Filtration of the preferred catalyst for reverse water-gas shift among Rh ( = 3-11) clusters by mass spectrometry under variable temperatures.

The key to optimizing energy-consuming catalytic conversions lies in acquiring a fundamental understanding of the nature of the active sites and the mechanisms of elementary steps at an atomically precise level, while it is challenging to capture the crucial step that determines the overall temperature of a real-life catalytic reaction. Herein, benefiting from a newly-developed high-temperature ion trap reactor, the reverse water-gas shift (CO + H → CO + HO) reaction catalyzed by the Rh ( = 3-11) clusters was investigated under variable temperatures (298-783 K) and the critical temperature that each elementary step (Rh + CO and RhO + H) requires to take place was identified. The Rh cluster strikingly surpasses other Rh clusters to drive the catalysis at a mild starting temperature (∼440 K). This finding represents the first example that a specifically sized cluster catalyst that works under an optimum condition can be accurately filtered by using state-of-the-art mass spectrometric experiments and rationalized by quantum-chemical calculations.