Aluminum phosphate-modified red clay as a stable nanocomposite catalyst for the selective conversion of methanol to dimethyl ether.

Aluminum phosphate-modified Egyptian red clay (AlPO4/ERC) nanocomposites were developed as low-cost solid acid catalysts for methanol dehydration to dimethyl ether (DME). Structural and physicochemical analyses (XRD, FTIR, N₂ adsorption-desorption, TEM, SEM, and acid-probe reactions) show that AlPO4 incorporation preserves the aluminosilicate framework while tuning surface acidity, porosity, and active-site accessibility. XRF and XRD confirm that ERC consists mainly of quartz, kaolinite, and iron oxides, whereas AlPO4 introduces additional phosphate phases that interact with the clay matrix. Catalytic testing reveals a strong dependence on AlPO4 loadings, with 5 wt.% AlPO4/ERC exhibiting optimal performance and achieving 90% methanol conversion with 100% DME selectivity at 200 °C. This enhancement correlates with an optimal balance of weak and intermediate acid sites (~ 2.5 mmol g-1) and a high specific surface area (52 m2 g-1), which maximizes the number of accessible active centers. Higher loadings reduce activity because of pore blockage and decreased site accessibility. Mechanistically, methanol dehydration proceeds via acid-catalyzed surface methoxy intermediates, with activity governed by acid-site distribution rather than iron species. The catalyst shows excellent stability over 15 days without deactivation, confirming its strong structural robustness. Overall, controlled AlPO4 incorporation optimizes the acidity-porosity synergy, enabling efficient and stable DME production.