Multi-Technique Characterization of Rhodium Gem-Dicarbonyls on TiO$_2$(110)

TL;DR

This study employs a multi-technique approach combining spectroscopy, microscopy, and DFT calculations to characterize rhodium gem-dicarbonyls on TiO$_2$(110), revealing their surface location, coordination, and complex behavior on metal oxide supports.

Contribution

It introduces an integrated multi-technique methodology to accurately identify and analyze rhodium gem-dicarbonyls on a single-crystalline TiO$_2$(110) surface, overcoming limitations of traditional IR spectroscopy.

Findings

Rhodium gem-dicarbonyls are successfully created on TiO$_2$(110) surface.

Microscopy confirms their alignment along the [001] direction.

XPS reveals multiple rhodium species despite IR signatures.

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 applied catalysts, the ill-defined crystallographic environment of species observed on powder catalysts 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 TiO$_2$(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.