These substances are regenerated by combustion after a layer of carbon inactivates or “cokes” them. In a packed bed, these substances are ground into pellets and immobilized on porous alumina or silica supports. The main unit operation at an oil refinery uses these substances to crack petroleum. (20[1])Zeolites (20[1])act (0[1])as adsorbents (20[4])and as (20[1])these (20[1]0[1])substances, (20[1])which (20[1])are powdered to increase their (20[1])specific (*) surface areas. (10[2]0[1])Per (0[1])gram, the most expensive chemicals in a reactor are usually these (10[1])solids, especially noble metals like rhodium. (10[1])Platinum (10[1])acts as a (10[3])heterogeneous (10[2])example of these (10[1])substances (10[2])in the device that converts the CO in car exhaust to CO2. (10[2])For 10 points, name these substances that reduce (10[1])activation energy (10[2])and (0[1])speed up (10[1])chemical reactions. ■END■ (10[5])