# The subsurface Pt-promoted TiO2−x overlayer enhances succinonitrile production in the photocatalytic C–C coupling of acetonitrile

## TL;DR

A new catalyst design using a titanium oxide overlayer on platinum improves the efficiency of a chemical reaction that produces a valuable compound from acetonitrile.

## Contribution

A Pt-promoted TiO2−x overlayer is shown to suppress reverse reactions in photocatalytic coupling, significantly enhancing product yield and efficiency.

## Key findings

- A TiO2−x/Pt catalyst achieves a 3-fold higher succinonitrile formation rate than conventional Pt-supported TiO2.
- The catalyst reaches a 67.3% radical-to-product efficiency and 5.6% apparent quantum yield.
- Suppression of radical–proton recombination is more critical than radical initiation for coupling performance.

## Abstract

Photocatalytic coupling of monofunctional molecules offers an atom-efficient route for the synthesis of value-added bifunctional organic compounds, yet its efficiency is significantly limited by the reverse reaction of radicals. Our density functional theory (DFT) calculations have indicated that a unique structure of partially exposed Pt encapsulated by a titanium oxide (TiO2) overlayer could intrinsically facilitate the desorption and suppress re-adsorption of reactive radicals, hence impeding the reverse reaction in the photocatalytic acetonitrile coupling reaction. A TiO2−x/Pt inverse heterostructure has then been developed via strong metal–support interaction (SMSI) with tunable TiO2−x coverage. Among the catalysts, an optimal partially encapsulated TiO2−x/Pt catalyst achieves a marked formation rate of succinonitrile of 8.41 mmol·gcat−1· h−1 from acetonitrile, reaching a 67.3% radical-to-product efficiency and a 5.6% apparent quantum yield, representing 3-fold enhancements over a conventional Pt-supported TiO2 catalyst, over 1.9-fold higher than bare Pt/TiO2 or fully encapsulated counterparts, respectively. Kinetic investigations demonstrate that the suppression of radical–proton recombination plays a more dominant role in the overall coupling performance compared to the radical initiation. This work underscores the critical role of tailored catalysts by coating with oxide domains to mitigate reverse reactions and establishes an effective strategy for advancing the efficiency in photocatalytic coupling.

A universal strategy of tailoring oxide overlayers on metals offers a decisive solution to suppress reverse reactions, unlocking high efficiency in photocatalytic radical coupling.