Mengzhu Li

Oxide-Modified Nickel Photocatalysts for the Production of Hydrocarbons in Visible Light

Metallic nickel nanostructures that were partially decorated by discrete nickel oxide layers were fabricated by in situ reduction of calcinated Ni-containing layered double hydroxide nanosheets, the structure of which was confirmed by extended X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The existence of the abundant interfaces between the surface Ni oxide overlayer and metallic Ni altered the geometric/electronic structure of the Ni nanoparticles, making them apt for CO activation under light irradiation. Most importantly, the unique structure favors the C-C coupling reaction on its surface, which confers the catalyst unexpected reaction power towards higher hydrocarbons at moderate reaction conditions. This study leads to a green and sustainable approach for the photocatalytic production of highly valuable chemical fuels.

Highly Tunable Selectivity for Syngas-Derived Alkenes over Zinc and Sodium-Modulated Fe5C2 Catalyst

Zn- and Na-modulated Fe catalysts were fabricated by a simple coprecipitation/washing method. Zn greatly changed the size of iron species, serving as the structural promoter, while the existence of Na on the surface of the Fe catalyst alters the electronic structure, making the catalyst very active for CO activation. Most importantly, the electronic structure of the catalyst surface suppresses the hydrogenation of double bonds and promotes desorption of products, which renders the catalyst unexpectedly reactive toward alkenes-especially C5+ alkenes (with more than 50% selectivity in hydrocarbons)-while lowering the selectivity for undesired products. This study enriches C1 chemistry and the design of highly selective new catalysts for high-value chemicals.

Tuning the Selectivity of Catalytic Carbon Dioxide Hydrogenation over Iridium/Cerium Oxide Catalysts with a Strong Metal–Support Interaction

A one-step ligand-free method based on an adsorption-precipitation process was developed to fabricate iridium/cerium oxide (Ir/CeO2 ) nanocatalysts. Ir species demonstrated a strong metal-support interaction (SMSI) with the CeO2 substrate. The chemical state of Ir could be finely tuned by altering the loading of the metal. In the carbon dioxide (CO2 ) hydrogenation reaction it was shown that the chemical state of Ir species-induced by a SMSI-has a major impact on the reaction selectivity. Direct evidence is provided indicating that a single-site catalyst is not a prerequisite for inhibition of methanation and sole production of carbon monoxide (CO) in CO2 hydrogenation. Instead, modulation of the chemical state of metal species by a strong metal-support interaction is more important for regulation of the observed selectivity (metallic Ir particles select for methane while partially oxidized Ir species select for CO production). The study provides insight into heterogeneous catalysts at nano, sub-nano, and atomic scales.

Hybrid Au–Ag Nanostructures for Enhanced Plasmon-Driven Catalytic Selective Hydrogenation through Visible Light Irradiation and Surface-Enhanced Raman Scattering

Herein, we report the successful application of hybrid Au-Ag nanoparticles (NPs) and nanochains (NCs) in the harvesting of visible light energy for selective hydrogenation reactions. For individual Au@Ag NPs with Au25 cores, the conversion and turnover frequency (TOF) are approximately 8 and 10 times higher than those of Au25 NPs, respectively. Notably, after the self-assembly of the Au@Ag NPs, the conversion and TOF of 1D NCs were approximately 2.5 and 2 times higher than those of isolated Au@Ag NPs, respectively, owing to the coupling of surface plasmon and the increase in the rate at which hot (energetic) electrons are generated with the formation of plasmonic hot spots between NPs. Furthermore, the surface-enhanced Raman scattering (SERS) activity of 1D Au@Ag NCs was strengthened by nearly 2 orders of magnitude.

Wet-chemistry synthesis of cobalt carbide nanoparticles as highly active and stable electrocatalyst for hydrogen evolution reaction

Transition metal carbide (TMC) nanomaterials are promising alternatives to Pt, and are widely used as heterogeneous electrocatalysts for the electrochemical hydrogen evolution reaction (HER). In this work, a bromide-induced wet-chemistry strategy to synthesize Co2C nanoparticles (NPs) was developed. Such NPs exhibited high electrocatalytic activity (η = 181 mV for j = −10 mA·cm−2) and long-term stability (no obvious performance decrease after 4,000 cycles) for the HER. This study will pave the way for the design and fabrication of TMC NPs via a wet-chemistry method, and will have significant impacts on broader areas such as nanocatalysis and energy conversion.

Reductive Transformation of Layered-Double-Hydroxide Nanosheets to Fe-Based Heterostructures for Efficient Visible-Light Photocatalytic Hydrogenation of CO

Conversion of syngas (CO, H2 ) to hydrocarbons, commonly known as the Fischer-Tropsch (FT) synthesis, represents a fundamental pillar in todays chemical industry and is typically carried out under technically demanding conditions (1-3 MPa, 300-400 °C). Photocatalysis using sunlight offers an alternative and potentially more sustainable approach for the transformation of small molecules (H2 O, CO, CO2 , N2 , etc.) to high-valuable products, including hydrocarbons. Herein, a novel series of Fe-based heterostructured photocatalysts (Fe-x) is successfully fabricated via H2 reduction of ZnFeAl-layered double hydroxide (LDH) nanosheets at temperatures (x) in the range 300-650 °C. At a reduction temperature of 500 °C, the heterostructured photocatalyst formed (Fe-500) consists of Fe0 and FeOx nanoparticles supported by ZnO and amorphous Al2 O3 . Fe-500 demonstrates remarkable CO hydrogenation performance with very high initial selectivities toward hydrocarbons (89%) and especially light olefins (42%), and a very low selectivity towards CO2 (11%). The intimate and abundant interfacial contacts between metallic Fe0 and FeOx in the Fe-500 photocatalyst underpins its outstanding photocatalytic performance. The photocatalytic production of high-value light olefins with suppressed CO2 selectivity from CO hydrogenation is demonstrated here.