A Comparative Study of Aromatization Catalysts: The Advantage of Hybrid Oxy/Carbides and Platinum-Catalysts Based on Carbon Gels

This manuscript is focused on the relationship between sol-gel synthesis processes and the development of new active phases with fitted morphology, porosity and surface chemistry. The influence of the above parameters on the catalytic performance of the prepared materials for the aromatization of n-hexane to benzene is also evaluated. Different series of catalysts were prepared, either using noble metals (i.e., Pt) or metal oxides (i.e., Mo, W), as active phases. In both cases, the catalytic performance and stability of classical aromatization catalysts was significantly improved. Interesting one-pot carboreduction process of the metal oxide during carbonization is suggested as a real alternative for the preparation of high-performance aromatization catalysts, leading to the formation of less acidic and non-stoichiometric oxides and carbides.

Nitrogen-Doped Carbons Derived from Imidazole-Based Cross-Linked Porous Organic Polymers

Nitrogen-doped and heteroatom multi-doped carbon materials are considered excellent metal-free catalysts, superior catalyst supports for transition metal particles and single metal atoms (single-atom catalysts), as well as efficient sorbents for gas- and liquid-phase substances. Acid-catalyzed sol–gel polycondensation of hydroxybenzenes with heterocyclic aldehydes yields cross-linked thermosetting resins in the form of porous organic polymers (i.e., organic gels). Depending on the utilized hydroxybenzene (e.g., phenol, resorcinol, phloroglucinol, etc.) and heterocyclic aldehyde variety of heteroatom-doped organic polymers can be produced. Upon pyrolysis, highly porous and heteroatom-doped carbons are obtained. Herein, polycondensation of phloroglucinol with imidazole-2-carboxaldehyde (and other, similar heterocyclic aldehydes with two heteroatoms in the aromatic ring) is utilized to obtain porous, N-doped organic and carbon gels with N-content of up to 16.5 and 12 wt.%, respectively. Utilization of a heterocyclic aldehyde with two different heteroatoms yields dually-doped carbon materials. Upon pyrolysis, the porous polymers yield ultramicroporous N-doped and N,S co-doped carbons with specific surface areas of up to 800 m2g−1. The influence of the initial composition of reactants and the pyrolysis temperature on the structure and chemical composition of the final doped organic and carbon materials is studied in detail.

Influence of Electrostatic Interactions During the Resorcinol-Formaldehyde Polymerization on the Characteristics of Mo-Doped Carbon Gels

The resorcinol (R)-formaldehyde (F) polymerization was carried out in different experimental conditions to obtain RF/Mo doped carbon xerogels with different morphology, porosity and nature and dispersion of metal. Attractive or repulsive electrostatic interactions were forced in the starting aqueous solution of RF-monomers using different synthesis conditions, namely, combinations of cationic or anionic surfactants, Mo-precursors and pH values. The results showed that when both cationic surfactant and Mo-precursor were used at neutral pH, attractive interactions with the anionic RF-macromolecules are favored during polymerization and the final carbon xerogel exhibited the most developed porosity and the strongest Mo-organic phase interaction, leading to deeper Mo-phase reduction during carbonization and the formation of highly-dispersed crystalline nanoparticles of Mo2C. On the contrary, the use of both anionic surfactant and Mo-precursor leads to repulsive interactions, which generates less porous carbon gels with a Mo-phase formed by large MoO3 platelet structures and low Mo-surface contents. RF/Mo-doped gels with intermediate properties were obtained by combining cationic and anionic surfactants, metal precursors or both. After carbonization, the obtained materials would be suitable to be used directly as catalysts with different physicochemical properties and active phases.

Synthesis and Study of Properties of Organic and Carbon Xerogels from Abies Bark Tannins

Methods of organic and carbon xerogels synthesis based on the use of condensed tannins isolated from abies bark were developed. Organic gels were synthesized by sol-gel condensation of tannins with formaldehyde in a solution of ethanol in the presence of catalysts (NaOH or HCl). The final gelation products were dried by alternating low (-18 – -40 °C) and room temperature to obtain tanninformaldehyde (TF) xerogels. FTIR study indicates that the formation of xerogels was accompanied by crosslinking reactions mainly due to the formation of carbon-carbon and alkyl ether bonds. Using the method of thermogravimetry, it was found that organic TF xerogels are thermally stable up to a temperature of 295 °C and they are resistant to ignition in air at temperatures up to 600 °C and can be used as thermo- and fire-retardant materials. Carbon tannin-formaldehyde xerogels were obtained by carbonization of organic xerogels at 800 °C in an argon atmosphere. The porous structure and surface morphology of organic and carbon xerogels was studied by BET- and SEM–methods. A significant development of the specific surface area (to 483–524 m2/g)as a result of the organic xerogels carbonization was established. Using SEM, it was shown that in carbon gels a spatially cross-linked structure of polymer chains consisting of 5-10 nmsized globule particles forming nanometer-sized pores is retained