Selectivity Of Reduction Products Research Articles

TiO2 thermal stress deformation induced to promote photocatalytic CO2 reduction

Semiconductor photocatalytic reduction of CO2 is an effective means to achieve the goal of double carbon. TiO2 has received extensive attention as an excellent photocatalyst, but the adsorption of CO2 on the surface of TiO2 is not stable, which greatly inhibits the yield and selectivity of reduction products. In this work, wollastonite was used to reduce the melting temperature of TiO2 and in turn induce thermal stress deformation on the surface of the TiO2 lattice. Characterization and DFT results certified that the lattice stress deformation caused by the contraction of oxygen vacancy enables TiO2 to obtain better carrier transport efficiency and lower activation energy barrier, and also stabilizes the adsorption state of CO2 on the surface of TiO2 crystal, which effectively improved the reduction yield and selectivity of CO2. The CO yield is increased by 5.1 times, reaching up to 2.09 μmolg-1h−1, and the CO selectivity is as high as 91 %. These findings provide valuable insights for the development of efficient and selective photocatalysts for carbon dioxide transformation and pave the way for novel avenues in this research field.

Structural construction of Bi-anchored honeycomb N-doped porous carbon catalyst for efficient CO2 conversion

Electrocatalytic CO2 reduction reaction (CO2RR) technology has attracted extensive attention owing to mild reaction conditions, high energy conversion efficiency, and facile adaptability. However, it remains a great challenge for the lack of highly active catalysts and the selectivity of reduction products. Herein, we successfully fabricated the Bi nanoparticles diffused in nitrogen-doped carbon frame catalysts (Bi@NCFs) by an in-situ pyrolysis process. The electrocatalytic test results demonstrate that the Faradaic efficiency of formate (FEHCOOH) of Bi@NCFs catalyst is higher than 79% in the potential range of −0.8～-1.3 V vs. RHE, of which FEHCOOH is as high as 95.70% at −1.0 V vs. RHE. After 48 h stability test, the FEHCOOH still preserves over 81.3%, indicating excellent durability and stability of the catalyst in H-cell. The synergistic effect between the honeycomb-like porous carbon framework and Bi NPs enhance the electrocatalytic activity of the catalyst; on the other hand, nano-scale Bi particles exist on the surface and inside of the porous carbon framework, increasing the active sites for CO2RR. Even under high current in the flow cell, the catalyst exhibits high formic acid selectivity and DFT calculation proves the superiority of formic acid generation. This work provides insights into synthesizing N-doped porous carbon framework supported nano-metal catalysts for CO2RR.

Regulating Cu atom orbital state on self-built photogate catalyst for improving HCOOH selectivity of CO2 reduction

While single atom site catalysts receive tremendous attention for CO2 reduction, the understanding of orbital coupling interaction between metal-atom and CO2 molecular remains challenging and rare toward CO2 activation and selectivity of reduction products. Herein, binuclear-site Zn/Cu-porphyrin covalent organic framework (ZnCu-COF) photogate catalyst was synthesized, with characterizations of intraskeletal photogate molecular device (PMD). The ZnCu-COF showed the HCOOH selectivity of 89.1%, which was superior than Zn-COF and Cu-COF counterparts. The in-depth experimental and theoretical analyses reveal that Cu atom centers can enrich the electrons of Zn photocenters via directional and stepwise electron diffusion, which remarkably affects the orbital energy of Cu-3d, further deciding the electron state re-distribution of Cu-3d (dxy, dyz, dzx, dz2, and dx2−y2) orbitals. By a strong orbital coupling strength between Cu-3dz2 and C-2pz, Cu atom centers promote CO2 activation and nucleophilic reaction of the unsaturated carbon of *COOH intermediate, which clearly accounts for the different HCOOH and CO selectivity in COFs. This work opens critical perspective to the rational engineering, catalytic mechanism, and application of PMD-derived atomic-site catalysts.

Manipulating the oxygen reduction reaction pathway on Pt-coordinated motifs

Electrochemical oxygen reduction could proceed via either 4e−-pathway toward maximum chemical-to-electric energy conversion or 2e−-pathway toward onsite H2O2 production. Bulk Pt catalysts are known as the best monometallic materials catalyzing O2-to-H2O conversion, however, controversies on the reduction product selectivity are noted for atomic dispersed Pt catalysts. Here, we prepare a series of carbon supported Pt single atom catalyst with varied neighboring dopants and Pt site densities to investigate the local coordination environment effect on branching oxygen reduction pathway. Manipulation of 2e− or 4e− reduction pathways is demonstrated through modification of the Pt coordination environment from Pt-C to Pt-N-C and Pt-S-C, giving rise to a controlled H2O2 selectivity from 23.3% to 81.4% and a turnover frequency ratio of H2O2/H2O from 0.30 to 2.67 at 0.4 V versus reversible hydrogen electrode. Energetic analysis suggests both 2e− and 4e− pathways share a common intermediate of *OOH, Pt-C motif favors its dissociative reduction while Pt-S and Pt-N motifs prefer its direct protonation into H2O2. By taking the Pt-N-C catalyst as a stereotype, we further demonstrate that the maximum H2O2 selectivity can be manipulated from 70 to 20% with increasing Pt site density, providing hints for regulating the stepwise oxygen reduction in different application scenarios.

Coupling of Pd nanoparticles and denitrifying biofilm promotes H2-based nitrate removal with greater selectivity towards N2

The concept of simultaneous microbial-driven and Pd-catalyzed nitrate (NO3−) reduction was evaluated in terms of NO3−-removal efficiency and reduction-product selectivity. Experiments were conducted in three identical H2-based membrane biofilm reactors (MBfR) operated in parallel: biogenic Pd nanoparticles (PdNPs) associated with biofilm (“Pd-biofilm”), biofilm alone (“Biofilm”), and abiotic PdNPs alone (“Pd-film”). Solid-state characterizations confirmed that the PdNPs in Pd-biofilm were dominated by Pd0 nanocrystallites similar to those in Pd-film, and molecular microbiological analyses confirm that the microbial community in Pd-biofilm were dominated by β-proteobacteria with denitrifying activity similar to Biofilm. Pd-biofilm accelerated NO3− reduction to NO2− mainly through enzymatic activity and accelerated subsequent NO2− reduction mainly through PdNP catalysis. When H2 could be delivered at a rate approximately equal to the total demand to reduce NO3− to N2, active biofilm reduced NO3−/NO2− exclusively to N2, and it also attenuated NH4+ formation; as a result, the overall selectivity towards N2 in Pd-biofilm was nearly 100% and higher than in Pd-film. Thus, coupling PdNP catalysis and microbial denitrification promoted H2-based NO3− reduction and led to greater selectivity towards N2 as long as H2 delivery was controlled. From a practical perspective, delivering H2 by diffusion through bubbleless membranes enabled accurate control of N selectivity.

Electrochemical Reduction of CO 2 on a Cu Electrode under High Pressure: Factors that Determine the Product Selectivity

The selectivity of the electrochemical reduction products of on a Cu electrode in aqueous solution depended remarkably on the pressure (<60 atm), stirring condition, and the current density. As the flux of to the Cu electrode surface was increased by increasing pressure and/or by stirring, the main reduction product was changed in the order of and/or . On the other hand, the selectivity of the reduction products was changed in the order of and/or by increasing the current density. From these results, it was concluded that the balance between the flux of from the bulk solution to the electrode surface and the current density determines which reduction products are produced. Hydrocarbon formation was preferential when the current density was comparable to the maximum flux under given condition. The partial current density for maximum hydrocarbon formation occurred at 375 mA cm−2 under pressure at 30 atm.