JOURNAL OF FUEL CHEMISTRY AND TECHNOLOGY

Volume 41, Issue 12, Dec 2013 Online English edition of the Chinese language journal

Received: 23-Jul-2013; Revised: 28-Sep-2013 * Corresponding author. SUN Cheng-lin, Tel: 0411-84379133, E-mail: clsun@dicp.ac.cn; QIU Jie-shan, Tel: 0411-84986080, E-mail: jqiu@dlut.edu.cn. Copyright 2013, Institute of Coal Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved.

RESEARCH PAPERCite this article as: J Fuel Chem Technol, 2013, 41(12), 14811487

Effect of alumina support on the performance of Pt-Sn-K/-Al2O3 catalyst in the dehydrogenation of isobutane LUO Sha1,2,3, WU Nan4, ZHOU Bo2, HE Song-bo2, QIU Jie-shan1,*, SUN Cheng-lin2,* 1State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116012, China; 2Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China; 3University of Chinese Academy of Sciences, Beijing 100049, China; 4School of Applied Chemistry, Shenyang University of Chemical Technology, Shenyang 110142, China

Abstract: Alumina supports were synthesized by hydrochloric acid reflux and ammonia precipitation methods; after that the

Pt-Sn-K/γ-Al2O3 catalysts were prepared by complex impregnation method under vacuum with alumina of different sources as the

supports. The catalysts were characterized by N2 physisorption, CO pulse chemisorption, H2 temperature-programmed reduction, NH3

temperature-programmed desorption and thermogravimetric analysis; the effect of the alumina support on the performance of

Pt-Sn-K/γ-Al2O3 catalysts in the dehydrogenation of isobutane was investigated. Compared with the catalyst supported on Al2O3 from

hydrochloric acid reflux, the catalyst supported on the Al2O3 from ammonia precipitation is provided with smaller platinum particle

size and weaker acidic distribution, and then exhibits higher activity and selectivity to isobutene in isobutane dehydrogenation.

Moreover, the catalyst with Al2O3 synthesized by ammonia precipitation as the support exhibits better resistance against coke

deposition and the coke deposited also has a lower degree of graphitization, which endues the catalyst with better stability. During a

long term test of 14 d over the catalyst with Al2O3 synthesized by ammonia precipitation as the support, the conversion of isobutane is

initially 56.67% and then decreased to 34.71% after 14 d; meanwhile, the initial selectivity to isobutene is 80% and it remains

approximate 94% after 7 d.

Key words: alumina; Pt-Sn-K/γ-Al2O3; isobutane; dehydrogenation; hydrochloric acid reflux; ammonia precipitation.

Isobutene as an important chemical is widely used to produce methyl tertiary butyl ether (MTBE), butyl rubber, polyisobutylene, methacrylate, isoprene, tert-butylphenol, tert-butylamine, 1,4-butanediol, ABS resin, and so on[1]. The supply of isobutene cannot meet the increasing demand from the world market due to the rapid development of isobutene downstream products and the lack of new isobutene sources. Isobutene is mainly obtained from the by-products of naphtha steam cracking and fluid catalytic cracking. In recent years, many researchers have focused on the development of efficient catalysts for isobutane dehydrogenation to produce isobutene[2] and bimetallic Pt-Sn/γ-Al2O3 catalysts have been successfully employed in the industrial process. However, undesirable reactions such as hydrogenolysis and cracking can lead to a significant decrease of the selectivity to isobutene product. In addition, the catalysts are rapidly deactivated by

the coke deposition and Pt sintering. To solve these problems, the addition of certain promoters

such as alkaline[3,4], alkaline-earth[5], transition[6] and rare-earth metals[7,8] is used to improve the performance of Pt-Sn/γ-Al2O3 catalysts. Duan et al[9] investigated the effect of the aluminum modification on the performance of Pt-Sn/SBA-15 catalysts in propane dehydrogenation. Qiu et al[10] studied the effect of the support composition on the properties of Pt-Sn/ZSM-5 catalysts in propane dehydrogenation. He et al[11] reported the effect of the alumina supports on the performance of Pt-Sn-K/γ-Al2O3 catalysts in long chain paraffin dehydrogenation; however, the effect of the alumina supports on the catalyst performance in the dehydrogenation of low paraffins has not been considered.

In this work, alumina supports were synthesized by

LUO Sha et al / Journal of Fuel Chemistry and Technology, 2013, 41(12): 14811487

hydrochloric acid reflux and ammonia precipitation methods, which were used to prepare the Pt-Sn-K/γ-Al2O3 catalysts by complex impregnation method under vacuum. The effect of the alumina support on the performance of Pt-Sn-K/γ-Al2O3 catalysts in the dehydrogenation of isobutane was investigated. 1 Experimental 1.1 Preparation of different alumina supports

Three kinds of alumina supports were used in this work.

Among them, Al2O3-A is a commercial alumina support, which was used in this work for reference.

Al2O3-B support is synthesized by hydrochloric acid reflux method. Aluminum foil (99.99%, 30 g) and hydrochloric acid (11%, 230 g) were mixed under a rotating rate of 50 r/min and slowly heated to 95°C; when the aluminum foil began to dissolve, the rotating rate was adjusted to 200 r/min. The alumina sol was obtained until the aluminum foil was completely dissolved. Hexamethylene tetramine solution (40%, 24 g) was then added to the above alumina sol (70 g).

After being well mixed, the mixture was dropped into the oil column. The alumina spheres were then aged at 126°C for 17 h in an autoclave, which were further treated by drying and calcining processes.

Al2O3-C support is synthesized by ammonia precipitation method. Ammonia (6%) was dropped into aluminum chloride solution (40 g·L–1, 1 L) at 70°C and 340 r/min until the pH value reached 8. The precipitation reaction lasted for 1 h and the precipitate was then subjected to aging, washing and filtering. The wet cake (100 g) obtained and nitric acid (13.5%, 13 g) were then mixed and stirred until it was completely dissolved. Hexamethylene tetramine solution (40%, 17 g) was then added. After being well mixed, the mixture was dropped into the oil column; after that, the alumina support was further treated by aging, drying and calcination. 1.2 Preparation of Pt-Sn-K/-Al2O3 catalysts

Pt-Sn-K/γ-Al2O3 catalysts were prepared by the vacuum

complex impregnation method[12]. Before impregnation, the alumina supports were degassed for 30 min to remove any impurities adsorbed.

Fig. 1 Isobutane conversion (a) and isobutene selectivity (b) during the dehydrogenation of isobutane over the Pt-Sn-K/γ-Al2O3 catalysts

Fig. 2 Isobutane conversion (a) and isobutene selectivity (b) during the dehydrogenation of isobutane over the Pt-Sn-K/γ-Al2O3 catalysts

LUO Sha et al / Journal of Fuel Chemistry and Technology, 2013, 41(12): 14811487

The alumina supports were then impregnated in the solution containing H2PtCl6, HCl, SnCl2 and KCl; the mixture was kept gently stirred for 30 min. Depending on the alumina supports of Al2O3-A, Al2O3-B, and Al2O3-C used, the catalysts obtained are designated as cat-A, cat-B and cat-C, respectively. All the catalysts have the same composition, i.e. 0.5% Pt, 1.5% Sn and 0.5% K.

1.3 Isobutane dehydrogenation reaction

The isobutane dehydrogenation reaction was performed in a quartz tubular fixed bed micro-catalytic reactor. 0.628 mL of the fresh catalysts (20–40 mesh) were charged to the reactor. Prior to the dehydrogenation reaction, the catalysts were heated to 580°C and reduced in situ in flowing H2 for 2 h. After that, the dehydrogenation was carried out at 580°C, atmospheric pressure, a weight hourly space velocity (WHSV) of 2 h–1 for isobutane, and a hydrogen/isobutane volume ratio of 1.

The products were analyzed by an on-line gas chromatograph (Agilent 7890A, American) equipped with a flame ionization detector (FID) using a HP-Al/KCl column. The gas chromatograph was operated under an inlet temperature of 180°C, an oven temperature of 105°C and detector temperature of 200°C.

The catalytic stability is expressed by the deactivation percentage (D), which is calculated by the equation,

D =[(x0–x)/x0]×100% (1) where x0 is the initial conversion and x is the final

conversion after reaction for certain time. The selectivity to isobutene (s) is defined as the fraction of

isobutene in total products, which is calculated by the equation,

s = (ciso/ctotal)×100% (2) where ciso is the isobutene concentration and ctotal is the total

concentration of products. 1.4 Characterization of different supports and catalysts

The special surface area of the catalyst and support samples

was determined by the adsorption isotherms of nitrogen at 77 K on a volumetric adsorption system (Quantachrome Autosorb-1, American). All samples were pretreated at 300°C for 2 h before measurements.

The reducibility of the catalysts was analyzed through

temperature-programmed reduction by hydrogen (H2-TPR, Micromeritics AutoChem II 2920, American). Prior to the measurement, the samples were pretreated in Ar (99.99%, 20 mL·min–1) at 600°C for 1 h. After cooling to 50°C in Ar, the gas flow was switched to 10% H2 in Ar and the samples were heated to 600°C with a temperature ramp of 10°C·min–1. The hydrogen consumption during TPR was determined by a thermal conductivity detector (TCD).

The particle sizes of Pt in the catalysts were measured by CO pulse chemisorption (Micromeritics AutoChem II 2920, American). The catalyst samples were reduced in H2 (99.99%, 20 mL·min–1) at 600°C for 1 h, purged with He (99.99%, 20 mL·min–1) at 600°C for 1 h and then cooled down to 50°C. The gas mixture of 5% CO in He were introduced into the reactor in pulses of 0.1 cm3 until saturated adsorption is achieved. The CO pulse signal was determined by TCD and the corresponding Pt particle size was calculated based on the CO adsorption amounts.

The acidic properties of the catalysts were analyzed by temperature-programmed desorption of ammonia (NH3-TPD, Micromeritics AutoChem II 2920, American). The samples were pretreated in He (99.99%, 20 mL·min–1) at 600°C for 1 h. After cooling down to 100°C, NH3 (99.96%) was adsorbed and then the catalysts were purged with He for 1 h. NH3-TPD was then performed at a temperature ramp of 10°C·min–1 until 600°C and the desorbed ammonia were detected by TCD.

The coke content of the used catalysts were measured by a thermogravimetric (TG) analysis instrument (TA Q600, American) from room temperature to 800°C at a heating rate of 10°C·min–1 in an air flow of 50 mL·min–1. 2 Results and discussion 2.1 Dehydrogenation performance of different catalysts

The conversions of isobutane and selectivities to isobutene

for isobutane dehydrogenation over various catalysts from different alumina supports during the tests of 7 d are depicted in Figure 1. The initial isobutane conversions over cat-A, cat-B and cat-C were 53.96%, 58.40% and 56.67%, respectively; after reaction for 7 d, they were decreased to 23.81%, 49.30% and 49.24%, respectively, corresponding to the deactivation percentages of 55.87%, 15.58% and 13.11%, respectively.

Table 1 Textural properties of the alumina supports

Support ABET/(m2·g–1) Vtotal/(cm3·g–1) dpore/nm

Al2O3-A 150.62 1.18 31.44

Al2O3-B 152.95 0.89 23.40

Al2O3-C 153.14 0.55 14.39

LUO Sha et al / Journal of Fuel Chemistry and Technology, 2013, 41(12): 14811487

Fig. 3 Physical adsorption-desorption isotherms of nitrogen on the

alumina supports

Such a result indicates that the catalyst (cat-A) with the

commercial alumina as support is very poor in terms of the stability, while the activities of the catalysts with the alumina supports prepared either by hydrochloric acid reflux (cat-B) or by ammonia precipitation (cat-C) are relatively much more stable.

The catalyst (cat-A) with the commercial alumina as support exhibits the highest initial selectivity to isobutene (86.84%). Although the initial selectivities to isobutene over the catalysts with the alumina supports prepared by hydrochloric acid reflux (cat-B) and ammonia precipitation (cat-C) are much lower (74.67% and 79.99%, respectively), with the prolongation of the reaction time, they are increased gradually and tend to be the same value as that over the catalyst (cat-A) with the commercial alumina as support after reaction for 7 d (93.5%). The average selectivities to isobutene over cat-A, cat-B and cat-C during the 7 d tests are 93.75%, 90.38% and 90.88%, respectively.

Figure 1 shows the conversions of isobutane and selectivities to isobutene for isobutane dehydrogenation over various catalysts (cat-B and cat-C) from different alumina supports (Al2O3-B and Al2O3-C) during the tests of 14 d. After 14 d on stream, the conversions of isobutane over cat-B and cat-C are decreased to 29.89% and 34.71%, respectively, corresponding to the deactivation percentages during the period of 7–14 d on stream are 39.37% and 29.51%, respectively. Such a result suggests that the catalyst (cat-C) with the alumina from ammonia precipitation as the support is superior to the catalyst (cat-B) supported on alumina from hydrochloric acid reflux in terms of activity and stability in the last 7 d tests. Meanwhile, the selectivities to isobutene over both catalysts are maintained at the same high level (ca. 94%) in the last 7 d tests.

2.2 Textural properties

The specific surface areas, total pore volumes and average

pore sizes of different supports determined from the adsorption isotherms of nitrogen are listed in Table 1. The three supports are almost identical in the specific surface area, but quite different in the total pore volume and average pore size. The total pore volume and average pore size of the commercial alumina are 1.18 cm3·g–1 and 31.44 nm, respectively; comparatively, the total pore volumes and average pore sizes of the supports prepared by hydrochloric acid reflux and ammonia precipitation methods are obviously much smaller. Al2O3-C has the smallest total pore volume (0.55 cm3·g–1) and average pore size (14.39 nm).

The total pore volume of the supports were dependent mainly on the pores larger than 10 nm[13], while the pores with smaller pore size played a decisive role in determining the specific surface area[14]. Compared with Al2O3-B and Al2O3-C, it can be speculated that Al2O3-A may have abundant small pores and the large pores in Al2O3-A may also be in larger size. Small pore structure is unfavorable for the migration of the coke deposited on the active sites to acidic sites. Hence, the stability of the catalyst supported on the commercial alumina is much poorer than that of the catalysts supported on other carriers prepared by hydrochloric acid reflux and ammonia precipitation methods. More detailed analysis for larger pores should be made by mercury intrusion method due to limitations of the BET method, which is here however not discussed.

Figure 3 shows the nitrogen physical adsorption-desorption isotherms of three supports. According to the IUPAC classification[15], the adsorption isotherms for all supports were of type IV. The adsorption isotherm of Al2O3-A does not display saturated adsorption at higher relative pressure (characteristics of H3 hysteresis loops), which are related to the slit-shaped pore structure. The hysteresis loops for Al2O3-B is vertical and parallel in a wide range (characteristics of type H1), which are related to the mesoporous or macroporous materials of cylindrical channels with a narrow pore size distribution.

Fig. 4 H2-TPR profiles of the catalysts

LUO Sha et al / Journal of Fuel Chemistry and Technology, 2013, 41(12): 14811487

Fig. 5 NH3-TPD profiles of the catalysts

Generally, such supports are composed of uniform spherical

particles. The adsorption isotherm for Al2O3-C shows the characteristics of H2 hysteresis loops, which are related to the ink-bottle pore structure. The network structure of such pores is usually relatively independent, and the boundary of pore size distribution and porous shape are not so distinct.

2.3 H2-TPR

The H2-TPR profiles of different catalysts are depicted in

Figure 4. All catalysts exhibit two reduction peaks; the peaks located at 220–300°C and 300–350°C are attributed to the reduction of PtOx and catalytic reduction of SnO2, respectively[16]. The first reduction peak of cat-C is approximately 20°C lower than that of cat-A and cat-B (280°C), indicating that the interaction of Pt with Al2O3-C is weaker than that of Pt with other two supports. However, the second reduction peak of cat-C is more intense, approximately 40°C higher than that of cat-A and cat-B (350°C), suggesting that the interaction of Pt with SnOx on cat-C is weaker than that on cat-A and cat-B. Hence, Sn4+ is more easily reduced to Sn0 on cat-A and cat-B, possibly with formation of the Pt-Sn alloy[17], which may also be concerned with their poor activity and stability compared with cat-C. 2.4 CO pulse chemisorption

As determined from CO pulse chemisorption, the Pt particle

sizes in cat-A, cat-B and cat-C are 7.26, 4.46 and 4.24 nm, respectively. Cat-A exhibits much larger Pt particle size,

which may be ascribed to the abundant micropores in Al2O3-A. The dehydrogenation reaction might take place on the small Pt clusters on the catalyst surface[18], and therefore, the Pt particle size has a significant influence on the dehydrogenation activity of Pt-Sn-K/Al2O3 catalysts. The better activity of cat-B and cat-C should then be attributed to the smaller Pt particles present on their surface.

2.5 NH3-TPD

The NH3-TPD profiles of different catalysts are shown in

Figure 5. All three catalysts exhibit a desorption peak around 160°C with a broad shoulder at 250–400°C. A semi-quantitative comparison of the acidic strength distribution is achieved by the deconvolution of the NH3-TPD profiles using the Gaussian method. The deconvoluted peaks are plotted as dashed lines in Figure 5 and the multi-peak fitting results are collected in Table 2.

The desorption peaks at 120–250°C, 250–350°C and 350–450°C should be attributed to the weak, medium and strong acidic centers, respectively[19]. Hence, it can be inferred that the acidic sites in all catalysts are weak-medium ones. According to the total desorption peak area, the total acid content in different catalysts is in the order of cat-C > cat-B > cat-A. The acidic centers on the catalyst surface may promote the activation of isobutane, but inhibit the desorption of isobutene. The side reactions such as cracking and coking takes place easily on the acidic sites of Pt-Sn/Al2O3 catalysts, especially on the medium-strong acidic sites. Therefore, cat-A gives the better selectivity to isobutene than other two catalysts because of its low total acid content and weak acidic strength. In addition, cat-B has poorer stability and selectivity to isobutene than cat-C, despite the lower total acid content on cat-B, which should be ascribed to the higher proportion of medium acidic sites on cat-B than that on cat-C. 2.6 TG-DTG

The TG curves of different deactivated catalysts (cat-A,

after reaction for 7 d; cat-B and cat-C, after reaction for 14 d) are depicted in Figure 6. The weight losses above 300°C are attributed to the combustion of coke deposited on the catalysts.

Table 2 Fitted results of NH3-TPD experiments of the catalysts

Catalyst tM/°C

Total area /(a.u.) Peak fraction /%

Fitted parameters R2 I II III I II III

Cat-A 157 196 303 29.51 23 19 58 0.991 0

Cat-B 157 191 308 31.04 19 17 64 0.992 1

Cat-C 166 213 325 38.05 24 25 51 0.991 3

LUO Sha et al / Journal of Fuel Chemistry and Technology, 2013, 41(12): 14811487

Fig. 6 TG profiles of the deactivated catalysts

Figure 6 illustrates that the contents of coke deposited on

cat-A (7 d on stream), cat-B and cat-C (14 d on stream) are 12.46%, 17.63% and 16.41%, respectively. The catalyst (cat-C) prepared with alumina support from ammonia precipitation has better resistance against coke deposition than the catalyst (cat-B) supported on the alumina obtained from hydrochloric acid reflux; however, both cat-B and cat-C have larger amounts of coke deposited than the catalyst (cat-A) prepared from the commercial alumina support.

The DTG curves of different deactivated catalysts are plotted in Figure 7. The coke oxidation zone at lower temperature (350–450°C) was attributed to the coke deposited on or around the Pt particles, while the oxidation zone at higher temperature (450–550°C) was related to the coke deposited on the support, which was composed of polymerized carbon species with high graphitization degree[20]. In Figure 7, all the deactivated catalysts display a broad combustion peak between 375 and 550°C. The combustion peak of coke deposited on the Pt particles is not obvious, as the Pt centers may be fully covered by the large amounts of coke deposited on the catalyst surface, possibly in multi-layers. The catalytic combustion of coke occurs when the upper-layer coke is burned off.

On the other hand, the deposited coke oxidized at higher temperature has high degree of graphitization[21]; the graphitization degrees of the cokes deposited on various catalysts are in the order of cat-A < cat-C < cat-B. The amounts and properties of coke deposited on the catalysts are related to their total acid content and acidic strength distribution. With the prolongation of the dehydrogenation reaction, the amount of coke deposited on the catalysts is gradually increased. Part of coke is deposited on the active centers, which leads to a decrease of the catalytic activity; other part of coke is located on the acidic centers, which is of benefit to improving the selectivity to isobutene.

3 Conclusions

Fig. 7 DTG profiles of the deactivated catalysts

Alumina supports were synthesized by hydrochloric acid

reflux and ammonia precipitation methods; after that the Pt-Sn-K/γ-Al2O3 catalysts were prepared by complex impregnation method under vacuum with alumina of various sources as the supports. The effect of the alumina support on the performance of Pt-Sn-K/γ-Al2O3 catalysts in the dehydrogenation of isobutane was investigated.

The catalyst with the commercial alumina as support is very poor in terms of the stability, which is rapidly deactivated during the 7 d test of isobutane dehydrogenation, while the activities of the catalysts with the alumina supports prepared either by hydrochloric acid reflux or by ammonia precipitation are much more stable.

Compared with the catalyst supported on Al2O3 from hydrochloric acid reflux, the catalyst supported on the Al2O3 from ammonia precipitation is provided with smaller platinum particle size and weaker acidic distribution, and then exhibits higher activity and selectivity to isobutene in isobutane dehydrogenation. Moreover, the catalyst with Al2O3 synthesized by ammonia precipitation as the support exhibits better resistance against coke deposition and the coke deposited also has a lower degree of graphitization, which endues the catalyst with better stability.

During a long term test of 14 d over the catalyst with Al2O3 synthesized by ammonia precipitation as the support, the conversion of isobutane is initially 56.67% and then decreased to 34.71% after reaction for 14 d; meanwhile, the initial selectivity to isobutene is 80% and it remains approximate 94% after reaction for 7 d. References

[1] Li L, Yan Z F. Review of catalytic dehydrogenation of isobutene.

Progress in Chemistry, 2005, 17(4): 651–659.

[2] Zhang M J, Yan Z F. Review of isobutane dehydrogenation

catalysts. Petrochemical Technology, 2004, 33(4): 377–381.

[3] Duan Y Z, Zhou Y M, Zhang Y W, Sheng X L, Xue M W. Effect

of sodium addition to PtSn/AlSBA-15 on the catalytic properties

LUO Sha et al / Journal of Fuel Chemistry and Technology, 2013, 41(12): 14811487

in propane dehydrogenation. Catal Lett, 2011, 141(1): 120–127.

[4] Tasbihi M, Feyzi F, Amlashi M A, Abdullah A Z, Mohamed A R.

Effect of the addition of potassium and lithium in Pt-Sn/Al2O3

catalysts for the dehydrogenation of isobutene. Fuel Process

Technol, 2007, 88(9): 883–889.

[5] Zhang Y W, Zhou Y M, Wan L H, Xue M W, Duan Y Z, Liu X.

Effect of magnesium addition on catalytic performance of

PtSnK/γ-Al2O3 catalyst for isobutane dehydrogenation. Fuel

Process Technol, 2011, 92(8): 1632–1638.

[6] Zhang Y W, Zhou Y M, Shi J J, Sheng X L, Duan Y Z, Zhou S J,

Zhang Z W. Effect of zinc addition on catalytic properties of

PtSnK/γ-Al2O3 catalyst for isobutane dehydrogenation. Fuel

Process Technol, 2012, 96: 220–227.

[7] Xue M W, Zhou Y M, Zhang Y W, Liu X, Duan Y Z, Sheng X L.

Effect of cerium addition on catalytic performance of

PtSnNa/ZSM-5 catalyst for propane dehydrogenation. J Nat Gas

Chem, 2012, 21(3): 324–331.

[8] Wan L H, Zhou Y M, Zhang Y W, Duan Y Z, Liu X, Xue M W.

Influence of lanthanum addition on catalytic properties of

PtSnK/Al2O3 catalyst for isobutane dehydrogenation. Ind Eng

Chem Res, 2011, 50(8): 4280–4285.

[9] Duan Y Z, Zhou Y M, Zhang Y W, Sheng X L, Zhou S J, Zhang

Z W. Effect of aluminum modification on catalytic properties of

PtSn-based catalysts supported on SBA-15 for propane

dehydrogenation. J Nat Gas Chem, 2012, 21(2): 207–214.

[10] Qiu A D, Li E X, Fan Y N. Effect of support composition on

catalytic performance of PtSn/ZSM-5 catalyst for propane

dehydrogenation. Chinese Journal of Catalysis, 2007, 28(11):

970–974.

[11] He S B, Sun C L, Bai Z W, Dai X H, Wang B. Dehydrogenation

of long chain paraffins over supported Pt-Sn-K/Al2O3 catalysts:

A study of the alumina support effect. Appl Catal A: Gen, 2009,

356(1): 88–98.

[12] Sun C L, Dai X H, He S B, Wang B, Du H Z, Bai Z W, Yang X,

Duan X, Zhao L, Zhang L, Guo Q. A kind of catalyst for the

dehydrogenation of long-chain normal paraffins(C16-C19) and

its preparation method: CN, 200810117891.3. 2011-12-07.

[13] Sharma L D, Kumar M, Saxena A K, Chand M, Gupta J K.

Influence of pore size distribution on Pt dispersion in

Pt-Sn/Al2O3 reforming catalysts. J Mol Catal A: Chem, 2002,

185(1/2): 135–141.

[14] He S B. Studies on the catalysts and the coke deposition

behavior of the dehydrogenation of long chain

paraffins(C10-C19). Dalian: Dalian Institute of Chemical

Physics, Chinese Academy of Sciences, 2009.

[15] Sing K S W, Everett D H, Haul R A W, Moscou L, Pierotti R A,

Rouquérol J, Siemieniewska T. Reporting physisorption data for

gas/solid systems with special reference to the determination of

surface area and porosity. Pure Appl Chem, 1985, 57(4):

603–619.

[16] Carvalho L S, Pieck C L, Rangel M C, Fígoli N S, Grau J M,

Reyes P, Parera J M. Trimetallic naphtha reforming catalysts. I.

Properties of the metal function and influence of the order of

addition of the metal precursors on Pt-Re-Sn/γ-Al2O3-Cl. Appl

Catal A: Gen, 2004, 269(1/2): 91–103.

[17] Dautzenberg F M, Helle J N, Biloen P, Sachtler W. Conversion

of n-hexane over monofunctional supported and unsupported

PtSn catalysts. J Catal, 1980, 63(1): 119–128.

[18] Biloen P, Dautzenberg F M, Sachtler W M H. Catalytic

dehydrogenation of propane to propene over platinum and

platinum-gold alloys. J Catal, 1977, 50(1): 77–86.

[19] Narayanan S, Sultana A, Le Q T, Auroux A. A comparative and

multitechnical approach to the acid character of templated and

non-templated ZSM-5 zeolites. Appl Catal A: Gen, 1998, 168(2):

373–384.

[20] Afonso J C, Schmal M, Fréty R. The chemistry of coke deposits

formed on a Pt-Sn catalyst during dehydrogenation of n-alkanes

to mono-olefins. Fuel Process Technol, 1994, 41(1): 13–25.

[21] Martín N, Viniegra M, Zarate R, Espinosa G, Batina N. Coke

characterization for an industrial Pt-Sn/γ-Al2O3 reforming

catalyst. Catal Today, 2005, 107–108: 719–725.