Effect of Nb doping in WO₃/ZrO₂ catalysts on gas phase dehydration of glycerol to form acrolein

Abstract

Gas-phase dehydration of glycerol to produce acrolein was investigated over tungstated zirconia catalysts with and without niobium doping, in order to correlate the catalytic activity and life-stability with the acid/ base properties of the catalysts. The results of NH 3 -and CO 2 -TPD experiments showed that the tungstated zirconia catalysts contained both acidic and basic sites, and the amounts decreased with the increase in calcination temperature. The most suitable calcination temperature for 20% WO 3 /ZrO 2 as the catalyst in the gas phase dehydration of glycerol to form acrolein was 450 C in consideration of achieving high acrolein yield and long lifetime of the catalyst. Not only the amount of acid but also the amount of base affected the acrolein yield. Doping a small amount of niobium further increased the life-stability of the catalysts, attributed to the decrease in the number of basic sites. The influence of Nb is mostly in neutralization of surface acidity electronically instead of geometric blocking of the basic sites. Moreover, fine tuning the ratio of acid/base sites was found to be important in achieving good catalytic performance in the gas-phase dehydration of glycerol to generate acrolein. The ratio of acid/base sites in the range of 4-5.4 gave the highest glycerol conversion, and acrolein yield and lowest catalyst decay rate. The spent catalysts were easily regenerated by calcination at 450 C, and the catalytic activities were retained well even after the second time of reuse.

Gas phase dehydration of glycerol to acrolein over WO3-based catalysts prepared by non-hydrolytic sol–gel synthesis

“…[4][5][6][7][9][10][11][12][13][14][15][16][17][18][19] In this case, Brønsted acids sites are more active and selective than Lewis acid sites, 13 and the reaction takes place via a two-step process that starts with the intramolecular dehydration of the internal hydroxyl group of glycerol, followed by tautomerization and subsequent dehydration of the terminal hydroxyl group. [4][5][6][7][9][10][11][12][13][14][15][16][17][18][19] Several type of catalysts have been proposed in the last years, [4][5][6][7] including zeolites, 9,10 heteropoly acids and acidic heteropoly salt, 11 phosphate-based materials 12 and oxides. [13][14][15][16][17][18][19][20][21] Among these, W-containing materials (both bulk and supported ones), [15][16][17][18][19][20][21] are promising catalysts d...…”

“…[4][5][6][7][9][10][11][12][13][14][15][16][17][18][19] Several type of catalysts have been proposed in the last years, [4][5][6][7] including zeolites, 9,10 heteropoly acids and acidic heteropoly salt, 11 phosphate-based materials 12 and oxides. [13][14][15][16][17][18][19][20][21] Among these, W-containing materials (both bulk and supported ones), [15][16][17][18][19][20][21] are promising catalysts due to their high selectivity to acrolein and catalyst stability. Nevertheless, the deactivation of the catalyst during the reaction is one of the major drawbacks.…”

“…Nevertheless, the deactivation of the catalyst during the reaction is one of the major drawbacks. [4][5][6][7][9][10][11][12][13][14][15][16][17][18][19][20][21] In this regard, Dubois et al 17 suggested the in situ regeneration of the catalyst by co-feeding molecular oxygen. In addition, it has been also observed that oxygen not only decreases the coking rate, but also improves the selectivity to acrolein.…”

“…17,18,18a Among all the catalysts proposed for glycerol dehydration to acrolein, supported tungsten oxide catalysts are one of the most efficient. [14][15][16][17][18][19][20][21] Although they are usually prepared by impregnation, the sol-gel method also appears as an attractive preparation route since it allows the synthesis of mixed oxide catalysts in one-step. Maksasithorn et al 22 reported the preparation of W-Si and W-Si-Al metathesis catalyst by sol-gel method which proved to be more active and selective than a catalyst of similar composition obtained by impregnation.…”

Catalytic Dehydration of Glycerol to Acrolein over Aluminum Phosphate Catalysts

“…Gas-phase conversion of glycerol is generally considered as an environmentally friendly and economical approach. Various solid acid catalysts have been studied in this important reaction, including phosphates, 9 metal oxides, 4,10 zeolites, 7,11 and heteropolyacids. 5,6,12,13 Among these acid catalysts, phosphate catalysts have been widely studied in the glycerol dehydration reaction due to its superior catalytic performance.…”