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The development of catalytic methods for xylose transformation as renewable raw material into value-added chemicals such as lactic and glycolic acid esters has been the subject of intensive research in recent years. Thus, methyl lactate and methyl glycolate are used as a starting material for the production of lactide and glycolide – an important monomers for the production of biodegradable polymers. The aim of this work was to search of simple effective catalyst for transformation of xylose into methyl esters of lactic and glycolic acids. For this purpose, tin-containing alumina doped with СeO2, MoO3 and CuO oxides were synthesized by impregnation method. Textural and structural parameters of obtained МeO‑SnO2/Al2O3 mixed oxides were estimated from the results of low-temperature adsorption-desorption of nitrogen and X-ray diffraction. The formation of morphology ceria close to octahedra for CeО2‑SnO2/Al2O3 sample is confirmed by the X-ray phase analysis data and SEM microphotographs. The UV spectroscopy data indicates the nanosize of tin dioxide particles on the γ‑Al2O3 surface. According to the titration results, CeО2‑SnO2/Al2O3 is acid mixed oxide with H0 ≤ –3.0. The catalytic conversion of xylose solution in methanol was carried out in rotated autoclaves and in a flow stainless steel reactor with a fixed bed of catalyst. The products of the target reaction C5H10O5+2CH3OH+1/2O2 = C4H8O3+C3H6O3+2H2O were analyzed by 13C NMR. It was found that a complete conversion of 4 % xylose solution in a 70 % aqueous methanol solution occurs with the formation of methyl lactate (42 %) and methyl glycolate (24 %) on the developed CeO2-SnO2/Al2O3 catalyst loading of 3.5 mmol C5H10O5/gcat/h at 190 °C/3.0 MPa in air flow. The path of the reaction is proposed, namely: the IVSn4+ ions in           CeO2-SnO2/Al2O3 catalyst as Lewis acid sites promote retro-aldol xylose condensation and further Cannizzaro rearrangement of intermediate methyl pyruval hemiacetal into methyl lactate. And CeO2 provides selective oxidation of glycol aldehyde formed as a result of aldol decondensation of xylose to methyl glycolate. [ABSTRACT FROM AUTHOR]

The conversion of dihydroxyacetone solution in methanol to methyl lactate has been studied in flow regime using xSnO2/Al2O3-supported catalysts that have been characterized by XRD, low-temperature nitrogen (ad)desorption analysis, and UV-Vis spectroscopy. It is found that Lewis and Brønsted acid sites of the surface of SnO2-containing catalysts play a crucial role in the selective conversion of dihydroxyacetone to methyl lactate. The formation of methyl lactate with a selectivity of 90% is achieved on 5%SnO2/Al2O3 catalyst at 160°C, 1.0 MPa, and under feed rate of 4 mmol C3H6O3/(gcat·h). [ABSTRACT FROM AUTHOR]

Nanosized TiO2/ZrO2=1:1 composites have been obtained by mechanochemical, ultrasonic, and coprecipitation methods. It is shown that mechanochemical and ultrasonic treatments of a TiO2 and ZrO2 mixture lead to size reduction of oxide particles, changes in X-ray diffraction spectra, the formation of a mesoporous structure of TiO2/ZrO2 samples, and an increase in their photocatalytic activity in the reaction of Gesagard (prometryn) herbicide destruction in an aqueous medium when compared to a mechanical TiO2 and ZrO2 mixture. It is found that the sample obtained by coprecipitation is X-ray amorphous with a well-developed surface, however, it is significantly inferior to samples obtained by alternative methods in terms of photoactivity. [ABSTRACT FROM AUTHOR]

Mixed ZrO2–SiO2–SnO2 oxides are synthesized by sol-gel method with atomic ratios of the components Zr : Si : Sn = 1 : 2 : x, where x = 0.1–4.0. By using thermogravimetric and XRD analysis, it is shown that the specimens with x ≤ 2 are characterized by highly homogeneous distributions of Sn4+ (x = 4) cations. As their content increases further, we observe the formation of a separate phase of tin dioxide, which corresponds to the tetragonal crystal structure of the rutile type. It is shown that the introduction of tin ions into the ZrO2–SiO2 matrix leads to an increase in the acidity of the obtained specimens. In particular, the maximal strength of the acid sites (H0) increases from – 11.35 for ZrSi2 to – 14.52 for ZrSi2Sn0.4 and ZrSi2Sn. In the XPS spectra, the high-energy shifts of Zr 3d5/2 and Sn 3d5/2 levels serve as an indication of the shift of electron density from zirconium and tin atoms to the atoms of silicon. We recorded the presence of octahedral and tetrahedral coordinated Sn4+ cations on the surface of ZrSi2Snx specimens, which can be referred to Brönsted and Lewis acid sites. The role of Brönsted sites can be played by bridging –OH groups on VIIIZr4+ and IVZr4+ cations, while the role of Lewis sites can be played by the coordinate-wise unsaturated zirconium and tin cations. [ABSTRACT FROM AUTHOR]