Titanium-doped alumina for catalytic dehydration of methanol to dimethyl ether at relatively low temperatures

Mesoporous Al-Ti oxide composites with molar %Ti of 3, 5, 10, and 20 as well as pure γ-alumina were prepared using a template-free sol-gel method in the absence of a catalyst. The prepared composites were characterized by powder XRD, FTIR spectroscopy and N₂ adsorption for BET surface area and porosity measurements. The composites and the pure alumina possessed relatively high surface areas, 350-410 m²/g, and high porosities after calcination at 500 °C. FTIR spectroscopy was employed to study the products of the catalytic dehydration of methanol to dimethyl ether, DME, over the prepared catalysts at reaction temperatures between 180 and 300 °C. Compared with pure γ-alumina, the Ti-modified alumina with %Ti < 10 showed higher catalytic activity in the methanol dehydration and better selectivity to DME. Composites with %Ti of 3 and 5 showed the highest activity at relatively lower temperatures than the other catalysts where they showed their highest activity at 190 and 200 °C, respectively. The activity of all studied catalysts slightly decreased as the temperature was raised to 300 °C and dropped considerably when the temperature was decreased to 180 °C. However, the activity of Al-Ti-3 dropped only slightly at both temperatures. The selectivity to DME was dependent on the reaction temperature where 100% DME selectivity was obtained at temperatures ?220 °C and as the temperature was raised to 300 °C, some CH₄ and CO₂ formed on the account of DME.