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Design and preparation of efficienthydroisomerization catalysts by the formationof stable SAPO-11 molecular sieve nanosheetswith 10–20 nm thickness and partially blockedacidic sites†

Fen Zhang,a Yan Liu,b Qi Sun,a Zhifeng Dai,a Hermann Gies,c Qinming Wu,a

Shuxiang Pan,a Chaoqun Bian,a Zhijian Tian,d Xiangju Meng,*a Yi Zhang,e

Xiaodong Zou,e Xianfeng Yi,f Anmin Zheng,f Liang Wanga and Feng-Shou Xiao *a

SAPO-11 nanosheets with partially filled micropores (N-SAPO-11) and

a thickness of 10–20 nm were synthesized using polyhexamethylene

biguanide hydrochloride (PHMB) as a mesoporogen and di-n-

propylamine (DPA) as a microporous template. After Pt loading

(0.5 wt%), the Pt/N-SAPO-11 catalyst exhibits higher selectivity for

the isomers and lower selectivity for cracking products than conven-

tional Pt/SAPO-11 catalysts in the hydroisomerization of n-dodecane.

Zeolites have been widely used as catalysts in industrial pro-cesses for the production of fuels and chemicals.1–3 Recently,zeolite nanosheets with advantages of a larger exposed surfaceand faster mass transfer than conventional zeolite crystals havebeen successfully synthesized in the presence of unique surfac-tants, and their compositions mainly include silica-based zeo-lites and aluminophosphate-based molecular sieves.4,5

As one of the industrially important molecular sieves, SAPO-11with medium pore size and low acidity, which is loaded withnoble metals such as Pt (Pt/SAPO-11), has high viscosity indicesand low pouring points in catalytic hydroisomerization of long-chain n-paraffins.6 The enhancement of the branched isomers is

strongly desirable to increase the octane number of gasoline, andto improve the low-temperature fluidity of diesel, lubricant basestocks, and the fuels obtained from FT synthesis.7 In thesecatalytic processes, more pore mouths can enhance the activities,and less Brønsted acidic sites in the micropores should reduce thecracking of the products.8

One strategy to obtain more pore mouths in hydroisomer-ization zeolite catalysts is to synthesize mesoporous molecularsieves. For example, a mesoporous SAPO-11 supported Ptcatalyst (Pt/M-SAPO-11) with more pore mouths was reported,which exhibits higher isomer selectivity in the hydroisomeriza-tion of n-dodecane than a conventional SAPO-11 supported Ptcatalyst (Pt/C-SAPO-11).9 Reasonably, a series of mono- to multi-layered molecular sieve nanosheets should have much morepore mouths than these mesoporous molecular sieves.4,5 How-ever, the industrial application of these molecular sievenanosheets for hydroisomerization is still challenging, becauseof the reduced stability of these nanosheets compared to that ofbulk zeolite crystals and relatively high cost of the uniquesurfactants for the large-scale synthesis.10

SAPO-11 crystallizes as thin sheets with the channel runningperpendicular to the sheet surface. In order to find out how toincrease the stability of SAPO-11 nanosheets, the crystal energyis calculated as a function of the thickness of SAPO-11nanosheets, as given in Fig. 1A and B as well as Table S1 (ESI†).Obviously, the crystal energy decreases rapidly at the beginningfrom two to five unit cell periods, and then slowly and finallyreaches a constant value after 12 unit cell thick (ca. 10 nm).SAPO-11 nanosheets with 10 nm thickness have a similarcrystal energy to that of bulk SAPO-11 crystals. This suggeststhat nanosheets thicker than 10 nm should have a similarstability to that of the bulk SAPO-11 crystals.

One strategy to reduce the catalytic cracking of the productsis to partially block the Brønsted acidic sites in the microporesof SAPO-11 using non-acidic and/or weak acidic species. Anideal nanosheet of SAPO-11 as an efficient catalyst support for

a Key Lab of Applied Chemistry of Zhejiang Province, Department of Chemistry,

Zhejiang University, Hangzhou 310028, China. E-mail: mengxj@zju.edu.cn,

fsxiao@zju.edu.cnb Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences,

Beijing 100700, Chinac Institute of Geology, Mineralogy and Geophysics, Ruhr-University Bochum,

44780 Bochum, Germanyd State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics,

Chinese Academy of Sciences, Dalian 116023, Chinae Department of Materials and Environmental Chemistry, Stockholm University,

SE-106 91 Stockholm, Swedenf State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics,

Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences,

Wuhan 430071, China

† Electronic supplementary information (ESI) available: Experimental and char-acterization details, XRD patterns, SEM images, BET curves, TG-DSC curves,pyridine IR spectra, and NMR spectra. See DOI: 10.1039/c7cc01519d

Received 28th February 2017,Accepted 6th April 2017

DOI: 10.1039/c7cc01519d

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hydroisomerization should be 10 nm or more thick and containpartially blocked acidic sites in the micropores, as illustrated inFig. 1C.

Fig. 2A shows the experimental XRD pattern of SAPO-11nanosheets we synthesized (N-SAPO-11) and the simulated XRDpattern of the SAPO-11 nanosheets with ca. 15 nm, giving char-acteristic peaks of the AEL framework structure (Fig. S1, ESI†),which are in good agreement with those of conventional SAPO-11crystals (C-SAPO-11, Fig. S2, ESI†). The N2 sorption isotherm of thecalcined N-SAPO-11 shows a very low uptake at low relative pressure(10�6 o P/P0 o 0.01), with an obvious hysteresis loop at highrelative pressure (0.4–0.95, Fig. 2B). Correspondingly, N-SAPO-11exhibits a very small microporous volume of 0.01 cm3 g�1 but alarge external pore volume of 0.29 cm3 g�1. These results suggest

that the micropores in N-SAPO-11 have been partially blocked, andthe major contribution for the N2 uptake in the sample resultedfrom the external surfaces. In contrast, C-SAPO-11 (Fig. S3, ESI†)has a much larger microporous volume (0.06 cm3 g�1). The para-meters of N-SAPO-11 and C-SAPO-11 are presented in Table S2(ESI†). Fig. 2C shows the TG and DSC curves of N-SAPO-11 fromroom temperature to 1200 1C. In the TG curve, the weight lossbelow 200 1C corresponds to the removal of adsorbed water, whilethe loss ranging from 200 to 650 1C is mainly due to the decom-position of the organic templates. After 700 1C, no obvious weightloss was observed. In the DSC curve, it is notable that, in additionto the signals associated with water and organic templates, a signalappeared at 940 1C, which is assigned to the collapse of theSAPO-11 structure.11 This temperature is very similar to that of

Fig. 1 (A) The selected cluster models of 1 layer [view along the a-axis (a) and z-axis (b)], 6 layers (c), and 12 layers (d) nanosheet structures of the SAPO-11zeolite used in the theoretical calculations, (B) the calculated formation energies of nanosheet structures of the SAPO-11 zeolite with varying layers and(C) proposed model for SAPO-11 nanosheets with blocked acidic sites in the micropores.

Fig. 2 Characterization of the N-SAPO-11 sample. (A) XRD pattern, (B) N2 sorption isotherms obtained from a calcined sample, (C) TG-DSC curves,(D) SEM image, (E) TEM image viewed in parallel to the nanosheets, and (F) HRTEM image viewed perpendicular to a nanosheet with the correspondingSAED pattern as an inset. The HRTEM image and SAED pattern show that the 10-ring channels (along the [100] direction) are perpendicular to thenanosheets. The structural model is overlaid on the right-bottom corner of the HRTEM image.

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C-SAPO-11 (950 1C, Fig. S4, ESI†). These results suggest thatN-SAPO-11 and C-SAPO-11 have similar thermal stabilities, whichis well consistent with the energy simulation (Fig. 1B).

Fig. 2D shows the SEM image of N-SAPO-11, giving a flower-like morphology. TEM images of the cross-sections of N-SAPO-11show the thicknesses of N-SAPO-11 to be 10–20 nm (Fig. 2E). Incontrast, C-SAPO-11 displays spherical particles aggregated by cubiccrystals (Fig. S5, ESI†). The HRTEM image of N-SAPO-11 takenperpendicular to the nanosheet shows 10-ring channels (Fig. 2Fand Fig. S6, ESI†). The corresponding SAED pattern can be indexedto the [100] zone axis pattern using the unit cell parameters of AEL(the inset in Fig. 2F). Both the HRTEM and the SAED patternconfirm that the nanosheets have the AEL framework structure.

It is worth mentioning that introduction of mesoporosity inSAPO-11 using PHMB as a mesoporogen was successful in aprevious report.9 In this work, it is interesting to note thatSAPO-11 nanosheets are obtained when more PHMB is used inthe synthesis. In addition, the SEM and TEM images (Fig. 2D–F)show a very pure phase of SAPO-11, and there are still verybroad XRD peaks (around 13 and 251) for N-SAPO-11 (Fig. 2A),which might be related to the presence of an amorphous phasewith small domains in the sample.

Fig. S7 (ESI†) shows 29Si, 31P and 27Al MAS NMR spectra ofthe calcined N-SAPO-11 and C-SAPO-11 samples. In the 27AlNMR spectra (Fig. S7C, ESI†), C-SAPO-11 gives one strong peakat 38.1 ppm and two weak peaks at 16.3 ppm and 8.9 ppm,while N-SAPO-11 has an additional peak at �10.2 ppm. The signalat 38.1 ppm is assigned to the tetrahedral Al in the AEL framework,the signals at 16.3 ppm and 8.9 ppm are attributed to the hydrationof the tetrahedral Al sites, and the signal at�10.2 ppm is related to6-coordinated extra framework Al3+ species.12 These results confirmthat the extra framework Al3+ species exist in N-SAPO-11. Thepresence of 6-coordinated Al3+ species (Fig. S7C, ESI†) and theblocked micropores observed from N2 soprtion (Fig. 2B) indicatesthat the micropores of N-SAPO-11 are filled with 6-coordinated Al3+

species of amorphous alumina, in good agreement with the XRDresult of N-SAPO-11 (Fig. 2A). This is further supported by ICP-AESanalysis. The Al/P ratio of N-SAPO-11(0.86) is significantly higherthan that (0.75) of C-SAPO-11.

Fig. S8 (ESI†) shows the IR spectra of pyridine on the calcinedC-SAPO-11 and N-SAPO-11 samples at 150 1C. The bands at 1540and 1450 cm�1 are assigned to the adsorption of pyridine onBrønsted and Lewis acid sites, respectively. Interestingly, N-SAPO-11 exhibits much weaker band intensity associated with theBrønsted acid sites than C-SAPO-11. Considering the same amountof silica for the generation of acidic sites added in the synthesis, aweaker 1540 cm�1 peak intensity of N-SAPO-11 than C-SAPO-11might mean partial blocking of the Brønsted acid sites by the6-coordinated Al3+ species, particularly in the micropores ofN-SAPO-11. Apparently, blocking the Brønsted acid sites in themicropores should facilitate the hydroisomerization of long-chain n-paraffins and reduce hydrocracking at the acidic sites.

The Pt/N-SAPO-11 and Pt/C-SAPO-11 catalysts with a similar Ptloading (0.5 wt%) show a similar Pt size distribution (Fig. S9, ESI†).The N2 sorption isotherms of the calcined Pt/N-SAPO-11 andPt/C-SAPO-11 catalysts are shown in Fig. S10A (ESI†), and their

textural parameters are presented in Table S3 (ESI†). Pyridine IRspectra of those samples (Fig. S10B, ESI†) confirm that Pt/C-SAPO-11has higher Brønsted density than Pt/N-SAPO-11. Fig. 3 shows thecatalytic data obtained in hydroisomerization of n-dodecane overthe Pt/N-SAPO-11 and Pt/C-SAPO-11 catalysts. In this reaction, theproducts are mono-branched isomers, di-branched isomers, andcracked hydrocarbons C4–C6. With an increase in the temperature,both the conversion of n-dodecane and cracking of the products aresignificantly enhanced, while the isomer selectivity is remarkablyreduced. It is worth mentioning that at any temperaturePt/N-SAPO-11 always shows higher selectivity for isomers andlower selectivity for cracking products than Pt/C-SAPO-11. Thesuperior catalytic properties of Pt/N-SAPO-11 could be assignedto the stable SAPO-11 nanosheets with a thickness of 10–20 nmand partially blocked acidic sites.

In order to understand the formation mechanism of the growingprocess, an investigation throughout the duration of N-SAPO-11 wasmade by XRD (Fig. S11, ESI†) and SEM (Fig. S12, ESI†) techniques.When the crystallization time reaches 2 h, the sample is well crystal-lized and the crystal morphology is similar to those of SAPO-11crystals reported previously.13 Upon increasing the crystallization

Fig. 3 Dependence of (A) conversion of n-dodecane, (B) C12 isomerselectivity, and (C) cracking product selectivity on reaction temperatureover (a) Pt/C-SAPO-11 and (b) Pt/N-SAPO-11.

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time from 2 to 48 h, the crystals become thinner and thinner. Wefound that the presence of PHMB is crucial in the synthesis ofN-SAPO-11 and no N-SAPO-11 could be obtained in the absence ofPHMB. It is thus important to understand the role of PHMB inthe synthesis. Fig. S13 (ESI†) shows 13C NMR spectra of theas-synthesized N-SAPO-11 solid and aqueous PHMB liquid. Theas-synthesized N-SAPO-11 exhibits peaks at 50.3, 26.2 and 11.1 ppmassociated with the organic template of di-n-propylamine (DPA)added in the starting gel, and at 40.8 and 26.2 ppm associated with1,6-hexamethylenediamine (1,6-HMD). We cannot observe thepeaks at 158 and 159 ppm associated with the guanidyl speciesin PHMB. At the same time, CO2 and NH3 are found in the gasphase. These results indicate that PHMB could be decomposedinto 1,6-HMD, CO2, and NH3 under hydrothermal conditions, asproposed in Fig. S14 (ESI†). Possibly, the expansion of the gases bydecomposition of PHMB results in the formation of N-SAPO-11nanosheets. To confirm this hypothesis, we replaced PHMB byNH4HCO3 in the synthesis, which can also be decomposed intoammonia and carbon dioxide under hydrothermal treatments. Asexpected, SAPO-11 nanosheets were obtained (Fig. S15, ESI†), whichhave a similar XRD pattern and morphology to N-SAPO-11. Theemployment of the gaseous expansion should open a novelavenue for a low-cost synthesis of zeolite nanosheets. Currentlycostly organic surfactants are needed for the synthesis of zeolitenanosheets.4,5,10

Besides the formation of gases in the synthesis, PHMB withthree N atoms can coordinate to Al3+ in the starting gels andthus play a critical role in blocking the micropores. Possibly, thePHMB–Al complex could be transformed into the 6-coordinatedaluminum species filled in the micropores after decompositionof PHMB under the hydrothermal treatments. As a result, the N2

sorption measurement shows that N-SAPO-11 has low microporesurface area (32 m2 g�1) and the 27Al NMR data show that thereis 6-coordinated Al3+ in N-SAPO-11.

In summary, stable SAPO-11 nanosheets with a thickness of10–20 nm and partially blocked acidic sites have been synthe-sized in the presence of PHMB under hydrothermal conditions.The formation of SAPO-11 nanosheets is associated with gaseousexpansion formed by PHMB decomposition. The presence of6-coordinated Al3+ species in the micropores is related tothe strong coordination of PHMB with Al3+ species. The10–20 nm thick SAPO-11 nanosheets have a comparablethermal stability to the bulk SAPO-11 crystals. The SAPO-11nanosheets modified with Pt nanoparticles (Pt/N-SAPO-11)exhibit higher isomerization selectivity and lower crackingselectivity in n-dodecane hydroisomerization than Pt/SAPO-11,which is directly attributed to the increased pore mouths in thenanosheets and reduced Brønsted acid sites in the micropores ofN-SAPO-11. The synthesis of zeolite nanosheets reported hereoffers new opportunities to obtain stable and low-cost zeolitenanosheets in the future.

This work was supported by the National Natural ScienceFoundation of China (91634201, 91545111, 21333009 and21422306) and the Knut and Alice Wallenberg Foundationthrough the 2DEM-NATUR project and the grant for purchasingthe TEMs.

Notes and references1 (a) H. Gies and B. Marler, Zeolites, 1992, 12, 42; (b) M. E. Davis and

R. F. Lobo, Chem. Mater., 1992, 4, 756; (c) M. E. Davis, Nature, 2002,417, 813; (d) C. S. Cundy and P. A. Cox, Chem. Rev., 2003, 103, 663;(e) A. Jackowski, S. I. Zones, S. J. Hwang and A. W. Burton, J. Am. Chem.Soc., 2009, 131, 1092; ( f ) J. H. Lee, M. B. Park, J. K. Lee, H. K. Min,M. K. Song and S. B. Hong, J. Am. Chem. Soc., 2010, 132, 12971.

2 (a) J. Kim, S. Bhattacharjee, K.-E. Jeong, S.-Y. Jeong, M. Choi, R. Ryoo andW.-S. Ahn, New J. Chem., 2010, 34, 2971; (b) H. Y. Chen, J. Wydra,X. Y. Zhang, P. S. Lee, Z. P. Wang, W. Fan and M. Tsapatsis, J. Am. Chem.Soc., 2011, 133, 12390; (c) M. Moliner, J. Gonzalez, M. T. Portilla,T. Willhammar, F. Rey, F. J. Llopis, X. D. Zou and A. Corma, J. Am.Chem. Soc., 2011, 133, 9497; (d) K. Na, C. Jo, J. Kim, K. Cho, J. Jung, Y. Seo,R. J. Messinger, B. F. Chmelka and R. Ryoo, Science, 2011, 333, 328;(e) P. S. Lee, X. Y. Zhang, J. A. Stoeger, A. Malek, W. Fan, S. Kumar,W. C. Yoo, S. Al Hashimi, R. L. Penn, A. Stein and M. Tsapatsis, J. Am.Chem. Soc., 2011, 133, 493; ( f ) F. J. Liu, T. Willhammar, L. Wang,L. F. Zhu, Q. Sun, X. J. Meng, W. Carrillo-Cabrera, X. D. Zou andF.-S. Xiao, J. Am. Chem. Soc., 2012, 134, 4557.

3 (a) S. Goel, Z. J. Wu, S. I. Zones and E. Iglesia, J. Am. Chem. Soc.,2012, 134, 17688; (b) C. Jo, J. Jung, H. S. Shin, J. Kim and R. Ryoo,Angew. Chem., Int. Ed., 2013, 52, 10014; (c) A. Rojas, O. Arteaga,B. Kahr and M. A. Camblor, J. Am. Chem. Soc., 2013, 135, 11975;(d) K. Moller and T. Bein, Chem. Soc. Rev., 2013, 42, 3689;(e) S. Q. Ma, D. F. Sun, X. S. Wang and H. C. Zhou, Angew. Chem.,Int. Ed., 2007, 46, 2458; ( f ) Z. P. Wang, P. Dornath, C. C. Chang,H. Y. Chen and W. Fan, Microporous Mesoporous Mater., 2013, 181, 8.

4 (a) M. Choi, K. Na, J. Kim, Y. Sakamoto, O. Terasaki and R. Ryoo,Nature, 2009, 461, 246; (b) X. Y. Zhang, D. X. Liu, D. D. Xu, S. Asahina,K. A. Cychosz, K. V. Agrawal, Y. Al Wahedi, A. Bhan, S. Al Hashimi,O. Terasaki, M. Thommes and M. Tsapatsis, Science, 2012, 336, 1684;(c) A. Inayat, I. Knoke, E. Spiecker and W. Schwieger, Angew. Chem.,Int. Ed., 2012, 51, 1962; (d) D. D. Xu, Y. H. Ma, Z. F. Jing, L. Han,B. Singh, J. Feng, X. F. Shen, F. L. Cao, P. Oleynikov, H. Sun,O. Terasaki and S. Che, Nat. Commun., 2014, 5, 4262.

5 (a) Y. Seo, S. Lee, C. Jo and R. Ryoo, J. Am. Chem. Soc., 2013, 135, 8806;(b) Q. M. Sun, Y. H. Ma, N. Wang, X. Li, D. Y. Xi, J. Xu, F. Deng,K. B. Yoon, P. Oleynikov, O. Terasaki and J. H. Yu, J. Mater. Chem. A,2014, 2, 17828; (c) B. B. Gao, P. Tian, M. R. Li, M. Yang, Y. Y. Qiao,L. Y. Wang, S. T. Xu and Z. M. Liu, J. Mater. Chem. A, 2015, 3, 7741.

6 (a) A. Corma, Chem. Rev., 1995, 95, 559; (b) J. A. Martens, P. J. Grobetand P. A. Jacobs, J. Catal., 1990, 126, 299; (c) R. J. Taylor andR. H. Petty, Appl. Catal., A, 1994, 119, 121; (d) J. M. Campelo,F. Lafont and J. M. Marinas, J. Catal., 1995, 156, 11; (e) A. K. Sinhaand S. Sivasanker, Catal. Today, 1999, 49, 293; ( f ) K. C. Park andS. K. Ihm, Appl. Catal., A, 2000, 203, 201; (g) J. Walendziewski andB. Pniak, Appl. Catal., A, 2003, 250, 39; (h) H. Deldari, Appl. Catal., A,2005, 293, 1; (i) T. Blasco, A. Chica, A. Corma, W. J. Murphy,J. Agundez-Rodrıguez and J. Perez-Pariente, J. Catal., 2006, 242, 153;( j) L. Guo, Y. Fan, X. Bao, G. Shi and H. Liu, J. Catal., 2013, 301, 162.

7 (a) X. B. Peng, K. Cheng, J. C. Kang, B. Gu, X. Yu, Q. H. Zhang andY. Wang, Angew. Chem., Int. Ed., 2015, 127, 4636; (b) Z. P. Liu andP. Hu, J. Am. Chem. Soc., 2002, 124, 11568; (c) W. Chen, Z. L. Fan,X. L. Pan and X. H. Bao, J. Am. Chem. Soc., 2008, 130, 9414;(d) H. Schulz, Appl. Catal., A, 1999, 186, 3; (e) A. A. Adesina, Appl.Catal., A, 1996, 138, 345; ( f ) K. Cheng, V. Subramanian, A. Carvalho,V. V. Ordomsky, Y. Wang and A. Y. Khodakov, J. Catal., 2016, 337, 260.

8 (a) J. A. Martens, G. Vanbutsele, P. A. Jacobs, J. Denayer, R. Ocakoglu,G. Baron, J. A. Munoz Arroyo, J. Thybaut and G. B. Marin, Catal.Today, 2001, 65, 111; (b) M. Y. Kim, K. Lee and M. Choi, J. Catal., 2014,319, 232.

9 Y. Liu, W. Qu, W. W. Chang, S. X. Pan, Z. J. Tian, X. J. Meng,M. Rigutto, A. van der Made, L. Zhao, X. M. Zheng and F.-S. Xiao,J. Colloid Interface Sci., 2014, 418, 193.

10 J. Jung, C. Jo, K. Cho and R. Ryoo, J. Mater. Chem., 2012, 22, 4637.11 (a) Z. M. Liu, X. Y. Huang, C. Q. He, Y. Yang, L. X. Yang and G. Y. Cai,

Chin. J. Catal., 1996, 17, 540; (b) L. Han, X. Cui and X. M. Liu, Chin.J. Inorg. Chem., 2013, 29, 565.

12 (a) C. S. Blackwell and R. L. Patton, J. Phys. Chem., 1988, 92, 3965;(b) A. M. Prakash, S. V. V. Chilukuri, R. P. Bagwe, S. Ashtekar andD. K. Chakrabarty, Microporous Mater., 1996, 6, 89.

13 H. Q. Yang, Z. C. Liu, H. X. Gao and Z. K. Xie, J. Mater. Chem., 2010,20, 3227.

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