Materials Today Catalysis最新文献

The conversion of carbon dioxide (CO₂) into valuable chemicals, specifically C₂ and C₃, through metal-free electrocatalysis remains a formidable challenge. Breaking away from traditional transition metal complexes, the focus is on designing and selecting efficient organic catalysts. In this pursuit, a diazo-based organic bulky ligand emerges as a promising candidate, offering a solution that is both sustainable and renewable. The key feature of this ligand is its low-lying π* (LUMO), enabling it to readily accept an electron in an electrochemical environment when a potential is applied. The synthesized Diazo-based ligands have been meticulously characterized using various techniques, including ¹H NMR, ¹³C NMR, UV-Vis, and IR spectroscopy. This diazo-based ligand serves as an electrocatalyst, undergoing reduction to a triplet diradical that acts as a nucleophile. In an aqueous medium, it forms an adduct with CO₂, leading to the generation of a formyl radical. This radical further couples to produce acetic acid and acetone with efficiencies of 19.6% and 24.2%, respectively, at pH 5.5. To provide a deeper understanding, we present a proposed mechanism pathway supported by in-situ UV-Vis spectroscopy and a comprehensive Density Functional Theory (DFT) study. These findings mark a significant step forward in the field of metal-free electrocatalysis, offering a sustainable approach to the conversion of CO₂ into valuable chemicals, contributing to the development of renewable and environmentally friendly systems.

Although single-atom catalysts (SACs) are emerging as potential contenders for heterogeneous catalysis, interactions between metal single-atom active sites and support matrix remain uncertain. In a recent issue of Nature, Zhang and coworkers revealed the phase-dependent growth of single atom Pt on 1 T′ phase MoS₂ for efficient hydrogen evolution. However, some analyses of the nature of catalyst structure and properties are still lacking, and the relevant large-scale commercial application is still difficult.

The electrochemical carbon dioxide reduction (ECR) to profoundly diminished chemical entities offers a compelling avenue for transforming sporadic energy resources into enduring fuels while forging an enclosed anthropogenic carbon cycle. Metal-organic frameworks (MOFs) has been extensively investigated as a promising multifunctional material for ECR. Notably, two-dimensional (2D) MOFs attract particular research attention due to their specific chemical and structural properties, i.e., enhanced electrical conductivity, increased open sites, improved mass transport and tunable interfacial environments. In this review, the recent progress of 2D MOFs for ECR is summarized. We begin with the introduction of the synthetic strategies of 2D MOFs. Then, we mainly focus on the advanced 2D MOF electrocatalysts for ECR in recent years, which are clarified by the products. The mechanism underlying the conversion of carbon dioxide (CO₂) into carbon products, the factors influencing product formation and a summary of selected 2D MOF catalysts and their synthetic methods are presented. By consolidating the potential factors contributing to the products, we anticipate that the review will offer fresh opportunities for further advancements in CO₂ reduction with 2D MOF catalysts.

The global energy crisis and environmental pollution issues caused by the continuous consumption of fossil fuels are increasingly becoming severe. Developing clean and sustainable hydrogen (H₂) energy and corresponding storage and conversion devices have attracted increasing attention. The utilization of H₂ energy highly depends on the fuel cell (FC). However, the slow kinetics of oxygen reduction reaction (ORR) on the cathode of FC cannot be improved without efficient catalysts. Currently, precious metal platinum (Pt) and its alloys are commonly used catalysts for ORR process. However, the scarcity and high cost of Pt hinder their large-scale practical application. To replace typical Pt-based catalysts, non-precious metal electrocatalysts have been investigated for ORR. Inspired by the catalytic ORR active center Fe porphyrin of cytochrome c oxidase in nature, metalloporphyrin-based frameworks and their derivatives have become promising electrocatalysts due to their abundant conjugated electronic structure, tunable functional groups, and large specific surface area. First, this review briefly introduces porphyrins and catalytic ORR mechanisms. Second, recent progress on porphyrin-based ORR catalysts including porphyrin-based frameworks, framework@substrate composites, and framework-based derivatives was summarized. Porphyrin-based frameworks mainly include metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), and polymers constructed with porphyrin building blocks. Porphyrin-based framework@substrate composites were usually assembled and constructed to improve the electron transfer rate of frameworks. To further improve the conductivity, framework-based derivatives, usually named metal, nitrogen-doped carbon (M-N-C) materials, were synthesized through pyrolyzing frameworks at high temperatures. Finally, research challenges and directions of porphyrin-based electrocatalysts for ORR were discussed. This review is meaningful and enlightening for designing and developing other porphyrin-based electrocatalysts for ORR.

Identifying active platinum species at the surface of Pt/CeO₂ catalysts is still a hot topic in the literature. In this work, an oxidizing pretreatment at 500 °C was applied to generate ultradispersed PtO_x species before the reaction. It is shown that the molar activity of such catalysts for the water-gas shift reaction is strongly dependent on the platinum content, increasing by a factor of 2.5 from 0.1 to 0.6 wt% and stabilizing from 0.6 to 1.4 wt%. The tracking of Pt species present under reaction conditions (230 °C, H₂O/CO=4) was performed using operando DRIFT spectroscopy, CO-TPR and STEM in connection with the catalytic activity. A major structural change was found for Pt loadings above 0.6 wt% through the formation of metallic Pt⁰ nanoparticles of ca 1.4 nm from oxidized Pt single atoms and clusters. Conversely, for Pt contents below 0.6 wt%, Pt species possess a stronger interaction with CeO₂ as well as a lower nuclearity, limiting their activation under reaction conditions. This strongly suggests that metallic Pt nanoparticles, prevalent at high loading, are more active than oxidic Pt single atoms and small clusters, which are predominantly present at low loading. This study highlights the key role of PtO_x reducibility and the importance to optimize the Pt loading to obtain active catalysts for the water-gas shift reaction.

The major limitations of photoelectrochemical (PEC) water splitting lies in the currently unsatisfying efficiency and stability of the semiconductor materials-based water splitting systems. By addressing these limitations, the immobilization of the molecular catalysts on semiconductor photoanodes to establish a hybrid inorganic-organic PEC system has attracted an increasing research attention. It is crucial to choose a suitable molecular catalyst and effectively couple it into a hybrid photoelectrode system. In this review, focusing on the water oxidation process, molecular catalysts integrated photoelectrochemical water oxidation systems are highlighted from the perspective of the roles of molecular catalysts and the integration strategies in the hybrid system. The most recent advances are summarized with various case studies presented, based on which perspectives are proposed to provide guidance toward the rational design of an integrated system for future development.

Atomic-site electrocatalysts are being considered as potential alternative catalysts due to their exceptionally high atom utilization efficiencies, well-defined active sites and high selectivities. However, the presence of nanoparticles in the single-atom catalysts may affect the catalytic performance. Herein, single-copper-atoms and copper nanoparticles co-embedded in nitrogen-doped carbon nanosheets (Cu_NPs@Cu/NCNSs) were synthesized for 5-hydroxymethylfurfural electro-oxidation. Single copper atoms supported on nitrogen-doped carbon nanosheets (Cu/NCNSs) and copper nanoparticles supported on carbon (Cu_NPs/C) were also synthesized for comparison. The Cu_NPs/C exhibited high efficiency in electro-oxidation of HMF to 2,5-furandicarboxylic acid (FDCA) at a low potential of 1.42 V. However, the Cu_NPs@Cu/NCNSs showed a high 5-formyl-2-furancarboxylic acid (FFCA) selectivity of 86.7%. Oxalic acid (OA) treatment experiments showed that single copper atoms played a major role on the oxidation of HMF to FFCA. Cu(OH)₂ active species generated by electrochemical oxidation were demonstrated as the primary catalytic sites for HMF oxidation on the Cu_NPs/C. In-situ Raman spectra results demonstrated that HMF oxidation on the Cu_NPs/C followed the path to 5-hydroxymethyl-2-furancarboxylic acid (HFCA), while on the Cu_NPs@Cu/NCNSs and Cu/NCNSs, HMF was oxidized along the 5-diformylfuran (DFF) pathway.

Accelerated advances in photocatalysis demand alignment with a well-defined Technology Readiness Levels (TRLs) roadmap to overcome bottlenecks and attain TRLs of 3 or beyond. This minireview highlights the key components for the development of device technology for photocatalytic hydrogen production, focusing on visible-light responsive catalysts and lab-scale setups. Two main aspects are critically discussed: modifications in semiconductor-based materials and progress in device engineering design. In the first section, the emphasis is on two specific energy materials: visible-light active carbon nitrides (CN) and the established benchmark titanium dioxide (TiO₂). Examples of both CN and TiO₂ modified by heteroatom doping, semiconductor heterojunction, metal Schottky junction, pre- and post-thermal treatments are showcased. Furthermore, Imogolite nanotubes are introduced as evolving 1D nanostructured nanoreactors for energetic photoelectrocatalysis. In the second section, the emphasis is on two types of laboratory batch photoreactors tailored for hydrogen production. Their main features are critically discussed in terms of their impact on the overall photonic, heat, and mass profiles. Moreover, a continuous flow water disinfection system is introduced as promising environmental technology. The objective to showcase these devices is to underscore the significance of advancing TRLs from 3 to 4–6. A few perspectives, routes, and challenges on visible-light absorbers and photoreactors devices are stated. Research trends are included to stay update with the latest advances in engineering and materials, specifically polyheptazine imides, computational modeling, machine learning, biomass conversion, single-atom catalysis, operando characterization, and the use of sea and wastewater for solar liquid fuels. This mini-review succinctly updates experts and non-experts on the author's recent works.