Performance analysis of hybrid catalytic conversion of CO₂ to DiMethyl ether

The performance of the single-step and sequential-steps catalytic CO2-hydrogenation to DiMethyl Ether (DME) was systematically analyzed. CuO–ZnO model-catalysts for CO2-hydrogenation to methanol were synthesized via different methods namely co-precipitation, sequential precipitation and precipitation-impregnation of the precursors. Moreover, co-precipitation and co-impregnation methods were applied to establish bifunctional catalytic structures composed of CuO–ZnO over HZSM-5 for direct CO2-hydrogenation to DME in a single-step. In addition, the performance of the catalytic bed made of sequential layered-arrangements of the CuO–ZnO and ZSM-5 catalysts as well as random mixture of these catalysts were also analyzed both experimentally as well as through the performed model-based study. It was observed that a faster conversion of the generated methanol to DME, secured by establishing a closer distance between the catalytic materials responsible for CO2-hydrogenation to methanol and methanol-dehydration to DME, will improve the overall selective CO2-conversion. This was demonstrated by obtaining the highest combined yield of methanol and DME products at the reactor outlet in those cases. Similarly, a bifunctional catalyst, for instance synthesized by co-impregnation method (made of 1:2 CuO–ZnO:ZSM-5), showed one of the most promising DME selectivity of 65% and DME yield of 12.5% under the highest reaction temperature of 260 °C, lowest tested GHSV of 200 h−1, and maximum operating pressure 20 bar for the lowest H2/CO2 ratio of 3.