Cooperativity of Brønsted and Lewis Acid Sites on Zeolite for Glycerol Dehydration

Abstract

Selective dehydration of glycerol, a byproduct from the biodiesel industry, on solid acids is an important reaction in the production of the value-added chemical acrolein for economic-sustainable biorefinery. Most efforts have been made on the development of strong Brønsted acid sites (BAS) to improve the production of acrolein, because the Lewis acid sites (LAS) generally promote the generation of the byproduct acetol. However, exclusively tuning the properties of BAS or LAS did not well-promote the acrolein production from glycerol as indicated in this work. We provide a new route for efficient and selective glycerol transformation to acrolein via the cooperative dehydration between the BAS and LAS. The role of LAS (extra-framework aluminum species on zeolites) was altered from competition with BAS to generate the byproduct acetol to cooperation with the neighboring BAS. It is very beneficial for the sequential two-step dehydration of the internal and terminal hydroxyl groups of glycerol to value-added acrolein. This cooperativity of BAS and LAS significantly improved the yield of acrolein from the selective glycerol dehydration.

Gas-phase dehydration of glycerol over calcined tungsten-modified Zn–Al–O hydrotalcite-type catalysts

“…The observed correlations are consistent with the published data [34] on the mechanism of glycerol dehydration and acrolein and acetol formation with participation of Bronsted and Lewis acid sites, respectively.…”

Probing zeolites by vibrational spectroscopies

“…electron acceptor centers) in zeolites can be of three main types: (i) charge-balancing extraframework cations, 204,224-231 discussed in Section 3.1; (ii) extraframework aluminum species Al 3+ , 113,204,[232][233][234][235][236][237][238][239][240][241][242][243][244] reviewed in Section 3.2; and (iii) heteroatoms substituted at framework T positions, 21,22,[245][246][247][248][249][250][251][252][253][254][255][256][257] described in Section 3.3. electron acceptor centers) in zeolites can be of three main types: (i) charge-balancing extraframework cations, 204,224-231 discussed in Section 3.1; (ii) extraframework aluminum species Al 3+ , 113,204,[232][233][234][235][236][237][238][239][240][241][242][243][244] reviewed in Section 3.2; and (iii) hete...…”

Reaction-dependent heteroatom modification of acid–base catalytic cooperativity in aminosilica materials

“…None of the M 3+ elements (B, Al, Ga) formed ␤-nitroalcohol, but all three M 4+ elements (Ti, Zr, Ce) did, though Ti-A3-SBA-15 formed ␤-nitroalcohol in a trace amount. Catalysts containing Brønsted acid sites are known to be more selective toward the dehydration of secondary alcohols while catalysts containing Lewis acid sites are more selective toward dehydration of primary alcohols [96,97]. The large number of Brønsted acid sites for the Zr-A3-SBA-15 material seems to contradict this notion because this catalyst formed the ␤-nitroalcohol, a secondary alcohol, with moderate selectivity (32%).…”