Correlating Oxidation State and Surface Ligand Motifs with the Selectivity of CO₂ Photoreduction to C₂ Products

Abstract

The design for non-Cu-based catalysts with the function of producing C 2 + products requires systematic knowledge of the intrinsic connection between the surface state as well as the catalytic activity and selectivity. In this work, photochemical in situ spectral surface characterization techniques combined with the first principle calculations (DFT) were applied to investigate the relationships between the composition of surface states, coordinated motifs, and catalytic selectivity of a titanium oxynitride catalyst. When the catalyst mediates CO 2 photoreduction, C 2 product selectivity is positively correlated with the surface Ti 2 + /Ti 3 + ratio and the surface oxidation state is regulated and controlled by coordinated motifs of NÀ Ti-O/V [O], which can reduce the potential dimerization energy barriers of *COÀ CO* and promote spontaneous formation of the subsequent *COÀ CH 2 * intermediate. This phenomenon provides a new perspective for the design of heterogeneous catalysts for photoreduction of CO 2 into useful products.

Selective CO2 Photoreduction to Acetate at Asymmetric Ternary Bridging Sites

“…The band at around 1034 cm –1 is related to C–O–H stretching and/or CH 3 rocking. Moreover, the band at around 2909 cm –1 is assigned to CO stretching vibration for CO*, validating the CO* coupling to generate acetic acid. , …”

Deciphering the Stability Mechanism of Cu Active Sites in CO2 Electroreduction via Suppression of Antibonding Orbital Occupancy in the O 2p-Cu 3d Hybridization

“…Furthermore, the generation of the *OCCO intermediate on the Cu v -Cu 2 O (111) facet occurs with a reduced energy barrier of 0.23 eV, a substantial improvement compared to the 0.48 eV observed in the pure Cu 2 O (111) (Figure b). This reduction in energy hints at a thermodynamically favorable scenario for facilitating C–C coupling, a crucial step that significantly escalates C 2 H 4 formation on the Cu v -Cu 2 O (111) surface. , To synthesize these insights into a coherent mechanism detailing the CO 2 RR, we integrated a comprehensive schematic representation in Figure c. This depiction clearly conveys that the Cu v -Cu 2 O catalyst possesses the ability to stabilize Cu + sites, thereby fostering efficient C–C coupling processes that enhance C 2 H 4 production while concurrently mitigating hydrogen evolution, a pivotal balance in achieving the desired selectivity.…”

Fundamentals and Challenges of Engineering Charge Polarized Active Sites for CO2 Photoreduction toward C2 Products

“…Therefore, the charge polarized Co pairs acted as catalytic sites to facilitate the C–C coupling process and subsequent selective protonation during CO 2 photoreduction into CH 3 COOH. Similarly, Li et al also utilized quasi- in-situ XPS spectra for monitoring the charge polarized Ti 2+ /Ti 3+ sites of N-doped TiO 2 with oxygen vacancies, which promoted C–C coupling to selectively achieve C 2 H 4 and C 2 H 6 . As illustrated by the quasi- in-situ XPS spectra, the Ti 2+ amount was in a dynamic equilibrium (7.40% → 7.29%), while the slight oxidation of Ti 3+ led to an increase in the amount of Ti 4+ (81.42% → 83.10%) (Figure e–g).…”

“…(e) Quasi- in-situ Ti 2p XPS spectra for the N-doped TiO 2 with oxygen vacancies during CO 2 photoreduction and (f) the corresponding atomic content of Ti 2+ and Ti 3+ as well as (g) the Ti 2+ /Ti 3+ ratio. Reproduced with permission from ref . Copyright 2023 Wiley-VCH.…”

“…38 Bearing the above in mind, we have designed metal pair sites with charge polarization for acquiring C 2 products, in which the real active sites were determined by quasi-in-situ XPS spectra (Figure 6b). 39 As an example, the quasi-in-situ XPS spectra in Figure 6c,d 40 As illustrated by the quasi-in-situ XPS spectra, the Ti 2+ amount was in a dynamic equilibrium (7.40% → 7.29%), while the slight oxidation of Ti 3+ led to an increase in the amount of Ti 4+ (81.42% → 83.10%) (Figure 6e−g). Thus, the polarization sites (Ti 2+ /Ti 3+ ) did not change much (0.66 → 0.75).…”