Catalyst activation involves using a substance called a promotor or activator to increase the activity of a catalyst. This allows reactions to proceed faster and at lower temperatures. Some examples given include using copper and tellurium to increase the activity of nickel in hydrogenating vegetable oil, and adding aluminum oxide or chromium oxide to increase the activity of iron in the Haber process for ammonia synthesis. Catalyst activity can also be increased or auto-catalyst activated by products formed in the reaction itself, such as nitrous acid increasing the rate of a copper-nitric acid reaction. Modifying the catalyst material or process conditions such as temperature, pressure or flow rate can enhance catalyst activation for industrial processes where high yields and short time