Zeolite-Coated Mesostructured Cellular Silica Foams

Transcription

1 Pulished on We 12/19/22 Zeolite-Coted Mesostructured Cellulr Silic Foms Do Trong On nd Serge Kliguine* Deprtment of Chemicl Engineering, LVl UniVersity, Queec G1K 7P4, Cnd Received Septemer 23, 22 ; E-mil: kligui@gch.ulvl.c Recent effort hs een focused on improving oth the cidity nd the hydrotherml stility of mesoporous luminosilictes through the use of zeolite seeds to construct the wlls of mesoporous mterils. 1-5 For exmple, zeolite colloidl gels of ZSM-5, TS-1 (MFI), et (BEA), nd fujsite (FAU) were utossemled to form stem-stle mesostructured mteril. 2,3 Mesoporous mterils (UL-zeolites) with semicrystlline zeolitic mesopore wlls were lso prepred using templted solid-stte crystlliztion method. Bright- nd drk-field TEM imges of UL-zeolites indicted tht nnocrystls were emedded in the continuous morphous inorgnic mtrix to form semicrystlline wll structures. 4 Recently, we hve descried new concept exemplified y the production of unusul ZSM-5-coted mesoporous luminosilicte SBA-15 using diluted cler solution contining primry zeolite units. Stem-ultrstle nd highly cidic mterils were chieved due to the nnocrystlline zeolitic nture of their pore wll surfce. 5 Unlike MCM-41 nd SBA-15, which hve monodimensionl mesopore structures leding to serious mss trnsfer limittions, 6,7 mesostructured cellulr silic foms (MCF) re composed of uniformly sized, lrge sphericl cells (up to 5 Å) with high surfce res tht re interconnected y uniformly sized windows to crete continuous 3-D pore system. 8 It would therefore e lso of interest to imprt to these new lrger pore mterils the high hydrotherml stility lredy otined y zeolite coting of SBA-15. Our ojective here is thus to prepre new type of zeolite-coted MCF using cler ZSM-5 (MFI) nd fujsitic zeolite type Y (FAU) gel solutions. Zeolite-coted mesocellulr lumosilicte foms (zeolite-coted MCF) were synthesized y two-step procedure. The first step consists of the preprtion of the mesocellulr lumosilicte fom precursor (MCF) ccording to the method descried in ref 8 nd the desired cler zeolite gel solution contining primry zeolite seeds (NY nd ZSM-5). 9,1 The second step is coting of nnozeolite seeds on the MCF surfce using the diluted cler zeolite gel. The detiled synthesis procedure is etter descried in the Supporting Informtion. Figure 1 shows the N 2 dsorption/desorption isotherms nd BdB- FHH cell size distriutions clculted from the dsorption rnch of the isotherm for the MCF smple efore nd fter coting using cler ZSM-5 gel solution. 11 Tle 1 summrizes for the sme smples the BdB-FHH sphericl cell sizes long with the BET surfce res nd pore volumes. Significnt decreses in surfce re, sphericl cell size, nd pore volume clerly indicte tht zeolite nnoclusters were locted inside the mesopore chnnels. XRD digrms of the coted smples show no peks in the 2θ rnge of 1-5, indicting tht the coting contins no crystls hving dimeters ove 5 Å. Figure 2 shows the TEM imges of the prent MCF nd ZSM-5-coted MCF smples. The prent smple presents typicl strutlike MCF structure (Figure 2A). For the coted smple, slight deformtion of the sphericl cells ws oserved. However, some spots of 3 Å in size (due to higher density of zeolite prticles s compred to the morphous mesopore Figure 1. N 2 dsorption/desorption isotherms t -196 C nd BdB-FHH pore dimeter distriutions clculted from the dsorption rnch of the isotherm (inset) for () prent MCF nd () ZSM-coted MCF. Tle 1. Physicochemicl Properties of the Prent Mesocellulr Alumnosilic Fom (PMCF) nd Zeolite-Coted Mesocellulr Fom (Zeolite-MCF) Smples mterils Si/Al (tom) S BET (m 2 /g) meso vol (cm 3 /g) sphericl cvity dimeter (Å) PMCF ZSM-5-coted MCF NY-coted MCF Atomic Si/Al rtios otined y tomic dsorption spectroscopy. Cell dimeter determined ccording to the BdB-FHH method using the sphericl pore model (ref 11). wlls) ecome visile s distriuted homogeneously over the coted smple (Figure 2B). A lnk experiment consisting of heting the prent MCF smple in glycerol without tretment with the cler ZSM-5 gel yielded mteril which did not show these spots. The formtion of 3 Å prticles is in greement with the initil stge of the ZSM-5 crystl growth mechnism reported in the literture. 9,1 Furthermore, 129 Xe NMR ws lso used s sensile proing technique for studying the internl pore structure of these mterils. A wek nd t 174 ppm, which is chrcteristic of xenon dsored in the ZSM-5 micropore chnnels, ws oserved for the ZSM-5-coted smple. Such nd ws indeed not present in the prent MCF smple. 12 Similr trends were lso oserved for the NY-coted MCF smple (Tle 1 nd Figure S1). The 29 Si MAS spectrum of the prent MCF smple exhiited two rod resonnces t -11 ppm for Q 4 environment nd t -1 ppm for Q 3 environment together with shoulder t 9 ppm scrile to Q 2 species. However, the spectr of the coted MCF smples show min Q 4 pek t ppm nd smll Q 3 shoulder pek t -98 ppm, nd essentilly no Q 2 pek ws found (Figure 3). These reflect lower OH concentrtion in the coted smples, which indictes the coting procedure led to grfting nnoclustered zeolite prticles on the mesopore surfce y the condenstion rection of silnol groups t the interfce. Aluminum environments in these mterils were lso quntified y ultrhigh field 27 Al MAS nd J. AM. CHEM. SOC. 23, 125, /j28656 CCC: $ Americn Chemicl Society

2 COMMUNICATIONS site density of the HY-coted smple could e due to the high luminum loding in the fujsite gel (Si/Al ) 1) s compred to tht in ZSM-5 gel (Si/Al ) 5). Figure S3 shows the N 2 dsorption/ desorption isotherms for the prent MCF nd ZSM-5- nd NYcoted smples efore nd fter exposure to 2% stem t 8 C for 2 h. The mesopore structure of the prent smple hd collpsed fter this tretment. By contrst, no significnt chnge in the mesopore structure under the sme tretment conditions indictes tht the coted smples re much more hydrothermlly stle thn is the prent MCF smple. This could e ttriuted to the zeolite seeds coted on the mesopore surfce, which crete vlence onds with the precursor nd hel defect sites, reducing consequently the concentrtion of silnol groups. It cn e concluded tht zeolitecoted MCF re promising s new cid ctlysts for the conversion of ulky molecules t high temperture. The methodology of coting zeolite seeds into the wll surfce of mesoporous luminosilictes s mens of improving hydrotherml stility nd cidity is quite simple, generl, nd pplies to vrious kinds of zeolite guests nd mesoporous mterils hosts. Figure 2. TEM imge of (A) prent MCF nd (B) ZSM-5-coted MCF. Figure Si MAS NMR spectr of () prent MCF, () NY-coted MCF, nd (c) ZSM-5-coted MCF. MQMAS (75 MHz for 1 H) NMR. 12 For the prent MCF smple, two distinct luminum environments were detected; rod pek is typicl tetrhedrl luminum in morphous mterils, nd the second is n extrfrmework luminum species. However, the coted smples (e.g., ZSM-5- nd NY-coted MCF) show n dditionl shrp pek, which is chrcteristic of the tetrhedrl luminum in the zeolite frmework. 12,13 The comintion of these results suggests tht zeolite nnoprticles were locted within the mesopore chnnels. The ctul decrese in sphericl cvity dimeter (Tle 1) indictes tht this coting encompsses more thn one monolyer of nnoprticles. The IR spectr of pyridine dsored on protonted smples in the region cm -1 fter evcution t different tempertures show tht oth Brönsted nd Lewis cid sites of the coted smples re in much higher concentrtion thn those of the corresponding MCF smple (Figure S2). The higher cidity cn e ttriuted to secondry uilding units chrcteristic of zeolite within the mesopore wlls. The order of the cid site density is HY-coted MCF > H-ZSM-5-coted MCF. prent MCF. The higher cid Acknowledgment. This work ws supported y the Nturl Sciences nd Engineering Reserch Council of Cnd (NSERC) through strtegic grnt. We thnk Mr. S. Royer for the recording of NMR dt nd Professor Stucky for providing us with the BdB- FHH method progrm. Supporting Informtion Aville: Figures S1-S3 nd synthesis procedure (PDF). This mteril is ville free of chrge vi the Internet t References (1) Trong On, D.; Giscrd, D.; Dnumh, C.; Kliguine, S. Appl. Ctl., A 21, 222, (2) () Liu, Y.; Zhng, W.; Pinnvi, T. J. J. Am. Chem. Soc. 2, 122, () Liu, Y.; Zhng, W.; Pinnvi, T. J. Angew. Chem., Int. Ed. 21, 4, Liu, Y.; Pinnvi, T. Chem. Mter. 22, 14, 3. (3) () Zhng, Z.; Hn, Y.; Zhu, L.; Wng, R.; Yu, Y.; Qiu, S.; Zho, D.; Xio, F.-S. Angew. Chem., Int. Ed. 21, 4, () Xio, F. S.; Hn, Y.; Yu, Y.; Meng, X.; Yng, M.; Wu, S. J. Am. Chem. Soc. 22, 122, 888. (c) Hn, Y.; Wu, S.; Sun, Y.; Li, D.; Xio, F. S. Chem. Mter. 22, 14, (4) () Trong On, D.; Kliguine, S. Angew. Chem., Int. Ed. 21, 4, () Trong On, D.; Lutic, D.; Kliguine, S. Microporous Mesoporous Mter. 21, 44, 435. (5) Trong On, D.; Kliguine, S. Angew. Chem., Int. Ed. 22, 41, 136. (6) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vrtuli, J. C.; Beck, J. S. Nture 1992, 359, (7) () Zho, D.; Feng, J.; Huo, Q.; Melosh, N.; Fredrickson, G. H.; Chmelk, B. F.; Stucky, G. D. Science 1998, 279, () Yng, P.; Zho, D.; Mrgolese, D. I.; Chmelk, B. F.; Stucky, G. D. Nture 1998, 396, 152. (8) () Schmidt-Winkel, P.; Lukens, W. W., Jr.; Zho, D.; Yng, P.; Chmelk, B. F.; Stucky, G. D. J. Am. Chem. Soc. 1999, 121, () Schmidt- Winkel, P.; Lukens, W. W., Jr; Yng, P.; Mrgolese, D. I.; Lettow, J. S.; Ying, J. Y.; Stucky, G. D. Chem. Mter. 2, 12, 686. (9) () Kirschhock, C. E. A.; Buschmnn, V.; Kremer, S.; Rvishnkr, R.; Houssin, C. J. Y.; Mojet, B. L.; vn Snten, R. A.; Groet, P. J.; Jcos, P. A.; Mrtens, J. A. Angew. Chem., Int. Ed. 21, 4, () de Moor, P. P. E. A.; Beelen, T. P. M.; vn Snten, R. A.; Beck, L. W.; Dvis, M. E. J. Phys. Chem. B 2, 14, 76. (1) de Moor, P. P. E. A.; Beelen, T. P. M.; Komnschek, B. U.; Beck, L. W.; Wgner, P.; Dvis, M. E.; vn Snten, R. A. Chem.-Eur. J. 1999, 5, 283. (11) Lukens, W., Jr.; Schmidt-Winkel, P.; Zho, D.; Feng, J.; Stucky, G. D. Lngmuir 1999, 15, 543. (12) Trong On, D.; Kliguine, Springuel-Huet, M. A.; Fyfe, C., in preprtion. (13) Fyfe, C. A.; Bretherton, J. L.; Lm, L. Y. J. Am. Chem. Soc. 21, 123, JA28656A J. AM. CHEM. SOC. 9 VOL. 125, NO. 3,

3 14 12 Volume dsored (cm 3 g -1, STP) P/P Fig. S1: N 2 dsorption/desorption isotherms t -196ºC for: ) prent MCF nd ) NY coted MCF.

4 .32.3 Lewis Brönsted d Asornce c Wvenumer (cm -1 ) Fig. S2: FT-IR spectr of pyridine dsored on the protonted smples in the cm -1 rnge fter pyridine dsorption nd then desorption t 15ºC: ) prent MCF in H-form, ) H-ZSM-5 coted MCF, c) HY coted MCF nd d) H-ZSM-5.

5 16 14 A Vd (cm 3 g -1, STP) Vd (cm 3 g -1, STP) B C Vd (cm 3 g -1, STP) P/P Fig. S3: N 2 dsorption/desorption isotherms for (A) prent MCF smple, (B) ZSM-5 coted MCF nd (C) NY coted MCF ) efore nd ) fter steming with 2% H 2 O in N 2 t 8ºC for 2 h.