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Shedding light on the nature of the catalytically active species in photocatalytic reactions using Bi₂O₃ semiconductor.

ABSTRACT: The importance of discovering the true catalytically active species involved in photocatalytic systems allows for a better and more general understanding of photocatalytic processes, which eventually may help to improve their efficiency. Bi₂O₃ has been used as a heterogeneous photocatalyst and is able to catalyze several synthetically important visible-light-driven organic transformations. However, insight into the operative catalyst involved in the photocatalytic process is hitherto missing. Herein, we show through a combination of theoretical and experimental studies that the perceived heterogeneous photocatalysis with Bi₂O₃ in the presence of alkyl bromides involves a homogeneous Bi_nBr_m species, which is the true photocatalyst operative in the reaction. Hence, Bi₂O₃ can be regarded as a precatalyst which is slowly converted in an active homogeneous photocatalyst. This work can also be of importance to mechanistic studies involving other semiconductor-based photocatalytic processes.

SUBMITTER: Riente P

PROVIDER: S-EPMC7841156 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Shedding light on the nature of the catalytically active species in photocatalytic reactions using Bi2O3 semiconductor.

Riente Paola P Fianchini Mauro M Llanes Patricia P Pericàs Miquel A MA Noël Timothy T

Nature communications 20210127 1

The importance of discovering the true catalytically active species involved in photocatalytic systems allows for a better and more general understanding of photocatalytic processes, which eventually may help to improve their efficiency. Bi2O3 has been used as a heterogeneous photocatalyst and is able to catalyze several synthetically important visible-light-driven organic transformations. However, insight into the operative catalyst involved in the photocatalytic process i ...[more]

PMID: 33504763

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Project description:We report on the design and testing of new graphite and graphene oxide-based extended ?-conjugated synthetic scaffolds for applications in sustainable chemistry transformations. Nanoparticle-functionalised carbonaceous catalysts for new Fischer Tropsch and Reverse GasWater Shift (RGWS) transformations were prepared: functional graphene oxides emerged from graphite powders via an adapted Hummer's method and subsequently impregnated with uniform-sized nanoparticles. Then the resulting nanomaterials were imaged by TEM, SEM, EDX, AFM and characterised by IR, XPS and Raman spectroscopies prior to incorporation of Pd(II) promoters and further microscopic and spectroscopic analysis. Newly synthesised 2D and 3D layered nanostructures incorporating carbon-supported iron oxide nanoparticulate pre-catalysts were tested, upon hydrogen reduction in?situ, for the conversion of CO2 to CO as well as for the selective formation of CH4 and longer chain hydrocarbons. The reduction reaction was also carried out and the catalytic species isolated and fully characterised. The catalytic activity of a graphene oxide-supported iron oxide pre-catalyst converted CO2 into hydrocarbons at different temperatures (305, 335, 370 and 405?°C), and its activity compared well with that of the analogues supported on graphite oxide, the 3-dimensional material precursor to the graphene oxide. Investigation into the use of graphene oxide as a framework for catalysis showed that it has promising activity with respect to reverse gas water shift (RWGS) reaction of CO2 to CO, even at the low levels of catalyst used and under the rather mild conditions employed at atmospheric pressure. Whilst the ?-Fe2O3 decorated graphene oxide-based pre-catalyst displays fairly constant activity up to 405?°C, it was found by GC-MS analysis to be unstable with respect to decomposition at higher temperatures. The addition of palladium as a promoter increased the activity of the iron functionalised graphite oxide in the RWGS. The activity of graphene oxide supported catalysts was found to be enhanced with respect to that of iron-functionalised graphite oxide with, or without palladium as a promoter, and comparable to that of Fe@carbon nanotube-based systems tested under analogous conditions. These results display a significant step forward for the catalytic activity estimations for the iron functionalised and rapidly processable and scalable graphene oxide. The hereby investigated phenomena are of particular relevance for the understanding of the intimate surface morphologies and the potential role of non-covalent interactions in the iron oxide-graphene oxide networks, which could inform the design of nano-materials with performance in future sustainable catalysis applications.

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Shedding light on the nature of the catalytically active species in photocatalytic reactions using Bi₂O₃ semiconductor.

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Shedding light on the nature of the catalytically active species in photocatalytic reactions using Bi<sub>2</sub>O<sub>3</sub> semiconductor.

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