Effect of ZrO2 Loading on the Structure, Acidity, and Catalytic Activity of the SO42−/ZrO2/MCM-41 Acid Catalyst

The regular hexagonal structure of siliceous MCM-41 with a uniform mesopore size is still maintained after 48.5 wt% ZrO2 loading. Under high loadings (≥26.7%) of ZrO2, a very small amount of ZrO2 clusters (present as tetragonal ZrO2 phase) might be formed inside or outside the MCM-41 structure. The hydrophobicity of the SO42−/ZrO2/MCM-41 catalysts is stepwise enhanced by increasing the ZrO2 loading. The covalent SO band 1378-cm−1 for the SO42−/ZrO2 catalyst shifts to 1363 cm−1 for SO42−/ZrO2/MCM-41 materials. Under identical ZrO2 loading, SO42−/ZrO2/MCM-41 has stronger Brønsted and Lewis acidities than PMSZM/ZrO2 (physical mixture of SO42−/ZrO2 and MCM-41). The SO42−/ZrO2/MCM-41 catalysts show high activity with a selective conversion of >95 mol% ButOH to MTBE at low temperatures below 160°C, further showing the excellent on-stream stability of these catalysts for this reaction. The rather poor activity of PMSZM/ZrO2 catalysts has been ascribed to their weak acidity.