Catalytic synthesis of dimethyltoluene-2,4-dicarbamate over nano CeO₂ prepared by cerium based DES

Nano CeO₂ catalysts were prepared using cerium-based deep eutectic solvents （DESs） as both the cerium source and template, and were subsequently applied in the catalytic synthesis of methyl 2,4-toluenedicarbamate （TDC） from 2,4-toluenediamine （TDA） and dimethyl carbonate （DMC）. The catalytic performances of CeO₂ prepared by the DES template method, hydrothermal method, mechanical grinding method, and commercial CeO₂ were systematically compared. The results showed that the DES template method effectively inhibited the grain growth of CeO₂, yielding CeO₂ with smaller grain size, higher oxygen vacancy content and acid amount, as well as a higher proportion of medium-strong acid sites and Lewis acid sites on its surface. Consequently, the DES-derived CeO₂ exhibited the best catalytic performance. Under the reaction conditions of 170 ℃, 8 h, m_catal/m_TDA = 1, and n_DMC/n_TDA = 20, the TDA conversion reached 100.0% and the TDC selectivity was 82.6%. Moreover, the catalyst prepared by this method demonstrated good stability in the TDC synthesis reaction. Furthermore, a series of CeO₂ catalysts with different particle sizes were prepared by adjusting the calcination temperature. It was found that the particle size of CeO₂ influenced its oxygen vacancy content and acid site distribution, thereby affecting its catalytic performance: the selectivity to TDC decreased with increasing particle size. When the CeO₂ particle size was smaller than 8.4 nm, TDA was completely converted; further increase in particle size led to a decrease in TDA conversion.