Critical approaches in the catalytic transformation of sugar isomerization and epimerization after Fischer-History,challenges,and prospects

The transformation of aldose to ketose or common sugars into rare saccharides,including rare ketoses and aldoses,is of great value and interest to the food industry and for saccharidic biomass utilization,medicine,and the synthesis of drugs.Nowadays,high-fructose corn syrup(HFCS)is industrially produced in more than 10 million tons annually using immobilized glucose isomerase.Some low-calorie saccharides such as tagatose and psicose,which are becoming popular sweeteners,have also been produced on a pilot scale in order to replace sucrose and HFCS.However,current catalysts and catalytic processes are still difficult to utilize in biomass conversion and also have strong substrate dependence in producing high-value,rare sugars.Considering the specific reaction properties of saccharides and catalysts,since the pioneering discovery by Fischer,various catalysts and catalytic systems have been discovered or developed in attempts to extend the reaction pathways,improve the reaction efficiency,and to potentially produce commercial products.In this review,we trace the history of sugar isomerization/epimerization reactions and summarize the important breakthroughs for each reaction as well as the difficulties that remain unresolved to date.

Effect of hydrothermal treatment on the carbon structure of Inner Mongolia lignite

Understanding the structural properties of lignite during hydrothermal treatment would aid in predicting the subsequent behavior of coal during the pyrolysis,liquefaction,and gasification processes.Here,hydrothermal treatment of Inner Mongolia lignite(IM)was carried out in a lab autoclave.The distribution of carbon in the lignite was monitored via solid 13C nuclear magnetic resonance spectroscopy,and the functional groups of oxygen in lignite were determined by Fourier transform infrared spectroscopy.The curve-fitting method was used to calculate the content of the functional groups quantitatively.The results show that hydrothermal treatment is an effective method for upgrading the lignite.The side chains of the aromatic ring in lignite are altered,while the main macromolecular structure remains nearly the same.The hydrothermal treatment of IM could be divided into three temperature-dependent stages.The first stage(<493 K)is the decomposition reaction of oxygen functional groups,where the O/C ratio decreases from 0.203 in raw IM to 0.185 for the IM treated at 493 K.In the second stage(493–533 K),hydrolysis of functional groups and hydrogen transfer between water and lignite occur.Here,the ratio of methylene to methyl increases from 0.871 in IM-493 to 1.241 for IM-533,and the content of quinone generates from the condensation of free phenol increased.The third stage(>533 K)involves breakage of the covalent bond,and the content of CH4 and CO in the emission gas clearly increase.

Construction of Synergistic Co and Cu Diatomic Sites for Enhanced Higher Alcohol Synthesis

Higher alcohol synthesis(HAS)from syngas could efficiently alleviate the dependence on the traditional fossil resources.However,it is still challenging to construct high-performance HAS catalysts with satisfying selectivity,space–time yield(STY),and stability.Herein,we designed a diatomic catalyst by anchoring Co and Cu sites onto a hierarchical porous N-doped carbon matrix(Co/Cu–N–C).The Co/Cu–N–C is efficient for HAS and is among the best catalysts reported.With a COconversion of 81.7%,C2+OHselectivity could reach 58.5%with an outstanding C2+OH STY of 851.8 mg/g·h.We found that the N4–Co1 and Cu1–N4 showed an excellent synergistic effect.The adsorption of CO occurred on the Co site,and the surrounding nitrogen sites served as a hydrogen reservoir for the CO reduction reactions to form CHxCo.Meanwhile,the Cu sites stabilized a CHOCu species to interact with CHxCo,facilitating a barrier-free formation of C2 species,which is responsible for the high selectivity of higher alcohols.