The structure of Co species in novel active and selective Co/MCM41 catalyst in the COProx reaction prepared by supercritical CO₂ reactive deposition

Full text: Co/MCM41 catalyst with 4.3 wt. % Co (Co/sc) has been prepared by supercritical CO₂ reactive deposition (SCFRD) and characterized by different physicochemical techniques. This synthesized method was compared with others conventional methodologies such as template-ion exchanged (Co/TIE) and incipient wet impregnation (Co/IWI) with similar cobalt content. All the samples were studied as catalysts on the CO total oxidation (COTox) and preferential oxidation of CO on H2-rich streams (COProx). The Co/sc catalyst was the most active and selective for the COProx reaction. This enhanced performance of the Co/sc catalyst has been explained in terms of the characteristics of the Co active sites. Temperature-Programmed Reduction (TPR), X-ray Photoelectronic (XPS) and X-ray Absorption spectroscopic (XANES/EXAFS) studies suggested that TIE and IWI methods can provide tetrahedrally coordinated Co(II) ions mainly dispersed on the internal surface of MCM41. The SCFRD method generated the Co₃O₄ spinel nanoparticles and Co(II) species into the framework of MCM41. Even though IWI and TIE methods are simpler for cobalt incorporation, they caused a significant loss of surface area, thus blocking the pores. In particular, a core-shell structure was formed with TIE method, with outer cobalt layers. Thus, the combination of Co₃O₄ nanoparticles and Co(II) sites interacting with the siliceous structure, highly dispersed on the surface and inside the mesoporous support obtained by the SCFRD method resulted in a more active and selective catalyst for the COProx reaction. (author)