Both hydrogenation and dehydrogenation of LOHCs requires catalysts. Processes include hydrogenation, hydroformylation, oxidation. Many higher alcohols are produced by hydroformylation of alkenes followed by hydrogenation. Iridium complexes are being investigated as catalysts for asymmetric hydrogenation. The hydrogenation of alkenes to alkanes is exothermic. Chiral ligands are used in homogeneous catalysis, such as asymmetric hydrogenation. Heterogeneous catalysts for hydrogenation are more common industrially. It is used as a catalyst in reactions such as alkylation, dealkylation, hydrogenation and oxidation. Shale oil is extracted by pyrolysis, hydrogenation, or thermal dissolution of oil shale. The temperature required for hydrogenation and dehydrogenation drops significantly for heterocycles vs simple carbocycles. Transition metals are often used to catalyze redox reactions (oxidation, hydrogenation). THF can also be synthesized by catalytic hydrogenation of furan. Such fine powders are useful as hydrogenation catalysts. Nickel and its alloys are frequently used as catalysts for hydrogenation reactions. The process is conducted by pyrolysis, hydrogenation, or thermal dissolution.