Two-step synthesis of dimethyl carbonate from urea, ethylene glycol and methanol using acid–base bifunctional zinc-yttrium oxides

The binary zinc-yttrium oxides with different precursors were prepared by co-precipitation method and used in the catalytic synthesis of dimethyl carbonate (DMC) via a two-step process using urea, ethylene glycol and methanol as raw feed-stocks. The first step involves reaction of urea with ethylene glycol (EG) to form ethylene carbonate (EC), and 96% conversion of urea with 98% selectivity of EC was obtained. In the second step, namely transesterification of EC formed with methanol to give DMC and EG, the conversion of EC was up to 72% in 15 min with a 99% selectivity of DMC, corresponding to a TOF of 864 mmol/h gcat. XRD results showed that the catalyst with a zinc nitrate precursor has a remarkable interaction between zinc and yttrium oxides. TPD characterization indicated that in the catalyst with a zinc nitrate precursor there was a cooperative effect between weak acid and medium base sites on the surface of the catalyst, suggesting that the prepared catalysts are acid–base bifunctional. The synergistic effect between zinc and yttrium oxides, in combination with acidity of zinc oxide and basicity of yttrium oxide, may be responsible to the high catalytic activity and selectivity.