Photoassisted CO2Conversion to Fuels

Enhancing photocatalytic CO2 reduction with TiO2-based materials: Strategies, mechanisms, challenges, and perspectives

The concentration of atmospheric CO2 has exceeded 400 ppm, surpassing its natural variability and raising concerns about uncontrollable shifts in the carbon cycle, leading to significant climate and environmental impacts. A promising method to balance carbon levels and mitigate atmospheric CO2 rise is through photocatalytic CO2 reduction. Titanium dioxide (TiO2), renowned for its affordability, stability, availability, and eco-friendliness, stands out as an exemplary catalyst in photocatalytic CO2 reduction. Various strategies have been proposed to modify TiO2 for photocatalytic CO2 reduction and improve catalytic activity and product selectivity. However, few studies have systematically summarized these strategies and analyzed their advantages, disadvantages, and current progress. Here, we comprehensively review recent advancements in TiO2 engineering, focusing on crystal engineering, interface design, and reactive site construction to enhance photocatalytic efficiency and product selectivity. We discuss how modifications in TiO2's optical characteristics, carrier migration, and active site design have led to varied and selective CO2 reduction products. These enhancements are thoroughly analyzed through experimental data and theoretical calculations. Additionally, we identify current challenges and suggest future research directions, emphasizing the role of TiO2-based materials in understanding photocatalytic CO2 reduction mechanisms and in designing effective catalysts. This review is expected to contribute to the global pursuit of carbon neutrality by providing foundational insights into the mechanisms of photocatalytic CO2 reduction with TiO2-based materials and guiding the development of efficient photocatalysts.

Semiconductor photocatalysts and mechanisms of carbon dioxide reduction and nitrogen fixation under UV and visible light

The review summarizes the current knowledge about heterogeneous semiconductor photocatalysts that are active towards photocatalytic reduction of carbon dioxide and molecular nitrogen under visible and near-UV light. The main classes of these photocatalysts and characteristic features of their application in the target processes are considered. Primary attention is given to photocatalysts based on titanium dioxide, which have high activity and stability in the carbon dioxide reduction. For the first time, the photofixation of nitrogen under irradiation in the presence of various semiconductor materials is considered in detail.

The bibliography includes 264 references.

The Reaction of CO2 with a Borylnitrene: Formation of an 3-Oxaziridinone

The reaction of a borylnitrene with carbon dioxide is studied under cryogenic matrix isolation conditions. Photogenerated CatBN (Cat=catecholato) reacts with CO₂ under formation of the cycloaddition product CatBNCO₂, a 3‐oxaziridinone derivative, after photoexcitation (>550 nm). The product shows Fermi resonances between the CO stretching and ring deformation modes that cause unusual ¹³C and ¹⁸O isotopic shifts. A computational analysis of the 3‐oxaziridinone shows this cyclic carbamate to be less strained than an α‐lactone or an α‐lactame.

Fe clusters embedded on N-doped graphene as a photothermal catalyst for selective CO2 hydrogenation

In comparison with the Co analog, small Fe clusters incorporated in a graphene matrix exhibit a photo-assisted increase of 110% in reverse water gas shift CO₂ hydrogenation under UV-Vis light irradiation. Available data indicate that the photo-assistance derives from light absorption by the N-doped graphene followed by charge recombination at the Fe clusters, increasing their local temperature.

The room-temperature, ambient-pressure conversion of CO2 into value-added pharmaceutical products quinazoline-2,4(1H,3H)-diones

As global warming due to CO₂ emissions has become a widely recognized concern, CO₂ capture, sequestration, neutralization, and conversion have become possible solutions to address this concern. Among these approaches, the conversion of CO₂ into fuels or value-added products has attracted considerable attention. In this work, we report the high-efficiency conversion of CO₂ to important industrial raw materials for pharmaceutical compounds, quinazoline-2,4(1H,3H)-diones, via reactions with 2-aminobenzonitriles at room temperature and under ambient pressure, with high conversion yields (91.5-99.3%). 1,8-Diazabicyclo-[5.4.0]-undec-7-ene (DBU), 1,1,3,3-tetramethylguanidine (TMG), and cholinium (Ch) ammonium-based ionic liquids (ILs) are employed as catalysts during the process. Cations with a pK_a value near 11.9 and anions with a pK_a value range of 10 to 15 are necessary for the reaction. The experimental results indicate that the ionic liquid pair [HDBU⁺][3-Cl-PhO^-] has high efficiency under very mild conditions, obtaining high product yields of 91.5% at 25 °C and 1 atm and 99.3% at 30 °C and 1 atm. More importantly, the catalysts retain high efficiency and activity after 5 consecutive cycles. To gain insightful understanding of the reaction, density functional theory (DFT) calculations were conducted to study the reaction mechanism. The computational results indicate that the catalytic process contains three stages: cyano activation, intramolecular rearrangement, and intramolecular cyclization. Of these, the rate-determining step is cyano activation, which shows an energy barrier of 24.5 kcal mol^-1. Tuning the types of ions in ILs can effectively reduce this energy barrier and allow high efficiencies.

Light-Induced Charge Transfer from Transition-Metal-Doped Aluminum Clusters to Carbon Dioxide

Charge transfer between molecules and catalysts plays a critical role in determining the efficiency and yield of photochemical catalytic processes. In this paper, we study light-induced electron transfer between transition-metal-doped aluminum clusters and CO₂ molecules using first-principles time-dependent density-functional theory. Specifically, we carry out calculations for a range of dopants (Zr, Mn, Fe, Ru, Co, Ni, and Cu) and find that the resulting systems fall into two categories: Cu- and Fe-doped clusters exhibit no ground-state charge transfer, weak CO₂ adsorption, and light-induced electron transfer into the CO₂. In all other systems, we observe ground-state electron transfer into the CO₂ resulting in strong adsorption and predominantly light-induced electron back-transfer from the CO₂ into the cluster. These findings pave the way toward a rational design of atomically precise aluminum photocatalysts.

Comparison of CO2 Reduction Performance with NH3 and H2O between Cu/TiO2 and Pd/TiO2

The aim of this study is to clarify the effect of doped metal type on CO₂ reduction characteristics of TiO₂ with NH₃ and H₂O. Cu and Pd have been selected as dopants for TiO₂. In addition, the impact of molar ratio of CO₂ to reductants NH₃ and H₂O has been investigated. A TiO₂ photocatalyst was prepared by a sol-gel and dip-coating process, and then doped with Cu or Pd fine particles by using the pulse arc plasma gun method. The prepared Cu/TiO₂ film and Pd/TiO₂ film were characterized by SEM, EPMA, TEM, STEM, EDX, EDS and EELS. This study also has investigated the performance of CO₂ reduction under the illumination condition of Xe lamp with or without ultraviolet (UV) light. As a result, it is revealed that the CO₂ reduction performance with Cu/TiO₂ under the illumination condition of Xe lamp with UV light is the highest when the molar ratio of CO₂/NH₃/H₂O = 1:1:1 while that without UV light is the highest when the molar ratio of CO₂/NH₃/H₂O = 1:0.5:0.5. It is revealed that the CO₂ reduction performance of Pd/TiO₂ is the highest for the molar ratio of CO₂/NH₃/H₂O = 1:1:1 no matter the used Xe lamp was with or without UV light. The molar quantity of CO per unit weight of photocatalyst for Cu/TiO₂ produced under the illumination condition of Xe lamp with UV light was 10.2 μmol/g, while that for Pd/TiO₂ was 5.5 μmol/g. Meanwhile, the molar quantity of CO per unit weight of photocatalyst for Cu/TiO₂ produced under the illumination condition of Xe lamp without UV light was 2.5 μmol/g, while that for Pd/TiO₂ was 3.5 μmol/g. This study has concluded that Cu/TiO₂ is superior to Pd/TiO₂ from the viewpoint of the molar quantity of CO per unit weight of photocatalyst as well as the quantum efficiency.

Capture and Reuse of Carbon Dioxide (CO2) for a Plastics Circular Economy: A Review

Plastic production has been increasing at enormous rates. Particularly, the socioenvironmental problems resulting from the linear economy model have been widely discussed, especially regarding plastic pieces intended for single use and disposed improperly in the environment. Nonetheless, greenhouse gas emissions caused by inappropriate disposal or recycling and by the many production stages have not been discussed thoroughly. Regarding the manufacturing processes, carbon dioxide is produced mainly through heating of process streams and intrinsic chemical transformations, explaining why first-generation petrochemical industries are among the top five most greenhouse gas (GHG)-polluting businesses. Consequently, the plastics market must pursue full integration with the circular economy approach, promoting the simultaneous recycling of plastic wastes and sequestration and reuse of CO2 through carbon capture and utilization (CCU) strategies, which can be employed for the manufacture of olefins (among other process streams) and reduction of fossil-fuel demands and environmental impacts. Considering the previous remarks, the present manuscript’s purpose is to provide a review regarding CO2 emissions, capture, and utilization in the plastics industry. A detailed bibliometric review of both the scientific and the patent literature available is presented, including the description of key players and critical discussions and suggestions about the main technologies. As shown throughout the text, the number of documents has grown steadily, illustrating the increasing importance of CCU strategies in the field of plastics manufacture.

The mechanism for CO2 reduction over Fe-modified Cu(100) surfaces with thermodynamics and kinetics: a DFT study

The adsorption, activation and reduction of CO₂ over Fe_x/Cu(100) (x = 1–9) surfaces were examined by density functional theory. The most stable structure of CO₂ adsorption on the Fe_x/Cu(100) surface was realized. The electronic structure analysis showed that the doped Fe improved the adsorption, activation and reduction of CO₂ on the pure Cu(100) surface. From the perspective of thermodynamics and kinetics, the Fe₄/Cu(100) surface acted as a potential catalyst to decompose CO₂ into CO with a barrier of 32.8 kJ mol⁻¹. Meanwhile, the first principle molecular dynamics (FPMD) analysis indicated that the decomposition of the C–O1 bond of CO₂ on the Fe₄/Cu(100) surface was only observed from 350 K to 450 K under a CO₂ partial pressure from 0 atm to 10 atm. Furthermore, the results of FPMD analysis revealed that CO₂ would rather decompose than hydrogenate when CO₂ and H co-adsorbed on the Fe₄/Cu(100) surface.

The adsorption, activation and reduction of CO₂ over Fe_x/Cu(100) (x = 1–9) surfaces were examined by density functional theory.

Coupling of Solar Energy and Thermal Energy for Carbon Dioxide Reduction: Status and Prospects

Enormous efforts have been devoted to the reduction of carbon dioxide (CO₂ ) by utilizing various driving forces, such as heat, electricity, and radiation. However, the efficient reduction of CO₂ is still challenging because of sluggish kinetics. Recent pioneering studies from several groups, including us, have demonstrated that the coupling of solar energy and thermal energy offers a novel and promising strategy to promote the activity and/or manipulate selectivity in CO₂ reduction. Herein, we clarify the definition and principles of coupling solar energy and thermal energy, and comprehensively review the status and prospects of CO₂ reduction by coupling solar energy and thermal energy. Catalyst design, reactor configuration, photo-mediated activity/selectivity, and mechanism studies in photo-thermo CO₂ reduction will be emphasized. The aim of this Review is to promote understanding towards CO₂ activation and provide guidelines for the design of new catalysts for the efficient reduction of CO₂ .

Nanosheet-assembled hierarchical flower-like g-C3N4 for enhanced photocatalytic CO2 reduction activity

Nanosheet-assembled hierarchical flower-like g-C₃N₄ prepared by a molecular self-assembly and ethanol insertion strategy shows enhanced photocatalytic CO₂ reduction activity.

Spiers Memorial Lecture. Artificial photosynthesis: An introduction

A brief introduction into artificial photosynthesis technologies is presented. Following the basic concepts of biological photosynthesis, light energy is directly or sequentially used for the synthesis of valuable chemicals with the help of man-made catalysts. Differences between artificial, hybrid and natural photosynthesis are shown and the possible advantages and disadvantages are highlighted.