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Thiophene hydrodesulfurization over alumina-supported β-Mo2N0.78 catalyst
Catalysis Communications 5 (2004) 621–624 www.elsevier.com/locate/catcom
Thiophene hydrodesulfurization over alumina-supported b-Mo2N0.78 catalyst Shuwen Gong, Haokan Chen *, Wen Li, Baoqing Li State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, P.O.Box 165, Taiyuan, Shanxi 030001, PR China Received 16 April 2004; accepted 23 July 2004 Available online 1 September 2004
Abstract Alumina supported b-Mo2N0.78 catalyst was synthesized via temperature programmed reaction in the N2–H2 mixture gases. Catalyst properties were also investigated by X-ray diffraction (XRD), BET surface area and temperature programmed reduction (TPR) methods. The HDS activity of the catalyst was measured under different Mo loading. The HDS results indicated that there was a suitable Mo loading of b-Mo2N0.78/c-Al2O3 catalyst with high HDS activity. The TPR result suggested that sulfur replaced the surface oxygen of the passivated catalyst in the HDS reaction. 2004 Elsevier B.V. All rights reserved. Keywords: Thiophene; Hydrodesulfurization; b-Mo2N0.78
1. Introduction Catalytic hydroprocessing to remove heteroatoms such as sulfur, nitrogen, and oxygen from petroleum feedstock is a critical step in refining processing. To meet the goal of reducing sulfur emissions, increasing interest has recently been developed in exploring the catalytic properties of molybdenum nitrides and carbides for hydrodesulfurization (HDS) [1–4]. These studies have found that unsupported and supported Mo nitride catalysts have HDS activities similar to or higher than those of conventional sulfide catalysts. Sajkowski and Oyama [5] found that unsupported Mo2N was nearly twice as active as a commercial Ni–Mo/Al2O3 catalyst in HDS reaction. However, the majority of research was focused on the c-Mo2N (fcc) catalysts, which were prepared by temperature programmed reaction of Mo oxides with
*
Corresponding author. Tel.: +86 351 4048967; fax: +86 351 4048967/+86 351 404 1153. E-mail address: [email protected] (H. Chen). 1566-7367/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2004.07.012
NH3 [1–7] or N2–H2 [8]. Recently, some studies found that c-Mo2N transformed to b-Mo2N0.78 (tetragonal) when it was heated to 1123 K in He [9]. Hadas result showed that b-Mo2N0.78 also could form during temperature programmed reaction [10]. There is little relevant experimental data about the HDS behavior of bMo2N0.78 although its synthesis was reported. We recently synthesized bulk b-Mo2N0.78 via temperature programmed reaction of MoO3 and N2–H2 mixture gases, and found that b-Mo2N0.78 also had good HDS activity [11]. In this paper, c-Al2O3 supported bMo2N0.78 catalyst was synthesized by temperature programmed reaction and its HDS behavior was firstly studied with thiophene as the model compound.
2. Experimental Series of c-Al2O3 supported catalysts were prepared by the nitridation of supported molybdenum oxides, which was prepared by the calcine of molybdates. The
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S. Gong et al. / Catalysis Communications 5 (2004) 621–624
molybdates were prepared by impregnation of c-Al2O3 with ammonium heptamolybdate ((NH4)6Mo7O24 Æ 4H2O) aqueous solution. The resulting molybdenum loading was determined on the basis of the initial concentration of the ammonium heptamolybdate solution. For catalysts with Mo loading greater than 10 wt%, multiple impregnations were needed. Following impregnation the catalysts were dried for 3 h at 383 K and then calcined for 5 h in air at 773 K. The oxidized precursor was packed on the center of a quartz tube reactor (15 mm ID · 20 mm OD · 60 cm). It was treated in N2–H2 mixture gases from room temperature to 573 K at a heating rate of 10 K min 1, from 573 to 773 K at 0.6 K min 1, then from 773 to 973 K at 2 K min 1 and hold at this temperature for 2 h. After the nitriding reaction, the reactor was cooled down to room temperature under N2, and a mixture of 1% O2 in N2 was used to passivate the product for 2 h, which was called as passivated molybdenum nitride. The crystalline phase of alumina-supported molybdenum nitride was determined by X-ray diffraction (XRD) using packed powder method. The diffraction patterns were collected using a D/MAX-rA (Rigaku) diffractom˚ ). The tube volteter with CuKa radiation (k = 1.542 A age and current are 30 kV and 20 mA, respectively. Specific surface areas of the catalysts were evaluated by applying the BET method to the nitrogen adsorption isotherms measured at 77 K. Temperature programmed reduction (TPR) experiment was carried out in 10% H2 in Ar (by volume) with a flow rate of 30 ml/min and a temperature ramping rate of 10 K/min. TPR profiles were recorded with a thermal conductivity detector. The measurements of catalytic activities were carried out using an atmospheric pressure flow reactor. A gas chromatograph equipped with a flame ionization detector (FID) was used to analyze thiophene and hydrocarbon products. Catalyst samples (0.2 g) were loaded in the reactor. A stream of 2.8% thiophene in hydrogen flowed over the bed of catalyst. The major HDS products of C4 compounds were calibrated with analytical gas standards to facilitate conversion calculations.
0.345 0.231
0.381
(a)
0.326
0.238
(b) 0.209 0.201
20
30
40
0.148 0.145
50
60
70
o
2θ ( ) Fig. 1. XRD patterns of: (a) MoO3; (b) b-Mo2N0.78.
The XRD patterns of c-Al2O3 supported oxidized precursor MoO3 and different Mo loading catalysts are shown in Fig. 2. Besides the diffraction peaks of the c-Al2O3 support, the rest peaks are mainly from MoO3 (JCPDS, 35-609, d = 0.381, 0.345, 0.326, 0.231 nm) for oxidized precursor. For the supported nitridation sample with 10 wt% Mo loading, only diffraction peaks associated with the c-Al2O3 support are observed. At higher Mo loadings (P20 wt%), only three peaks of bMo2N0.78 (d = 0.238, 0.209, 0.148 nm) can be slightly distinguished. For all nitridation samples, the absence of diffraction peaks of oxide and other molybdenum compounds suggests that the precursors can be completely converted to b-Mo2N0.78 during nitridation. Some studies [12,13] also indicated that the diffraction
3. Results and discussion Fig. 1 shows the XRD pattern of the product from the reaction of MoO3 and N2–H2 mixture gases. The diffraction peaks at d = 0.238, 0.209, 0.201, 0.148, and 0.145 nm are from b-Mo2N0.78 (JCPDS, 25-1368), which can be assigned to the {1 1 1}, {2 0 0}, {0 0 2}, {2 2 0}, and {2 0 2} reflections, respectively. It can be seen that there is no other diffraction peak besides these of b-Mo2N0.78. So the product from our reaction is b-Mo2N0.78 and the nitridation is fairly complete.
Fig. 2. XRD patterns of MoO3 and b-Mo2N0.78/c-Al2O3 catalysts: (a) MoO3/c-Al2O3; Mo content (wt%); (b)10; (c) 20; (d) 30.
S. Gong et al. / Catalysis Communications 5 (2004) 621–624
peaks of c-Al2O3 supported c-Mo2N are very weak, and the presumable reason is c-Mo2N domains were too highly dispersed and broad peaks produced by support. The surface areas of the b-Mo2N0.78/c-Al2O3 samples with different Mo loadings are shown in Table 1. The surface area of catalyst has few variation when the Mo loading is low (610 wt%) or high ( P 20 wt%), but it decreases greatly when Mo loading changes from 10 to 20 wt%, which is presumably because that the c-Al2O3 support is fully covered by Mo species in the range of 10–20 wt%. In addition, c-Al2O3 is a effective support to produce high surface area nitride catalyst because the surface area of unsupported b-Mo2N0.78 is only 3 m2 g 1. The TPR profiles of bulk b-Mo2N0.78 and supported b-Mo2N0.78 are shown in Fig. 3. For the bulk passivated b-Mo2N0.78 sample, two hydrogen consumption peaks are observed: a low temperature peak around 700 K and a high temperature peak around 900 K. The TPR curve of the fresh sample (without passivation) does not display any peak in the low temperature region, which strongly suggests that the hydrogen consumption of passivated sample at low temperature is caused by the reduction of surface oxynitride species and/or surface
Table 1 The inference of Mo content on the BET surface area of catalyst Mo loadinga /wt%
Catalyst phaseb
SBET/m2 g
0 2 5 10 20 30 No support
c-Al2O3 c-Al2O3 c-Al2O3 c-Al2O3 b-Mo2N0.78/c-Al2O3 b-Mo2N0.78/c-Al2O3 b-Mo2 N0.78
160 145 144 142 128 125 3
1
a Mo loading was determined on the basis of the initial concentration of the ammonium heptamolybdate solution. b Catalyst phase determined by XRD patterns.
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molybdenum oxides created during passivation. Zhang et al. [14] also found passivated c-Mo2N presents reduction peaks in the ranges of 623–832 K and 923–1123 K. They attributed the hydrogen consumption peak between 623–832 K to the reduction of surface oxynitride species or oxides which formed during the passivating progress, and the high one to the reduction of bulk molybdenum nitride. For the supported catalysts, two reduction peaks are also observed for 30 wt% Mo loading catalyst, which are similar to these of bulk b-Mo2N0.78based on the peak location. It indicates that the supported catalysts exhibit the same reduction character of bulk b-Mo2N0.78. The activities of catalysts with different Mo loading at HDS reaction temperature of 633 K are shown in Fig. 4. The thiophene conversion increases with the increase of Mo loading between 2 and 20 wt%, but when the loading is 30 wt% the catalytic activity turns low. It indicates that there is a suitable molybdenum loading for supported b-Mo2N0.78 having high HDS activity. The study of Dolce et al. [15] also indicated that hydrotreatment (HDS, HDO, HDN) activities of supported c-Mo2N catalyst on the mass basis first increased with the increasing of molybdenum loading and then decreased when the loading increased further. The activities of the supported catalysts with loading of 2–30 wt% are all higher than that of unsupported catalyst, which may be due to the active sites highly disperse on the surface of c-Al2O3 support. Aegerter et al. [13] reported that the HDS activity (expressed as percent thiophene conversion) of c-Al2O3 supported c-Mo2N has similar activity with our synthesized b-Mo2N0.78/c-Al2O3. The TPR profile of catalyst with 20 wt% Mo loading after HDS reaction is shown in Fig. 5. The peak at 700 K shifts slightly and a new reduction peak at about 540 K appears. Compared with the TPR profile of molybde-
100 Mo loading(wt%) 20 2 30 5 no support 10
90
Thiophene conversion (%)
Intensity (Arbitrary Unit)
Fresh Passivated Supported(30wt%)
80 70 60 50 40 30 20
300
400
500
600 700 800 Temperature (K)
900
1000
Fig. 3. TPR profiles of bulk b-Mo2N0.78 and supported (30 wt%) b-Mo2N0.78 (passivated).
10 0
100
200
300
400
500
600
t/min Fig. 4. Influence of Mo content on the HDS activity of catalyst at 633 K.
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S. Gong et al. / Catalysis Communications 5 (2004) 621–624
Intensity (Arbitrary Unit)
2. In the range of 2–20 wt%, the activity of c-Al2O3 supported b-Mo2N0.78 catalyst increases with the increase of Mo loading, and there is a suitable Mo loading to get high HDS activity catalyst. 3. Although the bulk structure of catalyst is kept, sulfur replaces the surface oxygen of passivated nitride, which results in the new TPR peak of catalyst after HDS reaction. Before HDS After HDS Molybdenum sulfide
400
600 800 Temperature (K)
Acknowledgements 1000
We are grateful to the Shanxi Youth Foundation, P.R. China, Grant No. 20001014.
Fig. 5. TPR profiles of b-Mo2N0.78/c-Al2O3 (20 wt%) before and after HDS reaction.
References
num sulfide, the new peak can be attributed to the reduction of sulfided molybdenum nitride in HDS reaction. In our previous work [11] it was found that the bulk structure of unsupported b-Mo2N0.78 catalyst was kept after thiophene HDS at same condition. These facts indicate that sulfur replaces the surface oxygen of passivated nitride in the HDS condition.
4. Conclusions 1. The c-Al2O3 supported b-Mo2N0.78 catalyst is synthesized by temperature programmed reaction in N2–H2 mixture gases. XRD and TPR characterizations indicate that the relevant crystal phase and surface properties of catalyst are similar to the unsupported b-Mo2N0.78.
[1] M. Nagai, T. Miyao, T. Tuboi, Catal. Lett. 18 (1993) 9. [2] E.J. Markel, J.W. Van Zee, J. Catal. 126 (1990) 643. [3] J.-G. Choi, H.J. Brenner, C.W. Colling, et al., Catal. Today 15 (1992) 201. [4] E. Furimsky, Appl. Catal. A: General 240 (2003) 1. [5] D.T. Sajkowski, S.T. Oyama, Appl. Catal. A: General 134 (1996) 339. [6] J.A. Melo-Bana, J.M. Domı´nguez, G. Sandoval-Robles, Catal. Today 65 (2001) 279. [7] J. Trawczyn´ski, Catal. Today 65 (2001) 343. [8] R.S. Wise, E.J. Markel, J. Catal. 145 (1994) 344. [9] M. Nagai, Y. Goto, A. Miyata, et al., J. Catal. 182 (1999) 292. [10] K. Hada, J. Tanabe, S. Omi, et al., J. Catal. 207 (2002) 10. [11] S.W. Gong, H.K. Chen, W. Li, et al., Fuel Chem. Div. Prep. 48 (2003) 191. [12] K.R. McCrea, J.W. Logan, T.L. Tarbuck, et al., J. Catal. 171 (1997) 255. [13] P.A. Aegerter, W.W.C. Quigley, G.J. Simpson, et al., J. Catal. 164 (1996) 109. [14] Y.J. Zhang, Q. Xin, I. Rodriguez-Ramos, et al., Appl. Catal. A: General 180 (1999) 237. [15] G.M. Dolse, P.E. Savage, L.T. Thompson, Energy & Fuels 11 (1997) 668.
Thiophene hydrodesulfurization over alumina-supported b-Mo2N0.78 catalyst Shuwen Gong, Haokan Chen *, Wen Li, Baoqing Li State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, P.O.Box 165, Taiyuan, Shanxi 030001, PR China Received 16 April 2004; accepted 23 July 2004 Available online 1 September 2004
Abstract Alumina supported b-Mo2N0.78 catalyst was synthesized via temperature programmed reaction in the N2–H2 mixture gases. Catalyst properties were also investigated by X-ray diffraction (XRD), BET surface area and temperature programmed reduction (TPR) methods. The HDS activity of the catalyst was measured under different Mo loading. The HDS results indicated that there was a suitable Mo loading of b-Mo2N0.78/c-Al2O3 catalyst with high HDS activity. The TPR result suggested that sulfur replaced the surface oxygen of the passivated catalyst in the HDS reaction. 2004 Elsevier B.V. All rights reserved. Keywords: Thiophene; Hydrodesulfurization; b-Mo2N0.78
1. Introduction Catalytic hydroprocessing to remove heteroatoms such as sulfur, nitrogen, and oxygen from petroleum feedstock is a critical step in refining processing. To meet the goal of reducing sulfur emissions, increasing interest has recently been developed in exploring the catalytic properties of molybdenum nitrides and carbides for hydrodesulfurization (HDS) [1–4]. These studies have found that unsupported and supported Mo nitride catalysts have HDS activities similar to or higher than those of conventional sulfide catalysts. Sajkowski and Oyama [5] found that unsupported Mo2N was nearly twice as active as a commercial Ni–Mo/Al2O3 catalyst in HDS reaction. However, the majority of research was focused on the c-Mo2N (fcc) catalysts, which were prepared by temperature programmed reaction of Mo oxides with
*
Corresponding author. Tel.: +86 351 4048967; fax: +86 351 4048967/+86 351 404 1153. E-mail address: [email protected] (H. Chen). 1566-7367/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2004.07.012
NH3 [1–7] or N2–H2 [8]. Recently, some studies found that c-Mo2N transformed to b-Mo2N0.78 (tetragonal) when it was heated to 1123 K in He [9]. Hadas result showed that b-Mo2N0.78 also could form during temperature programmed reaction [10]. There is little relevant experimental data about the HDS behavior of bMo2N0.78 although its synthesis was reported. We recently synthesized bulk b-Mo2N0.78 via temperature programmed reaction of MoO3 and N2–H2 mixture gases, and found that b-Mo2N0.78 also had good HDS activity [11]. In this paper, c-Al2O3 supported bMo2N0.78 catalyst was synthesized by temperature programmed reaction and its HDS behavior was firstly studied with thiophene as the model compound.
2. Experimental Series of c-Al2O3 supported catalysts were prepared by the nitridation of supported molybdenum oxides, which was prepared by the calcine of molybdates. The
622
S. Gong et al. / Catalysis Communications 5 (2004) 621–624
molybdates were prepared by impregnation of c-Al2O3 with ammonium heptamolybdate ((NH4)6Mo7O24 Æ 4H2O) aqueous solution. The resulting molybdenum loading was determined on the basis of the initial concentration of the ammonium heptamolybdate solution. For catalysts with Mo loading greater than 10 wt%, multiple impregnations were needed. Following impregnation the catalysts were dried for 3 h at 383 K and then calcined for 5 h in air at 773 K. The oxidized precursor was packed on the center of a quartz tube reactor (15 mm ID · 20 mm OD · 60 cm). It was treated in N2–H2 mixture gases from room temperature to 573 K at a heating rate of 10 K min 1, from 573 to 773 K at 0.6 K min 1, then from 773 to 973 K at 2 K min 1 and hold at this temperature for 2 h. After the nitriding reaction, the reactor was cooled down to room temperature under N2, and a mixture of 1% O2 in N2 was used to passivate the product for 2 h, which was called as passivated molybdenum nitride. The crystalline phase of alumina-supported molybdenum nitride was determined by X-ray diffraction (XRD) using packed powder method. The diffraction patterns were collected using a D/MAX-rA (Rigaku) diffractom˚ ). The tube volteter with CuKa radiation (k = 1.542 A age and current are 30 kV and 20 mA, respectively. Specific surface areas of the catalysts were evaluated by applying the BET method to the nitrogen adsorption isotherms measured at 77 K. Temperature programmed reduction (TPR) experiment was carried out in 10% H2 in Ar (by volume) with a flow rate of 30 ml/min and a temperature ramping rate of 10 K/min. TPR profiles were recorded with a thermal conductivity detector. The measurements of catalytic activities were carried out using an atmospheric pressure flow reactor. A gas chromatograph equipped with a flame ionization detector (FID) was used to analyze thiophene and hydrocarbon products. Catalyst samples (0.2 g) were loaded in the reactor. A stream of 2.8% thiophene in hydrogen flowed over the bed of catalyst. The major HDS products of C4 compounds were calibrated with analytical gas standards to facilitate conversion calculations.
0.345 0.231
0.381
(a)
0.326
0.238
(b) 0.209 0.201
20
30
40
0.148 0.145
50
60
70
o
2θ ( ) Fig. 1. XRD patterns of: (a) MoO3; (b) b-Mo2N0.78.
The XRD patterns of c-Al2O3 supported oxidized precursor MoO3 and different Mo loading catalysts are shown in Fig. 2. Besides the diffraction peaks of the c-Al2O3 support, the rest peaks are mainly from MoO3 (JCPDS, 35-609, d = 0.381, 0.345, 0.326, 0.231 nm) for oxidized precursor. For the supported nitridation sample with 10 wt% Mo loading, only diffraction peaks associated with the c-Al2O3 support are observed. At higher Mo loadings (P20 wt%), only three peaks of bMo2N0.78 (d = 0.238, 0.209, 0.148 nm) can be slightly distinguished. For all nitridation samples, the absence of diffraction peaks of oxide and other molybdenum compounds suggests that the precursors can be completely converted to b-Mo2N0.78 during nitridation. Some studies [12,13] also indicated that the diffraction
3. Results and discussion Fig. 1 shows the XRD pattern of the product from the reaction of MoO3 and N2–H2 mixture gases. The diffraction peaks at d = 0.238, 0.209, 0.201, 0.148, and 0.145 nm are from b-Mo2N0.78 (JCPDS, 25-1368), which can be assigned to the {1 1 1}, {2 0 0}, {0 0 2}, {2 2 0}, and {2 0 2} reflections, respectively. It can be seen that there is no other diffraction peak besides these of b-Mo2N0.78. So the product from our reaction is b-Mo2N0.78 and the nitridation is fairly complete.
Fig. 2. XRD patterns of MoO3 and b-Mo2N0.78/c-Al2O3 catalysts: (a) MoO3/c-Al2O3; Mo content (wt%); (b)10; (c) 20; (d) 30.
S. Gong et al. / Catalysis Communications 5 (2004) 621–624
peaks of c-Al2O3 supported c-Mo2N are very weak, and the presumable reason is c-Mo2N domains were too highly dispersed and broad peaks produced by support. The surface areas of the b-Mo2N0.78/c-Al2O3 samples with different Mo loadings are shown in Table 1. The surface area of catalyst has few variation when the Mo loading is low (610 wt%) or high ( P 20 wt%), but it decreases greatly when Mo loading changes from 10 to 20 wt%, which is presumably because that the c-Al2O3 support is fully covered by Mo species in the range of 10–20 wt%. In addition, c-Al2O3 is a effective support to produce high surface area nitride catalyst because the surface area of unsupported b-Mo2N0.78 is only 3 m2 g 1. The TPR profiles of bulk b-Mo2N0.78 and supported b-Mo2N0.78 are shown in Fig. 3. For the bulk passivated b-Mo2N0.78 sample, two hydrogen consumption peaks are observed: a low temperature peak around 700 K and a high temperature peak around 900 K. The TPR curve of the fresh sample (without passivation) does not display any peak in the low temperature region, which strongly suggests that the hydrogen consumption of passivated sample at low temperature is caused by the reduction of surface oxynitride species and/or surface
Table 1 The inference of Mo content on the BET surface area of catalyst Mo loadinga /wt%
Catalyst phaseb
SBET/m2 g
0 2 5 10 20 30 No support
c-Al2O3 c-Al2O3 c-Al2O3 c-Al2O3 b-Mo2N0.78/c-Al2O3 b-Mo2N0.78/c-Al2O3 b-Mo2 N0.78
160 145 144 142 128 125 3
1
a Mo loading was determined on the basis of the initial concentration of the ammonium heptamolybdate solution. b Catalyst phase determined by XRD patterns.
623
molybdenum oxides created during passivation. Zhang et al. [14] also found passivated c-Mo2N presents reduction peaks in the ranges of 623–832 K and 923–1123 K. They attributed the hydrogen consumption peak between 623–832 K to the reduction of surface oxynitride species or oxides which formed during the passivating progress, and the high one to the reduction of bulk molybdenum nitride. For the supported catalysts, two reduction peaks are also observed for 30 wt% Mo loading catalyst, which are similar to these of bulk b-Mo2N0.78based on the peak location. It indicates that the supported catalysts exhibit the same reduction character of bulk b-Mo2N0.78. The activities of catalysts with different Mo loading at HDS reaction temperature of 633 K are shown in Fig. 4. The thiophene conversion increases with the increase of Mo loading between 2 and 20 wt%, but when the loading is 30 wt% the catalytic activity turns low. It indicates that there is a suitable molybdenum loading for supported b-Mo2N0.78 having high HDS activity. The study of Dolce et al. [15] also indicated that hydrotreatment (HDS, HDO, HDN) activities of supported c-Mo2N catalyst on the mass basis first increased with the increasing of molybdenum loading and then decreased when the loading increased further. The activities of the supported catalysts with loading of 2–30 wt% are all higher than that of unsupported catalyst, which may be due to the active sites highly disperse on the surface of c-Al2O3 support. Aegerter et al. [13] reported that the HDS activity (expressed as percent thiophene conversion) of c-Al2O3 supported c-Mo2N has similar activity with our synthesized b-Mo2N0.78/c-Al2O3. The TPR profile of catalyst with 20 wt% Mo loading after HDS reaction is shown in Fig. 5. The peak at 700 K shifts slightly and a new reduction peak at about 540 K appears. Compared with the TPR profile of molybde-
100 Mo loading(wt%) 20 2 30 5 no support 10
90
Thiophene conversion (%)
Intensity (Arbitrary Unit)
Fresh Passivated Supported(30wt%)
80 70 60 50 40 30 20
300
400
500
600 700 800 Temperature (K)
900
1000
Fig. 3. TPR profiles of bulk b-Mo2N0.78 and supported (30 wt%) b-Mo2N0.78 (passivated).
10 0
100
200
300
400
500
600
t/min Fig. 4. Influence of Mo content on the HDS activity of catalyst at 633 K.
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S. Gong et al. / Catalysis Communications 5 (2004) 621–624
Intensity (Arbitrary Unit)
2. In the range of 2–20 wt%, the activity of c-Al2O3 supported b-Mo2N0.78 catalyst increases with the increase of Mo loading, and there is a suitable Mo loading to get high HDS activity catalyst. 3. Although the bulk structure of catalyst is kept, sulfur replaces the surface oxygen of passivated nitride, which results in the new TPR peak of catalyst after HDS reaction. Before HDS After HDS Molybdenum sulfide
400
600 800 Temperature (K)
Acknowledgements 1000
We are grateful to the Shanxi Youth Foundation, P.R. China, Grant No. 20001014.
Fig. 5. TPR profiles of b-Mo2N0.78/c-Al2O3 (20 wt%) before and after HDS reaction.
References
num sulfide, the new peak can be attributed to the reduction of sulfided molybdenum nitride in HDS reaction. In our previous work [11] it was found that the bulk structure of unsupported b-Mo2N0.78 catalyst was kept after thiophene HDS at same condition. These facts indicate that sulfur replaces the surface oxygen of passivated nitride in the HDS condition.
4. Conclusions 1. The c-Al2O3 supported b-Mo2N0.78 catalyst is synthesized by temperature programmed reaction in N2–H2 mixture gases. XRD and TPR characterizations indicate that the relevant crystal phase and surface properties of catalyst are similar to the unsupported b-Mo2N0.78.
[1] M. Nagai, T. Miyao, T. Tuboi, Catal. Lett. 18 (1993) 9. [2] E.J. Markel, J.W. Van Zee, J. Catal. 126 (1990) 643. [3] J.-G. Choi, H.J. Brenner, C.W. Colling, et al., Catal. Today 15 (1992) 201. [4] E. Furimsky, Appl. Catal. A: General 240 (2003) 1. [5] D.T. Sajkowski, S.T. Oyama, Appl. Catal. A: General 134 (1996) 339. [6] J.A. Melo-Bana, J.M. Domı´nguez, G. Sandoval-Robles, Catal. Today 65 (2001) 279. [7] J. Trawczyn´ski, Catal. Today 65 (2001) 343. [8] R.S. Wise, E.J. Markel, J. Catal. 145 (1994) 344. [9] M. Nagai, Y. Goto, A. Miyata, et al., J. Catal. 182 (1999) 292. [10] K. Hada, J. Tanabe, S. Omi, et al., J. Catal. 207 (2002) 10. [11] S.W. Gong, H.K. Chen, W. Li, et al., Fuel Chem. Div. Prep. 48 (2003) 191. [12] K.R. McCrea, J.W. Logan, T.L. Tarbuck, et al., J. Catal. 171 (1997) 255. [13] P.A. Aegerter, W.W.C. Quigley, G.J. Simpson, et al., J. Catal. 164 (1996) 109. [14] Y.J. Zhang, Q. Xin, I. Rodriguez-Ramos, et al., Appl. Catal. A: General 180 (1999) 237. [15] G.M. Dolse, P.E. Savage, L.T. Thompson, Energy & Fuels 11 (1997) 668.