The temperature must be controlled, because if the high temperatures will occur on coke and cause loss of catalyst.Products that do not need. Or potentially dangerous and damaged reactors.
If you need to control the temperature, high temperature will result in the loss of coke and the catalyst was the product of unwanted or potentially dangerous and cause damage to the reactor.
To control the temperature of high temperature will occur if the coke and causing the loss of catalyst.What the byproducts.Or potential dangers and make the reactor damaged.