Understanding the Role of Gallium as a Promoter of Magnesium Silicate Catalysts for the Conversion of Ethanol into Butadiene

Abstract

In this study we explore the use of Ga as a new component in MgO‐SiO2 catalysts for the Lebedev reaction (the one‐pot conversion of ethanol to butadiene). Several characterisation techniques (XRD, temperature‐programmed desorption of NH3, BET measurements, IR spectroscopy) and in situ spectroscopic studies (DRIFTS‐MS) were performed with the aim to correlate the properties of the modified materials with the catalytic results. We concluded that the wet impregnation of Ga3+ on the MgO‐SiO2 catalyst creates new Ga−O(H)−Si sites. These sites interact strongly with alcohol and not only facilitate its dehydrogenation to acetaldehyde and its transformation into the intermediate crotyl alcohol but also enhance the dehydration of the latter because of an improved acidity. However, an appropriate amount of gallium oxide is needed to avoid excessive acidity, which is conducive to an increased selectivity to ethylene.

MgO−SiO2 Catalysts for the Ethanol to Butadiene Reaction: The Effect of Lewis Acid Promoters

“…Due to the low level of crystallization XRD could not provide adequate information about the bulk structure of the samples. Therefore, 1 H MAS NMR, 29 Si CP MAS NMR, and 1 H- 29 Si FSLG HETCOR NMR spectra were recorded to evaluate the environment of the Si atoms and the possible formation of magnesium silicate phases. Figure 2A shows that all the hydroxyl groups have identical environment in the crystal structure of the NT sample resulting in a single 1 H MAS NMR signal at 0.3 ppm.…”

“…The CP sample contains less hydrogen atoms than the NT sample. Two different signals 29 Si { 1 H} cross-polarization MAS NMR spectra, and (C) 1 H- 29 Si FSLG HETCOR representation of the results. could be distinguished.…”

“…The Lebedev-process [3] where the ethanol is converted to BD over mixed oxide catalyst, like MgOÀ SiO 2 or ZnO-Al 2 O 3 , and the process of Ostromislensky [4] where a mixture of ethanol and acetaldehyde is reacted over alumina or clay catalysts. Recently, different oxides, mixed oxides, and zeolite supported catalysts, such as, SiO 2, [5][6][7][8] SiO 2 -ZrO 2, [9] zeolite Beta, [10] and MgOÀ SiO 2 [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] promoted with metals and/or metal oxides, such as oxides of Zn, [8,9,17,24,25,27] Ag, [10,27,28] Cu, [10,27] Au, [11] and Ga, [15,29] and metal combinations, like Zn-Hf, [5] Zn-Ta [7,30] and Zn-Zr [13,23,26] have been reported to be active in the ETB process.…”

“…Chung et al [14] conducted NMR studies on wetkneaded MgOÀ SiO 2 catalysts, synthesized using different magnesia sources. The BD selectivity was linked to hydrous magnesium silicates giving 29 Si-NMR signals in the region of À 85 to À 98 ppm. In contrast, Zhu et al [32] attributed favourable activity to amorphous magnesium silicate phases, giving Si signals at À 70, À 75 and À 92 ppm.…”

The deactivation of a ZnO doped ZrO2–SiO2catalyst in the conversion of ethanol/acetaldehyde to 1,3-butadiene

“…Many literature studies on the mechanism of the reaction, 1 active components of catalyst [2][3][4][5] and the function of additives [6][7][8][9] were reported previously. Good catalytic performances have been reported by Huang et al 10 and Jian et al, 11 but challenges also existed in the reaction, among which, the deactivation should be the most important problem of these highly active catalysts.…”