Insight into Copper‐Based Catalysts: Microwave‐Assisted Morphosynthesis, In Situ Reduction Studies, and Dehydrogenation of Ethanol

Abstract

Herein, we report results of three distinct controlled CuO morphologies, urchin-like (CuO-UC), fiber-like (CuO-FB) and nanorods (CuO-NR), prepared by MWA method. These well-designed structures were then dispersed in silica (SiO2) and reduced in a H2 flow that produced the following catalysts: CuO1� xUC, CuO1� xFB, and CuO1� xNR (x = 0, 1, and/or 2); their subsequent activity for the dehydrogenation of ethanol is also discussed herein. The activity and selectivity of these catalysts depend on the physical and chemical structure of the active components, which are largely influenced by the catalyst preparation method. [13] In particular, the use of small-sized CuO crystals produced a highly active and selective catalyst for the dehydrogenation of ethanol into acetaldehydes with high turnover frequencies (TOF). The structural characterization of catalysts was carried out by using several ex situ techniques; highresolution field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), conventional temperature-programmed reduction under H2 (TPR-H2), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) method for surface area determination, and in situ time-resolved X-ray absorption near-edge structure (XANES) spectroscopy at the Cu K-edge during TPR under H2 experiments (XANES–TPR-H2). Complete experimental details are provided in the Supporting Information. In addition, the Cu metal surface after the reduction treatment of the samples was subjected to TPR measurements with N2O oxidation. [14] FESEM images of CuO assemblies with different morphologies obtained by efficient MWA synthesis are shown in Figure 1 . Our results show that both the solvent and the base influence the final shape of crystals. By using copper(II) chloride dihydrate in deionized water and ammonium hydroxide as the base, CuO-UC structures were obtained with an average size of 3 mm in diameter and nanostructured spines (10 nm of