No abstract

The effects of surface acidity on the cascade ethanol-to-isobutene conversion were studied using ZnxZryOz catalysts. The ethanol-to-isobutene reaction was found to be limited by the secondary reaction of the key intermediate, acetone, namely the acetone-to-isobutene reaction. Although the catalysts with coexisting Brønsted acidity could catalyze the rate-limiting acetone-to-isobutene reaction, the presence of Brønsted acidity is also detrimental. First, secondary isobutene isomerization is favored, producing a mixture of butene isomers. Second, undesired polymerization and coke formation prevail, leading to rapid catalyst deactivation. Most importantly, both steady-state and kinetic reaction studies as well as FTIR analysis of adsorbed acetone-d6 and D2O unambiguously showed that a highly active and selective nature of balanced Lewis acid-base pairs was masked by the coexisting Brønsted acidity in the aldolization and self-deoxygenation of acetone to isobutene. As a result, ZnxZryOz catalysts with only Lewis acid-base pairs were discovered, on which nearly a theoretical selectivity to isobutene (∼ 88.9%) was successfully achieved, which has never been reported before. Moreover, the absence of Brønsted acidity in such ZnxZryOz catalysts also eliminates the side isobutene isomerization and undesired polymerization/coke reactions, resulting in the production of high purity isobutene with significantly improved catalyst stability (<2% activity loss after 200 h time-on-stream). This work not only demonstrates a balanced Lewis acid-base pair for the highly active and selective cascade ethanol-to-isobutene reaction but also sheds light on the rational design of selective and robust acid-base catalyst for C-C coupling via aldolization reaction.

Analysis of MCPD esters and glycidyl esters in vegetable oils using the indirect method proposed by the DGF gave inconsistent results when salting out conditions were varied. Subsequent investigation showed that the method was destroying and reforming MCPD during the analysis. An LC time of flight MS method was developed for direct analysis of both MCPD esters and glycidyl esters in vegetable oils. The results of the LC–TOFMS method were compared with the DGF method. The DGF method consistently gave results that were greater than the LC–TOFMS method. The levels of MCPD esters and glycidyl esters found in a variety of vegetable oils are reported. MCPD monoesters were not found in any oil samples. MCPD diesters were found only in samples containing palm oil, and were not present in all palm oil samples. Glycidyl esters were found in a wide variety of oils. Some processing conditions that influence the concentration of MCPD esters and glycidyl esters are discussed.

2,5-furandicarboxylic acid (FDCA) is a valuable non-phthalate biomass-based plastic precursor with the potential to replace terephthalic acid (TPA) in a variety of polymer applications. In this work, the Co/Mn/Br catalyzed semi-continuous oxidation of 5hydroxymethylfurfural (HMF) to FDCA has been carried out at temperatures lower than those of the traditional Mid-Century (MC) process. As HMF is more susceptible to side reactions (e.g. the over-oxidation to CO and CO 2 ), lower temperatures compared to the MC process are typically used to prevent substrate burning. However, lower temperatures afford much decreased FDCA yield compared to that of TPA in p-xylene oxidation. Therefore, optimization of other operating variables such as catalyst composition, water concentration in the acetic acid solvent and pressure are essential to maximize FDCA yield. Using such optimization, we show that the FDCA yield can be enhanced to 90% at 1/0.015/0.5 molar ratio of Co, Mn and Br, 7% (v/v) water, 30 bar (CO 2 /O 2 = 1/1, mol/mol) and 180 o C, the highest value reported for HMF oxidation using Co/Mn/Br catalyst. The use of Zr(IV) as co-catalyst facilitates FDCA formation, but only at lower temperatures (120-160 °C) where the FDCA yield is compromised. These findings broaden the scope of the application of the industrial MC catalytic process for FDCA production. use) by 65%. As a result, FDCA has been identified by DOE as one of the top twelve building blocks for the future green chemicals industry. 12, 13 The oxidation of HMF to FDCA was originally carried out in presence of strong oxidants, such as nitric acid or KMnO 4 . 2,14 Apart from environmental concerns, these systems produced only modest FDCA yield owing to substrate destruction under the harsh oxidizing conditions. Alternatively, oxidation with molecular oxygen, a much milder and cleaner oxidant, has been developed, employing noble metals such as platinum, 15-20 gold 21-27 and Pd 28-33 as active catalysts.During the past five years, these heterogeneous catalytic systems have been extensively studied and shown to provide nearly quantitative FDCA yield at relatively mild reaction temperatures (65-130 °C). However, because of its low solubility in the reaction medium, FDCA tends to precipitate out in the course of reaction, which might not only deactivate the catalysts by blocking the active sites but also causes separation problems. For this reason, sodium hydroxide is added in some cases to convert the diacid product into its sodium salt, which, after removal of the catalysts, must be treated with a strong acid for recovery of FDCA. 18,23,24 More recently, several base-free processes have been reported by using hydrotalcite-supported gold nanoparticles, 25 carbon nanotube-supported gold-palladium alloy nanoparticles 34 , covalent triazine supported ruthenium 35 and magnetic Fe 3 O 4 −CoO x 36 as catalysts. Nevertheless, even in these cases, the substrate (HMF) concentration needs to be maintained very low to avoid FDCA precipitation. The potential for practical appl...

We report the direct conversion of mixed carboxylic acids to C-C olefins with up to 60 mol% carbon yield through cascade (cross) ketonization, (cross) aldolization and self-deoxygenation reactions. Co-feeding hydrogen provides an additional ketone hydrogenation/dehydration pathway to a wider range of olefins.