Co3+–O Bond Elongation Unlocks Co3O4 for Methane Activation under Ambient Conditions

Abstract

The pursuit of low-temperature methane activation is a paramount challenge for heterogeneous catalysis because of the high stability of the C–H bonds (435 kJ mol–1). Very few catalysts fulfill this through either constructing complex interfaces or using special noble metal oxides. Bond length, which is highly temperature-sensitive, has long been ignored in catalyst studies. Here, we exploit a bond-length elongation strategy to unlock a nonprecious metal oxide for dissociating methane at normal temperature and pressure. Mesoporous bubblelike Co3O4 with elongated Co3+–O bonds, synthesized through a unique “melting–foaming–solidifying” route, is found to activate methane at room temperature to form COx species on the very surface revealed by temperature-programmed reaction spectroscopy experiments. A combination of experimental and theoretical methods suggests that the elongated Co3+–O bonds contribute to the greatly enhanced methane adsorption, in contrast to the weak adsorption of methane on conventional nonprecious metal oxides. Accordingly, the activation energy for the C–H bond cleavage is smaller than that for methane desorption, which finally leads to the low-temperature methane activation. The simultaneous enhancement in intrinsic activity and mass transfer endows mesoporous bubblelike Co3O4 with excellent catalytic activity for methane combustion, where the complete conversion temperature is much below that over the conventional Co3O4 nanocatalysts.