The first reaction (main reaction, intra-molecular dehydration of ethanol to ethylene) is endothermic while the second one (side reaction, inter-molecular dehydration of ethanol to diethyl-ether) is exothermic. Diethyl-ether is produced in significant quantities at low temperature; however, high temperatures favor intramolecular dehydration. Therefore, it was a critical issue to find catalyst with high catalytic activity for ethylene at relatively low temperature