The conversion of glycerol to methyl lactate catalyzed by tin‐exchanged montmorillonite‐supported gold catalysts

Abstract

BACKGROUND Glycerol is a versatile platform compound to produce valuable chemicals. One‐pot direct conversion of glycerol into methyl lactate with methanol as solvent is very attractive, because it can reduce intermediate steps and avoid the separation of glycerol/methanol mixtures. RESULTS A series of tin (Sn)‐exchanged montmorillonite(M)‐supported Au catalysts were prepared by a combination of ion exchange and colloidal deposition methods, and designed as bifunctional catalysts containing gold (Au) and solid acid. These catalysts were employed for one‐pot conversion of glycerol to methyl lactate in methanol. The Au/Sn(20)‐Mt catalyst gave a high yield of methyl lactate of 54% upon conversion of 0.25 mol L–1 glycerol methanol solution over 0.07 g catalyst at 210 °C under 3 MPa air for 5 h. The good performance of Au/Sn(20)‐Mt was ascribed to the coexistence of small Au particle and abundance of acid sites. The glycerol conversion remained almost unchanged in the five recycled runs, whereas the methyl lactate yield decreased after the first run but kept stably in the later four catalytic runs. CONCLUSIONS Among the series of Sn‐exchanged Mt‐supported Au catalysts, Au/Sn(20)‐Mt showed the highest glycerol conversion and methyl lactate yield. Containing both small Au particles and having an abundance of acid sites contributed to the excellent catalytic activity of Au/Sn(20)‐Mt. © 2019 Society of Chemical Industry

Bifunctional Au–Sn-SiO2 catalysts promote the direct upgrading of glycerol to methyl lactate

“…Indeed, a facile substrate channeling between the two active sites could effectively drive the reaction to the desired methyl lactate. The synthesis of such bifunctional catalysts was attempted before (using mostly intricate multi-step preparation procedures), 11,31,33,65,66 but the resulting material showed impaired catalytic performance, mostly due to the difficulty to stabilize both the Au and the Sn species in their most active forms. Here, the aerosol-assisted sol-gel synthesis was exploited to synthesize bifunctional catalysts in one step ( plus calcination).…”

“…Yet only a few research groups have addressed this possibility. 9,11,[31][32][33] Pescarmona et al demonstrated that a mechanical mixture of Au/CuO and Sn-MCM-41-XS could reach a 95% glycerol conversion with a ML yield up to 62% in 10.5 h. 11 Similarly, Zhou et al worked with Au/CuO and Snβ zeolites to obtain similar resultsglycerol conversion of 86% and ML yield of 60%. 33 Moving further, Tang et al emphasized that the selectivity of the first step of the cascade reaction should be targeted to increase the overall yields and focused on the improvement of the noble metal catalyst.…”

“…In another example, colloidal gold was immobilized on a tin-exchanged montmorillonite but this resulted in relatively large gold nanoparticles and in a decrease in the acidity of the material, leading to modest ML yields. 31 On the other hand, an intricate multi-step process was recently reported to prepare an Au/Snβ@mesosilica composite featuring a sandwich-like structure to avoid gold sintering while maintaining the acidity of the zeolites; this material reached high ML yields (but very low specific productivity). As demonstrated through these examples, the synthesis of effective bifunctional catalysts is challenging.…”

Recent advances in the utilization of glycerol for the production of lactic acid by catalysis

“…Hence, a series of Sn-exchanged montmorillonite (Mt)-supported Au catalysts were investigated, among them, Au/Sn(20)-Mt was the best for the one-pot conversion of glycerol to methyl lactate. 61 The coexistence of small Au particles and abundant acid sites on the catalyst surface should contribute to the good performance. In the system Au-based catalyst for conversion of glycerol into lactic acid, the high cost and limited availability urgently needed for improvement.…”

“…Moreover, Sn ion‐exchanged Mt was demonstrated to display outstanding activity and stability in the conversion of glucose to methyl lactate using methanol as a solvent. Hence, a series of Sn‐exchanged montmorillonite (Mt)‐supported Au catalysts were investigated, among them, Au/Sn(20)–Mt was the best for the one‐pot conversion of glycerol to methyl lactate 61 . The coexistence of small Au particles and abundant acid sites on the catalyst surface should contribute to the good performance.…”