两种铜物种的、或者处于不同位置的铜的可能性更大。可以参考：
Journal of Catalysis, Volume 296, December 2012, Pages 1-11
Applied Catalysis A: General, Volume 403, Issues 1–2, 22 August 2011, Pages 173-182
载体和铜的作用强弱，也会引起还原温度的变化。
Bioresource Technology, Volume 101, Issue 18, September 2010, Pages 7088-7092
做过很多铜基催化剂的还原，还真没有遇到过分步还原的情况。
Hydrogenolysis of glycerol to 1,2-propanediol over Cu-based catalysts: A short review
Catalysis Today, In press, corrected proof, Available online 13 March 2019
