Adsorption of CO₂ on Heterostructures of Bi₂O₃ Nanocluster-Modified TiO₂ and the Role of Reduction in Promoting CO₂ Activation

Abstract

The capture and conversion of CO 2 are of significant importance in enabling the production of sustainable fuels, contributing to alleviating greenhouse gas emissions. While there are a number of key steps required to convert CO 2 , the initial step of adsorption and activation by the catalyst is critical. Well-known metal oxides such as oxidized TiO 2 or CeO 2 are unable to promote this step. In addressing this difficult problem, a recent experimental work shows the potential for bismuth-containing materials to adsorb and convert CO 2 , the origin of which is attributed to the role of the bismuth lone pair. In this paper, we present density functional theory (DFT) simulations of enhanced CO 2 adsorption on heterostructures composed of extended TiO 2 rutile (110) and anatase (101) surfaces modified with Bi 2 O 3 nanoclusters, highlighting in particular the role of heterostructure reduction in activating CO 2 . These heterostructures show low coordinated Bi sites in the nanoclusters and a valence band edge that is dominated by Bi–O states, typical of the Bi 3+ lone pair. The reduction of Bi 2 O 3 –TiO 2 heterostructures can be facile and produces reduced Bi 2+ and Ti 3+ species. The interaction of CO 2 with this electron-rich, reduced system can produce CO directly, reoxidizing the heterostructure, or form an activated carboxyl species (CO 2 – ) through electron transfer from the reduced heterostructure to CO 2 . The oxidized Bi 2 O 3 –TiO 2 heterostructures can adsorb CO 2 in carbonate-like adsorption modes, with moderately strong adsorption energies. The hydrogenation of the nanocluster and migration to adsorbed CO 2 is feasible with H-migration barriers less than 0.7 eV, but this forms a stable COOH intermediate rather than breaking C–O bonds or producing formate. These results highlight that a reducible metal oxide heterostructure composed of a semiconducting metal oxide modified with suitable metal oxide nanoclusters can activate CO 2 , potentially overcoming the difficulties associated with the difficult first step in CO 2 conversion.

Metal Oxides as Catalyst/Supporter for CO2 Capture and Conversion, Review

“…The results showed that the properties of bismuth-containing oxides could be utilized to adsorb and excite carbon dioxide, which is the crucial first step in the reductive conversion of CO 2 to valuable molecules. This combination of Bi 3+ in TiO 2 species offers a fascinating composite that can stimulate CO 2 by strong adsorption and alteration or electron transfer to produce a carboxylate or by direct breaking of the C−O bond [76]. The use of metal oxides to load the noble elements in carbon dioxide conversion reactions was carried out using different oxides (TiO 2 , SiO 2 , γ-Al 2 O 3 , ZrO 2 , and CeO 2 ).…”

Oxide based Heterostructured Photocatalysts for CO2 Reduction and Hydrogen Generation

“…The group converted CO 2 at an accelerated rate to CH 4 with 100 % selectivity. Nolan et al [61] investigated the CO 2 reduction response of Bi 2 O 3 -TiO 2 heterostructured photocatalysts and found out that the Bi 3 + rich oxide can be employed in the adsorption and excitation of CO 2 . As this activation process is the initial step in the CO 2 reduction and its conversion into useful chemical livestock, therefore this Bi 3 + rich TiO 2 system can enhance the CO 2 conversion attributed to the superior interaction and transfer of electrons to yield carboxylates or through CÀ O bond cleavage.…”

Impacts of the Catalyst Structures on CO2 Activation on Catalyst Surfaces

“…The formation of a transient negative ion by the injected electron is an important step in the CO 2 dissociation, and this can only be possible above the threshold voltage. TiO 2 modified with metal oxide nanoclusters possess enhanced activity to adsorb and convert CO 2 [26,140]. The Bi 2 O 3 -TiO 2 heterostructures obtained by modifying TiO 2 with Bi exhibited low coordinated Bi sites in the nanoclusters and a valence band edge consisting mainly of Bi-O states due to the presence of the Bi lone pair.…”

“…The Bi 2 O 3 -TiO 2 heterostructures obtained by modifying TiO 2 with Bi exhibited low coordinated Bi sites in the nanoclusters and a valence band edge consisting mainly of Bi-O states due to the presence of the Bi lone pair. Upon interaction of CO 2 with the reduced heterostructures, CO or CO 2 − were observed mainly through electron transfer to CO 2 , and the Bi 2 O 3 -TiO 2 heterostructures became oxidized in the process with adsorbed CO 2 in carbonate form [140]. In a related study, clean or hydroxylated extended rutile and anatase TiO 2 surfaces modified with Cr nanoclusters presented an upshift valence band edge related to the existence of Cr 3d-O 2p interactions, which promoted the CO 2 activation.…”