Highly Dispersed CuO/ZnO Nanocomposite Supported on MgO as Catalyst for the Purification of Trioxane: Transfer Hydrogenation of Formaldehyde Impurities to Methanol

Abstract

In trioxane (TOX) production, unreacted formaldehyde (HCHO) readily forms a hard-to-separate ternary azeotrope with TOX and water, impairing purification efficiency and increasing energy demand. We report a green catalytic strategy that selectively converts azeotropic HCHO into methanol without degrading TOX. A CuZn-MgO catalyst prepared by deposition–precipitation fully converts HCHO in 6 h at 105 °C and atmospheric pressure, with 64% methanol selectivity; TOX remains fully stable, and no formic acid is detected. XRD, TG, TEM, EDS mapping, H2-TPR, and N2O chemisorption reveal that MgO, as a high-surface-area inert support, anchors the Cu–Zn precursor and suppresses its crystallization. During calcination, ZnO precipitates preferentially and confines CuO growth, yielding highly dispersed Cu nanoparticles (dCu = 3.3 nm), a high Cu metal surface area (214 m2·g–1), and high dispersion (31.6%). This optimized nanostructure accounts for the catalyst’s superior activity compared to those on other supports. The process requires no external H2 or additives and proceeds via water-mediated hydrogenation. It is fully compatible with existing HCHO recovery systems, demonstrating strong industrial potential.