Investigation of the interaction between Cu(acac)2 and NH4Y in the preparation of chlorine-free CuY catalysts for the oxidative carbonylation of methanol to a fuel additive

Abstract

The high temperature anhydrous interaction between copper(II) acetylacetonate Cu(acac)₂ and NH₄Y was investigated to prepare a chlorine-free CuY catalyst for the oxidative carbonylation of methanol to dimethyl carbonate. When a physical mixture of Cu(acac)₂ and NH₄Y is heated from ambient temperature to 230 °C, Cu(acac)₂ firstly sublimates and then is adsorbed immediately onto the surface of the Y zeolite. Simultaneously the ion exchange between Cu(acac)₂ and NH₄Y occurs at about 174 °C. During the activation process from 230 to 500 °C, the exchanged Cu²⁺ is reduced to a Cu⁺ active center, and the adsorbed and unreacted Cu(acac)₂ on the NH₄Y surface decomposes to nano-CuO. For NaY zeolite, no solid state ion-exchange occurs between Cu(acac)₂ and NaY during the heat treatment and only CuO exists on the Cu/NaY catalyst surface. While for HY zeolite, there is less ion-exchanged Cu⁺ in the supercages. The Cu/NaY catalyst has no catalytic activity and the Cu/HY catalyst exhibits lower activity than the Cu/NH₄Y catalyst. Strong evidence is provided that during heat treatment, a solid state ion-exchange between Cu(acac)₂ and NH₄Y occurs and makes more of the Cu⁺ located in the supercages accessible to reactants.