Surface polarization enhancement: high catalytic performance of Cu/CuOx/C nanocomposites derived from Cu-BTC for CO oxidation

Abstract

Heterogeneous catalysts facilitate various chemical reactions through the changing of its surface charge density. However, the easy agglomeration of nano-sized heterogeneous catalysts and either expensive techniques or a multistep method involved in the fabrication of such hybrid structures makes developing low-cost, agglomeration-free heterogeneous catalysts highly desirable. Copper and its oxides have long been studied as catalysts towards CO oxidation. Few reports have appeared concerning the catalytic activity of Cu/Cu₂O and Cu/CuO interface because the interfaces tend to form core–shell structures in oxygen atmospheres, making the interface buried inside the oxide layers. Herein, we designed Cu/Cu₂O nanojunctions wrapped and supported by porous carbon through the direct annealing of a Cu-based metal–organic framework (Cu-BTC) in N₂, followed by testing its catalytic activity towards CO oxidation. In addition, CO oxidation reactions over Cu, Cu₂O, CuO and the interface of Cu/Cu₂O and Cu/CuO are studied via density functional theory (DFT) simulations. The catalyst shows a complete CO conversion temperature (T₁₀₀) of 155 °C under both 1 vol% and 5 vol% CO. In addition, it maintains long-term durability even after 40 h under 1 vol% CO. Our DFT calculations demonstrate that the significant increase in electron density on the Cu/Cu₂O and Cu/CuO interface plays a pivotal role in the enhancement of CO oxidation. Moreover, this study provides a new strategy for synthesizing carbon supported metal/metal oxide hybrid catalysts.