Most industrial chemical processes use catalysts, because they bring large economic and environmental benefits.Benefits of catalysts• An acceptable rate can be reached at a lower temperature (and sometimes lower pressure), so less energy is needed. Less fossil fuel is burned, which cuts costs and carbon dioxide emissions.
• Product is made faster, so more is produced per day from the same plant.
• Catalysts can make new reaction routes possible, with fewer steps, higher atom economy and less waste.
• Catalysts are not used up, so a small amount can be used many times.Examples• Iron in the Haber process for ammonia: N2(g) + 3H2(g) ⇌ 2NH3(g).
• Vanadium(V) oxide, V2O5, in the Contact process for sulfuric acid.
• Zeolites in the catalytic cracking of long-chain alkanes.
• Platinum, palladium and rhodium in catalytic converters, which convert carbon monoxide, nitrogen oxides and unburnt hydrocarbons into carbon dioxide, nitrogen and water.Heterogeneous catalysts are spread thinly on a support, or used as powders, pellets or gauzes, to give a large surface area and reduce the mass of expensive metal needed.DrawbacksCatalysts can be poisoned: impurities bond strongly to the surface and block the active sites. Sulfur compounds poison the iron catalyst in the Haber process, and lead poisons catalytic converters, which is one reason leaded petrol is no longer used. Some catalysts are expensive rare metals, and some are toxic, so they must be recovered and disposed of carefully.
• Product is made faster, so more is produced per day from the same plant.
• Catalysts can make new reaction routes possible, with fewer steps, higher atom economy and less waste.
• Catalysts are not used up, so a small amount can be used many times.Examples• Iron in the Haber process for ammonia: N2(g) + 3H2(g) ⇌ 2NH3(g).
• Vanadium(V) oxide, V2O5, in the Contact process for sulfuric acid.
• Zeolites in the catalytic cracking of long-chain alkanes.
• Platinum, palladium and rhodium in catalytic converters, which convert carbon monoxide, nitrogen oxides and unburnt hydrocarbons into carbon dioxide, nitrogen and water.Heterogeneous catalysts are spread thinly on a support, or used as powders, pellets or gauzes, to give a large surface area and reduce the mass of expensive metal needed.DrawbacksCatalysts can be poisoned: impurities bond strongly to the surface and block the active sites. Sulfur compounds poison the iron catalyst in the Haber process, and lead poisons catalytic converters, which is one reason leaded petrol is no longer used. Some catalysts are expensive rare metals, and some are toxic, so they must be recovered and disposed of carefully.