Abstract Transient isotopic methods have been used to study the COH2 reaction over 5% RhAl2O3 in the temperature range 180–260 C. The steady-state tracing method permits the determination of the surface coverage of CO and active carbon C α during reaction, without the need for quenching in helium and subsequent titration by hydrogen. The results confirm that the sequence of steps for methane formation passes through a small reservoir of ...