Zeolite MCM-22 Modified with Au and Cu for Catalytic Total Oxidation of Methanol and Carbon Monoxide

Abstract

The goal of this work was to use MCM-22 zeolites for preparation of monometallic (Cu or Au) and bimetallic (Cu and Au) catalysts for oxidation reactions. The focus was on precise determination of the nature of gold and copper species and their activity in the oxidation processes. For that purpose several characterization techniques were applied (XRD, N₂ adsorption/desorption, TEM, SEM, UV–vis, H₂-TPR, ²⁷Al MAS NMR, FT-IR with the adsorption of pyridine, NO, and CO, ESR spectroscopy). They allowed us to define the following species formed on MCM-22 surface: metallic gold particles (XRD, UV–vis), isolated Cu²⁺ with octahedral coordination (UV–vis, ESR), square planar Cu²⁺ cations (ESR, IR), Cu⁺ species (ESR+NO, FTIR+CO, and FTIR+NO), and oligonuclear clusters (UV–vis) as well as CuO-like species (H₂-TPR). The presence of gold on the MCM-22 surface modified further by copper species caused the interaction between two modifiers leading to much easier reduction of CuO-like species and higher mobility of oxygen-promoting oxidative properties. The bimetallic catalyst was highly active in total oxidation of methanol and CO in the temperature range 523–623 K. Cu/Au-MCM-22 zeolite appeared useful for simultaneous removal of CO and methanol (by total oxidation) from gases emitted from automotive devices and during a variety of industrial process operations