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Oxidative dehydrogenative coupling (ODC) is a useful tool for the formation of new C–C, C–O and NN bonds in an atom-economic and sustainable manner. Although this strategy is versatile, it is much less introduced to prepare N-heterocycles. Herein, we report the oxidative dehydrogenative coupling of anilines and 2-aminoanilies with vicinal diols to selectively produce azobenzenes (34–95% yield), quinolines (65–100% yield) and quinoxalines (78–100% yield) utilizing an environmentally friendly synthesis strategy. The reactions were catalysed by cooperative bifunctional catalysts based on transition metal oxides/Bi(iii) which allow solvent-, additive-, oxidant- and base-free cyclisations/couplings. In addition, the catalysts were proven to be highly robust and reusable.

Although using supported noble-metal catalysts for CO2hydrogenation is an effective solution due to their excellent catalytic properties, metal oxide supports themselves can exhibit good activity being more economically feasible. This work focuses on investigating the complexity of the Co3O4system during the CO2methanation reaction, which is usually accompanied by the formation of unstable dispersions of cobalt oxide and metallic Co. Herein, we have tested different types of Co3O4: synthetically prepared mesoporous m-Co3O4(BET surface area, 95 m2/g) and commercial c-Co3O4(BET surface area, 15 m2/g; purchased from Merck) in the CO2methanation reaction under different reduction temperatures (273–673 K). The reduction temperature was adjusted to 573 K for both the catalysts to reach the optimal Co/cobalt oxide ratio and consequently the best catalytic performance. m-Co3O4is more active (CO2conversion 95%) and stable at higher temperatures compared to c-Co3O4(CO2conversion 63%) due to its morphology-induced ∼66 times higher surface basicity. DRIFTS results showed differences in the detected surface species: formate was observed on m-Co3O4and was proven to contribute to the total methane formation. It was revealed that in CO2methanation reaction, both bulk and surface properties such as morphology, cobalt oxidation states, acid–base properties, and presence of defect sites directly affect the catalytic performance and reaction mechanism. Furthermore, 1% 5 nm Pt nanoparticles were loaded onto the Co3O4s to check the competitiveness of the catalysts. This study evidences on a cheap noble-metal-free catalyst for CO2methanation consisting of m-Co3O4with competitive activity and ∼100% CH4selectivity.

Thermo-catalytic bio-SNG (CH4) production is one of the useful tools for converting waste to gaseous fuels through CO2conversion. To abundant properly, however, efficient, robust and cost-effective catalysts would be required. Bimetallic systems based on transition metals seem to be promising candidates for this task. The CoCu bimetallic system with in-situ generated interfaces was synthesized and used as a catalyst for CO2methanation. The in-depth analysis of the structure-activity-selectivity relationships involving XRD, (NAP-)XPS, EXAFS and TEM-EDX revealed that the co-existence of Co0, CoO, and Cu0in the proper distribution on the surface can ensure the selective production of methane. To fine-tune the surface composition of the bimetallic systems, a systematic alteration of the Cu:Co ratio in the precursor spinel structures must be performed. Cu0.4Co2.6O4derivative, stabilizing subsurface Cu(I)–O specimen, showed the best performance with high activity (12,800 nmol g–1s–1) and a remarkable selectivity of 65–85% for methane in a wide temperature range (250–425 °C). In studying the mechanistic aspects of methanation, it has been shown that the hydrogenation of active carbon at the surface or below the surface is the key step for the production of methane. So far, this cobalt-catalyzed sub-step has been proposed in catalytic Fischer-Tropsch syntheses.

The use of rare nickel-poor and aluminum-rich layered double hydroxides (LDHs) as catalyst precursors in CO2hydrogenations has revealed the key importance of chemical quality of the interlayer anions for the achievable CO2conversion and CH4/CO selectivity. At atmospheric pressures between 300 and 700 °C, the obtained CH4and CO formation rates varied widely, reaching up to the remarkable 76.8 (LDH-NO3) and 47.7 μmol/gcats (LDH-NH2SO3), respectively, competing with Pt and Co containing catalysts. Depending on thermal stability of the interlayer anions, their partial or complete removal resulted in significant differences in LDH transformation and thus in reducibility of Ni(II) and specific surface area values of the resulting metal oxides. Moreover, clear correlation was found between the conversion, selectivity and the abundance, strength of base and acid sites presented in the calcined LDHs related to the nature of starting interlamellar anions. Incorporation of nitrate and perchlorate ions into the precursors helped the formation of weak basic sites, while sulphate and sulphamate ions resulted in a large number of strong acid and base sites. The high-resolution quasi in situX-ray photoelectron spectra revealed the effect of the anions on chemical composition of the forming catalytic interfaces. Meantime, the in situdiffuse reflectance infrared spectroscopy measurements indicated multifarious CO2hydrogenation pathways viaformate (LDH-NO3, -Br, -I), carboxylate (LDH-Cl, -ClO4) intermediates and CO2dissociation (LDH-SO4, -NH2SO3).