Restructuring Co-CoO_x Interface with Titration Rate in Co/Nb-CeO₂ Catalysts for Higher Water-Gas Shift Performance

H₂ production via water-gas shift reaction (WGS) is an important process and applied widely. Cobalt-modified CeO₂ are promising catalysts for WGS reaction. Herein, a series of Co/Nb-CeO₂ catalysts were prepared by varying the rate of precipitant addition during the coprecipitation method and examined for hydrogen generation through WGS reaction. The rates of precipitant addition were 1, 5, 15, and 25 mL/min. We obtained ceria supported cobalt catalysts with different sizes and morphology such as 3, 8 nm nanoclusters, 30 nm cubic nanoparticles, and 50 nm hexagonal nanoparticles. The well dispersed small cobalt particles in Co/Nb-CeO₂ that was prepared at 5 mL/min titration rate exhibit strong interaction between cobalt oxide and CeO₂ that retards the reduction of CoO_x producing Co-CoO_x pairs. In contrast, 1-Co/Nb-CeO₂ and 25-Co/Nb-CeO₂ result in bigger and aggregated Co particles, resulting in fewer interfaces with CeO₂. The Co⁰, Co^δ+, Ce³⁺, and O_v species are responsible for improved reducibility in Co/Nb-CeO₂ catalysts and were quantitively measured using XPS, XAS, and Raman spectroscopy. The Co-CoO_x interface assists dissociation of the H₂O molecule; CO oxidation requires low activation energy and realizes a high turnover frequency of 9.8 s^-1. The 5-Co/Nb-CeO₂ catalyst achieved thermodynamic equilibrium equivalent CO conversion with efficient H₂ production during WGS reaction at a gas hourly space velocity of 315,282 h^-1. Successively, the 5-Co/Nb-CeO₂ catalyst exhibited stable performance for straight 168 h attributed to stable CO-Co^δ+ intermediate formation, achieving efficient inhibition of typical CO chemistry over the Co metal, suitable for hydrogen generation from waste derived synthesis gas.