Effect of Mg modification on the catalytic performance of zinc malachite for methanol synthesis

Abstract

The complex conditions of methanol production from coke-oven gas have brought challenges to the copper-based methanol synthesis catalyst. In this work, a series of zinc-malachite samples with different Mg contents were prepared. The zinc-malachite and calcined samples were characterized by in-situ X-ray diffraction (XRD), thermogravimetry-mass spectrometry (TG-MS), N₂ physical adsorption, H₂ programmed temperature reduction (H₂-TPR), CO₂ programmed temperature desorption (CO₂-TPD) and other methods. The effects of Mg addition on the structure of zinc-malachite and its catalytic performance of methanol synthesis were investigated. The results showed that the addition of Mg increased the degree of Cu substitution inside the zinc-malachite structure and promoted the formation of high temperature carbonates in the catalyst after roasting. With the increase of Mg content, the specific surface area of the calcined catalyst increased gradually, and the Cu grain size decreased simultaneously. In-situ XRD results showed that a small amount of Mg could effectively inhibit the growth of copper grain size during the heat treatment. The evaluation showed that the initial activity of the catalyst increased first and then decreased with Mg addition, and the activity of the Mg-doped catalyst remained at a relatively high level after heat treatment. The appropriate Mg addition is beneficial to the initial activity and thermal stability of Cu-based methanol synthesis catalyst.