Low-temperature activation of methane on doped single atoms: descriptor and prediction

Catalytic transformation of methane under mild conditions remains a grand challenge. Fundamental understanding of C-H activation of methane is crucial for designing a catalyst for the utilization of methane at low temperature. Recent experiments show that strong methane chemisorption on oxides of precious metals leads to facile C-H activation. However, only a very few such oxides are capable (for example, IrO2 and PdO). Here we show for the first time that strong methane chemisorption and facile C-H activation can be accomplished by single transition-metal atoms on TiO2, some of which are even better than IrO2. Using methane adsorption energy as a descriptor, we screened over 30 transition-metal single atoms doped on TiO2 for the chemisorption of methane by replacing a surface Ti atom with a single atom of another transition metal. It is found that the adsorption energies of methane on a single atom of Pd, Rh, Os, Ir, and Pt doped on rutile TiO2(110) are greater than or similar to those on rutile IrO2(110), a benchmark for the chemisorption of methane on transition oxides. Electronic structure analysis uncovered orbital overlap and mixing between methane and the single atom, as well as significant localization of the charge between the molecule and the surface, demonstrating chemical bonding of CH4 to doped single atoms. Facile C-H dissociation has been found on the single-atom sites with the transition state energies lower than desorption energies. Our computational studies predict that Pd, Rh, Os, Ir, and Pt single atoms on rutile TiO2(110) can activate C-H of methane at a temperature lower than 25 degrees C.