When: January 15, online 15:00

The role of water for CO₂ activation on highly defective rutile TiO₂

Titanium dioxide (TiO₂) has emerged as a promising candidate for effective CO₂ conversion. Structural defects, such as oxygen vacancies, are known to substantially enhance TiO₂ reactivity toward oxygenates, rendering defective TiO₂ particularly attractive as a catalyst. [1] Nonetheless, CO₂ adsorption on TiO₂ under ultrahigh vacuum (UHV) conditions is weak and does not adequately represent realistic reaction conditions. [2]

To bridge this gap, we probe the interaction of CO₂ with highly oxygen-deficient rutile TiO₂ (110) single crystals under millibar pressures of CO₂ and different H donors with near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). Herein, in-situ XPS allows unprecedented insights in the activation of CO₂ accompanied by titania reoxidation, under formation of a variety of activated carbon surface intermediates. The spectral signature of these intermediates represents a fingerprint of the population of reaction pathways.

Our findings demonstrate the potential of reduced titania as a noble-metal-free CO₂ activation catalyst and reveal how water, serving as an efficient H and OH donor, can be used to direct reaction pathways toward favourable product distributions. By varying the reaction temperature and environment we show that the population of different reaction pathways heavily depends on the presence of efficient H/OH donors. The spectral fingerprint indicates that low temperatures and the presence of surface hydroxyls lead to parallel CO₂ conversion along the Formyl, Formaldehyde and Glyoxal pathway. Temperatures above 550 K lead to the desorption of these hydroxyls favouring oxygen-deficient reactions along the carbene pathway, eventually leading to surface coking. [3]

[1] L. Mohrhusen et al., Phys. Chem. Chem. Phys. 2021, 23, 12137. [2] M. A. Henderson, Surf. Sci. 1998, 203. [3] J. Klimek, et al., under review at Angew. Chem. Int. Ed.

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