Role of Benzene-1,3,5-Tricarboxylate Ligand in CuO–CeO₂ Catalysts Derived from Metal–Organic Frameworks for Carbon Monoxide Oxidation

Abstract

We prepared a CuO–CeO₂–M catalyst, where M refers to MOFs, by calcinating a mixture of Cu–benzene-1,3,5-tricarboxylate (BTC) and Ce–(BTC), which was obtained through a process similar to co-precipitation under mild conditions. The catalyst exhibited good performance for CO oxidation and almost completely converted CO at 80 °C. However, CO conversion over a CuO–CeO₂–C catalyst, where C refers to co-precipitation, prepared by co-precipitation was only 81% at 80 °C. To understand the reason for the difference in activity between the two catalysts and clarify the effect of BTC ligands on CuO–CeO₂–M, we prepared CuO–CeO₂–H1 and CuO–CeO₂–H2 catalysts by adding various quantities of benzene-1,3,5-tricarboxylic acid (H₃BTC) during the co-precipitation process. The catalytic activity was in the following order: CuO–CeO₂–M > CuO–CeO₂–H1/H2 > CuO–CeO₂–C. There were three distinct copper species in the aforementioned catalysts: highly dispersed copper, copper doped into CeO₂ lattices, and crystalline copper. For CuO–CeO₂–M catalyst, the high content of Ce³⁺, Cu⁺, and surface-adsorbed oxygen was the cause for high activity. By adding H₃BTC, the Cu⁺ content and dispersion of copper species in CuO–CeO₂–H1/H2 was higher than that in CuO–CeO₂–C. Accordingly, organic ligands can separate metal ions and prevent aggregation of oxides during calcination, which facilitates dispersion of copper species. In addition, CO can be released by thermal decomposition of organic ligands during calcination; CO is conducive to the formation of more Cu⁺ in the catalyst.

Graphical Abstract