A DRIFTS Study of Catalyzed Dehydration of Alcohols by Alumina-supported Heteropoly Acid

Abstract

Selectively catalyzed dehydration of ethanol, 1,2-propylene glycol, and glycerol on supported heteropoly acid (HPA) was studied using transient diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). Tungstosilicic acid (H 4 [SiW 12 O 40 ] denoted as H 4 SiW), supported on neutral mesoporous alumina as a catalyst, was studied to investigate the formation of intermediate products and desired dehydration products on the catalyst surface. Both ethylene-containing species and surfacebound carboxyl species were detected for all three alcohols. The formation of ethylene was promoted at lower temperatures while an increased reaction temperature facilitated the formation of acetate products when ethanol was used. When 1,2-propylene glycol was used, surfacebound carboxyl species were found as major intermediate products; these might have formed from propanal produced from the hydration reaction catalyzed by acid sites on HPA. Intermediate species from more complicated reactions were detected on the catalyst surface when glycerol was used, including aldehyde, surface-bound carboxyl species, and alkene species. The results indicated that acid dehydration might be facilitated either by the addition of water or lowering the reaction temperature. The work provides insight into reaction pathways for bio-polyols, and therefore is informative for designing cost-effective and efficient chemical catalysis systems for the conversion of bio-renewables.

Gas phase dehydration of glycerol catalyzed by rutile TiO2-supported heteropolyacids

“…Referring to earlier publications [1,2,5,11,19,21] and our present results, the possible reaction route was proposed as Scheme 1.…”

“…It was explained as that at lower temperatures, the intermolecular dehydration, yielding oligomers of glycerol, was thermodynamically favored over the desired intramolecular dehydration forming acrolein [20]. On the other hand, when the reaction temperature was raised to 300 8C, the decrease in acrolein selectivity can be explained as that high reaction temperature caused the formation of acrolein oligomers [11] or the cracking of acrolein to acetaldehyde and formaldehyde [21].…”

“…The formation of acetaldehyde was proposed through the cracking of 3-hydroxypropanal and acrolein [5,21]. The TiO 2 -supported heteropolyacid catalyst with lower acidity was beneficial to the cracking reaction, giving high acetaldehyde selectivity.…”

Gas-phase Dehydration of Glycerol over Supported Silicotungstic Acids Catalysts

“…Various solid acid catalysts, viz. metal phosphates, 8,9,[13][14][15][16] metal sulfates, 17 metal oxides, [17][18][19] supported heteropolyacids (HPAs) 17,[20][21][22][23][24][25][26] and zeolites, 11,17,27,[28][29][30][31][32] have been reported. HPAs with well defined Keggin structures are well-known solid acid catalysts.…”

Catalytic conversion of glycerol to acrolein over MCM‐41 by the grafting of phosphorus species

“…So far, various catalysts have been investigated in glycerol dehydration to acrolein not only in gas or liquid phases but also in sub‐ and supercritical reaction conditions . In gaseous phase, many solid acid catalysts, including sulphates, metal phosphates, metal oxides, heteropolyacids, and zeolites, have been studied.…”