Hydrogenation is the catalytic syn addition of hydrogen (H₂) across a multiple bond, which reduces an alkene to an alkane. It is carried out over a metal catalyst such as palladium on carbon (Pd/C), platinum oxide (PtO₂) or Raney nickel, on whose surface the two hydrogen atoms are delivered to the same face of the double bond. It matters in industry, for example in hardening vegetable oils. Note that 'reduction' here means gain of hydrogen, the opposite of the everyday sense of 'reducing'.

氢化是 H₂(氢)在催化下对多重键的顺式加成,可把烯烃还原为烷烃。它在金属催化剂(如钯碳(Pd/C)、氧化铂(PtO₂)或雷尼镍)上进行,两个氢原子在催化剂表面被加到双键的同一面。它在工业上很重要,例如用于使植物油硬化。注意这里的“还原”意为得到氢,与“减少”的日常含义相反。