Redução De Co2 Em Hidrocarbonetos E Oxigenados: Fundamentos, Estratégias E Desafios

Abstract

CO2 REDUCTION TO HYDROCARBONS AND OXYGENATES: FUNDAMENTALS, STRATEGIES AND CHALLENGES. The development of renewable energy sources (e.g., solar and wind) moves foward, the tendance for replacing fossil fuels increases. However, these technologies have as primary barriers to industrial processes’ efficiency and especially storage. Thus, CO2 reduction routes using these energy sources could chemically store part of the energy as fuels or chemicals, offering alternatives to current oil and gas industry. This process is inspired by photosynthesis, e.g., photochemical or electrochemical processes, using homogeneous or heterogeneous catalysts. Nevertheless, this reaction is thermodynamically unfavorable and has very slow kinetics, given the high stability of the CO2 molecule and the complexity of the redox reactions involved. Therefore, this review addresses this process’s kinetic and thermodynamic challenges, and the fundamental concepts of the photo(electro)chemical processes for CO2 reduction, besides presenting and discussing the materials with the potential to act as catalysts. The main reaction mechanisms and advances in the understanding of such processes are discussed, as well as future perspectives

The Effect of SnO2 Surface Properties on CO2 Photoreduction to Higher Hydrocarbons

“…On the other hand, SnO 2 ′s use as a photocatalyst in the CO 2 photoreduction process is constrained by its high theoretical reduction potential in the conduction band (E°=∼0.5 V, V vs. NHE, pH 7). Since the photogenerated electrons in the reaction system should be transferred to the CO 2 molecule, it won't happen if the reduction potential of the semiconductor conduction band (CB) is less than the reduction potential, for example, from the conversion of CO 2 to methane (CH 4 =E° (CO 2 /CH 4 )=−0,24 V) [24,25] …”

“…Since the photogenerated electrons in the reaction system should be transferred to the CO 2 molecule, it won't happen if the reduction potential of the semiconductor conduction band (CB) is less than the reduction potential, for example, from the conversion of CO 2 to methane (CH 4 = E°( CO 2 /CH 4 ) = À 0,24 V). [24,25] However, Chowdhury et al experimentally verified the ability to convert CO 2 to formic acid (HCOOH) using mesoporous SnO 2 nanoparticles in photocatalysis in aqueous media under ultraviolet radiation (UV) and visible radiation. [26] In addition, preliminary studies by our research group experimentally verified the activity of SnO 2 nanoparticles in the CO 2 photoreduction process, converting CO 2 into CH 4 , carbon monoxide (CO), and ethylene, showing that surface hydroxyls played a crucial role in the photocatalytic activity of the semiconductor, in which these groups increased CO 2 affinity and possibly decreased its reduction potential.…”

Visible-Light-Driven Photocatalytic CO2 Reduction by Re(I) Photocatalysts with N-Heterocyclic Substituents

“…To the best of our knowledge, these compounds outperformed even the most efficient Lehn-type photocatalysts reported up to date to promote photoreduction of CO 2 using triethanolamine (TEOA) as the sacrificial electron donor. 5,31 A detailed characterization and mechanistic investigation revealed that the benchmark efficiencies and robustness could be tracked not only to the enhancement of the visible-light absorption properties of the complexes bearing N-heterocyclic substituents but also on (i) fine-tuning of the kinetics and thermodynamics of each individual step of the photocatalysis, (ii) the inhibition of deactivation of the photocatalysts by dimerization, (iii) the expressive stabilization of reduced Re intermediates, and (iv) an unusual CO 2 photoreduction pathway that proceeds predominantly through a two-electron reduced species, [Re(NN)(CO) 3 ] − .…”

Effect of the oxidation state and morphology of SnOx-based electrocatalysts on the CO2 reduction reaction

“…This process carries several advantages, such as low-temperature operation, that it can be run at ambient pressure, and the required energy input can be supplied from renewable energy sources (i.e., solar or wind), creating a netzero CO 2 emission condition in certain energy business cases [5][6][7]. Moreover, the performance and selectivity of such an electrochemical reaction can be tuned, and the scale-up of this process becomes simpler than other such as: photochemical and thermochemical process [8][9][10].…”

“…Formic acid has been receiving significant attention as an CO 2 RR product due to its stability, remarkably high volumetric capacity, and its versatile potential use in various applications (e.g., direct formic acid fuel cells, and the leather, textile, food, and chemical industries) [12,13]. The economic viability of various chemicals from the CO 2 RR demonstrated that formic acid has a great business value, which is one of the most desired products [10]. However, the inertness of CO 2 due to its high chemical stability results in a process with high overpotential, sluggish kinetics, and broad distribution of products [3,14,15].…”