Formic acid-assisted synthesis of highly efficient Cu/ZnO catalysts: effect of HCOOH/Cu molar ratiosElectronic supplementary information (ESI) available. See DOI: 10.1039/c5cy02010g

• Main Authors: Shi, Lei, Sun, Dong, Wang, Yuxin, Tan, Yisheng, Li, Jie, Yan, Shirun, Fan, Ronggang, Tsubaki, Noritatsu
• Format: Journal Article
• Published: 28.06.2016
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/c5cy02010g

A series of metallic Cu/ZnO catalysts were prepared by a novel formic acid-assisted solid-state combustion method with and without further reduction using metal nitrates and varied amounts of formic acid as raw materials. The states of the copper species of the as-burnt catalysts were mainly affected by two important catalyst preparation routes. One route was dissolution and reduction during the solid-state process; another was reduction during the calcination process. By gradually increasing the formic acid content, the copper species in the as-burnt catalysts changed from CuO to Cu 2 O, and from Cu 2 O to metallic Cu 0 . The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Energy Dispersive Spectroscopy (EDS), Temperature-Programmed Reduction (TPR), and High-Resolution Transmission Electron Microscopy (HRTEM) analysis revealed that the precursors with a HCOOH/Cu 2+ ratio greater than 12/1, after being burnt in argon atmosphere and without further reduction, were absolutely converted into metallic Cu 0 and ZnO species. With gradually increasing formic acid content, the catalysts exhibited a larger BET surface area, larger metallic Cu 0 area, and smaller Cu crystallite size. The activity of the as-prepared catalysts was tested for low-temperature methanol synthesis. The total carbon conversion increased with increasing formic acid content. The variation trend was in accordance with that of the metallic Cu 0 surface area. The methanol selectivity was closely related to metallic Cu 0 crystallite size. The Cu crystallites with a smaller size exhibited higher hydrogenation capability to yield methanol. Metallic Cu/ZnO catalysts were directly prepared by a formic acid-assisted solid-state combustion method without further reduction.