Breakthrough in CO2 Hydrogenation by Integration of Quantum Confinement and Alloy Effect

Recently, the research group of Prof. Zeng has applied quantum confinement and alloy effect in CO₂ hydrogenation to achieve remarkable catalytic activity by fabricating RhW Nanocrystals as a catalyst. The d-band center and surface negative charge density generally determine the adsorption and activation of CO₂, thus serving as important descriptors of the catalytic activity towards CO₂ hydrogenation. Herein, researchers engineered the d-band center and negative charge density of Rh-based catalysts by tuning their dimensions and introducing non-noble metals to form an alloy. This work has been published on Nano Letters (Nano Lett. 2017, 17, 788-793) with the title of “Integration of Quantum Confinement and Alloy Effect to Modulate Electronic Properties of RhW Nanocrystals for Improved Catalytic Performance toward CO₂ Hydrogenation”. Master Wenbo Zhang and Doctor Liangbing Wang contributed equally to this work.

RhW nanocrystals and their catalytic performance

The fixation and reduction of CO₂ into useful chemicals and fuels have attracted tremendous interest to meet current energetic and environmental demands. Considering the high stability of a CO₂ molecule, activation of CO₂ plays a pivotal role in the chemical transformation of CO₂. This process can be realized through heterogeneous catalysis where the catalytic performance is largely determined by the electronic properties of the surface. Based on theoretical studies, tuning the dimension of nanostructures represents an effective strategy to engineer the surface electronic properties by varying the spatial distribution of electrons. Another strategy for electronic modification is to form an alloy by adding another metal; charge transfer will then occur owing to the different electro negativities of the constituent metals.

Herein, researchers combined these two strategies to tune the electronic properties of Rh-based nanocrystals in order to enhance the catalytic activity towards CO₂ hydrogenation. During CO₂ hydrogenation, RhW nanosheets exhibited remarkable catalytic activity with the turnover frequency (TOF) number of 592 h^-1, which was 5.9, 4.0, and 1.7 times as high as that of Rh nanoparticles, Rh nanosheets, and RhW nanoparticles, respectively. Mechanistic studies reveal that the remarkable activity of RhW nanosheets derives from the integration of quantum confinement and alloy effect. Specifically, the quantum confinement in one dimension shifts up the d-band center of RhW nanosheets, strengthening the adsorption of CO₂ relative to the nanoparticles. Moreover, the electron transfer from W to Rh enables the accumulation of negative charges on surface Rh atoms in the case of RhW nanosheets, benefiting the activation of CO₂. The enhancement in the adsorption and activation of CO₂ for RhW nanosheets was directly revealed by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectra. This approach paves the effective way to modulate the electronic properties of catalysts to achieve superior catalytic performance.

This work was supported by MOST of China, the National Natural Science Foundation of China, etc.

Publication link: http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b03967.