Zeolite-templated Carbon Research Articles

Pt supported on ordered microporous carbon as highly active catalyst for catalytic hydrodeiodination of iodinated X-ray contrast media

In this study, Pt catalysts supported on zeolite templated carbon (Pt/ZTC) were prepared by in-situ chemical vapor deposition using Pt exchanged Y zeolite as the template. For comparison, Pt catalysts supported on zeolite templated carbon (ZTC) and commercial activated carbon (AC) were prepared using the impregnation method. The liquid phase catalytic hydrodeiodination of two iodinated X-ray contrast media (ICM, i.e., diatrizoate and iopamidol) was investigated on the catalysts. The catalysts were characterized by X-ray diffraction, N2 adsorption–desorption isotherms, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy and zeta-potential measurement. The results showed that Pt/ZTC catalysts prepared by in-situ chemical vapor deposition (CVD) under varied reaction conditions were good replicas of Y zeolite in structure. Compared with the catalysts prepared by the impregnation method, Pt/ZTC had a higher Pt dispersion and more homogeneous Pt distribution. Increasing CVD temperature resulted in Pt particle growth in Pt/ZTC. The catalytic hydrodeiodination of diatrizoate and iopamidol proceeded via a sequential deiodination pathway, and followed the Langmuir-Hinshelwood model, reflecting that the conversion of adsorbed ICM was the rate-controlling step. Additionally, more effective conversion of iopamidol was observed than that of diatrizoate on Pt/ZTC. Furthermore, Pt/ZTC prepared at higher CVD temperature exhibited lower catalytic activities for the hydrodeiodination of diatrizoate and iopamidol. Solution pH markedly impacted the catalytic ICM conversion, and enhanced hydrodeiodination was observed with the increase of pH. As for catalyst reuse, Pt/ZTC remained about 80% of initial activity after 4 reuse cycles, exhibiting much higher stability than the catalyst prepared by the impregnation method. The present findings highlighted the Pt/ZTC catalysts prepared by in-situ CVD as highly active and stable catalysts for the removal of halogenated organic pollutants by catalytic hydrogenation.

Extremely high electrical conductance of microporous 3D graphene-like zeolite-templated carbon framework

We report the remarkably high electrical conductance of microporous 3D graphene-like carbons that were formed using lanthanum (La)-catalyzed synthesis in a Y zeolite (LaY) template investigated using conductive atomic force microscopy (C-AFM) and theoretical calculations. To uncover the relation between local electrical conductance and the microporous structures, we tuned the crystallographic ordering of LaY-templated carbon systems by changing the heating temperature. The structure of the LaY-templated carbon prepared at the higher temperature has graphene-like sp2 hybridized bonds, which was confirmed using high-resolution transmission electron microscopy and X-ray diffraction measurements. C-AFM current–voltage spectroscopy revealed that the local current flow in the LaY-templated carbon depends on the quantity of C–C bonds within the narrow neck between the closed supercages (i.e. there are three types of carbon: carbon with heat treatment, carbon without heat treatment, and carbon synthesized at low temperature). The difference in electrical conductance on the LaY-templated carbon was also confirmed via theoretical computation using the Boltzmann transport theory and the deformation potential theory based on the density functional theory. These results suggest that the degree of order of the pores in the 3D zeolite-templated carbon structures is directly related to electrical conductance.

Alumina based doped templated carbons: A comparative study with zeolite and silica gel templates

Alumina based templates were used for preparation of nitrogen and platinum doped templated carbons and compared with silica gel and zeolite templated carbons. For alumina based templated carbons, 5–6 times higher surface area was obtained compared to corresponding templates while that for zeolite and silica gel templates, it was only 1–2 times higher. The surface area of surfactant modified alumina templated carbon was comparable with that of microporous zeolite templated carbon but pore size and volume was comparable to that of mesoporous silica templated carbon. Higher dispersion of the Pt metal was observed within the matrix of mesoporous templates with highest for surfactant modified alumina templated carbon. The morphology of surfactant modified alumina templated carbon was similar to that of silica gel templated carbon and co-doping with platinum resulted in noddle like structure. At 25 bar and −196 °C the hydrogen uptake was in the range of 4–3.4 wt% and decreased linearly with decrease in surface area. Both surface area and pore volume dropped for all Pt co–doped samples. However uptake capacity varied; for co–doped silica gel and zeolite templated carbons it was reduced, while that of co–doped alumina based templated carbons it increased. The highest hydrogen uptake of 4.1 wt% for surfactant modified alumina templated co–doped carbon was attributed to synergistic effect of significant surface area, highest pore volume and highly dispersed platinum. The study concludes that alumina based templates are equally good or better for synthesis of the templated carbons.

Fine Dispersion of Pt4–5 Subnanoclusters and Pt Single Atoms over Porous Carbon Supports and Their Structural Analyses with X-ray Absorption Spectroscopy

We demonstrate the fine dispersion of Pt4–5 subnanoclusters or Pt single atoms on two types of porous carbon supports, Ketjen black (KB) and zeolite-templated carbon (ZTC). The loading amount of Pt4–5 subnanoclusters reached as much as ca. 4 and 13 wt % for KB and ZTC, respectively. For the fine dispersion of Pt subnanoclusters, simply filling an organoplatinum complex, (COD)PtMe2, as a Pt precursor into the micropores is found to be crucial to prevent agglomeration or sintering of Pt subnanoclusters. Moreover, it is possible to disperse Pt single atoms on ZTC, simply by decreasing the Pt loading amount down to ca. 0.9 wt %, owing to some stabilization effect by oxygen-containing functional groups. The detailed structural insights into the supported Pt subnanoclusters and Pt single atoms were analyzed by X-ray absorption spectroscopy (XAS). Extended X-ray absorption fine structure (EXAFS) analysis for Pt subnanoclusters reveals that the Pt–Pt bond is contracting to a large extent (∼2.8%) relative to balk ...

Evaluation of heavy crude oil from a water-oil model system as starting material for the preparation of adsorbents type NaY zeolite-templated carbon

In this work, NaY zeolite is explored as a possible “template” to obtain porous materials type ZTC from the adsorption of heavy crude oil in a water-oil model system (emulsion). In order to produce the adsorbents, a cationic surfactant is selected to facilitate the adsorption of the crude oil into the pores of the zeolite and to get the composite, which was activated with controlled thermal treatments (T: 700–800 °C and t: 0.5–1 h) in inert conditions (N2 gaseous). The starting materials, composite and porous carbons were characterized using structural/surface analysis techniques (API Gravity, SARA, IR, XRD, XRF, TGA, Langmuir isotherms, BET and SEM). The results showed that four types of mesoporous carbons were produced with specific surface areas between 70 ± 1 m2/g and 220 ± 3 m2/g, average pore volumes between 0.144 cm3/g and 0.40 cm3/g and average pore widths between 4.9 nm and 8.3 nm. The activation conditions of 800 °C and 1 h allowed to make the carbonaceous material with the best surface characteristics (220 ± 3 m2/g, 0.27 cm3/g, and 4.9 nm). Therefore, it is concluded that under assay conditions employed, the heavy crude oil, as a mixed model (water-oil), from an aqueous environment is a starting material suitable for preparation of “mesoporous” carbons.

Zeolite-Templated Carbon as an Ordered Microporous Electrode for Aluminum Batteries.

High surface area porous carbon frameworks exhibit potential advantages over crystalline graphite as an electrochemical energy storage material owing to the possibility of faster ion transport and up to double the ion capacity, assuming a surface-based mechanism of storage. When detrimental surface-related effects such as irreversible capacity loss due to interphase formation (known as solid-electrolyte interphase, SEI) can be mitigated or altogether avoided, the greatest advantage can be achieved by maximizing the gravimetric and volumetric surface area and by tailoring the porosity to accommodate the relevant ion species. We investigate this concept by employing zeolite-templated carbon (ZTC) as the cathode in an aluminum battery based on a chloroaluminate ionic liquid electrolyte. Its ultrahigh surface area and dense, conductive network of homogeneous channels (12 Å in width) render ZTC suitable for the fast, dense storage of AlCl4- ions (6 Å in ionic diameter). With aluminum as the anode, full cells were prepared which simultaneously exhibited both high specific energy (up to 64 Wh kg-1, 30 Wh L-1) and specific power (up to 290 W kg-1, 93 W L-1), highly stable cycling performance, and complete reversibility within the potential range of 0.01-2.20 V.

Electrospun zeolite-templated carbon composite fibres for hydrogen storage applications

The current study explored the application of the electrospinning technique to produce multi-hierarchical composites for hydrogen storage applications. Predetermined control of fibre porosity is expected to enable production of well-defined hierarchical pore structure. The study involved encapsulation of highly porous zeolite-templated carbon (ZTC) into electrospun fibres and testing of the resulting composites for hydrogen storage. The hydrogen storage capacity of the composite fibres was 1.83%, compared with 2.39 wt% for powder ZTC material. The potential of the electrospinning technique as a shaping option for preparing composites from loose powder is demonstrated. The ZTC–polyacrylonitrile (ZTC-PAN) composite retained about 76% of the hydrogen storage capacity of the ZTC. Vacuum degassing of the ZTC–PAN electrospun composite was also found to enhance the development of porosity, aiding hydrogen penetration into zeolite pores.

Effect of Heteroatoms in Ordered Microporous Carbons on Their Electrochemical Capacitance.

Micropores play a more important role in enhancing the electrochemical capacitance than mesopores and macropores; therefore, the effect of heteroatom doping into micropores on the electrochemical behavior is interesting. However, heteroatom doping into porous carbon materials would potentially change their pore structures and pore sizes, which also affect their electrochemical capacitive behaviors. To gain insight into the intrinsic effects of heteroatoms on the electrochemical capacitive behaviors, zeolite-templated carbon (ZTC) may be the most suitable candidate. ZTC is an ordered microporous carbon with a uniform micropore size of 1.2 nm, a high surface area, and a large micropore volume. In this work, a series of ZTCs containing oxygen, nitrogen, or boron as heteroatoms, with an ordered pore structure and the same pore size, are prepared. By examining their electrochemical capacitive behaviors in an organic electrolyte, the effect of heteroatom doping can be isolated and discussed without considering the effects of pore structure and pore size. Acid anhydride groups are found to generate pseudocapacitance in two potential ranges, -1.0 to -0.3 V (vs Ag/AgClO4) and -0.2 to 0.4 V. B is introduced into the ZTC framework solely as -B(OH)2, which is found to be an electrochemically inert species. N is introduced as pyridine (3.0%), pyridone/pyrrole (23.8%), quaternary (66.6%), and oxidized N (6.6%), and these species exhibit noticeable pseudocapacitance in the microporous carbon.

Zeolite-Templated Carbon Catalysts for Adsorption and Hydrolysis of Cellulose-Derived Long-Chain Glucans: Effect of Post-Synthetic Surface Functionalization

This manuscript quantitatively investigates the effect of weak acid site surface density on adsorption and catalytic hydrolysis of long-chain β-glucans, with post-synthetically modified zeolite-templated carbon (ZTC) catalysts. Our approach requires ZTC-surface modification and overcomes previous limitations of pore collapse in accomplishing this, which has previously necessitated electrochemical methods. We demonstrate that mild ZTC treatment in hydrogen peroxide preserves the 1.1 nm micropores of ZTC, which were previously shown to be ideal for β-glucan adsorption, while synthesizing surface-modified ZTC catalysts that hydrolyze adsorbed β-glucans to glucose in up to 87% yield. Our results demonstrate a direct increase in catalytic hydrolysis activity and glucose yield upon increasing acid site density via surface functionalization. Upon investigating the mechanism of catalytic hydrolysis under buffered conditions, we rule out the synthesis of acid sites with stronger acidity as a result of possible gre...

Nuclear magnetic resonance study of zeolite-templated carbon

We report on nuclear magnetic resonance (NMR) study of zeolite-templated carbon (ZTC) material. Analysis of 13C and 1H NMR spectra shows that its structure includes a condensed aromatic ring system and reveals hydrogen atoms bound to aromatic carbons. Small amount (∼3%) of sp3 carbons is also detected. The proposed ZTC structure consists of large conductive graphene units connected by carbon hexagons and rare sp3 carbon links. Such structure keeps electrical conduction throughout the carbon network by means of conductive sp2 carbon bridges and a charge hopping through the short non-conductive sp3 carbon links.

An organic proton battery employing two redox-active quinones trapped within the nanochannels of zeolite-templated carbon

For the first time, we present in this work a simple method to achieve high energy density device by functionalizing zeolite-templated carbon (ZTC) with quinone molecules. Two types of quinone, anthraquinone and tetrachlorohydroquinone, which have different redox potential, were introduced into ZTC framework by a wet impregnation method, and were characterized in a sulfuric acid. An organic proton battery was assembled from two different functionalized-ZTC electrodes in the sulfuric acid, where the energy is stored by a proton-rocking-chair mechanism resulting from a quinone couple trapped inside the nanopores of ZTC with a less crystalline or nanocrystalline structure. The assembled device possesses an energy density as high as 30.6 Wh kg−1, which is superior to the activated-carbon-based capacitors working in the organic electrolytes and lead batteries.

Synthesis and Photoproperties of Edge-functionalized Zeolite-templated Carbon with Bromine or Carbazole Groups

We succeeded in synthesizing edge-brominated zeolite-templated carbon (ZTC-Br) as the key intermediate of edge-functionalization of ZTC via an electrophilic aromatic substitution reaction using dib...

A Generalized Law of Corresponding States for the Physisorption of Classical Gases with Cooperative Adsorbate–Adsorbate Interactions

The Law of Corresponding States for classical gases is well established. Recent attempts at developing an analogous Law of Corresponding States for gas physisorption, however, have had limited success, in part due to the omission of relevant adsorption considerations such as the adsorbate volume and cooperative adsorbate–adsorbate interactions. In this work, we modify a prior Law of Corresponding States for gas physisorption to account for adsorbate volume, and test it with experimental data and a generalized theoretical approach. Furthermore, we account for the recently reported cooperative adsorbate–adsorbate interactions on the surface of zeolite-templated carbon (ZTC) with an Ising-type model and in doing so show that the Law of Corresponding States for gas physisorption remains valid even in the presence of atypically enhanced adsorbate–adsorbate interactions.

Complex investigation of charge storage behavior of microporous carbon synthesized by zeolite template

Microporous zeolite templated carbon (ZTC) was synthesized by impregnation method using zeolite Y (Na-form) as a template, and furfuryl alcohol as a carbon precursor. The characterization was carried out by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy, nitrogen physisorption, elemental analysis and electrochemical methods. Physisorption measurements evidenced high micropore volume of obtained material (∼0.43 cm3 g−1). The charge storage ability in aqueous KOH, H2SO4 and Na2SO4 solutions was systematically studied by cyclic voltammetry, galvanostatic charging/discharging and complex impedance measurements. Specific coulombic capacitance, the hydrogen storage, HZTC bonding and relaxation time of adsorption were found to be dependent on the type of electrolyte. Neutral Na2SO4 aqueous solution was found to be the best for supercapacitor application, thanks to: i) the highest available voltage window ii) lowest corrosion and iii) highest capacitance amounting to 123 F g−1 at 1 A g−1.

Tuning selectivity of electrochemical reactions by atomically dispersed platinum catalyst.

Maximum atom efficiency as well as distinct chemoselectivity is expected for electrocatalysis on atomically dispersed (or single site) metal centres, but its realization remains challenging so far, because carbon, as the most widely used electrocatalyst support, cannot effectively stabilize them. Here we report that a sulfur-doped zeolite-templated carbon, simultaneously exhibiting large sulfur content (17 wt% S), as well as a unique carbon structure (that is, highly curved three-dimensional networks of graphene nanoribbons), can stabilize a relatively high loading of platinum (5 wt%) in the form of highly dispersed species including site isolated atoms. In the oxygen reduction reaction, this catalyst does not follow a conventional four-electron pathway producing H2O, but selectively produces H2O2 even over extended times without significant degradation of the activity. Thus, this approach constitutes a potentially promising route for producing important fine chemical H2O2, and also offers opportunities for tuning the selectivity of other electrochemical reactions on various metal catalysts.

N-doped zeolite-templated carbon as a metal-free electrocatalyst for oxygen reduction

Nitrogen-doped zeolite-templated carbon having 3-dimensionally microporous structure exhibited low surface work function and high catalytic performance for oxygen reduction.

Successful functionalization of superporous zeolite templated carbon using aminobenzene acids and electrochemical methods

A novel and selective electrochemical functionalization of a highly reactive superporous zeolite templated carbon (ZTC) with two different aminobenzene acids (2-aminobenzoic and 4-aminobenzoic acid) was achieved. The functionalization was done through potentiodynamic treatment in acid media under oxidative conditions, which were optimized to preserve the unique ZTC structure. Interestingly, it was possible to avoid the electrochemical oxidation of the highly reactive ZTC structure by controlling the potential limit of the potentiodynamic experiment in presence of aminobenzene acids. The electrochemical characterization demonstrated the formation of polymer chains along with covalently bonded functionalities to the ZTC surface. The functionalized ZTCs showed several redox processes, producing a capacitance increase in both basic and acid media. The rate performance showed that the capacitance increase is retained at scan rates as high as 100 mV s−1, indicating that there is a fast charge transfer between the polymer chains formed inside the ZTC porosity or the new surface functionalities and the ZTC itself. The success of the proposed approach was also confirmed by using other characterization techniques, which confirmed the presence of different nitrogen groups in the ZTC surface. This promising method could be used to achieve highly selective functionalization of highly porous carbon materials.

Synthesis of a hybrid MIL-101(Cr)/ZTC composite for hydrogen storage applications

Metal–organic frameworks (MOFs) hybrid composites have recently attracted considerable attention in hydrogen storage applications. In this study a hybrid composite of zeolite templated carbon (ZTC) and Cr-based MOF (MIL-101) was synthesised by adding the templated carbon in situ during the synthesis of MIL-101(Cr). The obtained sample was fully characterized and hydrogen adsorption measurements performed at 77 K up to 1 bar. The results showed that the surface areas and the hydrogen uptake capacities of individual MIL-101 (2552 m2 g−1, 1.91 wt%) and zeolite templated carbon (2577 m2 g−1, 2.39 wt%) could be enhanced when a hybrid MIL-101(Cr)/ZTC composite (2957 m2 g−1, 2.55 wt%) was synthesized. The procedure presents a simple way for enhancement of hydrogen uptake capacity of the individual Cr-MOF and templated carbon samples.

Unusual Entropy of Adsorbed Methane on Zeolite-Templated Carbon

Methane adsorption at high pressures and across a wide range of temperatures was investigated on the surface of three porous carbon adsorbents with complementary structural properties. The measured adsorption equilibria were analyzed using a method that can accurately account for nonideal fluid properties and distinguish between absolute and excess quantities of adsorption, and that also allows the direct calculation of the thermodynamic potentials relevant to adsorption. On zeolite-templated carbon (ZTC), a material that exhibits extremely high surface area with optimal pore size and homogeneous structure, methane adsorption occurs with unusual thermodynamic properties that are greatly beneficial for deliverable gas storage: an enthalpy of adsorption that increases with site occupancy, and an unusually low entropy of the adsorbed phase. The origin of these properties is elucidated by comparison of the experimental results with a statistical mechanical model. The results indicate that temperature-dependent clustering (i.e., reduced configurations) of the adsorbed phase due to enhanced lateral interactions can account for the peculiarities of methane adsorbed on ZTC.

Long-Chain Glucan Adsorption and Depolymerization in Zeolite-Templated Carbon Catalysts

We demonstrate adsorption and depolymerization of long-chain β-glu strands derived from cellulose, within the microporous confines of a zeolite-templated carbon (ZTC) material. The ZTC adsorbs β-glu strands that have a radius of gyration several-fold larger than the ZTC micropore diameter and do so rapidly (less than 2 min) and in adsorbed β-glu coverages of up to 80% of the ZTC mass. Principles of supramolecular chemistry predict that such adsorption occurs inside of the ZTC based on its micropore size as host being nearly ideal for glucan guest. A comparative study of partially etched materials and nitrogen physisorption at −196 °C indeed demonstrates β-glu adsorption to occur within internal ZTC micropores rather than on the external surface. Such adsorption under micropore confinement is expected to place significant mechanical strain on the β-glu strand, and this strain can be in principle relieved by depolymerization via hydrolysis. This hypothesis motivated us to investigate depolymerization of ads...