磁性纳米复合氧化物固体酸催化剂的制备及酯化性能景欢旺

Chinese Journal of Catalysis 36 (2015) 244–251 催化学报 2015年 第36卷 第2期 |   available at   journal homepage:   Article   Preparation of magnetic nanocomposites of solid acid catalysts and their applicability in esterification Huanwang Jing *, Xiaomei Wang, Yong Liu, Anqi Wang State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 73000, Gansu, China ARTICLE INFO  ABSTRACT Article history: Received 18 June 2014 Accepted 1 September 2014 Published 20 February 2015  Solid acid catalysts are superior to traditional liquid acids because they are noncorrosive, environ‐mentally benign, and recyclable. In addition, nano‐magnetic solid acid catalysts are preferable as they exhibit large specific surface areas together with good acidity and are also readily separated from the post‐reaction mixture. Three component nano‐magnetic solid catalysts TiO2‐Al2O3‐Fe3O4and CeO2‐Al2O3‐Fe3O4 and a four component catalyst ZrO2‐Al2O3‐CeO2‐Fe3O4 were synthesized by a co‐precipitation method and were subsequently characterized by inductively coupled plas‐ma‐atomic emission spectroscopy, Brunauer‐Emmett‐Teller surface area analysis, X‐ray diffraction, transmission electron microscopy, and thermal gravimetric analysis. Their catalytic activities were also evaluated in the esterification reaction of acetic acid with n‐butanol. The results demonstrated that these rare earth‐based magnetic nanocomposites exhibited good catalytic activity. © 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.Published by Elsevier B.V. All rights reserved.Keywords: Magnetic nanocomposite Solid acid catalyst Co‐precipitation method Esterification reaction  1. Introduction Acid catalysts have numerous applications in various indus‐trial organic reactions, and homogenous acids such as H2SO4, HCl, and HF have been widely used in chemical engineering. However, these mineral acids have serious drawbacks in terms of difficulties in post‐reaction separation and negative envi‐ronmental impact, as well as their tendency to contribute to the corrosion of reactors. Over the last few decades, many different solid acid catalysts have been developed as alternatives, in‐cluding metal oxides, zeolites, metal phosphates, and sulfated metal oxides [1–5], and these are widely used in alkylation [6], esterification [7,8], isomerization [9,10], nitration [11], and other reactions. In addition, it is well known that sulfated solid acids (SO42−/MOx) are potential candidates for the development of environmentally benign organic syntheses. Unfortunately, the activity of these materials decreases significantly during use because of sulfur reduction and the formation of surface coke [12–15], hindering their industrial applications. There‐fore, there is still a need to develop environmentally benign catalysts with high activity. Typically, these heterogeneous catalysts are separated by labor‐intensive filtration or centrifugation processes. Hence, much research has been devoted to the development of easily separable heterogeneous catalysts. Magnetic nanoparticles (MNPs) have been extensively researched with regard to their applications in disciplines, including magnetic resonance im‐aging [16], magnetic storage media [17], biotechnology [18], and ferrofluids [19]. Among these magnetic materials, Fe3O4 nanoparticles have been used as a versatile support for a vari‐ety of heterogeneous catalysts in different types of organic transformations [20]. Based on the above factors and our own previous research results [15], we have designed and synthesized several series of “green” solid acids, TiO2‐Al2O3‐Fe3O4 (TAF), CeO2‐Al2O3‐ Fe3O4 (CAF), and ZrO2‐Al2O3‐CeO2‐Fe3O4 (ZACF), each of which * Corresponding author. Tel/Fax: +86‐931‐8912585; E‐mail: [e-mail] DOI: 10.1016/S1872‐2067(14)60221‐7 | | Chin. J. Catal., Vol. 36, No. 2, February 2015 Huanwang Jing et al. / Chinese Journal of Catalysis 36 (2015) 244–251 245 has been applied to the esterification reaction between a car‐boxylic acid and an alcohol. We subsequently identified the best catalyst (i.e., that exhibiting the highest activity) by varying the molar ratio of different oxides in the catalyst. Furthermore, we propose a plausible mechanism for the esterification reaction based on characterization of the structures and morphologies of these materials. 2. Experimental 2.1. Preparation of catalysts ZrOCl2·8H2O, AlCl3·6H2O, Ce(SO4)2·4H2O, n‐butanol, acetic acid, tetrabutyl titanate, and toluene were all obtained from commercial sources and used as‐received without further puri‐fication. Fe3O4 MNPs were generated by dissolving FeCl3·6H2O (6.76 g) and FeSO4·7H2O (3.80 g) in 100 mL of deionized water to produce a clear solution, following which the pH was adjusted to 10 with NH4OH acting as a precipitant. After 2 h of v