Microporosity in Ordered Mesoporous Aluminosilicates Characterized by Catalytic Probing Reactions

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1 J. Phys. Chem. B 2003, 107, Microporosity in Ordered Mesoporous Aluminosilictes Chrcterized by Ctlytic Probing Rections Yinyong Sun, Yu Hn, Lin Yun, Shengqin M, Dzhen Jing, nd Feng-Shou Xio* Deprtment of Chemistry & Key Lbortory of Inorgnic Synthesis nd PreprtiVe Chemistry, Jilin UniVersity, Chng Chun , Chin ReceiVed: December 8, 2002 The microporosity of ordered mesoporous luminosilictes ssemblied from zeolite nnoclusters is investigted by ctlytic rections with vrious probing molecules. At first, the smples re treted by bulky bsic orgnic moleculr 5,7-dibrom-8-hydroxy-chinolin. In this cse, the cidic sites in mesopores re killed, nd the cidic sites in micropores tht re smller thn the moleculr dimeter of 5,7-dibrom-8-hydroxy-chinolin re still ctive. The crcking of 1,3,5-triisopropylbenzene shows tht the treted MAS-7 is still ctlyticlly ctive. In contrst, the treted MAS-9 nd treted Al-SBA-15 re lmost inctive. These results show tht MAS-7 contins micropores whose size is similr to tht of bet. Furthermore, the ctlytic crcking of cumene shows tht the treted MAS-7 nd treted MAS-9 re ctlyticlly ctive but tht the treted Al-SBA-15 is inctive. These results show tht MAS-9 lso contins micropores whose size is similr to tht of ZSM-5. Additionlly, the ctlytic dehydrtion of 2-propnol (moleculr dimeter of 3.4 Å) shows tht the treted MAS-7, treted MAS-9, nd treted Al-SBA-15 re ctlyticlly ctive. These results suggest tht Al-SBA- 15 lso contins micropores tht re lrger thn 3.4 Å, in good greement with erlier reports. * To whom correspondence should be ddressed. E-mil: fsxio@ mil.jlu.edu.cn. Phone: Fx: Introduction Since the M41S fmily of periodic mesoporous mterils 1,2 ws synthesized successfully by the ssembly of ctionic surfctnts with inorgnic precursors in the erly 1990s, number of investigtions hve been mde of their structures nd properties. 3-7 As result, it ws found tht MCM-41 exhibited hexgonl rry of uniform chnnel mesopores nd high surfce re, but it showed poor hydrotherml stbility. 8 Some successful exmples of incresing hydrotherml stbility re disordered KIT-1, 9 wormlike disordered MSU-X, 10,11 nd ordered hexgonl mesoporous SBA SBA-15 is usully prepred under strongly cidic conditions (ph < 1), nd under strongly cidic conditions, it is very difficult to introduce heterotoms into the frmework of SBA-15. To solve this problem, much effort hs been devoted to the incorportion of Al, Ti, nd V into the frmework of SBA-15, including postsynthesis grfting procedures nd direct synthesis. 16,17 However, lthough the heterotoms re introduced into SBA-15, they do not show s high ctlytic ctivity s they do in zeolites. More recently, the pore structure of SBA-15 hs been crefully investigted Dvidson et l. 18 hve reported the existence of microporous coron round the mesopores of silic-bsed SBA-15 mterils chrcterized by XRD, TEM, nd N 2 dsorption; Ryoo nd Jroniec et l. 19,20 hve reported mesopore-micropore network in ordered mesopores of SBA- 15 silic by TEM imging of the inverse pltinum replic nd nitrogen dsorption. Ingki et l. 21 hve reported the control of the microporosity within the pore wlls of ordered mesoporous silc SBA-15 by t-plots of nitrogen dsorption isotherms. In our cse, we hve synthesized couples of ordered mesoporous luminosilictes such s MAS-7 25 nd MAS-9 26 ssembled from zeolite bet nd zeolite ZSM-5 nnoclusters with tricopolymer surfctnts (P123), respectively, nd these mesoporous luminosilictes exhibited high hydrotherml stbility nd strong cidity s compred with those of Al-SBA-15. During the chrcteriztion of the pore structure of these mesoporous luminosilictes by TEM nd dsorption isotherms, 27 it ws suggested tht these ordered mesoporous luminosilictes contin micropores, but it is difficult to chrcterize the micropore size in the mesoporous mterils. 27 However, ctlytic rections re very useful techniques for distinguishing porous structures becuse of the shpe selectivity of rectnts. In 1960, shpe-selective ctlysis ws first reported by Weisz nd Frilette, 28 nd then mny studies were reported on moleculr shpe-selective ctlysis For exmple, Deroune 29 hs reported on moleculr shpe-selective ctlysis by zeolite ZSM-5. At the sme time, the selective poisoning of cidic centers in zeolite is lso very effective method for chrcterizing its porous structure nd properties In this pper, we chrcterize the microporosity in ordered mesoporous luminosilictes of Al-SBA-15, MAS-7, nd MAS-9 by using ctlytic rections of probing molecules with vrious dimeters. 2. Mterils nd Methods 2.1. Mterils. MAS-7 nd MAS-9 were prepred ccording to the following procedure reported by Xio nd co-workers. 25,26 The typicl synthesis for MAS-7 is s follows: (1) The zeolite precursors solution with zeolite bet primry structure units were prepred by dding 0.16 g of NOH, 0.30 g of NAlO 2, nd 4.8 g of fumed silic to 25 ml of TEAOH queous solution (20%) under stirring (Al 2 O 3 /SiO 2 /N 2 O/TEAOH/H 2 O molr rtios of 1.0/60/2.5/22/800) nd then trnsferring the mixture into n utoclve for ging for 4 h t 413 K to get cler solution. (2)EO20PO70EO20 (0.8 g, Pluronic P123) ws dis /jp027656u CCC: $ Americn Chemicl Society Published on Web 01/29/2003

2 1854 J. Phys. Chem. B, Vol. 107, No. 8, 2003 Sun et l. Figure 2. (A) Adsorption isotherms for N 2 nd (B) mesopore size distribution of Al-SBA-15 without DBHC tretment (b) nd with DBHC tretment (O). Figure 1. XRD ptterns of (A) Al-SBA-15 nd (B) MAS-9 without DBHC tretment (s) nd with DBHC tretment ( ). solved in 20 ml of H 2 O mixed with 5 ml of HCl (10 M/L), followed by 2.5 ml of precursors solution (contining 8 mmol of SiO 2 ) obtined in step one. The mixture ws stirred t 313 K for 20 h nd then trnsferred into n utoclve for dditionl rection t 373 K for 24 h. (3) The product (MAS-7) prepred from the luminosilicte precursors ws collected by filtrtion, dried in ir, nd clcined t 823 K for 5htoremove the templtes. MAS-9 is prepred ccording to the literture. 26 For comprison, the Al-SBA-15 (synthetic temperture t 313 K), 16 bet, 35 nd ZSM-5 36 smples re prepred ccording to the literture Mterils Tretment. 5,7-Dibrom-8-hydroxy-chinolin (0.08 g, DBHC) ws dissolved in 160 ml of nhydrous ethnol in seled continer, nd then 0.2 g of the smple ws dded to the solution under stirring. After stirring for 24 h t room temperture, the mixture ws filtered, wshed mny times with nhydrous ethnol to remove excess DBHC, nd dried for 20 h in n oven ( K) under vcuum Mesurements. X-ry powder diffrction ptterns were performed on Siemens D5005 instrument with Cu KR rdition, scnning speed of 2 /min, nd scnning regions t nd The dt of the BET surfce re nd the pore-size distribution of smples were mesured on Micromeritics ASAP 2010M system t 77 K using N 2 s n dsorbent, nd the pore-size distributions for the mesopores nd micropores were estimted by the Brrett-Joyner-Hlend (BJH) nd Horvth-Kwzoe (HK) models, respectively Ctlytic Rections of Probing Molecules. The 2-propnol dehydrtion rection ws performed t 473 K by pulse Figure 3. (A) Adsorption isotherms for N 2 nd (B) mesopore size distribution of MAS-9 without DBHC tretment (b) nd with DBHC tretment (O). injections. Cumene nd 1,3,5-triisopropylbenzene (TIPB) crcking rections were performed t 573 K by pulse injections. In ech run, 50 mg of ctlyst ws used, the pulse injection of the rectnt ws 0.4 µl, nd nitrogen ws used s the crrier gs t flow rte of 53.7 ml/min. The rection products were nlyzed by Shimdzu GC-8A equipped with TCD detector. 3. Results nd Discussion 3.1. XRD nd N 2 Adsorption. Figure 1 shows the XRD ptterns of Al-SBA-15 (Si/Al ) 20) nd MAS-9 (Si/Al ) 30) treted nd untreted with DBHC molecules. Obviously, Al- SBA-15 nd MAS-9 treted with DBHC molecules still exhibit their chrcteristic peks ssigned to hexgonl symmetry, but the XRD diffrction intensity is slightly reduced s compred to tht of untreted smples, indicting tht the smples treted with DBHC molecules bsiclly keep their mesostructures. Figures 2 nd 3 show N 2 dsorption isotherms nd pore distributions of Al-SBA-15 (Si/Al ) 20) nd MAS-9 (Si/Al ) 30) treted nd untreted with DBHC molecules, nd the prmeters for vrious smples re summrized in Tble 1. The BET surfce res of Al-SBA-15, MAS-7, nd MAS-9 without DBHC tretment re 752, 1183, nd 980 m 2 /g, respectively. However, fter DBHC tretment, Al-SBA-15, MAS-7, nd MAS-9 hve surfce res of 580, 1001, nd 820 m 2 /g, respectively. Correspondingly, the mesopore sizes of Al-SBA- 15, MAS-7, nd MAS-9 re lso reduced significntly, s

3 Microporosity in Mesoporous Aluminosilictes J. Phys. Chem. B, Vol. 107, No. 8, TABLE 1: Prmeters of N 2 Adsorption Isotherms over Vrious Smples Treted nd Untreted with DBHC Molecules smple surfce re (m 2 /g) volume (cm 3 /g) pore size (Å) Al-SBA treted Al-SBA MAS treted MAS MAS treted MAS bet treted bet ZSM treted ZSM TABLE 2: Moleculr Kinetic Dimeter of Rectnts nd DBHC regents 2-propnol cumene TIPB DBHC kinetic dimeter 3.4 Å 5.0 Å 7.4 Å 8.7 Å TABLE 3: Ctlytic Activities of Vrious Smples without Tretment of DBHC Molecules conversion (%) ctlyst (Si/Al) 2-propnol dehydrtion cumene crcking 1,3,5-triisopropylbenzene (TIPB) crcking ZSM-5 (30) bet (30) Al-SBA-15 (30) Al-SBA-15 (20) MAS-7 (30) MAS-9 (30) observed in Tble 1. These results indicte tht the DBHC molecules relly enter into the mesopores of mesoporous mterils. In contrst, ZSM-5 nd bet treted nd untreted with DBHC molecules show lmost the sme surfce re nd pore size. These results confirm tht DBHC molecules cnnot enter into the micropores of zeolites Ctlytic Rections nd Rectnt Dimeters. Ctlytic rections of probing molecules include the 2-propnol dehydrtion nd crcking of cumene nd TIPB. It is well known tht the 2-propnol dehydrtion is typicl wek cid-ctlyzed rection nd tht moleculr crcking is typicl strong cidctlyzed rection. 37 The kinetic dimeters of probing molecules in these ctlytic rections nd DBHC re presented in Tble 2. Notbly, the moleculr dimeters of 2-propnol, cumene, TIPB, nd DBHC re 3.4, 5.0, 7.4, nd 8.7 Å, respectively. 38 If the cidic smples re treted by bsic molecule DBHC, then the cidic sites in the pores lrger thn 8.7 Å will be killed nd the cidic sites in the pores smller thn 8.7 Å will still be ctive. Then we cn test their ctlytic ctivity by using probing molecules smller thn DBHC to judge wht kind of micropores these smples contin Ctlytic Activities of Vrious Smples without Tretment by DBHC. Ctlytic ctivities of vrious smples without tretment by DBHC re shown in Tble 3. In 2-propnol dehydrtion, ZSM-5, bet, Al-SBA-15, MAS-7, nd MAS-9 show very high ctivity, hving ner 100% conversion. These results indicte tht both microporous zeolites nd mesoporous luminosilictes re good ctlysts for 2-propnol dehydrtion. In cumene crcking, microporous zeolites of ZSM-5 nd bet exhibit high ctivity t 90.1 nd 93.4%, respectively. In contrst, the mesoporous luminosilictes of Al-SBA-15, MAS-7, nd MAS-9 show reltively low conversions of %. The big difference in ctlytic citivities over microporous zeolites TABLE 4: Ctlytic Activities of Vrious Smples with Tretment of DBHC Molecules conversion (%) ctlyst (Si/Al) 2-propnol dehydrtion cumene crcking 1,3,5-triisopropylbenzene crcking ZSM-5 (30) bet (30) Al-SBA-15 (30) 41.1 Al-SBA-15 (20) 100 MAS-7 (30) MAS-9 (30) Undetectble. nd mesoporous luminosilictes my result from their distinguishble cidic strengths. Furthermore, we find tht MAS-7 nd MAS-9 (conversions of 30.4 nd 29.5%, respectively) re more ctive thn Al-SBA-15 (conversion of 12.5%) under the sme Si/Al rtio, indicting tht the cidic strengths of MAS-7 nd MAS-9 re much stronger thn tht of Al-SBA-15. In TIPB crcking, the smples of bet, Al-SBA-15, MAS-7, nd MAS-9 show high ctivity, with conversions of 100, 92, 97, nd 95%, respectively. However, ZSM-5 shows reltively low ctlytic ctivity, with conversion of 4.5%. These results re ssigned to the following resons (1) The rectnt molecule of TIPB cnnot enter the pores of ZSM-5 becuse the pore size of ZSM-5 is only bout 5.5 Å nd the TIPB dimension is ner 7.4 Å. (2) The ctlytic ctivity is contributed from the few cidic sites on the externl surfce Ctlytic Activities of Vrious Smples Treted by DBHC. Ctlytic ctivities of vrious smples treted by DBHC re presented in Tble 4. In the ctlytic crcking of the lrge molecule TIPB, the treted ZSM-5 is completely inctive, which is ttributed to the fct tht the cidic sites of ZSM-5 on the externl surfce re poisoned nd the probing molecule of TIPB (7.4 Å) cnnot enter its pore (5.5 Å). The treted bet still shows high ctivity (conversion ner 100%), which is ttributed to the fct tht the cidic sites of bet zeolite re mostly locted in the internl surfce nd DBHC (8.7 Å) cnnot enter its pores (7.7 Å) to kill its cidic sites in the internl surfce, but the probing molecule of TIPB (7.4 Å) cn esily enter its pores, recting with the cidic sites in the internl surfce. However, the treted Al-SBA-15 (Si/Al ) 20 nd 30) smples re inctive, suggesting tht the cidic sites in the pores lrger thn 8.7 Å re killed nd tht there re no micropores with sizes between 7.4 nd 8.7 Å. However, the treted MAS-7 still shows conversion of 12.5%, suggesting tht there re micropores with sizes between 7.4 nd 8.7 Å in the smple of MAS-7 becuse the cidic sites in the pores lrger thn 8.7 Å re killed by the DBHC molecule nd the TIPB molecule cnnot touch the cidic sites in micropores with sizes less thn 7.4 Å. Considering tht the pore size of zeolite bet is bout t 7.7 Å, we propose tht the micropores with sizes between 7.4 nd 8.7 Å re introduced by zeolite bet nnoclusters used in the synthesis. Additionlly, we find tht the treted MAS-9 is lso inctive, suggesting tht there re no micropores with sizes between 7.4 nd 8.7 Å in the smple of MAS-9. In the ctlytic crcking of the smll molecule cumene, the treted ZSM-5 shows high conversion of 89.2%, which is little lower thn tht of untreted ZSM-5 (90.1%) becuse its few cidic sites on the externl surfce re killed by the DBHC molecule nd the internl cidic sites re unffected. These results indicte tht the cidic sites in the internl surfce ply mjor role in cumene crcking. The treted bet lso shows high ctivity (conversion of 92.7%), which is little lower thn tht of untreted bet (93.4%) becuse its few cidic sites on

4 1856 J. Phys. Chem. B, Vol. 107, No. 8, 2003 Sun et l. the externl surfce re killed. Furthermore, we observe tht the treted Al-SBA-15 (Si/Al ) 20 nd 30) smples re inctive. Considering the fct the cidic sites in the pores lrger thn 8.7 Å re killed by the DBHC molecule, it is suggested tht there re no micropores with sizes between 5.0 nd 8.7 Å in Al- SBA-15. However, the treted MAS-7 nd MAS-9 smples show conversions of 3.5 nd 3.2%, respectively, suggesting tht the two smples contin micropores with sizes between 5.0 nd 8.7 Å. Becuse MAS-9 is inctive for TIPB crcking, we conclude tht the microporous size of MAS-9 should be t Å, which is consistent with tht of the ZSM-5 ( Å) nnoprecursors used for MAS-9. In the ctlytic dehydrtion of 2-propnol, the treted zeolites of ZSM-5 nd bet still show high ctivity (conversion of 100%) becuse their mostly cidic sites re not killed nd probing molecules of 2-propnol (3.4 Å) esily enter their micropores. Additionlly, the treted mesoporous luminosilictes of Al- SBA-15, MAS-7, nd MAS-9 lso show high ctivity (conversion of %), indicting tht these mesoporous luminosilictes contin micropores in the rnge of Å. By considering the fct tht the treted Al-SBA-15 is completely inctive for cumene nd TIPB crcking, it is suggested tht the microporous size in Al-SBA-15 is Å, which is in good greement with elier reports. 21 By summrizing the ctlytic dt over the treted smples, it is very interesting tht the microporous size of these mesoporous luminosilictes is distinguishble. For exmple, Al-SBA-15 contins micropores with sizes of Å; MAS-9 contins micropores with sizes of Å; nd MAS-7 contins micropores with sizes of Å. Obviously, the microporous size of mesoporous luminosilictes could be controlled by the synthetic conditions. In previous reports, it hs been reported tht SBA-15 contins micropores tht rise from the prtil occlusion of the PEO chins in the luminosilicte mtrix, which become microporous upon clcintion. However, it is difficult to chrcterize the microporous size in Al-SBA-15. In this pper, by using the ctlytic dehydrtion of 2-propnol, we hve directly obtined evidence tht Al-SBA-15 contins micropores with sizes of Å. The preprtions of MAS-7 nd MAS-9 were ssemblied from zeolite nnoclusters (zeolite structurl units) of bet nd ZSM-5, respectively. The existence of zeolite nnoclusters (zeolite structurl units) my be key fctor in the control of microporous structure. It hs been reported tht the micropore size of bet zeolite is bout Å nd tht the micropore size of ZSM-5 zeolite is bout Å. 42 Accordingly, ctlytic dt in the crcking of cumene nd TIPB show tht MAS-7 nd MAS-9 ssemblied from bet nd ZSM-5 nnoclusters contin micropores with sizes of Å nd Å, respectively. Significntly, the micropore size of mesoporous luminosilictes ssemblied from zeolite nnoclusters could be controlled by the use of vrious types of zeolite nnoclusters. Although our results show distinguishble micropores in MAS-7, MAS-9, nd Al-SBA-15, we believe tht in MAS-7 nd MAS-9 there re lso micropores resulting from the prtil occlusion of the PEO chins to the luminosilicte mtrix, just like those in Al-SBA-15. More recently, the HRTEM technique 27 showed the direct observtion of the micropores within these mesoporous luminosilictes, nd nnornge-ordered microporosity is found within the mesopore wlls of MAS-7 nd MAS-9. Liu et l. 27 proposed tht nnornge-ordered microporosity results from zeolite primry structurl units, in good greement with our results, which might be the key to the high hydrotherml stbility of MAS-7 nd MAS-9. Conclusions Ordered mesoporous luminosilictes of Al-SBA-15, MAS- 7, nd MAS-9 re treted by bulky bsic orgnic molecule (5,7-dibrom-8-hydroxy-chinolin, DBHC), nd the cidic sites in mesopores re killed. Ctlytic rections including the crcking of 1,3,5-triisopropylbenzene (TIPB) nd cumene nd the dehydrtion of 2-propnol directly show tht the micropore sizes of Al-SBA-15, MAS-7, nd MAS-9 re distinguishble. The treted Al-SBA-15 is ctlyticlly ctive for 2-propnol dehydrtion but not for the crcking of cumene nd TIPB; the treted MAS-9 is ctlyticlly ctive for 2-propnol dehydrtion nd cumene crcking but not for TIPB crcking; the treted MAS-7 is ctlyticlly ctive for 2-propnol dehydrtion nd the crcking of cumene nd TIPB. The ctlytic dt show tht Al-SBA-15 contins micropores with sizes of Å; MAS-9 contins micropores with sizes of Å; MAS-7 contin micropores with sizes of Å. Acknowledgment. This work ws supported by the Ntionl Nturl Science Foundtion of Chin ( , , nd ) nd the Stte Bsic Reserch Project (grnt number G ). References nd Notes (1) Kresge, C. T.; Leonowicz, M. E.; Vrtuli, J. C.; Beck, J. S. Nture (London) 1992, 359, 710. (2) Beck, J. S.; Vrtuli, J. C.; Roth, W. J.; Leonowic, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T.-W.; Olson, D. H.; Shepprd, E. W.; MCCullen, S. B.; Higgins, J. B.; Schlenkler, J. L. J. Am. Chem. Soc. 1992, 112, (3) Syri, A.; Liu, P.; Kruk, M.; Jroniec, M. Chem. Mter. 1997, 9, (4) Long, Y. C.; Xu, T. M.; Sun, Y. J.; Dong, W. Y. Lngmuir 1998, 14, (5) Kruk, M.; Jroniec, M.; Syri, A. Chem. Mter. 1999, 11, 492. (6) Jroniec, M.; Kruk, M.; Olivier, J. P. Lngmuir 1999, 15, (7) Biz, S.; Occelli, M. L. Ctl. ReV.sSci. Eng. 1998, 40, 329. (8) Corm, A. Chem. ReV. 1997, 97, (9) Kim, J. M.; Jun, S.; Ryoo, R. J. Phys. Chem. B 1999, 103, (10) Bgshw, S. A.; Prouzet, E.; Pinnvi, T. J. Science (Wshington, D.C.) 1995, 269, (11) Bgshw, S. A.; Pinnvi, T. J. 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5 Microporosity in Mesoporous Aluminosilictes J. Phys. Chem. B, Vol. 107, No. 8, (26) Hn, Y.; Wu, S.; Sun, Y. Y.; Li, D. S.; Xio, F.-S.; Liu, J.; Zhng, X. Z. Chem. Mter. 2002, 14, (27) Liu, J.; Zhng, X.; Hn, Y.; Xio, F.-S. Chem. Mter. 2002, 14, (28) Weisz, P. B.; Frilette, V. J. J. Phys. Chem. 1960, 64, 382. (29) Deroune, E. G. Stud. Surf. Sci. Ctl. 1980, 5, 5. (30) Csicsery, S. M. In Zeolite Chemistry nd Ctlysis; Rbo, J. A.; Ed.; ACS Monogrph No.171; Americn Chemicl Society: Wshington, DC, 1976; p 680. (31) Weisz, P. B. In Proc. 7th Inter. Congress Ctl., Tokyo, Jpn, (32) Hung, C. P.; Richrdon, J. T. J. Ctl. 1977, 57, 332. (33) Forni, P. Ctl. ReV. 1973, 8, 69. (34) Fejes, P.; Kiricsi, I.; Hnnus, I.; Tihnyi, T.; Kiss, A. Stud. Surf. Sci. Ctl. 1980, 5, 135. (35) Song, T.; Liu, L.; Xu, R. Cuihu Xuebo 1991, 12, 283. (36) Zhou, Q.; Png, W.; Qiu, S.; Ji, M. CN Ptent ZL , Zhou, Q.; Li, B.; Qiu, S.; Png, W. Chem. J. Chin. UniV. 1999, 20, 693. (37) Yue, Y. H.; Sun, Y.; Xu, Q.; Go, Z. Appl. Ctl., A 1998, 175, 131. (38) Cerius 2 ; Moleculr Simultion/Biosysm Corportion: Sn Diego, CA, (39) Zhng, Z.; Hn, Y.; Zhu, L.; Wng, R.; Yu, Y.; Qiu, S.; Zho, D.; Xio, F.-S. Angew. Chem., Int. Ed. 2001, 40, (40) Liu, Y.; Zhng, W.; Pinnvi, T. J. J. Am. Chem. Soc. 2000, 122, (41) Trong On, D.; Kliguine, S. Angew. Chem., Int. Ed. 2001, 40, (42) Atls of Zeolite Frmework Types, 5th ed.; Berlocher, Ch., Meier, W. M., Olson, D. H., Eds.; Elsevier: Amsterdm, 2001.

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