Dimethyl carbonate (DMC) synthesis from methanol and carbon dioxide in the presence of ZrO₂ solid solutions and yield improvement by applying a natural convection circulation system

In this study, we conducted an initial screening of ZrO₂ and M/ZrO₂ (M = Al, Ca, Ce, Pr, and Y) catalysts employing a batch apparatus first and then applied the selected catalyst (Ce_0.1Zr_0.9O₂) into a natural convection circulation system with dehydrating agents, for the direct synthesis of dimethyl carbonate (DMC) from methanol (MeOH) and CO₂. During the initial screening, Ce_0.1Zr_0.9O₂ showed the highest DMC yield at ∼ 0.64% with 100% selectivity at 170 °C. The catalytic reactivities of ZrO₂ and M/ZrO₂ solid solutions followed the order: Ce/ZrO₂ > Y/ZrO₂ > Pr/ZrO₂ ≈ ZrO₂ > Al/ZrO₂ > Ca/ZrO₂. The relationship between physical properties and the activity of the catalysts was evaluated. As a result, the specific surface area and the acidity/basicity were considered to be irrelevant to the catalytic activity. However, a clear relationship between the temperature-programmed desorption (TPD) profile of MeOH and the reactivity was revealed: the increase of the weak affinity sites leads to the increase of reactivity. During the direct DMC synthesis over Ce_0.1Zr_0.9O₂ catalyst employing the natural convection circulation system with molecular sieves 3A, the DMC yield reached up to 14.3% with 100% selectivity, which was the highest yield so far using M/ZrO₂ catalysts. Prior to the experiment with the natural convection circulation system, the initial conditions were determined based on the experimental results employing the batch apparatus, previous literature, and estimation results. Moreover, some factors affecting the DMC yield using the circulation system were studied, including the reaction rate, the circulation rate of the flow in the circulation system, and the dehydration rate in the dehydration part.