Introducing catalysis in photocatalysis: What can be understood from surface science studies of alcohol photoreforming on TiO₂

Abstract

Mechanisms in heterogeneous photocatalysis have traditionally been interpreted by the band-structure model and analogously to electrochemistry. This has led to the establishment of ‘band-engineering’ as a leading principle for the discovery of more efficient photocatalysts. In such a picture, mainly thermodynamic aspects are taken into account, while kinetics are often ignored. This holds in particular for chemical kinetics, which are, other than those for charge carrier dynamics, often not at all considered for the interpretation of the catalysts’ photocatalytic performance. However, while being usually neglected in photocatalyis, they are a traditional and powerful tool in thermal catalysis and are still applied with great success in this field. While surface science studies made substantial contributes to thermal catalysis, analogous studies in heterogeneous photocatalysis still play only a minor role. In this review, the authors show that the photo-physics of defined materials in well-defined environments can be correlated with photochemical events on a surface, highlighting the importance of well-characterized semiconductors for the interpretation of mechanisms in heterogeneous photochemistry. The work focuses on contributions from surface science, which were obtained for the model system of a titania single crystal and alcohol photo-reforming. It is demonstrated that only surface science studies have so far enabled the elucidation of molecularly precise reaction mechanisms, the determination of reaction intermediates and assignment of reactive sites. As the identification of these properties remain major prerequisites for a breakthrough in photocatalysis research, the work also discusses the implications of the findings for applied systems. In general, the results from surface science demonstrate that photocatalytic systems shall also be approached by a perspective originating from heterogeneous catalysis rather than solely from an electrochemical point of view.

Charge Carriers Cascade in a Ternary TiO2/TiO2/ZnS Heterojunction: A DFT Study

“…TiO 2 is widespread in material science applications spanning from environmental remediation to photocatalysis, because of its good performances and low cost . Some drawbacks, however, are present, such as the relatively high band gap (3.0–3.4 eV) and the fast charge carriers recombination.…”

“…TiO 2 is widespread in material science applications spanning from environmental remediation to photocatalysis, because of its good performances and low cost. [1][2][3][4][5][6][7][8][9] Some drawbacks, however, are present, such as the relatively high band gap (3.0-3.4 eV) and the fast charge carriers recombination. The first is responsible of low light absorption power (~5 %), while the second issue generally hinders photocatalytic applications, because the photoexcited charge carriers are annihilated with a faster kinetic compared to the desired photochemical process.…”

On the importance of catalysis in photocatalysis: Triggering of photocatalysis at well-defined anatase TiO2 crystals through facet-specific deposition of oxygen reduction cocatalyst

“…18,19,21,30,31 Indeed, it is possibly the very key aspect that is missing in such a picture, namely the redox catalytic properties of specific interfaces towards specific desired redox reactions, i.e., the specific surface chemistry and its kinetics, which should ensure that photogenerated electrons and holes are consumed in redox reactions before they recombine. Indeed, the key role of surface chemistry in photocatalysis has been recently highlighted by Heiz et al, 74 and can be also wellexemplified by recent theoretical work of Selcuk and Selloni that suggests that, for example, the photogenerated electron trapping properties of different facets of anatase TiO2 depend strongly on the environment and the nature of the electron donor. 75 In this context, we recall the seminal contribution by Peter Würfel on the nature of charge separation in solar energy-converting devices.…”

Light‐Driven Alcohol Splitting by Heterogeneous Photocatalysis: Recent Advances, Mechanism and Prospects

“…Rutile TiO 2 (110) is a readily available, one of the best understood crystalline materials (Figure 4); [76–79] therefore, it has been widely used as the semiconductor to elucidate fundamental mechanisms in LDAS [54,65,71–73,80–82] . Kollmannsberger and co‐workers investigated light‐driven splitting of methanol, ethanol, cyclohexanol, benzyl alcohol, and tert‐butanol on Pt cluster‐modified TiO 2 (110) single crystal under ultra‐high vacuum (UHV).…”