Chemicals from ethanol: the acetone synthesis from ethanol employing Ce0.75Zr0.25O2, ZrO2 and Cu/ZnO/Al2O3

Rodrigues et al. Chemistry Central Journal (2017) 11:30 DOI 10.1186/s13065-017-0249-5 Open Access RESEARCH ARTICLE Chemicals from ethanol: the acetone synthesis from ethanol employing Ce0.75Zr0.25O2, ZrO2 and Cu/ZnO/Al2O3 Clarissa Perdomo Rodrigues, Priscila da Costa Zonetti and Lucia Gorenstin Appel* Abstract Acetone is an important solvent and widely used in the synthesis of drugs and polymers. Currently, acetone is mainly generated by the Cumene Process, which employs benzene and propylene as fossil raw materials. Phenol is a coproduct of this synthesis. However, this ketone can be generated from ethanol (a renewable feedstock) in one-step. The aim of this work is to describe the influence of physical–chemical properties of three different catalysts on each step of this reaction. Furthermore, contribute to improve the description of the mechanism of this synthesis. The acetone synthesis from ethanol was studied employing Cu/ZnO/Al2O3, Ce0.75Zr0.25O2 and ZrO2. It was verified that the acidity of the catalysts needs fine-tuning in order to promote the oxygenate species adsorption and avoid the dehydration of ethanol. The higher the reducibility and the H2O dissociation activity of the catalysts are, the higher the selectivity to acetone is. In relation to the oxides, these properties are associated with the presence of O vacancies. The H2 generation, which occurs during the TPSR, indicates the redox character of this synthesis. The main steps of the acetone synthesis from ethanol are the generation of acetaldehyde, the oxidation of this aldehyde to acetate species (which reduces the catalyst), the H2O dissociation, the oxidation of the catalyst producing H2, and, finally, the ketonization reaction. These pieces of information will support the development of active catalysts for not only the acetone synthesis from ethanol, but also the isobutene and propylene syntheses in which this ketone is an intermediate. Keywords: Acetone, Ethanol, Zirconia, Copper, Ceria, Acetaldehyde, Acetate, Cu/ZnO/Al2O3 Background Acetone is an important solvent and widely used in the synthesis of drugs and polymers. The most significant industrial application of this ketone is the manufacture of the precursor for the synthesis of methyl methacrylate and meta-acrylic acid, which are monomers of polymers highly demanded nowadays. It is also employed in the synthesis of bisphenol-A (BPA polycarbonate), methyl isobutyl ketone and isopropanol among others [1]. Currently, acetone is mainly generated by the Cumene Process, which employs benzene and propylene as fossil raw materials. Phenol is a co-product of this synthesis [2]. At presents, ethanol is considered a special platform molecule [3, 4] since it can produce many chemicals *Correspondence: Divisão de Catálise e Processos Químicos, Instituto Nacional de Tecnologia, Av. Venezuela 82/518, Saúde, Rio de Janeiro, RJ CEP 21081‑312, Brazil employing one-pot processes and multifunctional catalysts. Acetone [5], ethyl acetate [6–9], n-butanol [10, 11], acetic acid [12], propylene [13], isobutene [14] and 1,3-butadiene [15] are good examples of these syntheses. The acetone synthesis from ethanol is quite interesting because not only this alcohol is a renewable feedstock, but also it does not generate phenol as a by-product. Recently, both Iwamoto [13] and Liu et al. [14] have suggested that acetone is the intermediate of the propylene and isobutene syntheses from ethanol, respectively. Surely, the understanding of the acetone synthesis will support future developments related to these subjects. Reaction 1 shows the synthesis of acetone from ethanol: 2 C2 H5 OH + H2 O → CH3 COCH3 + CO2 + 4H2 (1) Many different catalytic compositions have been employed for this synthesis. Murthy et al. [16] studied © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Rodrigues et al. Chemistry Central Journal (2017) 11:30 catalytic systems based on Fe, i.e., F e2O3–ZnO, Fe2O3– CaO and Fe2O3–Mn. Nakajima et al. [17–19] worked with mixed oxides based on Fe–Zn and Zn–Ca, which showed high activities and selectivities to acetone. Furthermore, Nishiguchi et al. [20] investigated the ethanol reforming reaction and noticed that acetone is a by-product when employing Cu/CeO2. Bussi et al. [21] verified that Cu/La2Zr2O7 produced high yields of acetone. Finally, Idris and Seebauer [22] and Yee et al. [23] studying ethanol reactions observed that Pd/CeO2 and CeO2 also synthesize acetone. As envisioned, some physical–chemical properties of the catalysts might be relevant for the acetone synthesis. However, there are very few correlations between the properties mentioned above and their catalytic performance. Moreover, despite the pieces of information available the reaction steps related to the acetone synthesis from ethanol have not been well established yet. Rodrigues et al. [5], using physicals mixtures composed of Cu/ZnO/Al2O3 + ZrO2 and other oxides, IR spectroscopy and catalytic tests at different experimental conditions, proposed the following reaction system. Firstly, ethanol is dehydrogenated to acetaldehyde on Cu surface; secondly, it migrates to the oxide surface and is oxidized to acetate (carboxylate species); finally, these species condensate and generate acetone and C O2. In order to regenerate the oxide surface (Mars and Van Krevelen mechanism, [24]), it was suggested that H2O should be dissociated on the Cu surface generating oxidant species which then migrate to the oxide and regenerate its surface. This proposal is based on the works of Idris & Seebauer [22], Yee et al. [23], and also on the research carried out by Voss et al. [25], which is related to the oxidation of ethanol employing H2O as an oxidant agent. Recently, Iwamoto [13] studying the propene generation from ethanol proposed two different mechanisms for the acetone synthesis. This author suggested that when Sc/In2O3 is employed as a catalyst, ethanol generates acetaldehyde, which is then oxidized by H 2O or surface hydroxyl groups to acetic acid. After that this compound reacts producing acetone and C O2 by the ketonization reaction. When the catalyst is Y2O3–CeO2, acetaldehyde is converted to ethyl acetate and then this ester decomposes to form acetic acid and ethene. Finally, this acid synthesizes acetone and CO2 by the ketonization reaction. Rodrigues et al. [5] analyzed the acidity and basicity of physical mixtures composed of Cu/ZnO/Al2O3 an (...truncated)