ИСТИНА

Poor yields and ecological problems of dimethylcarbonate (DMC) production using COCl2 require the search of new technologies to modify its synthesis. In order to propose alternative ways and to give interpretation of the carbonylation mechanism we have analyzed theoretically three reaction schemes. The first scheme that solves a crucial problem of renewable and cheap source of carbon is performed via direct involving of CO2 in the carbonate form in the reaction with methanol. Additionally, we have shown that this way could be also considered as the explanation of oxidative carbonylation mechanism because of possible CO oxidation to carbonate over copper binuclear oxide clusters like was earlier shown for alkaline earth ones [1]. Two-step reaction with consequent attacks of two methanol molecules has been modeled using both the isolated cluster (8R, 6R+4R, 10T) approach at the DFT and MP2 levels (GAUSSIAN09 [2]) and periodic boundary conditions (PBC). At the PBC level (CuMOR, CuX types), the projector augmented wave (PAW) method and the PBE functional were used with VASP5.3.3 code [3]. For calculating the minimum energy path between reagents and products, we have used the climbing image nudged elastic band method [4]. The limiting barrier corresponds to the attack of the first CH3OH molecule and is approximately two times greater than the known barriers for oxidative carbonylation (11.70 kcal/mole [5] or 14.80 kcal/mole [6] over Cu-form zeolites). Within scope of the second scheme the carbomethoxy-intermediate has been considered at Cu2+ or Cu1+ cationic sites in the CuMOR and isolated 8R clusters with the same computational tools. For both Cu2+ and Cu1+ cations respective reaction barrier between CH3OH and CO, which is considered usually as the limiting stage [7], turns out to be smaller than above mentioned experimental values [5, 6]. The third scheme we have considered was the CO reaction with Cu(OCH3)2Cu cluster whose barriers is closer to the experimental values. [1] A.V. Larin, et al., J. Catal. 281 (2011) 212-221. [2] M.J. Frisch, et al., Gaussian, Inc., Wallingford, CT, 2009. [3] G. Kresse, J. Hafner, Phys. Rev. B 47 (1993) 558-561; G. Kresse, J. Furthmüller, ibid. 54 (1996) 11169-11184. [4] G. Henkelman, et al., J. Chem. Phys., 113 (2000) 9901-9904. [5] J. Engeldinger, et al., Phys. Chem. Chem. Phys., 14 (2012) 2183-2191. [6] Y. Zhang, et al., J. Catal. 244 (2006) 219-229. [7] Y. Zhang, A.T. Bell, J. Catal. 255 (2008) 153-161.