Product tunable behavior of carbon nanotubes-supported Ni?Fe catalysts for guaiacol hydrodeoxygenation

Bimetallic Ni–Fe nanoparticles supported on carbon nanotubes (CNTs) are prepared and evaluated for the catalytic hydrodeoxygenation (HDO) of a lignin-derived model compound guaiacol. Appropriate combination of Ni and Fe affords high activity and significantly enhances selectivity to cyclohexane or phenol, whereas monometallic Ni and Fe catalysts display poor activities or selectivities. The product tunable behavior of guaiacol HDO is found to be dependent on Ni/Fe atomic ratios. Cyclohexane and phenol are the major products over Ni5–Fe1/CNT with Ni/Fe atomic ratio at 5/1 and Ni1–Fe5/CNT with Ni/Fe atomic ratio at 1/5, respectively. Characterization results confirm that Ni–Fe alloys are formed and elicit synergistic effects on the HDO performance. The selectivity-switchable performance of Ni–Fe/CNT can be assigned to the synergism between Ni domains, where H2 can be easily activated, and Fe domains, which exhibited strong oxophilicity. The bimetallic catalysts give an enhanced stability without significant sintering of metal nanoparticles, while the monometallic catalysts show obvious deactivation due to the agglomeration of metal nanoparticles. Further results reveal that the conversion of guaiacol depends on not only the chemical state but also the size of the metallic nanoparticles. The catalysts with appropriate Ni/Fe atomic ratio and smaller particle perform better hydrogenolysis of C–O bonds, resulting in high selectivity to cyclohexane or phenol

A study of FeNx/C catalysts for the selective oxidation of unsaturated alcohols by molecular oxygen

Transition-metal nitrides can exhibit catalytic performance comparable to that of noble metal catalysts in many reactions. However, investigations on the correlation of catalyst structure, performance, and stability are still highly demanded. Here, a series of metal nitrides were prepared and evaluated for the selective oxidation of alcohols by molecular oxygen. Among them, FeNx/C-T catalysts (T represents the pyrolysis temperature) display above 95% selectivity to the corresponding aldehydes in the selective oxidation of unsaturated alcohols. The optimized FeNx/C-900 catalyst gives the highest TOF of 7.0 h(-1) for the conversion of 5-hydroxymethylfurfural to 2,5-diformylfuran. A combination of characterizations and experiments suggests that Fe-N-4 species are the main active sites. In addition, we investigate the reasons for the catalyst deactivation and provide an effective approach to regenerating the catalysts. The results indicate that the deactivated catalysts can be regenerated by heat treatment under NH3/N-2 after each run. Based on these studies, a plausible reaction mechanism over the FeNx/C catalysts is proposed. (C) 2018 Elsevier Inc. All rights reserved

Mitigating Concentration Polarization through Acid–Base Interaction Effects for Long-Cycling Lithium Metal Anodes

Lithium (Li) metal has attracted great attention as a promising high-capacity anode material for next-generation high-energy-density rechargeable batteries. Nonuniform Li+ transport and uneven Li plating/stripping behavior are two key factors that deteriorate the electrochemical performance. In this work, we propose an interphase acid–base interaction effect that could regulate Li plating/stripping behavior and stabilize the Li metal anode. ZSM-5, a class of zeolites with ordered nanochannels and abundant acid sites, was employed as a functional interface layer to facilitate Li+ transport and mitigate the cell concentration polarization. As a demonstration, a pouch cell with a high-areal-capacity LiNi0.95Co0.02Mn0.03O2 cathode (3.7 mAh cm–2) and a ZSM-5 modified thin lithium anode (50 μm) delivered impressive electrochemical performance, showing 92% capacity retention in 100 cycles (375.7 mAh). This work reveals the effect of acid–base interaction on regulating lithium plating/stripping behaviors, which could be extended to developing other high-performance alkali metal anodes