Cheonwoo Jeong

Enhanced activity of CuO/ZnO catalyst on the decomposition of dimethylhexane-1,6-dicarbamate into dimethylhexane-1,6-diisocyanate

To decompose dimethylhexane-1,6-dicarbamate (HDC) to hexamethylene diisocyanate (HDI), mixed CuO and ZnO catalysts with Cu/(Cu + Zn) ratio of 4 and 8% were prepared by coprecipitation (CP), sequential precipitation (SP) and incipient wetness impregnation (IW). The SP-derived CuO/ZnO catalysts showed higher HDC yields than those derived by CP and IW. The IW method produced CuO/ZnO catalysts consisting of larger CuO and ZnO particles compared to the two precipitation methods. The CP method led to substitution of Zn2+ by Cu2+ in the hydrozincite precursor phase, resulting in higher BET and Cu surface areas of CuO–ZnO catalysts due to intimate intergrowth of nano-sized particles. However, the inherent character of ZnO in the CP-derived catalysts was modified by interfacial contact between CuO and ZnO identified by UV–visible and Raman spectra. In contrast, the properties of CuO and ZnO, as well as the relatively large surface areas, were kept in the SP-derived catalysts owing to deposition of Cu precipitates to fully aged Zn precipitates. This is believed to be a benefit of the SP method for the reaction. Therefore, our preparation approach has great potential to be extended to various mixed oxide catalysts.

Facile Structure Tuning of a Methanol-Synthesis Catalyst towards the Direct Synthesis of Dimethyl Ether from Syngas

Heterogeneous catalysts of bifunctionality offer improved process efficiency and enhanced product yield in multistep chemical transformations conducted in a consecutive manner. However, this has seldom been realized in coprecipitated catalysts owing to the complexity of the synthesis. By adjusting the synthesis protocol of an industrial methanol‐synthesis catalyst as a model system, herein we demonstrate the bifunctional effect of Al2O3/Cu/ZnO catalysts to enable the direct production of dimethyl ether from synthesis gas with yields that are 2–3‐fold higher than those obtained with their conventional counterparts, with a greater number of accessible Cu surface atoms and more Al2O3 acid sites existing at the external particle surface. This is achieved by preparing the fully developed Cu,Zn precursor of a specific structure with surface‐decorated Al species. Our approach paves the way towards the rational design of multicomponent precipitated catalysts with tunable bifunctionality for practical cascade reactions.