Significance Statement
The preparation of micro, meso, and nanosized materials with a better control of their shape is of outmost importance. This is because each of their application is dependent on their physicochemical attributes along with morphologies. The idea of morphology-controlled preparation with an aim of tailoring performances of catalysts, battery anodes, and semiconducting gas sensors, has been the focus of research in the recent past.
A good number of the preparation techniques center on the control of the character of exposed crystallographic planes as well as grain and pore structure. In the recent years, steps have been made in the controlled preparation of nanosized catalysts, and to the in-depth understanding of the shape dependent catalytic attributes.
Morphology-modulated catalytic activity exhibited by some metal oxide nanostructures is necessary in catalysis since it provides a potential path for tuning the rate of reaction, the extent of reactivity, and the main products. Copper oxide is such a transition metal oxide that exhibits morphology-dependent catalytic activity. Copper oxide is also an effective catalyst in the Rochow reaction. This is the direct process implemented to synthesize methylchlorosilanes.
The Rochow reaction entails a typical gas-solid-solid system used in industrial processes. Owing to the complexity of the reaction, the actual role of the copper-based catalysts is yet to be fully understood. Researchers led by Professor Fabing Su and Yongjun Ji from the Chinese Academy of Sciences, China, prepared a series of copper oxide catalysts with varying morphologies through a solution-based precipitation method implementing various organic ligands, and tested them for the Rochow reaction. Their work is published in peer-reviewed journal, Nano Research.
The authors synthesized four forms of copper catalysts with controlled leaf like, flower like, oatmeal like, and sea urchin-like morphologies through a facile precipitation approach in conjunction with a number of chelating ligands. Through fast Fourier transform infrared spectroscopy and high resolution transmission electron microscopy, the authors found that the dominant crystal facets of the four copper oxide catalysts were [001], [110], [001], and [110] and [001] and [110] for the leaf like, flower like, sea urchin-like and oatmeal-like copper oxide, respectively.
The researchers also tested the catalyst for the Rochow reaction, and found that their catalytic activities were mainly dependent on their structures. Among the selected copper oxide catalysts, the leaf-like copper oxide indicated the best catalytic performance, strongest adsorption ability for oxygen, and excellent reducibility. These attributes could be attributed to its largely exposed [001] facet as well as large specific surface area.
The researchers also measured for various catalysts the amount of Cu3Si alloy phase that was the most necessary reaction intermediate, which yielded in the reacted region of the silicon surface. Based on the findings of the study, the authors proposed a detailed reaction mechanism.
This study indicated that shape-controlled preparation of oxide catalysts could be an effective path for designing and developing effective catalysts.
Reference
Yu Zhang, Yongjun Ji*, Jing Li, Hezhi Liu, Xiao Hu, Ziyi Zhong, and Fabing Su. Morphology-dependent catalytic properties of nanocupric oxides in the Rochow reaction. Nano research DOI 10.1007/s12274-017-1689-x.
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