Cd cellular phone batteries. Then, the Ni was dissolved in hot 10M HNO3 and filtered off, and NH4OH (35% solution) was added until the ammonium blue complex of Ni was formed. In a similar way a Zn solution in NH4OH, from Zn sulfate (Merck, 99%), was prepared. At the same time, g-Al2O3 (200 m2/g) was impregnated by the incipient wetness method, with a solution of ammonium heptamolybdate, in order to get 15 wt.% of MoO3 in the final catalyst, and then calcined (500 8C) in flowing air for 4 h. This solid was then co-impregnated with the previously prepared Ni and Zn solutions, also by the incipient wetness impregnation method. The atomic Mo/ (Zn + Ni) atomic ratio was kept constant and equal to 3, while Zn/(Zn + Ni) atomic ratio was varied (0, 0.29, 0.38, 0.47 and 1.0). After impregnation with Zn and/or Ni, the solids were dried at 100 8C, and calcined again, to get the final catalysts. Temperature programmed reduction (TPR), were carried out in a Chemisorb Analizer 2900 from Micromeritics. The samples were heated up to 950 8C under flowing H2/Ar (10/ 90, v/v). Surface area determinations (BET) were done in a Beckman Coulter SA Plus instrument. Chemical analyses of Ni, Cd and Mo were performed, on samples dissolved in aqua regia, using ICP-plasma. 2.1. Catalytic tests 2.1.1. Vanadyl octaethyl porphyrin (VOOEP) hydrodeporphyrinization (HDP) HDP reactions were carried out batch wise in a 100 cm3 Parr reactor. Operating conditions were: 250 8C, 1000 psig
of hydrogen and a stirrer speed of 40 rpm. The reactor was fed with a 5 10 4 M solution of vanadyl octaethyl porphyrin (Aldrich 95%) in decahydro naphthalene (Aldrich 98%), with 2% in volume of CS2. 0.250 g of catalysts were used in each test, and reaction time was 6 h. Conversions were worked out by UV-visible measurements of the Soret and a and b bands of the metal prophyrin. All the catalysts were presulfided before reaction with a solution of CS2 in heptane (10, v/v%) at 400 8C and 160 psig of hydrogen. The sulfiding solution (10.5 mL h 1) was mixed with hydrogen (150 mL h 1) before entering the reactor. 2.1.2. Thiophene HDS Thiophene HDS was carried out on a continuous flow reactor working at atmospheric pressure. All catalysts were presulfided prior to catalytic tests in a H2S(15, v/v%)/H2 stream. The temperature was increased up to 400 8C, at a rate of 0.0833 8C s 1, and kept at these conditions for 4 h. Then the reaction was performed on 100 mg of catalyst using a liquid feed composed of 10 v% of thiophene in nheptane (2.7 10 4 cm3 s 1), and H2 (0.25 cm3 s 1), at 280 8C. The system was covered with a heating mantle (150 8C) in order to avoid any condensation of the reaction products. Reaction products were injected to a Perkin-Elmer (AutoSystem XL) gas chromatograph equipped with a flame ionization detector. Only n-butane, 1-butene, cis-2-butene and trans-2-butene were detected as reaction products.
3. Results and discussion Chemical analyses and surface areas, for the catalysts before sulfidation, are presented in Table 1. Chemical analyses revealed the presence of a small amount of Cd in the catalysts (less than 0.5 weight %). This metal is associated to the Ni extracted from the Ni–Cd cellular phone batteries. However, according to these results, the separation of Ni from Cd was fairly effective. As expected, the amount of Cd is slightly higher for the catalysts with higher amount of Ni. On the other hand, surface area decreases as the catalysts are impregnated with the metals (Mo, Ni and Zn). For Ni–Zn catalysts, it is observed that the higher the amount of Zn the lower the surface area, which could be due to the strong interaction of the Zn with the alumina leading to the formation of a Zn spinel [11], inducing some micropore
Table 1 Chemical analyses and surface area for ZnNiMo catalysts Catalysts
Zn(Zn + Ni) experimental ratios
Cd (%)
Surface area (m2/g)
Mo/Al2O3 NiMo/Al2O3 ZnMo/Al2O3 ZnNiMo/Al2O3 (0.29) ZnNiMo/Al2O3 (0.38) ZnNiMo/Al2O3 (0.47)
– 0 1 0.29 0.38 0.47
0.04 0.47 0.03 0.43 0.41 0.12
181 129 146 145 133 110
C.F. Linares et al. / Applied Catalysis A: General 292 (2005) 113–117 Table 2 TPR results Catalyst
Mo/Al2O3 NiMo/Al2O3 ZnMo/Al2O3 ZnNiMo/Al2O3(0.29) ZnNiMo/Al2O3(0.38) ZnNiMo/Al2O3(0.47)
Temperature a peak maximum (8C) Signal a
Signal b
500 420 500 420 430 430
860 750 800 760 770 770
a/b heights ratio
1.08 2.04 4.16 3.16 3.16 3.16
blocking. However, Zn spinel could not be detected by XRD, which is an indication that Zn is very well dispersed. TPR analyses are presented in Table 2. For the sake of comparison a Mo/Al2O3 sample is also included. Two reduction peaks were observed for this catalyst. The first one (signal a) is well defined in the range of 430–500 8C, which, according to the literature [12], is assigned to monocrystalline polymeric species of Mo in octahedral sites, where Mo is reduced from Mo6+ to Mo4+, and a second broader one (signal b) starts at 600 8C and goes up to 900 8C, which corresponds to more difficult to reduce Mo species in tetrahedral sites [12]. Both signals are present in all Mo containing catalysts. For the catalysts where the second metal (Ni or Zn) is added to Mo, the reduction peaks of each one of the second metal tend to overlap with Mo signal, making difficult any assignation to Zn or Ni reduction temperatures. However, some differences in the intensities of the peaks are observed. Thus, for ZnMo/Al2O3 catalysts, the intensity ratio between the first and second peak is four times higher than for the Mo catalysts. This increase in the intensity ratio could be due to the overlapping of the signals, and/or to the occupancy of the tetrahedral sites of the alumina by Zn2+, which reduces the amount of Mo that can occupy this type of sites. Thus the peak at around 800 8C, which is assigned to Mo in tetrahedral coordination (Mo(t)), decreases in favor of the peak at 500 8C which is due to Mo in octahedral coordination (Mo(o)). It is important to point out that the addition of Zn does not significantly change the position of the Mo peaks but their intensities, indicating that Zn does not change the reducibility of Mo but instead the amount of Mo in tetrahedral and octahedral coordination. For the NiMo/Al2O3 catalyst reduction peaks appear at lower temperatures than for Mo/Al2O3 (see Table 2). In this case Ni increases the reducibility of Mo. At the same time there is also an increase in the intensity ratio between the first and second Mo reduction peaks, as compare to Mo/ Al2O3, but to a lesser proportion than in the case where the Mo catalyst is only promoted by Zn. It its well known that Ni can also occupy alumina tetrahedral sites, then it can hinder some of the Mo from occupying tetrahedral sites, hence Ni could also increase the amount of Mo(o) and then increase the intensity of the first Mo reduction peak. When the catalysts are doubly promoted by Zn and Ni, both effects are observed, that is, Mo is reduced at lower
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temperatures and its amount in octahedral coordination is higher. Thus, the ratio between Mo(o) and Mo(t) reduction peaks increases from 1.1 for the unpromoted Mo catalyst to 3.2 for the promoted ones, and the temperature at peak maximum decreases, in average, 75 and 95 8C, for Mo(o) and Mo(t), respectively. A similar effect was reported by Fierro et al. [9] for thermogravimetric reduction of ZnCoMo catalysts at 450 8C. It was found that the reducibility of the catalysts increases when Mo is doubly promoted by Zn and Co and that the amount of metal reduced is maximum for the catalyst with a Zn/(Zn + Co) equal to 0.5. The dual effect, observed in our case, is due, on one hand to the interaction of the Zn with the alumina support occupying tetrahedral sites which does not allow Ni and Mo to go to this kind of sites, so there is more Ni in interaction with Mo instead of with the alumina; and on the other hand, to the increase in the amount of Ni which is not forming the spinel with alumina and promotes the reduction of Mo, maybe by a spillover effect. The first effect is supported by the reported fact that Zn easily occupies tetrahedral sites of the alumina [8,9]. For example, it has been reported [13] that Zn is preferentially adsorbed on alumina (forming Zn spinel), when in presence of Co. It is also important to point out that the small amount of Cd in the catalysts should not have any significant effect on the catalytic performance of the solids. According to its position in the periodic table one could expect Cd to form Cd spinels and have an effect similar to to the one found for Zn on Mo catalysts, however, even though the preparation of Cd spinels have been reported [14] partial substitution of Ni by Cd to produce CdxNi1 xAl2O4 takes place [15] at very high temperatures (1000 8C). It is then very difficult that in our preparation conditions this type of compound could be formed. Catalytic activities for HDP of VOOEP and HDS of thiophene are shown in Figs. 1 and 2, respectively. For HDP Ni and Zn promoted catalysts show similar activities, with the activity for ZnMo/Al2O3 catalyst being slightly higher. For doubly promoted catalysts a maximum in activity is found for the catalysts with a Zn/(Zn + Ni) atomic ratio of
Fig. 1. Activity for HDP of VOOEP vs. Zn/(Zn + Ni) atomic ratio (15 wt.% MoO3).
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Fig. 2. Activity for HDS of thiophene vs. Zn/(Zn + Ni) atomic ratio (15 wt.% MoO3).
0.29. This catalyst is 1.5 times more active than the catalyst promoted only by Ni. As far as the HDS of thiophene is concerned, a similar effect is observed, that is, a synergy with a maximum for a Zn/(Zn + Ni) atomic ratio of 0.29 is found. This result is in agreement with those previously reported by Fierro et al. [9]. However in Fierro‘s work the maximum in activity is observed for the catalyst with a Co/(Co + Zn) ratio of 0.48, instead of 0.29. The difference could be due to differences in the reaction (gas–oil HDS) and the total amount of metal in the catalysts (8 wt.% of MoO3, and 3 wt.% of CoO + ZnO) in Fierro‘s work [9]. It is also observed that the Zn promoted catalyst shows very low activity in comparison to the Ni promoted catalyst (6 times less). These results differ from what it was found for HDP. Apparently, for the HDP reaction the amount of octahedral Mo is as important as the interaction between Ni and Mo, while for the HDS the Ni–Mo interaction is more important. However, the fact that for both reactions a synergy is obtained at the same Zn/(Zn + Ni) ratio seems to indicate that active sites are similar for HDP and HDS. Product distribution for thiophene HDS is presented in Fig. 3. It was found that C4 hydrocarbon distribution is very similar for all Ni promoted catalysts (mono or doubly
promoted). This is an indication that the type of sites are the same, that is, the synergetic effect of Zn is not due to a change in the type but in the number of active sites in HDS of thiophene. This is in agreement with the proposal that Zn increases the amount of Ni and Mo in octahedral sites, which in turns increases the amount of Ni and Mo interacting with each other. For the ZnMo/Al2O3 catalyst product distribution changes, which is not surprising since for ZnMo/Al2O3 the active specie should be Mo sulfide, while in the case of the ZnNiMo/Al2O3 and NiMo/Al2O3 the active site should be the specie formed from the interaction between Ni and Mo, possibly a NiMoS phase [16]. The results presented here indicate that Ni recycled from cellular phone batteries can be used in the preparation of hydrotreating catalysts, and that the substitution of part of the Ni by Zn, in NiMo/Al2O3 catalysts, increases catalytic activity showing a synergetic effect between Ni and Zn. Thus, the used of a possible pollutant (cellular phone batteries) in the preparation of catalyst to reduce atmospheric pollution from fuels, was demonstrated in this work.
4. Conclusions It is possible to used Ni recovered from Ni–Cd cellular phone batteries in the preparation of ZnNiMo/Al2O3 catalysts for HDM and HDS. The use of Zn in those catalysts increases their activity in both reactions showing a synergetic effect for Zn/(Zn + Ni) atomic ratio of 0.29. TPR experiments show that Zn has the effect of augmenting the Mo(o)/Mo(t) ratio, while the main effect of Ni is to increase the reducibility of Mo. The combination of these two effects leads to the synergetic effect observed between Ni and Zn.
Acknowledgements Authors are grateful to FONACIT (Projects G-97000658 y F-2001000774) for funding the research carried out in this work.
References
Fig. 3. Product distribution for thiophene HDS.
[1] C.F. Linares, E. Figueredo, A. Tortosa, A. Scaffidi, C. Urbina de Navarro, C.E. Scott, Ciencia 12 (2004) 228. [2] N. Galindez, Bachelor’s thesis, University of Carabobo, Venezuela, 1999. [3] Ch. Marcilly, Stud. Surf. Sci. Catal. 135 (2001) 37. [4] C.F. Linares, P. Ame´ zqueta, M.L. de Armando, C.E. Scott, in: Proceedings of the 17th North American Meeting of the Catalysis Society, Toronto, Canada, 2001, p. 199. [5] R. Hubaut, A. Rives, M. Luis, C.E. Scott, F. Gonza´ lez-Jimenez, in: Proceedings of the Ninth International Symposium on Heterogeneus Catalysis, Varna, Bulgaria, 2000, p. 561.
C.F. Linares et al. / Applied Catalysis A: General 292 (2005) 113–117 [6] M. Luis, A. Rives, R. Hubaut, P. Embaid, F. Gonza´ lez-Jimenez, C.E. Scott, Stud. Surf. Sci. Catal. 127 (1999) 203. [7] C.L. Kibbi, H.E. Swift, J. Catal 45 (1976) 231. [8] N.P. Martı´nez, P.C.H. Mitchell, in: Proceedings of the Third International Conference on the Chemistry and Uses of Molybdenum, Climax Molybdenum Company, Ann Arbor, Michigan, 1979, p. 105. [9] J.L. Fierro, A. Lo´ pez-Agudo, P. Grange, B. Delmon, in: Proceedings of the Eighth International Congress on Catalysis, vol. 2, Berlin Germany, 1984, p. 363. [10] J. Brito, R. Golding, F. Severino, J. Laine, Prepints, Div. Petrol. Chem., ACS 27 (1982) 763.
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[11] C. Valenzuela, Introduccio´ n a la Quı´mica Inorga´ nica, Edt, Mac GrawHill, 1999, pp. 374–376. [12] N. Hurst, S. Gentry, A. Jones, Catal. Rev. 24 (1982) 233. [13] H. Thomas, C. Caceres, M. Blanco, J.L.G. Fierro, A. Lo´ pez Agudo, J. Chem. Soc., Faraday Trans. 90 (1994) 2125. [14] R.J. Hill, J.R. Craig, G.V. Gibbs, Phys. Chem. Miner. 4 (1979) 317. [15] C. Otero Arean, M.L. Rodrı´guez-Martinez, A.M. Arjona, Mater. Chem. Phys. 8 (1983) 443. [16] F. Vandeneeckoutte, R. Hubaut, S. Pietrzyck, T. Des Courrieres, J. Grimblot, J. React. Kinet. Catal. Lett. 45 (1991) 191.
Preparation of ZnNiMo/g-alumina catalysts from recycled Ni for hydrotreating reactions Carlos F. Linares a,*, Julio Lo´pez a, Adriana Scaffidi b, Carlos E. Scott b a
Laboratorio de Cata´lisis y Metales de Transicio´n, Facultad de Ciencias y Tecnologı´a, Departamento de Quı´mica, Universidad de Carabobo, Valencia Edo Carabobo, Apartado Postal 3336, Venezuela b Centro de Cata´lisis, Petro´leo y Petroquı´mica, Universidad Central de VenezuelaFacultad de Ciencias, Apartado 47102, Los Chaguaramos, Caracas, Venezuela Received 25 November 2004; received in revised form 19 May 2005; accepted 23 May 2005 Available online 18 July 2005
Abstract Ni, recovered from Ni–Cd cellular phone batteries, was used in the preparation of ZnNiMo/Al2O3 catalysts. The catalysts were characterized by temperature programmed reductions (TPR), surface area determinations (BET) and chemical analysis. Vanadyl octaethyl porphyrin (VOOEP) hydrodeporphyrinization (HDP) and thiophene hydrodesulfurization (HDS) were used as catalytic tests. It was found that the addition of Zn increases the ratio between octahedral and tetrahedral Mo in ZnMo and ZnNiMo catalysts, and that Ni addition lowers the reduction temperature of Mo species. Both results induce a positive synergetic effect for HDP and HDS reactions. An activity maximum was found for the catalyst with a Zn/(Zn + Ni) atomic ratio equal to 0.29, for both reactions. Finally, the use of a possible pollutant (Ni–Cd batteries) to produce a catalyst to eliminate contaminants in fuels was shown to be feasible. # 2005 Elsevier B.V. All rights reserved. Keywords: Ni–Zn–Mo Catalysts; Ni–Cd batteries; HDP; Tiophene HDS
1. Introduction Cellular phones is a rapidly growing marked in many countries, and they are widely used nowadays. Cell phone batteries are of many different kinds, but the more commons are the Ni–Cd ones. Their use imposed an important problem for some countries, since few of them are able to recycle this kind of disposed batteries, and the metals they contain are highly pollutant, so it is imperative to find practical uses for the metals in these materials [1], for example finding ways of recycling them, in order to avoid the ecological problems associated with their disposal. Thus, it has been determined that in the Venezuelan state of Carabobo, the amount of Ni and Cd in cellular phone batteries thrown away can be as much as 500 and 700 Kg per year, respectively [2]. Besides, there has been an increase in the need of cleaner fuels due to more stringent environmental legislations across * Corresponding author. Tel.: +58 241 8678805; fax: +58 241 8678805. E-mail address: [email protected] (C.F. Linares). 0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2005.05.013
the world [3,4]. Hence, much efforts has been spent in research and development of new hydrotreating catalysts [5,6], capable of more effectively diminishing the amount of toxic heteroatom in oils, in particular in heavy crude oils, since the reserve of light crude are becoming less abundant [3]. It is then clear that new catalysts more active and selective for treating heavier petroleum fractions are needed. Adding a third metal (such as Cr, V, Ti, Zr, Sn or Zn), to conventional Co(Ni)–Mo(W) catalysts, has been used as a way of improving catalyst activity and selectivity [7]. Some of them are said to have an electronic effect, while others, like Zn or Mg [8–10], are proposed to have a geometric effect. It has been proposed that the latter can substitute Co2+, in CoMo/ Al2O3 catalysts, thus diminishing the amount of tetrahedral Co (as cobalt aluminate), which is inactive in hydrotreating (HDT) reactions. However, no many papers have dealt with the characterization of such catalysts. Thus, Fierro et al. [9] reported that Zn, in ZnO–CoO– MoO3/Al2O3, increases the activity and stability of such catalysts, for the HDS of dibenzothiophene, and that the
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activity is maximum for the catalysts with an atomic Zn/ (Zn + Co) ratio of 0.48. The present work explores the use of Ni recycled from cellular phone batteries in the preparation of Zn–Ni–Mo catalysts for hydrotreatment. Hydrodesulphurization of thiophene (HDS) and hydrodeporphyrinization (HDP) of vanadyl octaethyl porphyrin (VOOEP) were used as catalytic tests.
2. Experimental Ni was recovered by manually separating the black particles (Ni) from the white ones (Cd) from previously opened Ni–Cd cellular phone batteries. Then, the Ni was dissolved in hot 10M HNO3 and filtered off, and NH4OH (35% solution) was added until the ammonium blue complex of Ni was formed. In a similar way a Zn solution in NH4OH, from Zn sulfate (Merck, 99%), was prepared. At the same time, g-Al2O3 (200 m2/g) was impregnated by the incipient wetness method, with a solution of ammonium heptamolybdate, in order to get 15 wt.% of MoO3 in the final catalyst, and then calcined (500 8C) in flowing air for 4 h. This solid was then co-impregnated with the previously prepared Ni and Zn solutions, also by the incipient wetness impregnation method. The atomic Mo/ (Zn + Ni) atomic ratio was kept constant and equal to 3, while Zn/(Zn + Ni) atomic ratio was varied (0, 0.29, 0.38, 0.47 and 1.0). After impregnation with Zn and/or Ni, the solids were dried at 100 8C, and calcined again, to get the final catalysts. Temperature programmed reduction (TPR), were carried out in a Chemisorb Analizer 2900 from Micromeritics. The samples were heated up to 950 8C under flowing H2/Ar (10/ 90, v/v). Surface area determinations (BET) were done in a Beckman Coulter SA Plus instrument. Chemical analyses of Ni, Cd and Mo were performed, on samples dissolved in aqua regia, using ICP-plasma. 2.1. Catalytic tests 2.1.1. Vanadyl octaethyl porphyrin (VOOEP) hydrodeporphyrinization (HDP) HDP reactions were carried out batch wise in a 100 cm3 Parr reactor. Operating conditions were: 250 8C, 1000 psig
of hydrogen and a stirrer speed of 40 rpm. The reactor was fed with a 5 10 4 M solution of vanadyl octaethyl porphyrin (Aldrich 95%) in decahydro naphthalene (Aldrich 98%), with 2% in volume of CS2. 0.250 g of catalysts were used in each test, and reaction time was 6 h. Conversions were worked out by UV-visible measurements of the Soret and a and b bands of the metal prophyrin. All the catalysts were presulfided before reaction with a solution of CS2 in heptane (10, v/v%) at 400 8C and 160 psig of hydrogen. The sulfiding solution (10.5 mL h 1) was mixed with hydrogen (150 mL h 1) before entering the reactor. 2.1.2. Thiophene HDS Thiophene HDS was carried out on a continuous flow reactor working at atmospheric pressure. All catalysts were presulfided prior to catalytic tests in a H2S(15, v/v%)/H2 stream. The temperature was increased up to 400 8C, at a rate of 0.0833 8C s 1, and kept at these conditions for 4 h. Then the reaction was performed on 100 mg of catalyst using a liquid feed composed of 10 v% of thiophene in nheptane (2.7 10 4 cm3 s 1), and H2 (0.25 cm3 s 1), at 280 8C. The system was covered with a heating mantle (150 8C) in order to avoid any condensation of the reaction products. Reaction products were injected to a Perkin-Elmer (AutoSystem XL) gas chromatograph equipped with a flame ionization detector. Only n-butane, 1-butene, cis-2-butene and trans-2-butene were detected as reaction products.
3. Results and discussion Chemical analyses and surface areas, for the catalysts before sulfidation, are presented in Table 1. Chemical analyses revealed the presence of a small amount of Cd in the catalysts (less than 0.5 weight %). This metal is associated to the Ni extracted from the Ni–Cd cellular phone batteries. However, according to these results, the separation of Ni from Cd was fairly effective. As expected, the amount of Cd is slightly higher for the catalysts with higher amount of Ni. On the other hand, surface area decreases as the catalysts are impregnated with the metals (Mo, Ni and Zn). For Ni–Zn catalysts, it is observed that the higher the amount of Zn the lower the surface area, which could be due to the strong interaction of the Zn with the alumina leading to the formation of a Zn spinel [11], inducing some micropore
Table 1 Chemical analyses and surface area for ZnNiMo catalysts Catalysts
Zn(Zn + Ni) experimental ratios
Cd (%)
Surface area (m2/g)
Mo/Al2O3 NiMo/Al2O3 ZnMo/Al2O3 ZnNiMo/Al2O3 (0.29) ZnNiMo/Al2O3 (0.38) ZnNiMo/Al2O3 (0.47)
– 0 1 0.29 0.38 0.47
0.04 0.47 0.03 0.43 0.41 0.12
181 129 146 145 133 110
C.F. Linares et al. / Applied Catalysis A: General 292 (2005) 113–117 Table 2 TPR results Catalyst
Mo/Al2O3 NiMo/Al2O3 ZnMo/Al2O3 ZnNiMo/Al2O3(0.29) ZnNiMo/Al2O3(0.38) ZnNiMo/Al2O3(0.47)
Temperature a peak maximum (8C) Signal a
Signal b
500 420 500 420 430 430
860 750 800 760 770 770
a/b heights ratio
1.08 2.04 4.16 3.16 3.16 3.16
blocking. However, Zn spinel could not be detected by XRD, which is an indication that Zn is very well dispersed. TPR analyses are presented in Table 2. For the sake of comparison a Mo/Al2O3 sample is also included. Two reduction peaks were observed for this catalyst. The first one (signal a) is well defined in the range of 430–500 8C, which, according to the literature [12], is assigned to monocrystalline polymeric species of Mo in octahedral sites, where Mo is reduced from Mo6+ to Mo4+, and a second broader one (signal b) starts at 600 8C and goes up to 900 8C, which corresponds to more difficult to reduce Mo species in tetrahedral sites [12]. Both signals are present in all Mo containing catalysts. For the catalysts where the second metal (Ni or Zn) is added to Mo, the reduction peaks of each one of the second metal tend to overlap with Mo signal, making difficult any assignation to Zn or Ni reduction temperatures. However, some differences in the intensities of the peaks are observed. Thus, for ZnMo/Al2O3 catalysts, the intensity ratio between the first and second peak is four times higher than for the Mo catalysts. This increase in the intensity ratio could be due to the overlapping of the signals, and/or to the occupancy of the tetrahedral sites of the alumina by Zn2+, which reduces the amount of Mo that can occupy this type of sites. Thus the peak at around 800 8C, which is assigned to Mo in tetrahedral coordination (Mo(t)), decreases in favor of the peak at 500 8C which is due to Mo in octahedral coordination (Mo(o)). It is important to point out that the addition of Zn does not significantly change the position of the Mo peaks but their intensities, indicating that Zn does not change the reducibility of Mo but instead the amount of Mo in tetrahedral and octahedral coordination. For the NiMo/Al2O3 catalyst reduction peaks appear at lower temperatures than for Mo/Al2O3 (see Table 2). In this case Ni increases the reducibility of Mo. At the same time there is also an increase in the intensity ratio between the first and second Mo reduction peaks, as compare to Mo/ Al2O3, but to a lesser proportion than in the case where the Mo catalyst is only promoted by Zn. It its well known that Ni can also occupy alumina tetrahedral sites, then it can hinder some of the Mo from occupying tetrahedral sites, hence Ni could also increase the amount of Mo(o) and then increase the intensity of the first Mo reduction peak. When the catalysts are doubly promoted by Zn and Ni, both effects are observed, that is, Mo is reduced at lower
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temperatures and its amount in octahedral coordination is higher. Thus, the ratio between Mo(o) and Mo(t) reduction peaks increases from 1.1 for the unpromoted Mo catalyst to 3.2 for the promoted ones, and the temperature at peak maximum decreases, in average, 75 and 95 8C, for Mo(o) and Mo(t), respectively. A similar effect was reported by Fierro et al. [9] for thermogravimetric reduction of ZnCoMo catalysts at 450 8C. It was found that the reducibility of the catalysts increases when Mo is doubly promoted by Zn and Co and that the amount of metal reduced is maximum for the catalyst with a Zn/(Zn + Co) equal to 0.5. The dual effect, observed in our case, is due, on one hand to the interaction of the Zn with the alumina support occupying tetrahedral sites which does not allow Ni and Mo to go to this kind of sites, so there is more Ni in interaction with Mo instead of with the alumina; and on the other hand, to the increase in the amount of Ni which is not forming the spinel with alumina and promotes the reduction of Mo, maybe by a spillover effect. The first effect is supported by the reported fact that Zn easily occupies tetrahedral sites of the alumina [8,9]. For example, it has been reported [13] that Zn is preferentially adsorbed on alumina (forming Zn spinel), when in presence of Co. It is also important to point out that the small amount of Cd in the catalysts should not have any significant effect on the catalytic performance of the solids. According to its position in the periodic table one could expect Cd to form Cd spinels and have an effect similar to to the one found for Zn on Mo catalysts, however, even though the preparation of Cd spinels have been reported [14] partial substitution of Ni by Cd to produce CdxNi1 xAl2O4 takes place [15] at very high temperatures (1000 8C). It is then very difficult that in our preparation conditions this type of compound could be formed. Catalytic activities for HDP of VOOEP and HDS of thiophene are shown in Figs. 1 and 2, respectively. For HDP Ni and Zn promoted catalysts show similar activities, with the activity for ZnMo/Al2O3 catalyst being slightly higher. For doubly promoted catalysts a maximum in activity is found for the catalysts with a Zn/(Zn + Ni) atomic ratio of
Fig. 1. Activity for HDP of VOOEP vs. Zn/(Zn + Ni) atomic ratio (15 wt.% MoO3).
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Fig. 2. Activity for HDS of thiophene vs. Zn/(Zn + Ni) atomic ratio (15 wt.% MoO3).
0.29. This catalyst is 1.5 times more active than the catalyst promoted only by Ni. As far as the HDS of thiophene is concerned, a similar effect is observed, that is, a synergy with a maximum for a Zn/(Zn + Ni) atomic ratio of 0.29 is found. This result is in agreement with those previously reported by Fierro et al. [9]. However in Fierro‘s work the maximum in activity is observed for the catalyst with a Co/(Co + Zn) ratio of 0.48, instead of 0.29. The difference could be due to differences in the reaction (gas–oil HDS) and the total amount of metal in the catalysts (8 wt.% of MoO3, and 3 wt.% of CoO + ZnO) in Fierro‘s work [9]. It is also observed that the Zn promoted catalyst shows very low activity in comparison to the Ni promoted catalyst (6 times less). These results differ from what it was found for HDP. Apparently, for the HDP reaction the amount of octahedral Mo is as important as the interaction between Ni and Mo, while for the HDS the Ni–Mo interaction is more important. However, the fact that for both reactions a synergy is obtained at the same Zn/(Zn + Ni) ratio seems to indicate that active sites are similar for HDP and HDS. Product distribution for thiophene HDS is presented in Fig. 3. It was found that C4 hydrocarbon distribution is very similar for all Ni promoted catalysts (mono or doubly
promoted). This is an indication that the type of sites are the same, that is, the synergetic effect of Zn is not due to a change in the type but in the number of active sites in HDS of thiophene. This is in agreement with the proposal that Zn increases the amount of Ni and Mo in octahedral sites, which in turns increases the amount of Ni and Mo interacting with each other. For the ZnMo/Al2O3 catalyst product distribution changes, which is not surprising since for ZnMo/Al2O3 the active specie should be Mo sulfide, while in the case of the ZnNiMo/Al2O3 and NiMo/Al2O3 the active site should be the specie formed from the interaction between Ni and Mo, possibly a NiMoS phase [16]. The results presented here indicate that Ni recycled from cellular phone batteries can be used in the preparation of hydrotreating catalysts, and that the substitution of part of the Ni by Zn, in NiMo/Al2O3 catalysts, increases catalytic activity showing a synergetic effect between Ni and Zn. Thus, the used of a possible pollutant (cellular phone batteries) in the preparation of catalyst to reduce atmospheric pollution from fuels, was demonstrated in this work.
4. Conclusions It is possible to used Ni recovered from Ni–Cd cellular phone batteries in the preparation of ZnNiMo/Al2O3 catalysts for HDM and HDS. The use of Zn in those catalysts increases their activity in both reactions showing a synergetic effect for Zn/(Zn + Ni) atomic ratio of 0.29. TPR experiments show that Zn has the effect of augmenting the Mo(o)/Mo(t) ratio, while the main effect of Ni is to increase the reducibility of Mo. The combination of these two effects leads to the synergetic effect observed between Ni and Zn.
Acknowledgements Authors are grateful to FONACIT (Projects G-97000658 y F-2001000774) for funding the research carried out in this work.
References
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