# Multi-technique characterization of rhodium gem-dicarbonyls on TiO2(110)

## TL;DR

This study uses multiple techniques to better understand rhodium gem-dicarbonyls on a titanium dioxide surface, important for catalysis.

## Contribution

The work demonstrates the necessity of combining multiple techniques to accurately characterize single-atom catalysts.

## Key findings

- Gem-dicarbonyls are aligned along the [001] crystallographic direction on TiO2(110).
- XPS reveals multiple rhodium species even when IR shows only gem-dicarbonyls.
- Multi-technique approaches are essential for characterizing single-atom catalysts.

## Abstract

Gem-dicarbonyls of transition metals supported on metal (oxide) surfaces are common intermediates in heterogeneous catalysis. While infrared (IR) spectroscopy is a standard tool for detecting these species on powder catalysts, the ill-defined crystallographic environment renders data interpretation challenging. In this work, we apply a multi-technique surface science approach to investigate rhodium gem-dicarbonyls on a single-crystalline rutile TiO2(110) surface. We combine spectroscopy, scanning probe microscopy, and density functional theory (DFT) to determine their location and coordination on the surface. IR spectroscopy shows the successful creation of gem-dicarbonyls on a titania single crystal by exposing deposited Rh atoms to CO gas, followed by annealing to 200–250 K. Low-temperature scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) data reveal that these complexes are mostly aligned along the [001] crystallographic direction, corroborating theoretical predictions. Notably, X-ray photoelectron spectroscopy (XPS) data reveal multiple rhodium species on the surface, even when the IR spectra show only the signature of rhodium gem-dicarbonyls. As such, our results highlight the complex behavior of carbonyls on metal oxide surfaces, and demonstrate the necessity of multi-technique approaches for the adequate characterization of single-atom catalysts.

The study investigates rhodium gem-dicarbonyls on titania with a multi-technique approach, using XPS, IR, DFT+U, and scanning probe microscopy. The findings have important implications for the rapidly growing field of single atom catalysis.