Mg–Al Mixed Oxide Derived from Hydrotalcites Prepared Using the Solvent-Free Method: A Stable Acid–Base Bifunctional Catalyst for Continuous-Flow Transesterification of Dimethyl Carbonate and Ethanol

Abstract

Mg–Al oxides were prepared by facile solvent-free grinding of Mg–Al layered double hydroxide and were used as catalysts for continuous-flow transesterification of dimethyl carbonate and ethanol. The surface and structure properties of the prepared Mg–Al oxides were characterized by X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectra, and N2 adsorption–desorption. Moreover, the acid–base properties of the prepared catalysts were characterized using NH3-TPD, CO2-TPD, and pyridine-IR. The Mg–Al oxides prepared using the solvent-free method with a molar ratio of 2.0 (CHT-2-SF) exhibit good catalytic performance, which has medium basic sites, weak acidic sites, and high Brunauer–Emmett–Teller surface areas. A correlation between basicity–acidity and catalytic activity demonstrates that the conversion of ethanol increases with increasing medium basicity and weak acidity of the catalyst. The activity of CHT-2-SF remained almost unchanged after 1800 h on stream.

Solvent-Free Synthesis of Jasminaldehyde in a Fixed-Bed Flow Reactor over Mg-Al Mixed Oxide

“…The Mg-Al dried sample showed a wide pore size distribution varied from 5 nm to about 30 nm, while the calcined sample showed a The diffraction peaks corresponding to the AlO x phase were not observed in the XRD pattern of the calcined catalysts. It could be due to the insertion of Al 3+ into the MgO lattice without any phase separation in the calcined samples [23,25].…”

“…The TG analysis of the synthesized Mg-Al hydrotalcite is in line with the results observed by Kloproggea et al [21], and the TGA-MS (mass spectrometry) of Mg-Al hydrotalcites confirmed a major loss of H2O (dehydroxylation) and CO2 at around 410 °C. [22][23][24]. After calcination at 450 °C under air atmosphere, the hydrotalcite structure of the sample is decomposed and converted into the mixed oxides of MgO and Al2O3.…”

CoMn Catalysts Derived from Hydrotalcite-Like Precursors for Direct Conversion of Syngas to Fuel Range Hydrocarbons

“…The X-ray diffraction (XRD) patterns of the prepared catalysts are shown in Figure 5. The XRD patterns of dried catalysts (Figure 5a) showed that the CoMn-HTC catalysts had crystallized hydrotalcite structure forms, with characteristic peaks at 11.9°, 23.5°, 34.3°, 39°, 47.5°, 60.8°, and 62.9°, which correspond to the (0 0 3), (0 0 6), (0 0 9), (0 1 5), (0 1 8), (1 1 0), and (1 1 3) planes (JCPDS #70−2151) [43][44][45]. The CoMn-HTC-IV, CoMn-HTC-V, and CoMn-HTC-VI catalysts had no clear layered structure and did not show apparent peaks belonging to the hydrotalcite structure.…”

Revisiting the Structural Evolution of Hydrotalcite‐Derived Mixed Metal Oxides upon Alkali Metal Doping and Its Impact on Base Catalysis

“…[1,2] These features together have greatly broadened their applications in diverse fields as adsorbents, [3][4][5] ion-exchangers, [6][7][8] or catalyst carriers [9][10][11][12][13][14] and base catalysts. [15][16][17][18][19][20] Among the diverse families of the hydrotalcites, magnesium and alumina hydrotalcites are among the most widely studied materials in the literature. [3,15,[21][22][23] Although different approaches have been disclosed to prepare this class of materials, such as the conventional co-precipitation [17,24] and hydrothermal synthesis methods, [25,26] the use of alkali metals (Na [16,18,27,28] or K [29] ) as the precipitators is frequently adopted.…”

“…[15][16][17][18][19][20] Among the diverse families of the hydrotalcites, magnesium and alumina hydrotalcites are among the most widely studied materials in the literature. [3,15,[21][22][23] Although different approaches have been disclosed to prepare this class of materials, such as the conventional co-precipitation [17,24] and hydrothermal synthesis methods, [25,26] the use of alkali metals (Na [16,18,27,28] or K [29] ) as the precipitators is frequently adopted. The complete elimination of these residual alkali metal species is very difficult by simple washing.…”