An alumina‐coated UiO‐66 nanocrystalline solid superacid with high acid density as a catalyst for ethyl levulinate synthesis

Abstract

BACKGROUND: The zirconium-containing metal-organic framework (MOF) UiO-66 was used as a cell to synthesize SO 4 2 − /ZrO 2 @Al 2 O 3 , a high-density superacid with relatively strong Brønsted acidity. The UiO-66 MOF was first coated with alumina to form ZrO 2 @Al 2 O 3. Impregnation with ammonium sulfate and calcination at 500°C afforded the bimetallic composite solid superacid SO 4 2− /ZrO 2 @Al 2 O 3. RESULTS: Scanning and transmission electron microscopy images confirmed that UiO-66 was successfully coated with aluminium oxide, and its octahedral structure and uniform size (400-600 nm) were retained. SO 4 2− /ZrO 2 @Al 2 O 3 had a Brunauer-Emmett-Teller specific surface area of 301-330 m 2 g −1 and average pore diameter of 9.6-10.7 nm. X-ray photoelectron spectroscopy and Fourier transform infrared analysis showed that SO 4 2− /ZrO 2 @Al 2 O 3 contained S 6+ and Al 3+. Temperatureprogrammed ammonia desorption analysis showed that SO 4 2− /ZrO 2 @Al 2 O 3 contained super-strong acid sites. The total volume of desorbed ammonia reached 90-109 cm 3 g −1. Infrared spectra of adsorbed pyridine indicated that SO 4 2− /ZrO 2 @Al 2 O 3 contained mainly Lewis acid sites and was relatively rich in Brønsted acid sites. Thermogravimetric analysis showed that the thermal stability of SO 4 2− /ZrO 2 @Al 2 O 3 was high. CONCLUSIONS: SO 4 2− /ZrO 2 @Al 2 O 3-3M (the impregnation concentration of ammonium sulfate was 3 mol L −1) and glucose were used to synthesize ethyl levulinate (EL) in ethanol. The highest EL yield of 37.5 mol% was obtained after reacting the mixture at 200°C for 5 h. An EL yield of 28.8 mol% was obtained after four consecutive reuses of the SO 4 2− /ZrO 2 @Al 2 O 3-3M catalyst.

Steady states and kinetic modelling of the acid-catalysed ethanolysis of glucose, cellulose, and corn cob to ethyl levulinate

“…8 Literature review of experimental yields of ethyl levulinate using various catalyst types. 17,18,21,22,27,29,30,32,[37][38][39][41][42][43]47,50,51,53,60,[67][68][69][70][71] All reaction systems use conventional heating and a one-pot process, excluding the H-USY-SnO 2 marked with a ''*'' symbol, which integrates heating and spinning. The feedstock loading (mass%), catalyst loading (mass%), and reaction times are displayed at the bottom of each column.…”

“…Point i underscores the unlikely economic feasibility of complex catalysts, regardless of the extensive efforts in different research areas, including mineral acids (Brønsted acids), 17–22 metal salts (Lewis acids), 23–26 ion exchange resins, 19,24,27 sulfonated nanomaterials, 18,24,27–31 polyoxometalates, 30,32–38 zeolites, 22,37,39–43 ionic liquids 44,45 and other miscellaneous nanomaterials. 27,41,43,46–53 Considering Silva et al 's analysis, the reactions investigated in this paper occur in ethanol medium (due to its cost-effectiveness and wider availability compared with bio-butanol 54 ) and sulfuric acid. 16…”

High Dispersion of Platinum Nanoparticles over Functionalized Zirconia for Effective Transformation of Levulinic Acid to Alkyl Levulinate Biofuel Additives in the Vapor Phase

“…Song et al examined the H 3 PW 12 O 40 /ZrO 2 for direct alcoholysis of furfural alcohol to EL yield (70.2%) at 120 • C for 3 h [25]. Zhang et al investigated the EL synthesis from glucose with ethanol over SO 4 2− /ZrO 2 @Al 2 O 3 -3M catalyst [26], and EL yielded 37.5 mol% at 200 • C for 5 h. Quereshi et al reported that 40 wt.% STA was loading in ZrO 2 support for LA transformation to EL yield (90 mol %) at 110 • C in 0.5 h in a microwave reactor [27]. However, several strategies and techniques have limitations, such as complex catalyst production, low catalyst stability, and expensive precursors or instrumentation.…”