Elucidating the role of Cu species in the oxidative carbonylation of methanol to dimethyl carbonate on CuY: An in situ spectroscopic and catalytic study

CuY catalysts with varied Cu content obtained by incipient-wetness-impregnation of commercial NH4-Y zeolite with copper nitrate solution and calcination at 400 °C in air were examined by in situ FTIR investigations to characterize the Cu species and elucidate their specific role in the oxidative carbonylation of methanol. The adsorption of CO was applied to check the state of Cu(I) species whereas the acidity was characterized by pyridine adsorption. Depending on the Cu content different intensity ratios of the characteristic Cu(I)–CO bands at 2160 and 2146 cm−1 were observed which give information about the distribution of Cu(I) cations at different positions near the supercage. Lewis sites of different strengths are created by introduction of Cu resulting from Cu(I)/Cu(II) cations positioned in the super cages.MeOH adsorbs dissociatively on preferable Cu(I) Lewis sites by formation of methoxy species without additional supply of oxygen. Methoxy species and CO adsorb at the same Cu sites. Oxygenated products (monomethyl carbonate, dimethyl carbonate, CO2) are formed during simultaneous adsorption of MeOH and CO with and without oxygen which indicates a participation of lattice oxygen of CuOx aggregates in the oxidation process and points to a Mars-van-Krevelen mechanism. Adsorbed formate species more pronounced at higher Cu loadings were additionally found. CO reacts with adsorbed methoxy species by formation of mainly monomethyl carbonate whereas the simultaneous presence of formate-like species promotes the formation of dimethyl carbonate. This implicates a specific role of adsorbed carbonate-like species for dimethyl carbonate formation. High Cu loadings were found to be beneficial because the additional formation of CuOx agglomerates in the super cages favors oxidation and oxocarbonylation reactions of methanol and enhances the formation of dimethyl carbonate which was also confirmed by the catalytic tests.

CuY catalysts with varied Cu content were examined by in situ FTIR investigations to characterize the Cu species and elucidate their specific role in the oxidative carbonylation of methanol. High Cu loadings favor oxidation and oxocarbonylation reactions of methanol and enhance the formation of dimethyl carbonate confirmed also by the catalytic tests.Figure optionsDownload high-quality image (78 K)Download as PowerPoint slide