Microemulsion solventing-out co-precipitation strategy for fabricating highly active Cu–ZnO/Al2O3 dual site catalysts for reverse water gas shift
The dispersity and the neighboring degree of different sites play crucial roles in the catalytic performance of dual site catalysts. The solution of precursors was encapsulated into microdroplets by forming a microemulsion. The average diameter of microdroplets was about 45 nm. This guaranteed that the dosage of precursors was at the attogram level and only about a thousand precursor molecules were encapsulated in each microdroplet. An anti-solvent extraction method was applied to extract water from the microdroplets with acetonitrile. The precursors co-precipitated in the microdroplets due to the loss of water. The encapsulated precursors in the microdroplets co-precipitated together in nanoscale space, so the neighboring degree of the two precursors was improved significantly. The prepared catalyst was characterized by ICP-OES, BET, XRD, H2-TPR, TEM and XPS. Compared with the Cu–ZnO/Al2O3 (CZA) catalysts prepared by the conventional impregnation method, the CZA catalysts prepared by the proposed strategy had much stronger interaction and a better neighboring degree of the dual active sites. They also showed very good catalytic performance for the reverse water gas shift (RWGS) reaction. The CO2 conversion of the designed CZA catalysts was about 1–2 times higher than that of the CZA catalysts prepared by the conventional impregnation method at 0.1 MPa, 300–400 °C and a CO2/H2 mole ratio of 1.