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J. Phys. Chem. C 2008, 112, 2764-2769
Synthesis and High Hydrogen Storage Capacity of Zeolite-Like Carbons Nanocast Using As-Synthesized Zeolite Templates A. Pacuła†,‡ and R. Mokaya*,† School of Chemistry, UniVersity of Nottingham, UniVersity Park, Nottingham NG7 2RD, U.K., and Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Krako´ w, Poland ReceiVed: August 16, 2007; In Final Form: NoVember 19, 2007
As-synthesized zeolite β has been successfully used as a template for the preparation, via chemical vapor deposition, of well ordered zeolite-like carbon materials. The carbon materials have high surface area (17202535 m2/g) and high pore volume (1.09-1.56 cm3 g-1) and exhibit some zeolite-like structural ordering replicated from the zeolite template. Carbon materials prepared at 800 and 850 °C are nongraphitic and retain the particle morphology of the zeolite templates. Carbon prepared at 900 °C contains some graphitic domains (as indicated by XRD patterns) and irregular particles that are dissimilar to the zeolite template particles. We observed hydrogen uptake of up to 5.3 wt % at -196 °C and 20 bar, and 2.3 wt % at 1 bar, for the carbon materials. The hydrogen uptake is dependent on the surface area of the carbons. The use of as-synthesized (rather than calcined) zeolite β significantly improves the carbon yield and reduces the number of steps in the preparation of the templated carbons.
1. Introduction Porous carbon materials have been intensively studied as hydrogen storage media because of their high surface area, chemical inertness, and thermal stability.1 Porous carbons may be obtained via carbonization of suitable precursors followed by activation.1 The ability to control pore size and structural ordering is a desirable feature of any synthesis process for porous carbons. Several methods have been explored for the preparation of porous carbons with controlled microporosity and/ or mesoporosity.2,3 In particular, the template carbonization route, in which microporous zeolites and mesoporous silicas and aluminosilicas are used as a hard template, has attracted much attention for the preparation of well ordered porous carbon materials with controlled pore size and particle morphology.2,3 In general, the structural ordering of mesoporous hard templates is readily replicated in mesoporous carbons,3 while for zeolite hard templates, the replication of zeolite structural ordering in carbons is much more difficult. Recent work has however shown that the structural regularity of zeolite templates may be replicated in carbons. Kyotani and co-workers prepared microporous carbon with high surface area, which retained the structural regularity of zeolite Y, via a twostep method.4 Garsuch and Klepel have also reported on carbons that preserve the structural regularity of zeolite Y templates,5 while Gaslain and co-workers have prepared a carbon replica with a well resolved X-ray diffraction pattern using zeolite EMC-2 as template.6 Most recently, we have prepared zeolitelike carbon materials that exhibit well resolved powder XRD patterns and high surface area via a chemical vapor deposition (CVD) route using zeolite β as a hard template.7 The zeolitelike carbons were found to possess high hydrogen uptake capacity.7 In an effort to simplify the hard templating process * Author to whom correspondence should be addressed. Tel.+44 115 8466174; fax: +44 0115 9513562; e-mail:
[email protected]. † University of Nottingham. ‡ Polish Academy of Sciences.
for carbon materials with potentially high hydrogen storage capacity, we have now explored the use of as-synthesized zeolites as hard templates. Here we report on the synthesis and hydrogen storage properties of porous carbon materials obtained by using as-synthesized zeolite β as template via CVD at 800900 °C, with acetonitrile as carbon precursor. The use of assynthesized (rather than calcined) zeolite β improves the carbon yield, enhances textural properties, and reduces the number of steps in the preparation of the templated carbons. 2. Experimental Section 2.1. Material Synthesis. The as-synthesized zeolite β templates were obtained as follows; 8.33 g of TEOS was added to a mixture of 0.066 g of NaAlO2, 5.22 g of H2O, and 4.07 g of tetraethylammonium fluoride (TEAF), and 0.048 g of zeolite β was added as a seed. This mixture was stirred overnight in a sealed beaker and then transferred into an autoclave for hydrothermal treatment 160 °C for 4 days. The resulting product was obtained by filtration, washed repeatedly with a large amount of water, and air-dried at room-temperature. The porous carbon materials were prepared as follows: an alumina boat with 0.5 g of dry as-synthesized zeolite β was placed in a flow through tube furnace. The furnace was heated to the required temperature (800-900 °C) under a flow of nitrogen saturated with acetonitrile and then maintained at the target temperature for 3 h, followed by cooling under a flow of nitrogen only. The resulting zeolite/carbon composites were recovered and washed with 25% hydrofluoric (HF) acid for 3 days to remove the zeolite framework. Finally the resulting carbon materials were dried in an oven at 50 °C. 2.2. Material Characterization. Powder XRD analysis was performed using a Philips 1830 powder diffractometer with Cu KR radiation (40 kV, 40 mA), 0.02° step size, and 2 s step time. Textural properties were determined via nitrogen sorption at -196 °C using a conventional volumetric technique on an ASAP 2020 sorptometer. Before analysis, the samples were oven dried at 150 °C and evacuated for 12 h at 200 °C under vacuum.
10.1021/jp076603f CCC: $40.75 © 2008 American Chemical Society Published on Web 01/31/2008
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Figure 2. Thermogravimetric analysis (TGA) curves (A) and differential thermogravimetric (DTG) profiles (B) of carbon materials prepared via CVD using as-synthesized zeolite β as template.
Figure 1. Powder XRD patterns of carbons prepared via CVD using as-synthesized zeolite β as template.
The surface area was calculated using the Brunauer-EmmettTeller (BET) method based on adsorption data in the partial pressure (P/Po) range 0.02 to 0.25, and total pore volume was determined from the amount of nitrogen adsorbed at P/Po ) ca. 0.99. Elemental analysis was carried out using a CHNS analyzer (Fishons EA 1108). Thermogravimetric analysis (TGA) was performed using a Perkin-Elmer TGA 6 analyzer with a heating rate of 2 °C/min under static air conditions. Scanning electron microscopy (SEM) images were recorded using a JEOL JSM-820 scanning electron microscope. Samples were mounted using a conductive carbon double-sided sticky tape. A thin (ca. 10 nm) coating of gold sputter was deposited onto the samples to reduce the effects of charging. X-ray photoelectron spectroscopy (XPS) was performed using a Kratos AXIS ULTRA spectrometer with a monochromated Al KR X-ray source (1486.6 eV) operated at 10 mA emission current and 15 kV anode potential. The analysis chamber pressure was better than 1.3 × 10-12 bar. The take off angle for the photoelectron analyzer was 90° and the acceptance angle was 30° (in magnetic lens modes). 2.3. Hydrogen Uptake Measurements. Hydrogen uptake measurements were performed using high purity hydrogen (99.9999%), additionally purified by a molecular sieve filter, over the pressure range 0 to 20 bar with an Intelligent Gravimetric Analyzer (IGA-003, Hiden) that incorporates a microbalance capable of measuring weights with a resolution of (0.2 µg. The samples in the analysis chamber of the IGA003 were vacuumed up to 10-10 bar under heating at 200 °C overnight before measurement. The hydrogen uptake measurements were carried out at -196 °C in a liquid nitrogen bath. 3. Results and Discussion To obtain carbon materials, ca. 0.5 g of dry as-synthesized zeolite β in an alumina boat was placed in a flow through tube furnace, which was then heated to 800, 850, or 900 °C under a flow of nitrogen saturated with acetonitrile and maintained at the target temperature for 3 h, followed by cooling under a flow of nitrogen only.8,9 The resulting zeolite/carbon composites were recovered and washed with 25% hydrofluoric (HF) acid for 3 days. Finally the resulting carbon materials were dried in an oven at 50 °C. Figure 1 shows the powder X-ray diffraction (XRD) patterns of the carbon materials. For comparison the XRD pattern for the as-synthesized zeolite β is also shown. The XRD patterns of the carbons show a peak, similar to the (100), (101) diffraction of the as-synthesized zeolite β template, at 2θ ) 8°. The XRD patterns of the carbons exhibit a further lowintensity peak at 2θ ) 15°, which is at a position similar to the
(201), (202) diffraction of the as-synthesized zeolite β template. The presence of these two peaks indicates that the carbon materials exhibit zeolite-like structural pore ordering replicated from the zeolite β template.4-9 The structural pore ordering, as observed via TEM analysis (Supporting Information Figure 1S), was comparable to that previously observed for similar materials.7 The XRD patterns of carbons prepared at 800 and 850 °C exhibit a broad and very low-intensity peak at 2θ of ca. 26°, which is the (002) diffraction from turbostratic carbon. The low intensity of this peak suggests that carbon materials prepared at 800 or 850 °C are essentially amorphous (i.e., nongraphitic). We have previously found that a combination of zeolite-like structural ordering and the absence of graphitization in zeolitetemplated carbons imply that most of the carbon precursor is deposited within the zeolite pores (rather than on the external surface of the zeolite particles).7 This assumption is based on the fact that it is only carbon that is deposited on the external surface of the zeolite particles (and which has no spatial limitations) that can undergo graphitization.10 The carbon sample prepared at CVD temperature of 900 °C contains some turbostratic/graphitic domains as indicated by the peak observed at 2θ ) 26°. Overall, the XRD patterns indicate that assynthesized zeolites may be succesfully used as templates to nanocast structurally well ordered carbons. The nature and thermal stability of the carbon materials were probed by thermogravimetric analysis (TGA). The TGA curves and corresponding DTG profiles are shown in Figure 2. Thermal treatment up to 1000 °C indicated that the carbon materials are template free, as no (zeolite) residue was observed. The carbons are therefore efficiently generated from the carbon/zeolite composites during the zeolite removal step (washing in HF acid). Data on the thermal behavior of the samples may yield information on the nature of the carbon framework. The mass loss events during thermal analysis are shown in the DTG profiles in Figure 2. The sample prepared at 800 °C exhibits one mass loss event in the temperature range 300-700 °C whereas the samples obtained at 850 and 900 °C have two mass loss events (Figure 2). We ascribe the mass loss centered at 518-535 °C to combustion of amorphous (nongraphitic) carbon, while for the sample prepared at 900 °C, the mass loss event at 630 °C is due to the combustion of turbostratic/graphitic carbon. The sample prepared at 850 °C exhibits a limited mass loss at 602 °C due to combustion of small amounts of turbostratic carbon. The thermal analysis data therefore confirms that the carbon in samples prepared at 800 and 850 °C is largely amorphous (i.e., nongraphitic). Significant amounts of turbostractic/graphitic carbon are only present for the sample prepared at 900 °C. These findings are consistent with the XRD patterns in Figure 1. As stated above, turbostratic/graphitic carbon can only form on the surface of the zeolite templates, and therefore the presence
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Figure 4. Nitrogen sorption isotherms of carbons prepared via CVD using as-synthesized zeolite β as template.
TABLE 1: Textural Properties, Elemental Composition and Hydrogen Uptake Capacity of Carbons Prepared via CVD at Various Temperatures Using As-Synthesized Zeolite β as Template
Figure 3. SEM images of carbon materials prepared using assynthesized zeolite β as template via CVD at various temperatures.
of such (nonzeolite-like) carbon may be probed using scanning electron microscopy (SEM).7 SEM images of the carbon materials shown in Figure 3 indicate that the sample prepared at 800 °C has well formed particles similar to those of zeolite β template, and there are no other irregular particles. The particle morphology is consistent with carbon deposition within the pores of the zeolite template, which forms amorphous carbon within the zeolite pores and eventually generates zeolite-like structural ordering after removal of the zeolite framework; this scenario allows the retention of the particle morphology of the zeolite in the replicated carbon. The SEM images indicate that the 850 °C sample contains a small amount of irregular particles, while the 900 °C sample has a significant amount of irregular particles. We ascribe the irregular particles to turbostratic/ graphitic carbon that grows outside the zeolite pore system free of spatial constraints. The SEM images are consistent with the XRD and TGA data described above with respect to the nature (graphitic or amorphous) of the carbon framework. The nitrogen sorption isotherms of the carbon materials are shown in Figure 4. The isotherms of all the samples exhibit significant adsorption below P/Po ) 0.02, due to micropore filling. The carbon materials are therefore predominantly microporous. The isotherms also exhibit some limited nitrogen uptake at P/Po > 0.2, which may be attributed to adsorption into mesopores. The isotherms are typical for zeolite-templated carbons that possess a high proportion of microporosity.4-9 The textural properties of the carbons are summarized in Table 1. All the carbons have high surface area (1700-2500 m2/g) and pore volume (1.1-1.6 cm3/g). The surface area is particularly high for carbon materials prepared at 800 °C (2535 m2/g) and 850 °C (2470 m2/g). The sample prepared at 900 °C has a lower surface area (1720 m2/g), which is consistent with the fact that it contains significant amounts of turbostratic/graphitic carbon. A large proportion of the surface area of the present carbons is due to micropores: 65% for 800 and 850 °C samples and 76% for the 900 °C sample.
CVD temp (°C)
N content (wt %)
surface area (m2/g)a
pore volume (cm3/g)b
hydrogen uptake (wt %)c,d
800 850 900
3.3 3.5 4.6
2535 (1631) 2470 (1611) 1721 (1310)
1.56 (0.77) 1.54 (0.76) 1.09 (0.61)
5.3 (2.3) 5.2 (2.0) 3.3 (1.2)
a Values in parenthesis are micropore surface area. b Values in parenthesis are micropore volume. c Hydrogen uptake capacity at -196 °C and 20 bar. d Values in parenthesis are hydrogen uptake capacity at -196 °C and 1 bar.
It is noteworthy that the surface area of the carbon samples prepared at 800 and 850 °C is higher than that of equiValent samples that were templated by calcined zeolite β (Supporting Information Table S1),9 i.e., 2535 m2/g from as-synthesized (cf. 1928 m2/g from calcined) and 2470 m2/g from as-synthesized (cf. 2272 m2/g from calcined). Furthermore, both the magnitude and proportion of surface area associated with micropores is higher for the carbons templated by as-synthesized zeolite. The magnitude of the micropore surface area (1300-1650 m2/g) for the present carbons compares with 700-1050 m2/g for carbons templated by calcined zeolite.9 The proportion of micropore surface area for carbons templated by calcined zeolite is 38%, 45%, and 46% (for CVD temperature of 800, 850, and 900 °C respectively, Supporting Information Table S1) compared with 65%, 65%, and 76% for 800, 850, and 900 °C for the present samples templated by as-synthesized zeolite. Moreover, both the magnitude and proportion of micropore volume is also higher for the carbons templated by as-synthesized zeolite. The magnitude of the micropore volume (0.61-0.77 cm3/g) of the present carbons is higher than that (0.32-0.45 cm3/g) for carbons templated by calcined zeolite.9 The proportion of micropore volume is also higher; 50%, 50%, and 55% for 800, 850, and 900 °C samples respectively compared to 18%, 23%, and 26% (for CVD temperature of 800, 850, and 900 °C respectively, Supporting Information Table S1) for carbons templated by calcined zeolite. Indeed, it is remarkable that the textural properties of the present samples are comparable or in some cases higher than those of samples templated by calcined zeolite but via modified CVD routes that have previously been shown to improve the overall porosity and microporosity (Supporting Information Table S1).7,9 It is likely that further improvements in the textural properties of the present samples may be achieved via the modified CVD routes.7
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TABLE 2: Bulk (derived from Elemental Analysis) and Surface (derived from XPS Analysis) CNH Composition of Carbons Prepared via CVD at Various Temperatures Using As-Synthesized Zeolite β as Template bulk elemental analysis (wt %)
surface XPS analysis (wt %)
temp (°C)
C
Na
Hb
C
Na
800 850 900
82.3 84.3 86.6
3.3 (28.5) 3.5 (28.1) 4.6 (22.5)
2.2 (3.2) 1.8 (3.9) 1.4 (5.3)
91.8 93.2 93.0
3.6 (29.4) 4.9 (22.2) 5.8 (19.0)
a Values in parenthesis are C/N molar ratio. b Values in parenthesis are C/H molar ratio.
A key difference between the use of as-synthesized rather than calcined zeolite as template is that the former contains some organic matter prior to the CVD process. The existing organic content may be retained/incorporated into the carbon material during the CVD process. The presence of carbon matter not derived from the acetonitrile may lead to (i) improved overall carbon yield, and (ii) change in elemental composition of the final carbon samples. Preliminary data shows that at least some of the organic matter in the as-synthesized template is incorporated into the carbon. Heating of the as-synthesized zeolite under conditions similar to those of the CVD process but in the absence of acetonitrile (i.e., heating the as-synthesized zeolite to between 800 and 900 °C under a flow of nitrogen) generated zeolite/carbon composites that contained at least 5-10 wt % carbon. It is reasonable to assume that such carbon is incorporated into the zeolite-like carbons during the CVD process. Indeed, for carbon materials prepared similarly and in the absence of externally deposited carbon, we generally observed a higher carbon yield from as-synthesized zeolite templates compared to clacined zeolite templates. For example, at CVD temperature of 800 °C, the yield of carbon was at least 20% higher from as-synthesized templates. The higher yield may also be related to a more hydrophobic surface in the as-synthesized templates, which favors greater carbon precursor (acetonitrile) deposition. It is likely that the higher carbon yield and associated better pore filling of the zeolite template contribute to the higher microporosity of the present carbons compared to equivalent samples that are templated by calcined zeolite.9 Use of acetonitrile as precursor allows the incorporation of some nitrogen in the carbon materials. The nitrogen content (given as wt % in Table 1) of the carbon materials varies between 3.3 and 4.8 wt % and increases for samples prepared at high CVD temperature. The N content is slightly higher than that observed for carbons templated by calcined zeolite β.9 Information on the nature of the binding between carbon and nitrogen in the carbons was obtained from X-ray photoelectron spectroscopy (XPS). We first note that the N content determined by XPS (3.6-5.8 wt %, Table 2) is very close to the bulk nitrogen content (3.3-4.6 wt %) calculated from elemental analysis. This suggests that nitrogen is uniformly distributed throughout the carbon materials. Figure 5 shows the wide angle XPS spectra, which indicate a N 1s signal that is split into two peaks centered at ca. 399 and 401 eV. The peaks may be ascribed to pyridine-like nitrogen (399 eV) and highly coordinated quaternary nitrogen (401 eV) atoms incorporated into graphene-like sheets respectively.11 The intensity of the 401 eV peak increases at higher synthesis temperature, which is consistent with higher levels of graphitization. The peak at 399 eV has previously also been ascribed to defects within graphenelike sheets, which are expected to be more prominent for less graphitized samples.11 The C 1s peak for the carbon materials (Figure 5B) was observed at ca. 284.5 eV and is consistent with
Figure 5. XPS of N1s and C1s of carbon materials prepared via CVD using as-synthesized zeolite β as template.
Figure 6. Hydrogen sorption isotherms at -196 °C of carbons obtained via CVD at various temperatures using as-synthesized zeolite β as template. (Carbon density of 1.5 g/cm3 was used, and hydrogen density of 0.04 g/cm3 was used for buoyancy correction of adsorbed H2).
sp2 graphitic carbon. It is noteworthy that the elemental analysis data of the carbon samples (Table 2) is consistent with partial graphitization of the carbon materials. A fully crystallized graphite sample should have a high C/H ratio, whereas that of a single hydrogen-terminated graphene ribbon (one ring wide and infinite in length) would be 2.0. The templated carbons are intermediate between these extremes, ranging from 3.2 for the less graphitised 800 °C sample to 5.3 for the more graphitic sample prepared at 900 °C. Figure 6 shows hydrogen sorption isotherms of the carbon materials, measured gravimetrically with an IGA.7,8 The sorption isotherms show that the uptake of hydrogen by the carbon materials is reversible with no hysteresis, and that the adsorption branch closely matches the desorption branch. It is also clear that hydrogen uptake does not approach saturation even at a pressure of 20 bar implying that even greater uptake capacity is possible at elevated pressure. The hydrogen uptake capacity of the carbon materials, at 1 and 20 bar, is given in Table 1. The hydrogen uptake capacity of the sample prepared at 900 °C is 3.3 wt % and 1.2 wt % at 20 and 1 bar, respectively. Samples prepared at 800 and 850 °C, have a much higher hydrogen uptake capacity that reaches 5.3 wt % and 2.3 wt % at 20 and 1 bar, respectively. The trend in hydrogen uptake capacity is clearly related to the textural properties of the carbon materials and in particular the surface area. The isosteric heat of adsorption may be estimated using the Clausius-Clapeyron equation applied to hydrogen sorption data obtained at -196 and -186 °C. The initial heat of adsorption (i.e., at low hydrogen
2768 J. Phys. Chem. C, Vol. 112, No. 7, 2008 uptake) is ca. 8.0 kJ/mol, and thereafter decreased at high uptake (i.e., higher surface coverage) to 4.5 kJ/mol.7 The initial heat of adsorption, which is higher or comparable to that of activated carbon and metal organic framework materials,12 suggests a strong interaction between adsorbed hydrogen and the carbon surface.7 The hydrogen uptake capacity (3.3 - 5.3 wt % at -196 °C and 20 bar) is in general comparable to that of carbons prepared using calcined zeolites as template and greater than that of most other porous carbon materials.8,13-18 Indeed, a recent evaluation of the hydrogen storage capacity of a wide range of high surface area carbon materials and found a maximum capacity of ca. 4.5 wt % at a much higher pressure of 70 bar.11 We have recently observed uptake of up to 4.5 wt % at 20 bar for zeolite-templated carbons with low levels of zeolite type structural ordering,8 and up to 6.9 wt % for zeolitelike carbons.7 The use of as-synthesized zeolites as template therefore presents no disadvantages with respect to hydrogen storage capacity. More specifically, the hydrogen uptake capacity of the present carbons is higher than that of equivalent samples templated by calcined zeolite (Supporting Information Table S1). The difference is particularly striking for samples prepared at 800 and 850 °C. Our data therefore indicates that when similar synthesis (i.e., CVD) conditions are applied, carbons templated by as-synthesized zeolites have higher hydrogen storage capacity compared to carbons templated by calcined zeolites. It is indeed noteworthy (Table 1 and Supporting Information Table S1) that the highest hydrogen uptake capacity observed for the present samples (5.3 wt % at -196 °C and 20 bar) is nearly as high as that of carbon samples templated by calcined zeolite but via modified CVD routes that enhance hydrogen uptake (up to 6.0 wt % at -196 °C and 20 bar).7,9 The hydrogen uptake of the present as-synthesized zeolite templated carbons may therefore also be improved further via modified CVD routes.7 The comparatively high hydrogen uptake of the present samples is related to their level of microporosity. This suggests that microporosity plays a beneficial role in hydrogen uptake of the present zeolite-templated carbons. Recent studies have shown that it is not simply the overall surface area that determines hydrogen uptake in porous carbons but the surface area associated with ‘optimal pores’ of a specific size ca. 0.7 nm.12a,19 The requirement of optimal pores means that it is not just the total micropore surface area that is important but also the surface area associated with the optimal sized micropores. This presents a significant difference between activated carbons and zeolite-templated carbons; in most activated carbons the microporosity covers a wide range of pore size (0.3-2.0 nm),18,20 while for zeolite-templated carbons, the microporosity is dominated by pores of size 0.6-0.8 nm.7 Therefore, although the total micropore surface area of some activated carbons is higher than that of zeolite-templated carbons,18 it is likely that the latter have higher surface area associated with ‘optimal pores’ of size ca. 0.7 nm. Indeed, the present zeolite-templated carbons (prepared at 800 or 850 °C) exhibit hydrogen uptake comparable to that of activated carbons18 despite apparently lower microporosity. 4. Conclusions In summary, carbon materials have been prepared using assynthesized zeolite β as template via CVD at 800-900 °C. The carbon materials have high surface area (1720-2535 m2/g) and high pore volume (1.09-1.56 cm3g-1) and exhibit high microporosity and some zeolite-like structural ordering replicated
Pacuła and Mokaya from the zeolite template. Carbon materials prepared at 800 and 850 °C are essentially amorphous (nongraphitic) and retain the particle morphology of the zeolite templates. Carbon prepared at 900 °C contains some turbostratic/graphitic domains and irregular particles that are dissimilar to the zeolite template particles. The carbons exhibit hydrogen uptake of up to 5.3 wt % at -196 °C and 20 bar, and 2.3 wt % at 1 bar. The hydrogen uptake is dependent on the surface area of the carbons. The use of as-synthesized (rather than calcined) zeolite β offers the attractive advantages of higher carbon yield and fewer steps in the preparation of the templated carbons but without any compromise on the textural properties and hydrogen sorption capacity. Acknowledgment. This research was funded by the European Commission within Marie Curie Host Fellowships for the Transfer of Knowledge, No MTKD-CT-2004509832. Supporting Information Available: One Figure showing TEM image of zeolite-templated carbon, and Table with textural properties, elemental composition and hydrogen uptake of carbons prepared using calcined zeolite β as template. This information is available free of charge via the Internet at http:// pubs.acs.org. References and Notes (1) Bansal, C. R.; Donnet, J. B.; Stoeckli, F. ActiVe carbon; Marcel Dekker: New York, 1988. (2) (a) Kyotani, T. Carbon 2000, 38, 269. (b) Kyotani, T.; Ma, Z. X.; Tomita, A. Carbon 2003, 41, 1451. (3) (a) Ryoo, R.; Joo, S. H.; Kruk, M.; Jaroniec, M. AdV. Mater. 2001, 13, 677. (b) Yang, H. F.; Zhao, D. Y. J. Mater. Chem. 2005, 15, 1217. (c) Ryoo, R.; Joo, S. H.; Jun, S. J. Phys. Chem. B 1999, 103, 7743. (a) Lee, J.; Han, S.; Hyeon, T. J. Mater. Chem. 2004, 14, 478. (b) Lee, J.; Kim, J.; Hyeon, T. AdV. Mater. 2006, 18, 2073. (4) (a) Ma, Z.; Kyotani, T.; Liu, Z.; Terasaki, O.; Tomita, A. Chem. Mater. 2001, 13, 4413. (b) Ma, Z. X.; Kyotani, T.; Tomita, A. Chem. Commun. 2000, 2365. (c) Hou, P.-X.; Orikasa, H.; Yamazaki, T.; Matsuoka, K.; Tomita, A.; Setoyama, N.; Fukushima, Y.; Kyotani, T. Chem. Mater. 2005, 17, 5187. (5) (a) Garsuch, A.; Klepel, O.; Sattler, R. R.; Berger, C.; Glaeser, R.; Weitkamp, J. Carbon 2006, 44, 593. (b) Garsuch, A.; Klepel, O. Carbon 2005, 43, 2330. (6) Gaslain, F. O. M.; Parmentier, J.; Valtchev, V. P.; Patarin, J. Chem. Commun. 2006, 991. (7) Yang, Z.; Xia, Y.; Mokaya, R. J. Am. Chem. Soc. 2007, 129, 1673. (8) Yang, Z.; Xia, Y.; Sun, X.; Mokaya, R. J. Phy. Chem. B 2006, 110, 18424. (9) (a) Yang, Z.; Xia, Y.; Mokaya, R. Microporous Mesoporous Mater. 2005, 86, 69. (b) Yang, Z.; Xia, Y.; Mokaya, R. Stud. Surf. Sci. Catal. 2005, 156, 573. (10) Johnson, S. A.; Brigham, E. S.; Ollivier, P. J.; Mallouk, T. E. Chem. Mater. 1997, 9, 2448. (11) (a) Sen, R.; Satishkumar, B. C.; Govindaraj, A.; Harikumar, K. R.; Renganathan, M. K.; Rao, C. N. R. J. Mater. Chem. 1997, 7, 2335. (b) Terrones, M.; Redlich, P.; Grobert, N.; Trasobares, S.; Hsu, W.-K.; Terrones, H.; Zhu, Y.-Q.; Hare, J. P.; Reeves, C. L.; Cheetham, A. K.; Ruhle, M.; Kroto, H. W.; Walton, D. R. M. AdV. Mater. 1999, 11, 655. (c) Terrones, M.; Grobert, N.; Terrones, H. Carbon 2002, 40, 1665. (d) Xu, W.; Kyotani, T.; Pradhan, B. K.; Nakajima, T.; Tomita, A. AdV. Mater. 2003, 15, 1087. (12) (a) Yushin, G.; Dash, R.; Jagiello, J.; Fischer, J. E.; Gogotsi, Y. AdV. Funct. Mater. 2006, 16, 2288. (b) Benard, P.; Chahine, R. Langmuir 2001, 17, 1950. (c) Lee, J. Y.; Li, J.; Jagiello, J. J. Solid State Chem. 2005, 178, 2527. (d) Lee, J. Y.; Pan, L.; Kelly, S. P.; Jagiello, J.; Emge, T. J.; Li, J. AdV. Mater. 2005, 17, 2703. (13) Hirscher, M.; Panella, B. J. Alloys Compd. 2005, 404, 399. (14) Zhao, X. B.; Xiao, B.; Fletcher, A. J.; Thomas, K. M. J. Phys. Chem. B 2005, 109, 8880. (15) Pang, J.; Hampsey, J. E.; Wu, Z.; Hu, Q.; Lu, Y. Appl. Phys. Lett. 2004, 85, 4887.
Zeolite-Like Carbons (16) Terres, E.; Panella, B.; Hayashi, T.; Kim, Y. A.; Endo, M.; Dominguez, J. M.; Hirscher, M.; Terrones, H.; Terrones, M. Chem. Phys. Lett. 2005, 403, 363. (17) Chen, L.; Singh, R. K.; Webley, P. Micropor. Mesopor. Mater. 2007, 102, 159. (18) Jorda-Beneyto, M.; Suarez-Garcia, F.; Lozano-Castello, D.; CazorlaAmoros, D.; Linares-Solano, A. Carbon 2007, 45, 292.
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