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Highly selective/enantioselective Pt-ReOx/C catalyst for hydrogenation of L-malic acid at mild conditions
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作者 Bair S.Bal'zhinimaev Eugene A.Paukshtis +1 位作者 Alexey P.Suknev Nikita V.Makolkin 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2018年第3期903-912,共10页
The catalyst preparation strategy was based on a strict introduction sequence of rhenium and platinum precursors and their strong interaction with carbon support resulted in the formation of 0.5 nm Pt-Re Ox species of... The catalyst preparation strategy was based on a strict introduction sequence of rhenium and platinum precursors and their strong interaction with carbon support resulted in the formation of 0.5 nm Pt-Re Ox species of atomic dispersion, where platinum is metallic, while monolayer rhenium is partially oxidized(Re2+). The reaction kinetics was studied taking into account the process of L-malic acid association leading to the formation of inactive cyclic oligomeric species. High TOFs(ca. 50 h-1), selectivities(ca. 99%)and stability of Pt-Re Ox/C catalysts in aqueous-phase hydrogenation of L-malic acid, which are close to those of the homogeneous pincer type complexes, were revealed at mild conditions(T = 90–130 ℃). Taking into account that(i) hydrogenation reaction occurred 2–3 orders of magnitude faster than its racemization and(ii) association of L-malic acid dominates at low temperatures and in a concentrated solution,special reaction conditions that allow obtaining chemically and optically(ee 〉 99%) pure(S)-3-hydroxy-γ-butyrolactone and(S)-1,2,4-butanetriol were found. Basing on HAADF-STEM, EDX, XPS, and kinetic studies, the structure of active species and basic reaction pathways are proposed. 展开更多
关键词 L-malic acid hydrogenation Enantioselectivity Platinum Rhenium Atomic dispersion
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Improved flotation performance of hematite fines using citric acid as a dispersant 被引量:3
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作者 Xi-mei Luo Wan-zhong Yin +3 位作者 Chuan-yao Sun Nai-ling Wang Ying-qiang Ma Yun-fan Wang 《International Journal of Minerals,Metallurgy and Materials》 SCIE EI CAS CSCD 2016年第10期1119-1125,共7页
In this study, citric acid was used as a dispersant to improve the flotation performance of hematite fines. The effect and mechanism of citric acid on the reverse flotation of hematite fines were investigated by flota... In this study, citric acid was used as a dispersant to improve the flotation performance of hematite fines. The effect and mechanism of citric acid on the reverse flotation of hematite fines were investigated by flotation tests, sedimentation experiments, scanning electron microscopy(SEM), zeta-potential measurements, and X-ray photoelectron spectroscopy(XPS). The results of SEM analysis and flotation tests reveal that a strong heterocoagulation in the form of slime coating or coagulation in hematite fine slurry affects the beneficiation of hematite ores by froth flotation. The addition of a small amount of citric acid(less than 300 g/t) favorably affects the reverse flotation of hematite fines by improving particle dispersion. The results of sedimentation experiments, zeta-potential measurements, and XPS measurements demonstrate that citric acid adsorbs onto hematite and quartz surfaces via hydrogen bonding, thereby reducing the zeta potentials of mineral surfaces, strengthening the electrical double-layer repulsion between mineral particles, and dispersing the pulp particles. 展开更多
关键词 hematite citric acid dispersion flotation hydrogen bonding
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