Abstract
The overview describes the main directions and results of the IV International Conference APITECH-IV 2022 held in Bukhara, Uzbekistan on 6-9 October 2022. It gives the details about the ...participants and the proceedings. The purpose of the Conference is to share the experience of leading experts in the application of modern methods of applied physics and information technology in high-tech production, in the fields of aerospace, energy, chemical and oil and gas engineering.
Conversion of CO2 to hard carbon is an interesting technology for the removal of carbon dioxide from the atmosphere. Recently, it was shown that CeO2 can selectively catalyze this reaction, but we ...still lack information regarding the reaction mechanism. Using density functional theory modeling, we explore possible reaction mechanisms that allow for the polymerization of CO2. According to our computations, the reaction is initialized by the adsorption of CO2 in an oxygen vacancy. Owing to the rich defect chemistry of ceria, a large number of suitable sites are available at the surface. C–C bond formation is achieved through an aldol condensation-type mechanism which comprises the electrochemical elimination of water to form a carbene. This carbene then performs a nucleophilic attack on CO2. The reaction mechanism possesses significant similarities to the corresponding reactions in synthetic organic chemistry. Since the mechanism is completely generic, it allows for all relevant steps of the formation of hard carbon like chain growth, chain linkage, and the formation of side chains or aromatic rings. Surprisingly, ceria mainly serves as an anchor for CO2 in an oxygen vacancy, while all other subsequent reaction steps are almost completely independent from the catalyst. These insights are important for the development of novel catalysts for CO2 reduction and may also lead to new reactions for the electrosynthesis of organic molecules.
Carbon dioxide reduction reaction (CO2RR) is a promising method for converting CO2 into value-added products. CO2RR over single-atom catalysts (SACs) is widely known to result in chemical compounds ...such as carbon monoxide and formic acid that contain only one carbon atom (C1). Indeed, at least two active sites are commonly believed to be required for C–C coupling to synthesize compounds, such as ethanol and propylene (C2+), from CO2. However, experimental evidence suggests that iron phthalocyanine (PcFe), which possesses only a single metal center, can produce a trace amount of C2+ products. To the best of our knowledge, the mechanism by which C2+ products are formed over a SAC such as PcFe is still unknown. Using density functional theory (DFT), we analyzed the mechanism of the CO2RR to C1 and C2+ products over PcFe. Due to the high concentration of bicarbonate at pH 7, CO2RR competes with HCO3– reduction. Our computations indicate that bicarbonate reduction is significantly more favorable. However, the rate of this reaction is influenced by the H3O+ concentration. For the formation of C2+ products, our computations reveal that C–C coupling proceeds through the reaction between in situ-formed CO and PcFe(“0”)–CH2 or PcFe(“-I”)–CH2 intermediates. This reaction step is highly exergonic and requires only low activation energies of 0.44 and 0.24 eV for PcFe(“0”)–CH2 and PcFe(“-I”)–CH2. The DFT results, in line with experimental evidence, suggest that C2+ compounds are produced over PcFe at low potentials whereas CH4 is still the main post-CO product.
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