Universal Kinetic Mechanism Describing CO2 Photoreductive Yield and Selectivity for Semiconducting Nanoparticle Photocatalysts

Carbon dioxide, global boiling, and climate carnage, from generation to assimilation, photocatalytic conversion to renewable fuels, and mechanism

The increasing CO2 concentration in the atmosphere has substantial impacts on the global temperature. For energy sustainability and minimization of the effects of global warming, an approach to understand CO2 capturing and a carbon neutral culture is extremely essential in the present circumstances. The CO2 emission from vehicles and industries can be minimized using energy cost-effective techniques and can be converted more selectively into reusable fuels via thermochemical, electrochemical, photochemical, photocatalytic, electrocatalytic, biological and inorganic carbonate-based approaches. In this review article, we have discussed the effects of increased global temperature on human beings, economy and climate change. Further, we have discussed the photocatalytic conversion of CO2 (PC-CO2) into gaseous and liquid fuels under solar light driven photocatalysis. The adsorption and activation of CO2, its conversion into various intermediates, their stability and selectivity of the final products have been elaborated comprehensively. The conversion mechanisms of CO2 into CO, CH4, alcohol, aldehyde and carboxylic acid have been discussed in detail. The role of defects and exposed facets of photocatalysts, effect of metal and non-metal dopants, and the additive role of co-catalyst on the mechanisms and selectivity of the conversion products have been discussed comprehensively. Finally, future perspective is discussed to highlight the research gap in the PC-CO2. We hope that this article will help to understand the mechanisms of PC-CO2 and will direct researchers to add their role in the reduction of CO2 to control global warming and make life easier on earth in the coming years.

Construction of ZnO/Zn3In2S6/Pt with integrated S-scheme/Schottky heterojunctions for boosting photocatalytic hydrogen evolution and bisphenol a degradation

Photocatalytic water splitting has been identified as a promising solution to tackle the current environmental and energy crisis in the world. However, the challenge of this green technology is the inefficient separation and utilization of photogenerated electron-hole pairs in photocatalysts. To overcome this challenge in one system, a ternary ZnO/Zn₃In₂S₆/Pt material was prepared as a photocatalyst using a stepwise hydrothermal process and in-situ photoreduction deposition. The integrated S-scheme/Schottky heterojunction in the constructed ZnO/Zn₃In₂S₆/Pt photocatalyst enabled it to exhibit efficient photoexcited charge separation/transfer. The evolved H₂ reached up to 3.5 mmol g^-1h^-1. Meanwhile, the ternary composite possessed a high cyclic stability against photo-corrosion under irradiation. Practically, the ZnO/Zn₃In₂S₆/Pt photocatalyst also showed great potential for H₂ evolution while simultaneously degrading organic contaminants like bisphenol A. It is hoped in this work that the incorporation of Schottky junctions and S-scheme heterostructures in the construction of photocatalysts would lead to accelerated electron transfer and high photoinduced electron-hole pair separation, respectively, to synergistically enhance the performance of photocatalysts.

Controllable CO2 Reduction or Hydrocarbon Oxidation Driven by Entire Solar via Silver Quantum Dots Direct Photocatalysis

The current solar-chemical-industry based on semiconductor photocatalyst is impractical. Metal catalysts are extensively employed in thermal- and electro-catalysis industries, but unsuitable for direct-driven photocatalysis. Herein, silver quantum dots (Ag-QDs) are synthesized on support via an in situ photoreduction method, and in situ photocatalysis temperature programmed dynamics chemisorption desorption analyses are designed to demonstrate that Ag-QDs should be the actual photocatalytic sites. The surface plasmon resonance of Ag-QDs could harvests entire visible solar, and the plasmon-driven charge-transfer exhibits opposite directions at the interface when supports are different. Consequently, Ag-QDs could be alternatively regulated as oxidation or reduction active centers. Furthermore, Ag-QDs excite electron tunneling transfer with adsorbate, which does not generate high-energy free-radical intermediates. As a result, the efficiencies of hydrocarbon photooxidation and CO₂ photoreduction are improved in several orders of magnitude. Evidently, the Ag-QDs direct photocatalytic technology greatly promotes solar-chemical-industry applications.

In situ catalytic cells for x-ray absorption spectroscopy measurement

In catalysis, determining the relationship between the dynamic electronic and atomic structure of the catalysts and the catalytic performance under actual reaction conditions is essential to gain a deeper understanding of the reaction mechanism since the structure evolution induced by the absorption of reactants and intermediates affects the reaction activity. Hard x-ray spectroscopy methods are considered powerful and indispensable tools for the accurate identification of local structural changes, for which the development of suitable in situ reaction cells is required. However, the rational design and development of spectroscopic cells is challenging because a balance between real rigorous reaction conditions and a good signal-to-noise ratio must be reached. Here, we summarize the in situ cells currently used in the monitoring of thermocatalysis, photocatalysis, and electrocatalysis processes, focusing especially on the cells utilized in the BL14W1-x-ray absorption fine structure beamline at the Shanghai Synchrotron Radiation Facility, and highlight recent endeavors on the acquisition of improved spectra under real reaction conditions. This review provides a full overview of the design of in situ cells, aiming to guide the further development of portable and promising cells. Finally, perspectives and crucial factors regarding in situ cells under industrial operating conditions are proposed.

Use of A-Site Metal Exsolution from a Hydrated Perovskite Titanate for Combined Steam and CO2 Reforming of Methane

Metal segregation from a perovskite oxide (ABO₃) usually referring to "redox metal exsolution" has recently been used for in situ preparation of a well-designed catalyst where metal nanoparticles are homogeneously and strongly embedded on perovskite scaffolds upon reduction. The exsolution concept of B-site transition metal ions has grown, but several issues such as segregation of A-site alkaline-earth metal ions (altering electronic structures of the perovskite surface, causing deformation of perovskite structures, or creating undesirable products via side reactions) and carbon formations on metal nanoparticles should be addressed for stable catalysts in greenhouse gas (CO₂ or CH₄) conversion. Here, we suggest a new approach to designing metal-perovskite composite catalysts via A-site metal segregation from a hydrated perovskite titanate. In situ formation of A-site-deficient hydrated CaTiO₃ accompanied with Ni exsolution solids leads to ∼78 and 65% of CH₄ and CO₂ conversion, respectively, suppressing carbon formations and alkaline-earth metal segregations in combined steam and carbon dioxide reforming of methane at 700 °C. It would help to design active and stable metal-perovskite catalysts for energy and environmental applications.

Revealing the stochastic kinetics evolution of photocatalytic CO2 reduction

Investigating kinetic mechanisms to design efficient photocatalysts is critical for improving photocatalytic CO₂ reduction, but the stochastic photo-physical/chemical properties of kinetics remain unclear. Herein, we propose a statistical study to discuss the stochastic feature evolution of photocatalytic systems. The uncertainties of light absorption, charge carrier migration, and surface reaction are described by nonparametric estimation methods in the proposed model, which includes the effect of operational and material parameters. The density distribution of surface electrons shifts from a skewed distribution to an approximate uniform distribution as incident photon density increases. The system temperature rising induces the rate-determining step of surface reactions to change from charge carrier kinetics to reactant activation processes. Benefiting from the synergistic optimization between the operational parameter and active site density, the electron-capturing probability of active sites is boosted from 0.06 to 0.17. The modified reaction kinetic equation is constructed based on the distribution function of charge carrier kinetics. Furthermore, the experimental photoactivity results are consistent with the statistical analysis, which proves the feasibility of the established model. The characterization tests show that the gap between testing activities and theoretical efficiency is caused by a mismatch between charge carrier supply and mass transfer. Our work unveils the stochastic features in photocatalytic CO₂ reduction, offering a comprehensive analytical framework for photocatalytic system optimization.