R. Khoshbin et al. / Materials Research Bulletin 48 (2013) 767–777
777
The reactions 8–14 in Table 3 (group B) were considered for the
methanol dehydration. It was reported that methanol was easily
decomposed to adsorbed CH3 and H2O species on the surface of
zeolite and then CH3OCH3 could be synthesized via combination of
CH3OH and CH3 groups under the acidic sites of the catalyst [42].
Water gas shift reaction also takes place on copper clusters.
There are several mechanisms for WGS reaction [43,44]. Here, two
sets of elementary reactions for the WGS reaction over Cu/ZnO
catalysts are listed (Table 3, group C: reactions 15–24). These
mechanisms are generally believed to be formate group or
regenerative. The first four reactions are common to all suggested
mechanisms: adsorption of reactants and desorption of products
plus. Reactions 19 and 20 describe the regenerative route consists
of surface oxidation of an oxygen vacant site by water vapor
followed with surface reduction by carbon monoxide. In another
mechanism, it is assumed that adsorbed intermediate (possibly a
formate species) is formed through reaction between carbon
monoxide and a hydroxyl species or water, which then decom-
poses to H2 and CO2. The hydroxyl intermediate is formed via
decomposition of water.
Nanotechnology Initiative Council for complementary financial
support.
References
[1] C. Arcoumanis, C. Bae, R. Crookes, E. Kinoshita, Fuel 87 (2008) 1014–1030.
[2] K.C. Tokay, T. Dogu, G. Dogu, Chem. Eng. J. 184 (2012) 278–285.
[3] J. Neutzler, G. Qian, K. Huang, B. Benicewicz, J. Power Sources 216 (2012) 471–474.
[4] C.A. Floudas, J.A. Elia, R.C. Baliban, Comput. Chem. Eng. 41 (2012) 24–51.
[5] R. Vakili, E. Pourazadi, P. Setoodeh, R. Eslamloueyan, M.R. Rahimpour, Appl. Eng.
88 (2011) 1211–1223.
[6] Z. Lei, Z. Zou, C. Dai, Q. Li, B. Chen, Chem. Eng. Sci. 66 (2011) 3195–3203.
[7] E. Leal, A.C.F. de Melo Costa, N.L. de Freita, H. de Lucena Lira, R.H.G.A. Kiminami, L.
Gama, Mater. Res. Bull. 46 (2011) 1409–1413.
[8] I.S. Ahmed, Mater. Res. Bull. 46 (2011) 2548–2553.
[9] Q. Zhang, Y. Tan, C. Yang, Y. Han, Catal. Commun. 9 (2008) 1916–1919.
[10] S.-T. Yang, J.-Y. Kim, H.-J. Chae, M. Kim, S.-Y. Jeong, W.-S. Ahn, Mater. Res. Bull. 47
(2012) 3888–3892.
[11] N.A. Khan, J.H. Park, S.H. Jhung, Mater. Res. Bull. 45 (2010) 377–381.
[12] S.D. Kim, S.C. Baek, Y.-J. Lee, K.-W. Jun, M.J. Kim, I.S. Yoo, Appl. Catal. A 309 (2006)
139–143.
[13] Z. Li, J. Li, C. Yang, J. Wu, J. Nat. Gas Chem. 21 (2012) 360–365.
[14] H. Jiang, H. Bongard, W. Schmidt, F. Schu¨th, Microporous Mesoporous Mater. 164
(2012) 3–8.
[15] M. Stiefel, R. Ahmad, U. Arnold, M. Do¨ring, Fuel Process. Technol. 92 (2011) 1466–
1474.
[16] A. Venugopal, J. Palgunadi, J.K. Deog, O.-S. Joo, C.-H. Shin, J. Mol. Catal. A: Chem.
302 (2009) 20–27.
4. Conclusions
During HNO3-treatment, the specific surface area of natural
zeolite increased obviously. On the other hand, crystallinity of the
clinoptilolite decreased. Furthermore, the FESEM analysis indicat-
ed that with the modification of zeolite, the morphology of the
clinoptilolite changed from the leaf-like to the needle-like.
Moreover, with increasing of CZA/clinoptilolite ratio, the specific
surface area decreased and the whole surface of the zeolite was
completely covered. The NH3-TPD profiles showed that both the
number and strength of the acid sites of the CZA/clinoptilolite
nanocatalysts decreased with increasing CZA content.
[17] J. Fei, Z. Hou, B. Zhu, H. Lou, X. Zheng, Appl. Catal. A 304 (2006) 49–54.
[18] J.-H. Kim, M.J. Park, S.J. Kim, O.-S. Joo, K.-D. Jung, Appl. Catal. A 264 (2004) 37–41.
[19] D. Mao, W. Yang, J. Xia, B. Zhang, G. Lu, J. Mol. Catal. A: Chem. 250 (2006) 138–144.
[20] W. Mozgawa, M. Kro´l, W. Picho´r, J. Hazard. Mater. 168 (2009) 1482–1489.
[21] H. Faghihian, M. Kabiri-Tadi, J. Hazard. Mater. 178 (2010) 66–73.
[22] M.K. Doula, A. Dimirkou, J. Hazard. Mater. 151 (2008) 738–745.
[23] Y. Wang, S. Liu, Z. Xu, T. Han, S. Chuan, T. Zhu, J. Hazard. Mater. 136 (2006) 735–
740.
[24] F. Cakicioglu-Ozkan, S. Ulku, Microporous Mesoporous Mater. 77 (2005) 47–53.
[25] E. Ivanova, B. Koumanova, J. Hazard. Mater. 167 (2009) 306–312.
[26] M. Sprynskyy, T. Ligor, M. Lebedynets, B. Buszewski, J. Hazard. Mater. 169 (2009)
847–854.
[27] W. Nimwattanakul, A. Luengnaruemitchai, S. Jitkarnka, IJHE 31 (2006) 93–100.
¨
[28] Z. Ozc¸elik, G.S.P. Soylu, I. Boz, Chem. Eng. J. 155 (2009) 94–100.
These results indicated that the optimum value for the
composition of CZA/clinoptilolite nanocatalysts depends on the
temperature range and at high temperatures region, the optimum
weight ratio for CZA/clinoptilolite has been found to be about 4:1.
The influence of reaction temperature and pressure was investi-
gated in detail. According to these results, the optimal reaction
temperature and pressure for this catalyst was 300 8C and 40 bar,
respectively. The results from durability tests indicate that
catalytic stability during reaction is receivable. In order to gain
a more complete understanding on the effect of modification of
clinoptilolite on its acidic properties and on performance of
clinoptilolite based nanocatalysts in the STD process, a thorough
study is necessary. It requires synthesizing different catalysts with
variable modifier such as HCl and NH4Cl, which are considered for
the future work.
[29] S.J. Royaee, C. Falamaki, M. Sohrabi, S.S. Ashraf Talesh, Appl. Catal. A 338 (2008)
114–120.
[30] K. Gedik, I. Imamoglu, J. Hazard. Mater. 155 (2008) 385–392.
[31] L. Wang, D. Fang, X. Huang, S. Zhang, Y. Qi, Z. Liu, J. Nat. Gas Chem. 15 (2006)
38–44.
[32] O. Korkuna, R. Leboda, J. Skubiszewska-Zie¸ba, T. Vrublevs’ka, V.M. Gun’ko, J.
Ryczkowski, Microporous Mesoporous Mater. 87 (2006) 243–254.
[33] D. Humelnicu, M.V. Dinu, E.S. Dragan, J. Hazard. Mater. 185 (2011) 447–455.
[34] M. Sprynskyy, T. Ligor, B. Buszewski, J. Hazard. Mater. 151 (2008) 570–577.
[35] H. Faghihian, M. Kabiri-Tadi, J. Hazard. Mater. 178 (2010) 66–73.
[36] L. Chen, L. Li, G. Li, J. Alloys Compd. 464 (2008) 532–536.
[37] K.H. Harold, Catal. Today 11 (1992) 443–453.
[38] K. Nishida, I. Atake, D. Li, T. Shishido, Y. Oumi, T. Sano, K. Takehira, Appl. Catal. A
337 (2008) 48–57.
[39] A.T. Aguayo, J. Eren˜a, I. Sierra, M. Olazar, J. Bilbao, Catal. Today 106 (2005)
265–270.
[40] K. Sun, W. Lu, F. Qiu, S. Liu, X. Xu, Appl. Catal. A 252 (2003) 243–249.
[41] Q. Sun, C.-W. Liu, W. Pan, Q.-M. Zhu, J.-F. Deng, Appl. Catal. A 171 (1998) 301–308.
[42] W.-Z. Lu, L.-H. Teng, W.-D. Xiao, Chem. Eng. Sci. 59 (2004) 5455–5464.
[43] R. Kam, C. Selomulya, R. Amal, J. Scott, J. Catal. 273 (2010) 73–81.
[44] C. Fukuhara, H. Ohkura, K. Gonohe, A. Igarashi, Appl. Catal. A 279 (2005) 195–203.
[45] J.-H. Fei, M.-X. Yang, Z.-Y. Hou, X.-M. Zheng, Energy Fuels 18 (2004) 1584–1587.
[46] R. Kam, J. Scott, R. Amal, C. Selomulya, Chem. Eng. Sci. 65 (2010) 6461–6470.
[47] G.D. Sizgek, H.E. Curry-Hyde, M.S. Wainwright, Appl. Catal. A 115 (1994)
15–28.
Acknowledgments
The authors gratefully acknowledge Sahand University of
Technology for the financial support of the project as well as Iran