Exploration of active copper species in copper containing MWW-type zeolitic catalysts for CO oxidation

Abstract

A series of copper-containing MWW-type zeolitic catalysts (Cu-DML-x) were synthesized at various hydrothermal temperatures (x = 80-200 degrees C), and the catalytic activity in CO oxidation was investigated depending on the copper species. The chemical states of copper on Cu-DML-x catalysts were identified as a framework and extraframework Cu in MWW structure and copper oxides on the external surface depending on the temperature, and these Cu species coexisted with one another. While the MWW structural property was lost with increasing the synthesis temperature, the copper oxide species were additionally formed at higher temperatures. Cu-DML-100 and-120, mainly containing extraframework Cu, demonstrated superior CO oxidation activity compared to Cu-DML-80 with dominant framework Cu. Cu-DML-160,-180, and-200 catalysts, in which extraframework Cu and copper oxides were dominantly present as dual sites, showed the lowest activation energies. This indicates the critical role of extraframework Cu and copper oxides in promoting CO oxidation over zeolites.