Defect-Engineered Ceria Interfaces Enable Nitro-Group Activation and Bond-Selective Dimethyl Carbonate Dissociation in Relay Catalysis

For the synthesis of dimethyl toluene-2,4-dicarbamate (TDC), a key precursor of toluene diisocyanate, it is challenging to avoid the tedious, material-intensive separation and purification of the air-sensitive intermediate 2,4-diaminotoluene (TDA). In the conventional stepwise route, 2,4-dinitrotoluene (2,4-DNT) is hydrogenated to TDA, which is then methoxycarbonylated with dimethyl carbonate (DMC). Herein, we develop a ceria-based relay-catalysis strategy that couples the two reactions in a single reactor, achieving a synthesis of TDC directly from 2,4-DNT, H2, and DMC without isolating TDA. In the hydrogenation step, a CeO2-nanorod-supported Pd catalyst (Pd/CeO2-R) activates –NO2 through the synergy of Pd clusters, interfacial oxygen vacancies (Ov), and Ce3+ sites, affording 98.4% TDA selectivity. In the methoxycarbonylation step, Bi2O3-doped Ce0.9Bi0.1 R enriches Ce3+/Ov and strengthens Lewis acidity, steering DMC dissociation toward the –COOCH3 pathway over the N-methylation-prone –OCOOCH3 pathway, as evidenced by in situ FTIR. The relay system delivers 99.9% 2,4-DNT conversion and 75.4% TDC selectivity, raising the overall TDC yield from 38.0% to 75.3%. Mechanistic studies reveal that Ce3+/Ov defects govern both –NO2 activation and bond-selective DMC dissociation, unifying two mechanistically distinct reactions under one defect-engineering principle.