Abstract
This study focuses on examining the isomerization of allyl alcohol using ruthenium (Ru) supported on alumina as a heterogeneous catalyst. The synthesized Ru/Al solids were characterized by various characterization techniques. The content of Ru was estimated by the energy dispersive x-ray technique. The x-ray diffraction (XRD) confirmed the presence of phases in the support and active species in the catalysts. The surface area of the support after Ru impregnation and the pore volume were determined by nitrogen physisorption. The analysis of programmed temperature (TPR and TPO) shows different redox sites which is confirmed by XPS. The catalytic results suggest a dependence on the amount of available metallic Ru, as well as the importance of the continuous regeneration of the metal using H2 to achieve a good conversion of the allyl alcohol. For comparison purposes, the commercial Ru on alumina 5% (CAS 908142) was used. The results show up to 68% alcohol conversion and 27% yield of the isomerization product using Ru(1,5.4h)/Al catalyst in comparison with 86% conversion and 39% yield of the isomerization product using CAS 908142. In contrast, our catalysts always presented higher TOF values (149–160) in comparison with CAS 908142 (101).
Highlights
Achieving a high atomic economy is essential in the search for new synthetic routes, adjusting the viability from the energy point of view, and being respectful of the environment
The results obtained by wavelength dispersive x-ray fluorescence (WDXRF) (Table 1) show that the prepared solids presented a Ru content very close to the desired values (1.5, 1, and 0.7%), which indicates that the wet impregnation method was effective
Conditioning Reaction To establish the temperature and duration of the reaction at which a higher conversion of allyl alcohol was obtained, the commercial catalyst was used in a neutral atmosphere (N2)
Summary
Achieving a high atomic economy is essential in the search for new synthetic routes, adjusting the viability from the energy point of view, and being respectful of the environment. To achieve the isomerization of allyl alcohol, the formation of the enol is essential first and a tautomerization process is carried out This process is accomplished with transition metal complexes, and several reports are found in the literature. One reason that fewer heterogeneous catalysts are used in this reaction than homogeneous catalysts may be due to the fact that it is critical to design a solid that is capable of adsorbing alcohol to the surface, and secondly, that this solid can promote isomerization In this sense, Zsolnai et al (2016) used Pd supported on alumina so that the support activated the allyl alcohol and, on the other hand, the palladium promoted a dehydrogenation oxidative with subsequent hydride transfer without the addition of H2 gas. The stability of the catalysts was evaluated by reuse as follows: (i) Once the first reaction cycle was finished, the catalyst was centrifuged, washed three times with 100 ml of deionized water, and dried at 80◦C for 12 h. (ii) After the end of the second reaction cycle, the catalyst was recovered, washed, and dried as in step (i). (iii) the solid was reduced for 4 h at 350◦C
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