Highly Active Cobalt Oxide Catalysts Prepared by SACOP for the Preferential Oxidation of CO in Excess Hydrogen

Abstract

AbstractCobalt based catalysts synthesized by the silica aquagel confined co‐precipitation (SACOP) method and analyzed at high spatial velocities (≈39 000 h−1) for the preferential oxidation (PROX) of CO in the presence of hydrogen showed the highest values of catalytic activity of all the cobalt‐based catalysts described in the literature, together with good values of selectivity and stability. The Co3O4/CoOOH nanocatalysts had specific surface areas of up to 120 m2 g−1 depending on the type of precipitation used. The SACOP samples precipitated by pouring aquagel into the NaOH solution (method A) gave rise to samples with less CoOOH than if the NaOH solution was poured over the aquagel (method B). This difference is ascribed to the migration of cobalt out of the aquagel microstructure during precipitation by method A. Precipitation by means of method B produced the most active catalyst, owing to the larger amount of amorphous CoOOH in the fresh sample, which was formed by the removal of silica from the cobalt silicate hydroxide. The CoOOH is gradually reduced to high surface area Co3O4 in the presence of H2 during the PROX reaction. The mechanisms of formation of CoOOH and Co3O4 by using SACOP are also discussed.