Synthesis, characterization and insights into stable and well organized hexagonal mesoporous zinc-doped alumina as promising metathesis catalysts carrier

Abstract

A series of highly ordered hexagonal mesoporous alumina and zinc-modified mesoporous alumina samples are synthesized via a sol-gel method through an evaporation-induced self-assembly process using Pluronic F127 as nonionic templating agent and several aluminum precursors. The process was mediated using several carboxylic acids along with hydrochloric acid in ethanol. Successful impregnation of ZnCl2 was achieved while maintaining the ordered structure. The surface and textural properties of the materials were investigated. N2-physisorption analysis revealed a BET surface area of 394 m(2) g(-1) and a pore volume around 0.55 cm(3) g(-1). Moreover, small-angle XRD diffraction patterns highlighted the well-organized hexagonal structure even upon the incorporation of zinc chloride. The organized-structure arrangement was further confirmed by transmission electron microscopy (TEM) analysis. The Zn/Al composition of the final materials was confirmed by EDX and XPS analysis, and the zinc amount incorporated was analyzed by ICP. Furthermore, the surface modification with zinc chloride impregnation was analyzed by XPS, (1)H and (27)Al MAS-NMR and FTIR spectroscopic techniques. In addition, the effects of synthesis conditions and the mechanism of the mesostructure formation were explored. The catalytic activity of several methyltrioxorhenium (MTO)-based catalysts supported on these hexagonal mesoporous alumina materials was tested for methyl oleate self-metathesis. The results showed improved kinetics using hexagonal alumina in comparison to those using wormhole-like alumina counterparts. This behavior could be attributed to better mass transfer features of hexagonal mesoporous alumina. The prepared materials with desirable pore size and structure are suitable candidates as catalyst supports for metathesis of bulky functionalized olefins and other catalytic transformations due to their enhanced Lewis acidity and more uniform pore networks favoring enhanced and selective mass transfer phenomena.

ZnCl2 loaded TiO2 nanomaterial: an efficient green catalyst to one-pot solvent-free synthesis of propargylamines

“…6c). The peak at 1022.20 eV could be assigned to Zn 2+ species in ZnO (1021.9 eV), 58 ZnCl 2 (1022.5 eV) 59 or Zn(OH) 2 (1022.6). 60 Subsequently, we studied the chloride XPS peak (Fig.…”

Heterogeneous olefin‐metathesis: Comparative perspective of the activity with respect to unsaturated fatty acid methyl esters

“…Rhenium‐based organometallic complexes, like MTO, deposited on a suitable dehydrated surface do not require co‐catalysts for generation of metal‐alkylidene moieties to start the metathesis reaction . Although in pure form MTO is inactive towards olefin metathesis, the activity can be bestowed by interaction with a Lewis acid …”

“…[119] Although in pure form MTO is inactive towards olefin metathesis, the activity can be bestowed by interaction with a Lewis acid. [120][121][122][123][124] Figure 14. Ethenolysis of methyl oleate À turnover number and conversion as a function of methyl oleate/Re 2 O 7 ratio: (a) 30 mg/g (3 wt%) Re 2 O 7 /SiO 2 .…”

Fatty acid methyl ester heterogeneous self‐metathesis in hydrophobic green solvent: Mass transfer limitations, catalyst recyclability, and stability

“…1 mg/mL catalyst-to-olefin ratio, reaction temperature of 45 8C, relatively dry inert atmosphere (<20 % humidity) were the optimum process conditions ensuring good activity and selectivity towards desired self-metathesis products 1, 2, 4, and 5 (see Figure 1). [5,8,9] This test was used as a control test for comparison purposes with tests carried out using other reaction conditions.…”

“…Therefore, research efforts have been diverted in search of heterogeneous catalytic systems that may promise easy catalyst separation and prolonged recyclability without undergoing significant activity loss. [5] In this context, various catalysts such as rhenium, ruthenium, molybdenum, and tungsten-based organometallic complexes immobilized on mesoporous support materials were tested for metathesis reactions. [6] Regarding this type of catalysts, it is worth mentioning that Pillai et al [7] have recently reported an efficient self-metathesis process mediated by a heterogeneous catalyst, methyltrioxorhenium (MTO)/ZnCl 2 -modified mesoporous alumina, involving chemical conversion of methyl oleate and trioleate as model molecules of vegetable oil origin.…”