H2 Sorption Research Articles

A metal-organic polyhedron based on dibenzothiophene ligand: Gas adsorption and reductive properties

A new metal–organic polyhedron Cu-MOP with octahedral geometry was constructed by 2,8-dibenzothiophenedicarboxylic acid and dicopper paddlewheel. Cu-MOP exhibited H2 and CO2 sorption behavior. Furthermore, Cu-MOP revealed reductive properties towards TCNQ, DDQ, CR and MB due to the electron-donating nature of DBT ligand.

Strategy for the enhancement of H2 uptake in porous materials containing TiO2

The good affinity of TiO2 surface for hydrogen sorption has prompted in the past the synthesis of high specific surface area, Ti-doped mesoporous silicas. Since most TiO2 is buried in the pore walls of the silicas, such materials did not express their full potential H2 uptake. In order to overcome this limitation, different amounts of titania were deposited on the pore surface of a pre-formed SBA-15 of 704 m2/g, and the resulting oxides were calcined at 300 or 500 °C. The hydrogen sorption–desorption isotherms of the materials prepared in this study, at 77.4 K and up to 100 kPa, reveal that a small amount of titania doubles the hydrogen storage capacity of SBA-15, provided that the materials are calcined at least at 300 °C. Reproducible H2 uptakes up to 1.4 wt.% at 77.4 K and 100 kPa have been measured. The optimal amount of TiO2 is 4.5% in moles, leading to a uniform dispersion in the mesopores. A higher loading (7.3%) brings about the formation of large titania particles that tend to block the lumen of the mesopores, with no gain in the H2 sorption capacity.

Optimization of biomass-based carbon materials for hydrogen storage

Hydrogen is considered as the most promising future fuel, as its combustion generates only water vapor besides energy. However, finding efficient, safe and low cost storage methods is the basic impediment for the adoption of hydrogen as fuel. For this purpose, five biomass-based carbon samples have been successfully prepared through KOH activation procedure. The microstructure of the prepared materials was tuned by varying KOH/precursor weight ratio from 1:1 to 5:1, in order to optimize their hydrogen storage behavior and to clarify the storage mechanism. A careful textural and morphological characterization of the prepared samples (N2 and CO2 adsorption, X-ray diffraction, electron microscopy observations) showed that by increasing the activation ratio the nature of the carbons changes from microporous to micro-mesoporous. Thus, an increase in the surface area was observed which enhanced H2 sorption capacity when high H2 pressures were adopted. At subatmospheric pressure, the role of active sites for H2 adsorption, located in the oriented graphene sheets, was clearly elaborated. Finally, the optimal carbon sample has shown a capacity of 6wt% and 1.22wt% at −196°C and 25°C respectively, and 200bar. These results make biomass-based carbons promising materials for H2 storage application.

Exceptional H2 sorption characteristics in a Mg(2+)-based metal-organic framework with small pores: insights from experimental and theoretical studies.

Experimental sorption measurements, inelastic neutron scattering (INS), and theoretical studies of H2 sorption were performed in α-[Mg3(O2CH)6], a metal-organic framework (MOF) that consists of a network of Mg(2+) ions coordinated to formate ligands. The experimental H2 uptake at 77 K and 1.0 atm was observed to be 0.96 wt%, which is quite impressive for a Mg(2+)-based MOF that has a BET surface area of only 150 m(2) g(-1). Due to the presence of small pore sizes in the MOF, the isosteric heat of adsorption (Qst) value was observed to be reasonably high for a material with no open-metal sites (ca. 7.0 kJ mol(-1)). The INS spectra for H2 in α-[Mg3(O2CH)6] is very unusual for a porous material, as there exist several different peaks that occur below 10 meV. Simulations of H2 sorption in α-[Mg3(O2CH)6] revealed that the H2 molecules sorbed at three principal locations within the small pores of the framework. It was discovered through the simulations and two-dimensional quantum rotation calculations that different groups of peaks correspond to particular sorption sites in the material. However, for H2 sorbed at a specific site, it was observed that differences in the positions and angular orientations led to distinctions in the rotational tunnelling transitions; this led to a total of eight identified sites. An extremely high rotational barrier was calculated for H2 sorbed at the most favorable site in α-[Mg3(O2CH)6] (81.59 meV); this value is in close agreement to that determined using an empirical phenomenological model (75.71 meV). This rotational barrier for H2 exceeds those for various MOFs that contain open-metal sites and is currently the highest yet for a neutral MOF. This study highlights the synergy between experiment and theory to extract useful and important atomic level details on the remarkable sorption mechanism for H2 in a MOF with small pore sizes.

An unusual H2 sorption mechanism in PCN-14: insights from molecular simulation.

Simulations of H2 sorption were performed in PCN-14, a metal-organic framework (MOF) that consists of Cu(2+) ions coordinated to 5,5'-(9,10-anthracenediyl)diisophthalate (adip) linkers. This MOF displays an excess H2 uptake of 2.70 wt% at 77 K and 1.0 atm and an initial H2Qst value of 8.6 kJ mol(-1) according to previous experimental measurements. The experimental H2 sorption isotherms and Qst values in PCN-14 were reproduced in simulations using well-known H2 potentials that have been widely used for MOF-H2 theoretical studies. H2 sorption in PCN-14 was dominated by repulsion/dispersion energetics; this allowed the experimental observables to be reproduced by a model that includes only Lennard-Jones parameters. The most energetically favorable H2 sorption site in PCN-14 corresponds to sorption within a small cage that is enclosed by three [Cu2(O2CR)4] units and three adip linkers. The anthracenyl rings of the adip linkers represent the secondary sorption sites within the MOF. In contrast to expectations, sorption of H2 onto the Cu(2+) ions of the copper paddlewheels was not observed within the simulations at low loading. The simulations revealed that the open-metal sites in PCN-14 were occupied at high loading. Control simulations of H2 sorption in PCN-14 for different cases in which the partial positive charge of one of the paddlewheel Cu(2+) ions was increased relative to the other revealed that sorption onto the open-metal sites can be captured if there is a very high positive charge on the metal. Otherwise, the calculated partial charge for the Cu(2+) ions in PCN-14 in this work was not high enough in magnitude to facilitate strong H2-metal interactions in simulation. This study shows the power of using molecular simulations to elucidate an unusual H2 sorption behavior in a MOF.

Dramatic Effect of the Electrostatic Parameters on H2 Sorption in an M-MOF-74 Analogue

Simulations of H2 sorption were performed in Cu-MOF-74, a recent addition to the M-MOF-74 series. Electronic structure calculations revealed that the Cu2+ ions exhibit an unusually low partial positive charge distribution in Cu-MOF-74, which is a direct consequence of the Jahn–Teller effect. This is in contrast to the charge environment for the metal ions in some of the other M-MOF-74 variants as determined in previous work [Pham, T.; J. Phys. Chem. C 2015, 119, 1078−1090]. Because of the low magnitude of the partial charges of the Cu2+ ions in Cu-MOF-74, this MOF displays the lowest H2 uptake and Qst values of the M-MOF-74 series, which is consistent with what was observed experimentally for H2 sorption in this series of MOFs. Control simulations of H2 sorption in a nonphysical Cu-MOF-74 variant were performed in which a set of calculated partial charges, appropriate for one of the other M-MOF-74 analogues, were used. These simulations utilize a much higher partial positive charge for the metal ions and,...

Inelastic Neutron Scattering and Theoretical Studies of H2 Sorption in a Dy(III)-Based Phosphine Coordination Material

A combined inelastic neutron scattering (INS) and theoretical study of H2 sorption was performed in PCM-16, a phosphine coordination material (PCM) with the empirical formula [(CH3)2NH2][Dy2(tctpo)2(O2CH)] (tctpo = tris(p-carboxylato)triphenylphosphine oxide). INS measurements at different loadings of H2 revealed a peak occurring at low rotational tunnelling energies (ca. 5–8 meV), which corresponds to a high barrier to rotation and, therefore, a strong interaction with the host. Molecular simulations of H2 sorption in PCM-16 revealed that the H2 molecules sorbed at two main sites in the material: (1) the (CH3)2NH2+ counterions and (2) within the small pores of the framework. Two-dimensional quantum rotation calculations revealed that the peak occurring from approximately 5–8 meV in the INS spectra for PCM-16 is associated with sorption onto the (CH3)2NH2+ ions. These counterions provide for the strongest H2 sorption sites in the material, which corresponds to an isosteric heat of adsorption (Qst) value of close to 8 kJ mol–1. The calculated rotational barrier for the (CH3)2NH2+–H2 interaction in PCM-16 (45.60 meV) is higher than those for a number of extant metal–organic frameworks (MOFs), especially those that contain open-metal sites. This study provides insights into the H2 sorption mechanism in a PCM for the first time and shows how the inclusion of counterions in porous materials is a promising method to increase the H2 sorption energetics in such materials.

A proposed kinetic model for hydrogen sorption in MgH2

The role of ternary Mg–Nb oxides on H2 absorption and desorption properties of ball milled MgH2 is discussed on the basis of a kinetic model involving the formation of reaction pathways of ternary oxide species with easier splitting of H2 that facilitate the transport of H2 into the solid structure. The kinetic model comprised three key steps: dissociation of molecular hydrogen into H atoms, diffusion of H into Mg to form MgH2 during adsorption, and successive recombination of H–H on the surface of the additives during desorption to make a pathway for H2 sorption in the structure. The presence of transition metal oxides remarkably increases the H2 sorption rates of nano-structured MgH2, as determined by a volumetric Sievert apparatus. The H2 desorption rate increases with increasing temperature from 593 to 673 K and under the same conditions, the absorption rate decreases. The most promising results were obtained for Mg3Nb6O11-doped MgH2 nanoparticles. The MgH2/Mg3Nb6O11 system is completely dehydrogenated at 673 K under 0.1 MPa H2 and the samples fully rehydrogenated at 613 K under 2.5 MPa H2 pressure. Activation energies were obtained for MgH2/Mg3Nb6O11 mixture, and without additive (ball milled MgH2), to be 88 and 127 kJ mol−1, respectively, underlying the effect of the ternary additive.

Comparing hydrogen sorption in different Pd-doped pristine and surface-modified nanoporous carbons

Three types of nanoporous carbons (a molecular sieve, an ordered mesoporous carbon and a carbon aerogel) with distinctively different porous properties were subjected to surface modification through wet oxidation and subsequent metal doping with Pd nanoparticles. The H2 sorption performance of the carbons and their doped analogues was examined at 298 K up to 20 bar. The introduction of different oxygen containing groups in the three carbons enhances the amount of sorbed hydrogen, while the rather complex mechanism of sorption seems to be positively influenced by the small size of the pores and the surface chemistry. It was shown that in all cases a synergistic effect between the metal and the oxidized carbon takes place, leading to enhanced hydrogen sorption through reversible processes, which however is not sufficient to meet the demanding targets for practical applications.

Nanoporous spongy graphene: Potential applications for hydrogen adsorption and selective gas separation

In the present work, a nanoporous (pore width~0.7nm) graphene-based sponge-like material with large surface area (~350m2/g) was synthesized by wet chemical reduction of graphene oxide in combination with freeze-drying. Surface morphology and elemental composition were studied by scanning and transmission electron microscopy combined with energy dispersive X-ray spectroscopy. Surface chemistry was qualitatively examined by Fourier-transform infrared spectroscopy, while the respective structure was investigated by X-ray diffraction analysis. Textural properties, including Brunauer–Emmet–Teller (BET) surface area, micropore volume and surface area as well as pore size distribution, were deduced from nitrogen gas adsorption/desorption data obtained at 77K and up to 1bar. Potential use of the spongy graphene for gas storage and separation applications was preliminarily assessed by low-pressure (0–1bar) H2, CO2 and CH4 sorption measurements at different temperatures (77, 273 and 298K). The adsorption capacities for each gas were evaluated up to ~1bar, the isosteric enthalpies of adsorption for CO2 (28–33kJ/mol) and CH4 (30–38kJ/mol) were calculated using the Clausius–Clapeyron equation, while the CO2/CH4 gas selectivity (up to 95:1) was estimated using the Ideal Adsorbed Solution Theory (IAST).

Facile synthesis of γ-Fe2O3@porous carbon materials using an Fe-based metal–organic framework: structure and porosity study

Metal oxide nanoparticle embedded porous carbon composite materials have various uses, including as catalyst supports and adsorbents, because of their good stability and unique porosity. Despite their importance, the synthetic strategies of metal-oxide nanoparticle-embedded porous carbon composites to control their properties have not been widely studied. Here, we present a facile synthesis method for γ-Fe2O3-embedded porous carbon materials via the pyrolysis of Fe-based metal–organic framework (MOF, MIL-100). We found that simple treatment to the starting material (MIL-100) allows control γ-Fe2O3 particle size, chemical composition, porosity, and H2 sorption property of the resulting composite materials. This work presents a synthesis of a series of porous carbon composites from a single MOF by treating further carbon source. This synthetic strategy may provide a clue for synthesis of a variety of composite materials using MOFs for battery electrode and catalyst applications.

Investigating H₂ Sorption in a Fluorinated Metal-Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering.

Simulations of H2 sorption were performed in a metal-organic framework (MOF) consisting of Zn(2+) ions coordinated to 1,2,4-triazole and tetrafluoroterephthalate ligands (denoted [Zn(trz)(tftph)] in this work). The simulated H2 sorption isotherms reported in this work are consistent with the experimental data for the state points considered. The experimental H2 isosteric heat of adsorption (Qst) values for this MOF are approximately 8.0 kJ mol(-1) for the considered loading range, which is in the proximity of those determined from simulation. The experimental inelastic neutron scattering (INS) spectra for H2 in [Zn(trz)(tftph)] reveal at least two peaks that occur at low energies, which corresponds to high barriers to rotation for the respective sites. The most favorable sorption site in the MOF was identified from the simulations as sorption in the vicinity of a metal-coordinated H2O molecule, an exposed fluorine atom, and a carboxylate oxygen atom in a confined region in the framework. Secondary sorption was observed between the fluorine atoms of adjacent tetrafluoroterephthalate ligands. The H2 molecule at the primary sorption site in [Zn(trz)(tftph)] exhibits a rotational barrier that exceeds that for most neutral MOFs with open-metal sites according to an empirical phenomenological model, and this was further validated by calculating the rotational potential energy surface for H2 at this site.

Heterometallic Coordination Polymers Assembled from Trigonal Trinuclear Fe2Ni-Pivalate Blocks and Polypyridine Spacers: Topological Diversity, Sorption, and Catalytic Properties.

Linkage of the trigonal complex [Fe2NiO(Piv)6] (where Piv(-) = pivalate) by a series of polypyridine ligands, namely, tris(4-pyridyl)triazine (L(2)), 2,6-bis(3-pyridyl)-4-(4-pyridyl)pyridine (L(3)), N-(bis-2,2-(4-pyridyloxymethyl)-3-(4-pyridyloxy)propyl))pyridone-4 (L(4)), and 4-(N,N-diethylamino)phenyl-bis-2,6-(4-pyridyl)pyridine (L(5)) resulted in the formation of novel coordination polymers [Fe2NiO(Piv)6(L(2))]n (2), [Fe2NiO(Piv)6(L(3))]n (3), [Fe2NiO(Piv)6(L(4))]n·nHPiv (4), and [{Fe2NiO(Piv)6}4{L(5)}6]n·3nDEF (5, where DEF is N,N-diethylformamide), which were crystallographically characterized. The topological analysis of 3, 4, and 5 disclosed the 3,3,4,4-connected 2D (3, 4) or 3,4,4-connected 1D (5) underlying networks which, upon further simplification, gave rise to the uninodal 3-connected nets with the respective fes (3, 4) or SP 1-periodic net (4,4)(0,2) (5) topologies, driven by the cluster [Fe2Ni(μ3-O)(μ-Piv)6] nodes and the polypyridine μ3-L(3,4) or μ2-L(5) blocks. The obtained topologies were compared with those identified in other closely related derivatives [Fe2NiO(Piv)6(L(1))]n (1) and {Fe2NiO(Piv)6}8{L(6)}12 (6), where L(1) and L(6) are tris(4-pyridyl)pyridine and 4-(N,N-dimethylamino)phenyl-bis-2,6-(4-pyridyl)pyridine, respectively. It was shown that a key structure-driven role in defining the dimensionality and topology of the resulting coordination network is played by the type of polypyridine spacer. Compounds 2 and 3 possess a porous structure, as confirmed by the N2 and H2 sorption data at 78 K. Methanol and ethanol sorption by 2 was also studied indicating that the pores filled by these substrates did not induce any structural rearrangement of this sorbent. Additionally, porous coordination polymer 2 was also applied as a heterogeneous catalyst for the condensation of salicylaldehyde or 9-anthracenecarbaldehyde with malononitrile. The best activity of 2 was observed in the case of salicylaldehyde substrate, resulting in up to 88% conversion into 2-imino-2H-chromen-3-carbonitrile.

Dual-enhanced steam methane reforming by membrane separation of H2 and reactive sorption of CO2

This study proposes a dual-enhanced steam methane reforming (SMR) method for hydrogen production with simultaneous H2 membrane separation and CO2 sorption. Thermodynamic calculations and experimental studies were carried out to study the effectiveness of the dual-enhanced. Theoretically, dual-enhanced SMR was found to decrease the reaction temperature to 500°C with a CH4 conversion of 86.2% under the H2 separation ratio of 0.6 and CO2 sorption ratio of 0.95, in contrast, the CH4 conversion was 52.1% under the same conditions but without any enhancement, thus lowering energy consumption by using dual-enhanced steam reforming. A palladium membrane tube was prepared by electroless plating and used for membrane separation of H2. A fixed-bed reactor packed with complex catalyst containing nano-CaO as CO2 sorbent and NiO/Al2O3 as reforming catalyst was assembled. Experimental results indicated that with a lowered reaction temperature to 500°C, the CH4 conversion can be 62.6%. The conversion of CH4 by dual-enhanced SMR was 27.2%, higher than that obtained by conventional SMR at a reaction temperature of 600°C and a steam-to-methane (S/M) molar ratio of 4. Product gas with 98.1% H2 was directly obtained by dual-enhanced SMR.

Metal–Organic Frameworks Based on Alkaline Earth Metals – Hydrothermal Synthesis, X‐ray Structures, Gas Adsorption, and Heterogeneously Catalyzed Hydrogenation Reactions

AbstractNew carboxylate systems with alkaline earth metals, namely, [Ca2Na2(L)2(H2O)6]n·nH2O (1, H3L = chelidamic acid) and [Sr3(L)2(H2O)9]n·2nH2O (2), have been prepared by hydrothermal reactions and characterized. The compounds featured different three‐dimensional (3D) structural motifs and new topologies. The amount of void space for the dehydrated materials of 1 and 2 was calculated to be ca. 19 and 35 %, respectively. The dehydrated materials are thermally stable to more than 450 °C. The dehydrated species of 1 and 2 displayed excellent N2, H2, and CO2 sorption capacity at 1 atm pressure. Furthermore, both compounds efficiently catalyze the hydrogenation of alkenes under mild heterogeneous conditions (60 °C, 1 atm H2). The porous catalysts demonstrate size selectivity towards substrates owing to presence of active sites inside the pores of the MOF.

Effect of phosphorus modification on the catalytic properties of Mo-Ni/Al2O3 in the hydrodenitrogenation of coal tar

Mo-Ni/Al2O3 catalysts were modified with phosphorus by using the impregnation method. By changing the addition sequence of phosphorus, three types of catalysts, viz. MoP-Ni/Al2O3, Mo-NiP/Al2O3 and Mo-Ni/PAl2O3, were obtained with a P loading of 1.34%. These catalysts were characterized by X-ray diffraction, temperature-programmed desorption of NH3, temperature-programmed reduction by H2 and N2 sorption experiment. The catalytic properties of these catalysts were investigated with the hydrodenitrogenation (HDN) of low- and middle-temperature coal tar obtained from Xinjiang province. It was shown that appropriate P addition sequence can alter acid site distributions, increase the proportion of effective pores between 10 and 13 nm, weaken the interaction of the support and active metal components and make the reduction of the active components easier, consequently, improving the catalytic performance. The HDN activity of the three types of catalysts decreased in the order of Mo-Ni/PAl2O3 (74.36%) > Mo-NiP/Al2O3 (72.74%) > Mo-Ni/Al2O3 (56.13%) > MoP-Ni/Al2O3 (71.72%).

Understanding the H2 Sorption Trends in the M-MOF-74 Series (M = Mg, Ni, Co, Zn)

Electronic structure calculations and simulations of H2 sorption were performed in four members of the M-MOF-74 series: Mg-MOF-74, Ni-MOF-74, Co-MOF-74, and Zn-MOF-74. Notable differences were observed in the partial charge and polarizability of the metal ions derived from the electronic structure calculations. The modeling parameters obtained from the electronic structure calculations were found to influence certain features in the experimentally observed H2 sorption trends in the M-MOF-74 series. The simulations were performed with the inclusion of explicit many-body polarization, which was required to reproduce the experimental H2 sorption observables (i.e., sorption isotherms and isosteric heats of adsorption (Qst)) and the H2–metal interaction in all four MOFs using classical molecular simulation. Consistent with experimental measurements, the simulations captured the following trend for the H2–metal interaction strength: Ni-MOF-74 > Co-MOF-74 > Mg-MOF-74 > Zn-MOF-74. The calculations revealed that stronger H2–metal interactions within the M-MOF-74 series corresponded to shorter H2–metal distances and higher induced dipoles on the metal-sorbed H2 molecules. In addition, it was observed that there was a strong correlation between the H2–metal interaction and the polarization contribution. Although Mg-MOF-74 has the highest calculated partial charge for the metal ion within the series, the Mg2+ ion has a very low polarizability compared to the other M2+ ions; this explains why the H2–metal interaction in this MOF is weaker compared to those for Ni-MOF-74 and Co-MOF-74. The sterics interactions, reflected in the crystal structure for all four MOFs, also played a role for the observed H2 sorption trends. Zn-MOF-74 has the lowest H2 uptakes and Qst within the series due to an unfavorable geometric environment for the Zn2+ ions within the ZnO5 clusters. Lastly, the two-dimensional quantum rotational levels were calculated for the H2–metal interaction in all four MOFs using the potential energy function employed herein and the calculated transitions were in good agreement with the corresponding peaks that were observed in the experimental inelastic neutron scattering (INS) spectra for the respective MOFs. This observation serves both to provide atomistic resolution to the spectroscopic experiments and to validate the molecular force field.

Hydrogen storage properties of Pd-doped thermally oxidized single wall carbon nanohorns

Single wall carbon nanohorns as well as their thermally oxidized derivatives were decorated with Pd nanoparticles and their H2 sorption performance was examined at 298K up to 20bar. The specific surface area of the nanohorns was increased through air oxidation, while both the thermal treatment and the metal doping led to the enhancement of the H2 uptake. The higher uptake of the hybrid materials could not be attributed only to the additive effect of the carbon support and Pd content suggesting the existence of a cooperative mechanism between the metal particles and the carbon surface. This weak chemisorption process was found to be fully reversible after mild heating; still, its contribution to the overall H2 uptake was not found to be of great significance.

Substituent Effects on the Gas Sorption and Selectivity Properties of Hexaphenylbenzene and Hexabenzocoronene Based Porous Polymers

Herein we report a series of porous organic polymers (POPs) synthesized through a Sonogashira cross-coupling reaction containing hexaphenylbenzene (HEX) and hexabenzocoronene (HBC) with varying peripheral substitution. We observed vastly different gas sorption properties depending on substituent size and the extent of conjugation in the monomer core structure with BET surface areas ranging from 320 m2/g for HBC-POP-4 to 1140 m2/g for HEX-POP-3. In order to more clearly understand the effects of functional group substitution on the properties of these materials, we have characterized these POPs using N2, CO2, and H2 sorption measurements, powder X-ray diffraction, FT-IR spectroscopy, TGA, and EDX.

Heterogeneous carbon gels: N-doped carbon xerogels from resorcinol and N-containing heterocyclic aldehydes.

Direct, acid (HCl) initiated sol-gel polycondensation of resorcinol with pyrrole-2-carboxaldehyde or its derivative N-methyl-2-pyrrolecarboxaldehyde yields thermosetting phenolic organic gels with N-content of up to 8.4 wt %. After carbonization, sturdy monoliths of N-doped carbon xerogels with N-content of up to 8 wt % are produced. The morphology and porosity of the doped carbons can be tuned by the solvent composition and the amount of polymerization catalyst used. An increase in carbonization temperature from 600 to 1000 °C strongly affects the carbon gels' microporosity, resulting in a decrease in N2 adsorption capacity, but a significant increase in H2 adsorption capacity (at -196 °C). The growing H2 sorption capacity with the decreasing specific surface area (measured by N2) is related to the gradual shrinkage of the carbon xerogel matrix and narrowing of the small micropores. In addition, it is demonstrated that pyridine-based heterocyclic aldehydes, that is, 2- or 4-pyridinecarboxaldehyde, condensate with resorcinol in basic conditions (KOH, NH4OH). However, in this case, monoliths cannot be produced and powders/rigid solid precipitates are obtained instead. If NH4OH is used as a sol-gel polycondensation catalyst, N-doped foams are obtained as a final carbonaceous product.