High-Performance Vapor-Phase Selective Oxidation of Ethyl Lactate to Ethyl Pyruvate over SiO2 Supported PMoVNb Oxides

Abstract

This paper describes the application of P-Mo-V-Nb/SiO 2 catalysts for the selective oxidation of ethyl lactate (EL) to ethyl pyruvate (EP). The P-Mo-V-Nb/SiO 2 catalysts exhibit superior performance for EP selectivity than the corresponding samples of binary V-Nb/SiO 2 ternary P-Mo-V/SiO 2 and P-Mo-Nb/SiO 2 catalysts at same temperatures. The origin of high EP selectivity of the P-Mo-V-Nb/SiO 2 catalysts is explored and attributed to the synergistic effect of P, Mo, V, and Nb mixed oxides presented on the surface of the catalyst. The highly dispersive sites separated active species under the action of phosphorus, suppressing over oxidation and improving the selectivity. The existence of MoO 3 to provide higher oxidation for catalyst. The redox cycle of V and Nb oxides could be completed through electron transfer between lattice oxygen and metal cations. Moreover, the weak acidity of catalyst surface is favorable to avoid the decarboxylation reaction to target a high selectivity of EP. Therefore, the P-Mo-V-Nb/SiO 2 catalyst obtained the maximum yield of 91.8% with a selectivity of 93.8% and a conversion of 99.0% simultaneously at 280 • C.

Selective Oxidation of Methyl Lactate over Carbon-Supported Noble Metal Catalysts under Base-Free Conditions

“…16,18 In fact, the hydrolysis of ester groups and further oxidations were identified as the main competing reaction for the oxidative dehydrogenation of lactate esters. 12,18,24 Obviously, the amount of water produced in the reactor will increase with increasing ML conversion, as water is an inevitable product in the oxidative dehydrogenation of ML, which would improve the hydrolysis of ML and MP.…”

“…Similar reaction pathways were also proposed for the oxidation of ethyl lactate. 12,18,24 3.2.2. Effects of Reaction Variables.…”

“…12 Thus, alkyl lactates (methyl, ethyl, isopropyl, n-butyl) would be better feedstocks for the production of alkyl pyruvates, as they are more stable and can be easily converted to PA by the hydrolysis process. 2,12−25 Much work has consequently been conducted to investigate the selective oxidation reaction of alkyl lactates to alkyl pyruvates in the liquid phase or gas phase over Mo-based, [12][13][14]17,22,24 V-based, 15,17−24 and Ti-based catalysts 2,16 using oxygen, 12−20,22−24 H 2 O 2 , 2,15 or tert-butyl hydroperoxide 15,21 as oxidants. The gas-phase oxidation was usually carried out at high temperature (>473 K) to get a relative high activity, but leading to a significant decrease in alkyl pyruvate selectivity, especially at high conversion.…”

“…The gas-phase oxidation was usually carried out at high temperature (>473 K) to get a relative high activity, but leading to a significant decrease in alkyl pyruvate selectivity, especially at high conversion. 12,14,17,20,22,24 The liquid-phase oxidation could be realized under milder conditions (temperature <423 K, pressure <2 MPa) that make it possible to avoid over-oxidation reactions to get a high alkyl pyruvate selectivity (>90%) even at high alkyl lactate conversions. Zhou et al reported the liquid-phase oxidation of ethyl lactate over TS-1 zeolite in the presence of aqueous H 2 O 2 (30 wt %), giving a 100% ethyl lactate conversion and 97.8% ethyl pyruvate yield at 323 K in 9 h. 2 V 2 O 5 exhibited up to 98% ethyl lactate conversion with 100% ethyl pyruvate selectivity at 80 °C in 10 h with 3 equiv TBHP as oxidant.…”

“…1 K). 24 Based on these findings, we propose to investigate activated carbon (AC) supported noble-metal nanoparticles (Pt, Pd, Rh, Ru, and Au) for the liquid-phase oxidative dehydrogenation of methyl lactate (ML) to methyl pyruvate (MP) with oxygen as the oxidant in the absence of base, as an alternative route to produce pyruvates. Information on the reaction variable effects (temperature, partial pressures of ML and O 2 , and solvent), kinetics and reaction pathways are also given for a better understanding of the catalysis chemistry relevant to this MLto-MP reaction.…”