Preparation of superhydrophobic materials

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In-situ DRIFTS results were studied to investigate the reaction mechanism of methanol dehydration over the pure η-Al2O3 catalyst. Moreover, the effect of silver loading on the catalytic performance of η-Al2O3 was examined in a fixed bed reactor under the reaction conditions where the temperature ranged from 180 to 300 °C with a WHSV = 48.4 h–1. The addition of silver to the support improved the catalytic activity, and herein, the optimum catalyst was 10% Ag/η-Al2O3. The Ag loadings clearly resulted in an improvement in the Lewis acidity and in the secondary improvement of the bulk surface properties by changing the surface from superhydrophilic to hydrophilic at 10% Ag loading with an increase in the CA from 1.6° to 50.7° for pure η-Al2O3 and 10% Ag/η-Al2O3, respectively. Furthermore, 10% Ag/η-Al2O3 catalyst exhibited a high degree of stability under steady-state conditions, and this is attributed to the enhancement in both the surface Lewis acidity and the hydrophobicity. To test the hypothesis that hydrophobicity is the only factor that affects the MTD reaction, a superhydrophobic alumina catalyst (H–Al2O3) was prepared and showed a CA of 170.6°; however, during the transformation of the superhydrophilic alumina into H–Al2O3, most of the acidic sites were removed and consequently the catalytic activity decreased compared with the pure η-Al2O3. In summary, a balance between acidity and hydrophobicity is needed to achieve an optimum activity during the MTD reaction which was achieved herein in the 10%Ag/η-Al2O3 catalyst.

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