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

H 2 production via water–gas shift reaction (WGS) is an important process and applied widely. Cobalt-modified CeO 2 are promising catalysts for WGS reaction. Herein, a series of Co/Nb–CeO 2 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-CeO 2 that was prepared at 5 mL/min titration rate exhibit strong interaction between cobalt oxide and CeO 2 that retards the reduction of CoO x producing Co–CoO x pairs. In contrast, 1-Co/Nb-CeO 2 and 25-Co/Nb-CeO 2 result in bigger and aggregated Co particles, resulting in fewer interfaces with CeO 2 . The Co 0, Co δ+, Ce 3+, and O v species are responsible for improved reducibility in Co/Nb–CeO 2 catalysts and were quantitively measured using XPS, XAS, and Raman spectroscopy. The Co–CoO x interface assists dissociation of the H 2 O molecule; CO oxidation requires low activation energy and realizes a high turnover frequency of 9.8 s –1 . The 5-Co/Nb-CeO 2 catalyst achieved thermodynamic equilibrium equivalent CO conversion with efficient H 2 production during WGS reaction at a gas hourly space velocity of 315,282 h –1 . Successively, the 5-Co/Nb-CeO 2 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.