Applied Catalysis B: Environmental最新文献

Photoreduction of CO₂ and H₂O into fuels and value-added chemicals is a promising green technology for solar-to-chemical conversion. However, improving the conversion efficiency with regulated product selectivity is a big challenge due to the sluggish dynamic transfer and insufficient active sites. Herein, we report on Pt single atoms anchored porous C₃N₄ nanosheet photocatalyst (Pt₁@CN) with Pt–N₄ coordination for stable and efficient CO₂ photoreduction using H₂O as reductant. The Pt₁@CN exhibits an evolution rate of 84.8 μmol g⁻¹ h⁻¹ with nearly 100% CO selectivity, outperforming most previous C₃N₄-based single-atom photocatalysts. Experimental and DFT calculation results reveal that the Pt–N₄ coordinated active sites promote the photogenerated electron transfer, CO₂ adsorption/activation, *COOH generation, and *CO desorption, thus accounting for the significantly improved CO₂ photoreduction activity with ∼100% CO selectivity. This study provides a deep insight into the significant roles of single-atom active sites in enhancing the CO₂ photoreduction activity and regulating the product selectivity.

A series of bimetallic hydroxides Co(M)_0.5O_xH_y (M = Cu, Ni, Mn, Zn) were fabricated for the benzyl alcohol oxidation reaction (BAOR). The active origin and synergistic effect of bimetallic electrocatalysts were adequately deciphered. The reaction was found be principally initiated from the sequential oxidation of Co²⁺ (i.e., Co²⁺ to Co³⁺ to Co⁴⁺), followed by the spontaneous proton–coupled electron transfer (PCET) process between Co⁴⁺ and benzyl alcohol (BA) molecules. Besides, the adsorption free energy of BA molecules on Co(Cu)_0.5O_xH_y was successfully optimized by Cu doping owing to the extraordinary d–d orbital hybridization between Co and Cu atom. As a result, an extra high conversion rate (95.3%) of BA and selectivity (98.2%) of benzoic acid were achieved under 0.5 V vs. Hg/HgO. These insights are essential for a comprehensive understanding of the BAOR mechanism and the design of Co–based catalysts.

Photoelectrochemical nitrate reduction reaction (PEC NO₃RR) is of interest as a promising route to directly realizing the solar-to-ammonia (NH₃) conversion but the limited efficiency and high applied bias voltage hamper its commercial prospects. Here, we report a bias-free photoelectrochemical cell for PEC NO₃RR in aqueous conditions, achieving a substantial NH₃ yield rate of 13.1 μmol·h⁻¹·cm⁻², high faradaic efficiency of 93.8%, and recorded solar-to-NH₃ conversion of ∼1.5% under 1 sun illumination. A hierarchical-structured Si-based photocathode with Cu⁺/Cu²⁺-containing Cu nanoparticles cocatalysts achieves a highly efficient PEC NO₃RR with NH₃ yield rate of 115.3 μmol·h⁻¹·cm⁻² in a three-electrode system. Integrating operando characterizations and systematic PEC measurements, the formation of Lewis acid sites on Cu nanoparticles by accepting the photoinduced electrons is the dominant factor for facilitating the absorption and hydrogenation of nitrate. This work will guide the development of a robust, high-performance, and unbiased PEC device for sustainable solar-to-NH₃/other fuels conversion.

Utilizing solar energy to drive the conversion of CO₂ into high-value chemicals emerged as a promising approach to decrease CO₂ emission. Yolk-shell or hollow structure have drawn much attention for photocatalytic CO₂ reduction, owing to their efficient CO₂ trapping and more active sites exposing. In this study, we employed a simple method to regulate the morphological evolution of K₃PW₁₂O₄₀ dodecahedra. After annealing, mono-/bimetallic active species are homogeneously dispersed on K₃PW₁₂O₄₀ framework forming PW₁₂ @Co and PW₁₂ @CoNi, which exhibit good CO production rates of 11.2 and 15.1 μmol/h, respectively, with selectivity of 90.7% and 92.6%. The differences in the activity and selectivity of CO₂RR are attributed to the morphology variations of POM and the influence of mono-/bimetallic species. These results are confirmed through the analysis of SEM, TEM, N₂ and CO₂ adsorption/desorption, PL, EIS and SPV characterizations. In-situ DRIFTS and DFT provide further support for the formation and transformation of intermediate products.

Biomass-based hydrogen generation has been showing a potential prospect in solving the global environment and energy challenges. This study introduces a novel chemical looping system, known as chemical looping partial oxidation and hydrogen generation (CLPH) process, which can generate inherently separated syngas from biomass, thus presenting a good application prospect. The feasibility of this system and the selection of appropriate oxygen carriers (OCs), which were the key to the success of this system, were investigated in this work. Four MFe₂O₄ (M=Ni, Co, Ca, Ba) OCs were chosen according to the modified Ellingham diagram, and their performances as well as the reaction pathway of BaFe₂O₄ and C were comprehensively investigated. The results show that all OCs exhibit a good solid-solid reactivity, but the CO selectivity of CaFe₂O₄ and BaFe₂O₄ (around 60%) are higher than that of CoFe₂O₄ and NiFe₂O₄ (around 20%). Additionally, the cycle performance of CaFe₂O₄ is worse than that of BaFe₂O₄, which is owing to the poor self-healing property. Thus, BaFe₂O₄ was chosen as the ideal OC for the CLPH process. A successful biomass gasification process for the generation of inherently separated syngas was developed, achieving a carbon conversion rate of 93%, CO selectivity of ≥ 60%, wonderful hydrogen yield of ≥ 1700 mL/g·biomass char and hydrogen purity of ≥ 94% over 5 cycles.

The role of 2D transition metal carbides, also known as MXenes, as active catalyst supports in Co-based oxygen evolution reaction (OER) catalysts was elucidated through a combination of experimental and computation electrochemistry. Through facile seeding of commericial Co nanoparticles on three different MXene supports (Ti₃C₂T_x, Mo₂Ti₂C₃T_x, Mo₂CT_x), Co@MXene catalysts were prepared and their electrochemical properties examined for alkaline OER electrocatalysts. The OER activity enhancement of Co was significantly improved for Mo₂CT_x and Mo₂Ti₂C₃T_x supports, but marginal on the Ti₃C₂T_x in rotating disk electrode and membrane electrode assembly tests. The Co@Mo₂CT_x exhibited the highest anion exchange water electrolysis performance of 2.11 A cm⁻² at 1.8 V with over 700 h of stable performance, exceeding previous benchmarks for non-platinum group (non-PGM) metal OER catalysts. The superior performance was attributed to the strong chemical interaction of Co nanoparticle with the Mo₂CT_x MXene support. Insights into the electrochemical and chemical oxidation according to MXene type as related to cell durability, as well the effect of electrical conductivity and inherent boosting of electrocatalytic activity of Mo-based MXenes elucidated through density functional theory (DFT) calculations helped explain the performance and durability enhancement of Mo-based MXene supports over Ti₃C₂T_x supports.