Structuring Cu/ZnO/Al2O3 catalyst for methanol synthesis: Slurry additive effect in the washcoating method

Abstract

The best slurry formulation to prepare a structured catalyst for methanol synthesis reaction by washcoating method was investigated. The effect of different inorganic oxide colloids in the slurry preparation of Cu/ZnO/Al2O3 catalyst was studied: colloidal ZnO, SiO2, and Al2O3. The addition of all these colloids showed an improvement in adherence obtained on Fecralloy® monoliths, but Al2O3 exhibited the best performance. Adherence >80% was obtained with a lower amount of Al2O3 than with the other colloids. Nevertheless, the addition of these additives changes the catalytic properties of the parent catalyst. Adding a high amount of colloids decreases the copper metallic surface area which is the active phase of the methanol synthesis reaction. Moreover, the addition of Al2O3 gave rise to the dehydration of methanol to dimethyl ether (DME) due to the high acidity that Al2O3 presents. Something similar happens but to a less extent with SiO2, which present weak acidity. In contrast, the basic character of ZnO neutralizes the parent catalyst's low acidity reducing the selectivity to DME. Finally, the slurry formulation containing 10% Al2O3 exhibited the best methanol yield. Hence, a methanol synthesis structured catalyst was successfully prepared with similar activity to the powder catalyst.