WGS catalysis and in situ studies of CoO_{1- x}, PtCo _n/Co₃O₄, and Pt_mCo _m′/CoO_1-x nanorod catalysts

Water-gas shift (WGS) reactions on Co₃O₄ nanorods and Co₃O₄ nanorods anchoring singly dispersed Pt atoms were explored through building correlation of catalytic performance to surface chemistry of catalysts during catalysis using X-ray absorption spectroscopy, ambient pressure X-ray photoelectron spectroscopy (AP-XPS), and environmental TEM. The active phase of pure Co₃O₄ during WGS is nonstoichiometric cobalt monoxide with about 20% oxygen vacancies, CoO _0.80. The apparent activation energy (E_a) in the temperature range of 180-240 C is 91.0 ± 10.5 kJ mol^-1. Co₃O₄ nanorods anchoring Pt atoms (Pt/Co₃O ₄) are active for WGS with a low E_a of 50.1 ± 5.0 kJ mol^-1 in the temperature range of 150-200 C. The active surface of this catalyst is singly dispersed Pt₁Co_n nanoclusters anchored on Co₃O₄ (Pt₁/Co₃O ₄), evidenced by in situ studies of extended X-ray absorption fine structure spectroscopy. In the temperature range of 200-300 C, catalytic in situ studies suggested the formation of Pt_mCo_m′ nanoclusters along with the reduction of Co₃O₄ substrate to CoO_1-x. The new catalyst, Pt_mCo_m′/ CoO_1-x is active for WGS with a very low E_a of 24.8 ± 3.1 kJ mol^-1 in the temperature range of 300-350 C. The high activity could result from a synergy of Pt_mCo_m′ nanoclusters and surface oxygen vacancies of CoO_1-x.