Q. Illustrate important catalyst of aluminium?

Anhydrous AlCl₃ is an important catalyst, used in organic synthesis and in the cracking of petroleum. Al₂(S0₄)₃ as such or as potash alum, K₂S0₄.Al₂(S0₄)₃.24H₂0  is used for sizing paper, for tanning leather, for waterproofing cloth and as a mordant  for dying cotton. It is extensively used for purification of water and in sewage treatment.

Because of its extreme hardness, high m.p., non-volatility, chemical inertness and good electrical insulating properties, corundum (Al₂0₃,) finds many applications in abrasives, refractories and ceramics. Large crystals of a-Al₂0₃ when coloured with metal-ion impurities are prized as gemstones, e.g., ruby (cr³⁺, red), sapphire (Fe²⁺³⁺Ti⁴⁺ , blue), oriental emerald (cr³⁺/V^3+, green), oriental topaz (Fe³⁺, yellow), etc. Aluminates are important constituents of Portland cement. Gallium has the longest liquid range (303-2343 K) of any known substance and so finds use as a high temperature thermometer liquid.