Efficient use of precious metal atoms in heterogeneous catalysis is important in chemical transformation and environmental remediation. Co3O4 with singly dispersed Rh atoms, Rh1/Co3O4, was synthesized for reduction of nitric oxide with hydrogen. Studies using extended X-ray absorption fine structure (EXAFS) showed that the singly dispersed Rh atoms are bonded to surface oxygen atoms before catalysis. In situ studies using ambient pressure X-ray photoelectron spectroscopy (APXPS), EXAFS, and X-ray Absorption Near Edge Structure (XANES) suggested that the surface of Rh1/Co3O4 with singly dispersed Rh atoms is restructured into a new geometry at 220 °C in the mixture of reactant gases (NO and H2). It forms RhCon nanoclusters singly dispersed in the surface layer of Co3O4. The restructured catalyst, RhCon/Co3O4 exhibits a much better catalytic performance in contrast to Rh1/Co3O4 without a restructuring. RhCon/Co3O4 is highly active for reduction of nitric oxide with hydrogen. Selectivity to the production of N2 at 220 °C is 87% and reaches 97% at 300 °C. In situ studies showed this catalyst maintains its single dispersion of Rh atoms up to 300 °C during catalysis.