Tandem nanocatalyst design: putting two step-reaction sites into one location towards enhanced hydrogen transfer reactions

Efficient tandem reactions on a single catalytic nanostructure would be beneficial to improving chemical transformation efficiency and reducing safety implications. It is imperative to identify the active sites for each single step reaction so that the entire reaction process can be optimized by designing and integrating the sites. Herein, hydrogen transfer reaction is taken as a proof-of-concept demonstration to show that the spatial integration of active sites is important to the catalytic efficiency of the entire process in tandem reactions. We identified specific active sites (i.e., various sites at faces versus corners and edges) for formic acid decomposition and alkene/nitrobenzene hydrogenation-the two steps in hydrogen transfer reactions, by employing three different shapes of Pd nanocrystals in tunable sizes. The investigation reveals that the decomposition of formic acid occurs preferentially at the edge sites of cubic nanocrystal and the plane sites of octahedral/ tetrahedral nanocrystals, while the hydrogenation takes place mainly at the edge sites of both cubic and octahedral/ tetrahedral nanocrystals. The consistency of active edge sites during different step reactions enables cubic nanocrystals to exhibit a higher activity than octahedral nanocrystals in hydrogen transfer reactions, although octahedrons offer comparable activities to cubes in formic acid decomposition and hydrogenation reactions. Guided by these findings, we further improved the overall performance of tandem catalysis by specifically promoting the limiting step through nanocatalyst design. This work provides insights into the rational design of heterogeneous nanocatalysts in tandem reactions.

Recent advances in 2D semiconductor nanomaterials for photocatalytic CO_(2)reduction

For decades,global warming and energy shortages have been two urgent problems in human society.The solar-driven photocatalytic conversion of carbon dioxide(CO_(2))into hydrocarbon fuels is expected to become a technology to solve these problems.Two-dimensional(2D)materials shine in the field of photocatalytic CO_(2)due to their layered structure,larger specific surface area,more active sites,and larger charge transfer efficiency.This article reviews the progress of CO_(2)reduction by several types of 2D materials in recent years.Generally,the reduction of CO_(2)is difficult in terms of kinetics and thermodynamics,but it is found through theoretical calculations and experiments that 2D materials have certain advantages in the reduction of CO_(2).Then the preparation methods of 2D materials are summarized and a variety of 2D materials are discussed and classified.Finally,an outlook on the development trend of 2D materials is made.This review aims to provide systematic and concise guidance for the design of 2D nanomaterials for photocatalytic CO_(2)reduction.

Photocatalytic water splitting on BiVO_(4):Balanced charge-carrier consumption and selective redox reaction

Surficial redox reactions play an essential role in photocatalytic water splitting,and are closely related to the surface properties of a specific photocatalyst.In this work,using monoclinic BiVO_(4)decahedral single crystals as a model photocatalyst,we report on the interrelationship between the photocatalytic activity and the surficial reaction sites for charge-carrier consumption.By controlled hydrothermal synthesis,the ratio of{010}to{110}facets on BiVO_(4),which respectively serve as reductive and oxidative sites,is carefully tailored.Our results show that superior photocatalytic water oxidation could be obtained on BiVO_(4)decahedrons with a medium ratio of reductive/oxidative sites and that efficient overall water splitting could be achieved via further modification of appropriate cocatalysts in Z-scheme system.The excellent photocatalytic performance is attributed to the accelerated selective redox reactions by realizing balanced charge-carrier consumption,which provides insightful guidance for prospering photocatalytic reactions in energy conversion.

Metal-induced oxygen vacancies on Bi_(2)WO_(6)for efficient CO_(2) photoreduction

Semiconductor-based photocatalysis for efficient solar energy conversion is an ideal strategy to tackle the growing global energy and environmental crisis.However,the development of photocatalysis is still limited by problems such as low utilization of visible light,low efficiency of charge transfer and separation,and insufficient reactive sites.Herein,Au nanoparticles(NPs)were deposited on the surface of Bi_(2)WO_(6)by a one-step reduction method,which simultaneously induced the formation of oxygen vacancies(OVs)on the surface of Bi_(2)WO_(6).The OVs concentration is found to be increased with the increase of Au loading.Au NPs and OVs improve the light absorption and facilitate the separation and transport of the photogenerated carriers.In addition,OVs act synergistically with the nearby metal active sites to optimize the adsorption energy of reactants on the catalyst surface,changing the adsorption form of CO_(2)molecules on the catalyst surface.The as-synthesized photocatalyst achieved a photocatalytic performance of up to 34.8μmol g^(−1)h^(−1)of CO_(2)reduction to CO without sacrificial agent in a gas-solid system,which is 9.4 times higher than that of the pristine Bi_(2)WO_(6).This work may further deepen our understanding on the relationship between metal NPs and OVs,and their combined role in photocatalysis.

Characterization of char from high temperature fluidized bed coal pyrolysis in complex atmospheres

The physiochemical properties of chars produced by coal pyrolysis in a laboratory-scale fluidized bed reactor with a continuous coal feed and char discharge at temperatures of 750 to 980 ~ C under N2-based atmospheres containing 02, H2, CO, CH4, and CO2 were studied. The specific surface area of the char was found to decrease with increasing pyrolysis temperature. The interlayer spacing of the char also decreased, while the average stacking height and carbon crystal size increased at higher temperatures, suggesting that the char generated at high temperatures had a highly ordered structure. The char obtained using an ER value of 0.064 exhibited the highest specific surface area and oxidation reactivity. Rela- tively high 02 concentrations degraded the pore structure of the char, decreasing the surface area. The char produced in an atmosphere incorporating H2 showed a more condensed crystalline structure and consequently had lower oxidation reactivity.

The origin of potential rise during charging of Li-O2 batteries

When aprotic Li-O2 batteries recharge, the solid Li2O2 in the positive electrode is oxidized, which often exhibits a continuous or step increase in the charging potential as a function of the charging capacity, and its origin remains incompletely understood. Here, we report a model study of electro-oxidation of a Li2O2 film on an Au electrode using voltammetry coupled with in situ Raman spectroscopy. It was found that the charging reaction initializes at the positive electrodelLizO2 interface, instead of the previously presumed Li2O2 surface, and consists of two temporally and spatially separated Li2O2 oxidation processes, accounting for the potential rise during charging of Li-O2 batteries. Moreover, the electrode surface-initialized oxidation can disintegrate the Li2O2 film resulting in a loss of Li2O2 into electrolyte solution, which drastically decreases the charging efficiency and highlights the importance of using soluble electro-catalyst for the complete charging of Li-02 batteries.

Multi-organ site metastatic reactivation mediated by non-canonical discoidin domain receptor 1 signaling

With the support of the National Natural Science Foundation of China and the Ministry of Science and Technology of China,the research teams led by Prof.Gao Hua(高华)from Tongji University,and Prof.Filippo Giancotti at Memorial Sloan Kettering Cancer Center,reported recently on the mechanism of multiorgan site metastatic creactivation,which was published in Cell(2016,166:47—62).

THE PRIMARY STRUCTURE OF ARROWHEAD PROTEINASE INHIBITOR

After the reduction and carboxymethylation of disulfide bonds, arrowhead proteinase inhibitors A and B were cleaved either by proteinases or by cyanogen bromide, the fractionated and purified peptides were then subjected to sequencing by a gas phase automatic sequencer, the primary structures were completed by the alignment of the peptides sequenced with overlapping peptides. Both inhibitors A and B consist of 150 amino acid residues with three pairs of disulfide bonds, share 90% homology in structure, and are markedly different from all other Ser proteinase inhibitors so far known. Hence, the arrowhead inhibitor may belong to a new inhibitor family. Based on their structure characteristics, it was deduced that both their two reactive sites might be located in the positions of Lys-Ser (45-46) and Arg-Tyr-Lys (77-79), respectively. Among 13 mutated residues in inhibitors A and B, the substitution of residue Arg in position 87 of inhibitor B for residue Leu in A might be the main cause of leading to difference in their inhibitory activities.