Single-atom Au-modified CeO2 catalyst: Structure and its catalytic performance in 2,4-diaminotoluene methoxycarbonylation reaction

In the reaction of dimethyl carbonate (DMC) and 2,4-diaminotoluene (TDA), Au/CeO2 exhibits higher selectivity than CeO2 for dimethyl toluene-2,4-dicarbamate (TDC). However, its catalytic activity drops after H2 reduction (denoted as Au/CeO2-R). The characterization results illustrate that Au exists as a single atom with the primary species as Auδ+ in Au/CeO2, forming CexAu1-xO2 structure similar to solid solution. Whereas for Au/CeO2-R catalyst, Au mainly exists as Au0, forming the Au-O-Ce structure on CeO2 surface. Significantly, the strong interaction between Au and CeO2 increases Ce3+ and oxygen vacancies content, as well as modulates their acidic property. However, the catalytic activity of Au/CeO2-R is found to be lower than Au/CeO2 as the species formed by DMC dissociation on its surface are not easily desorbed. Other transition metals supported on CeO2 are also prepared, wherein Pt/CeO2 and Pd/CeO2 exhibit good TDC selectivity. In the end, the electronegativity and catalytic activity of metals are correlated.