The oxidation of thirteen alcohols over sup-ported CeO2/Al2O3 catalyst with 10 wt.% of CeO2 have been studied using a desorption mass-spec-trometry technique. A catalyst sample 4–6 mg in quartz cuvette was evacuated at 100 0C, cooled to room temperature, and then adsorption of a alco-hol was provided. After vacuumation of alcohol excess, the TPR profiles of products of alcohol oxidation were recorded at sweep rate 2 a.u.m./sec and heating rate of 15 0C/min using MX-7304A monopole mass- spectrometer. Identification of formed aldehydes and ketones was provided on the bases of their characteristic ions in obtained mass-spectra, namely, acetaldehyde (m/e = 29, 44); pro-panal (29, 58); acetone (43, 58); butanal (44, 43); methyl propanal (43, 41, 72), 2-butanon (43, 72); methoxyacetone (45, 43); cyclohexanone (55); ace-tophenone (105, 77); benzaldehyde (77, 106). It was shown that the oxidation of several alcohols pro-ceeds in a wide temperature interval from 130 to 280 0C. So, peak of formaldehyde formation from me-thanol adsorbed on CeO2/Al2O3 is observed at 280 0C whereas peaks of methyl glyoxal and water formation from adsorbed hydroxyacetone are re-corded at 135 0 C. The linear correlation between activation energy of reaction and chemical shift δ (R13COH) of studied alcohols was found as Ea= 183 –1.4δ (kJ/mol). Respectively, the maximum oxi-dation rate, for instance, for methanol (50 ppm) is observed at 280 0C, for ethanol (58 ppm) at 215 0C, for n-butanol (62 ppm) at 200 0C, for n-propanol (64 ppm) at 190 0C, for 2-butanol (69 ppm) at 160 0C, for hydroxyacetone (69 ppm) at 135 0C, and for 1-phenylethanol (70 ppm) at 130 0C. Thus, ability of alcohols to oxidation decreases with increase of their electronic density on carbon atom of alcohol group in following order: 1-phenyl ethanol ≈ hyd-roxyacetone ≈ cyclohexanol > allyl alcohol ≈ 2-bu-anol ≈ i-butanol ≈ i-propanol > methoxypropanol-2 ≈ n-propanol ≈ n-butanol ≈ benzyl alcohol ≈ ethanol >> methanol. On an example of ethanol, the scheme of alcohol oxidation on ceria that assumes the addition of atomic oxygen to C–H bond of alcoho-lic group with intermediate acetaldehyde hydrate formation is discussed.
Catalytic conversion of fructose to levulinic and formic acids over tin-containing superacid (H0 = −14.52) mixed oxide was studied. Mesoporous ZrO2–SiO2–SnO2 (Zr:Si:Sn = 1:2:0.4) was synthesized by the sol–gel method. The fructose transformation was carried out in a rotated autoclave at 160–190 °C for 1–5 h using a 20 wt.% aqueous solution. The results showed that doping ZrO2–SiO2 samples with Sn4+ ions improved both fructose conversion and selectivity toward levulinic and formic acids. Under optimal conditions of 180 °C, 3.5 h and fructose to catalyst weight ratio 20:1, levulinic and formic acids yields were 80% and 90%, respectively, at complete fructose conversion. At this, humic substances formed in the quantity of 10 wt.% based on the target products.
In recent years, numerous researchers have focused on the development of catalytic methods for processing of biomass-derived sugars into alkyl lactates, which are widely used as non-toxic solvents and are the starting material for obtaining monomeric lactide. In this work, the transformation of fructose into methyl lactate on Sn-containing catalyst in the flow reactor that may be of practical interest was studied. The supported Sn-containing catalyst was ob-tained by a simple impregnation method of granular γ-Al2O3. The catalytic ex-periments were performed in a flow reactor at temperatures of 160-190 °C and pressure of 3.0 MPa. The 1.6-9.5 wt.% fructose solutions in 80% aqueous methanol were used as a reaction mixture. It was found that addition to a reac-tion mixture of 0.03 wt.% potassium carbonate leads to the increase in selec-tivity towards methyl lactate on 15% at 100% conversion of fructose. Prod-ucts of the target reaction С6Н12О6 + 2СН3ОН = 2С4Н8О3 + 2Н2О were ana-lyzed using 13C NMR method. The following process conditions for obtaining of 65 mol% methyl lactate yield at 100% fructose conversion were found: use of 4.8 wt.% fructose solution in 80% methanol, 180 °С, 3.0 МПа and a load on catalyst 1.5 mmol C6H12O6/mlcat/h at contact time of 11 minutes. The cata-lyst productivity is 2.0 mmol C4H8O3/mlcat/h and the by-productі are 1,3-dihydroxyacetone dimethyl acetal (20%) and 5-hydroxymethylfurfural (10%). It should be noted that a racemic mixture of L- and D-methyl lactates has been obtained by conversion of D-fructose on the SnO2/Al2O3 catalyst. The SnO2/Al2O3 catalyst was found to be stable for 6 h while maintaining full fruc-tose conversion at 55–70% methyl lactate selectivity. After regeneration the catalyst completely restores the initial activity.
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