Catalytic Hydrogenation of Unsaturated Aldehydes on Pt(111): Understanding the Selectivity from First-Principles Calculations

摘要

Selectivity is an essential aspect of chemistry in general and of heterogeneous catalysis in particular. It is commonly acknowledged that the CC bond is more reactive than the CO bond in the hydrogenation on metal surfaces of molecules with a vinyl or carbonyl bond.[1], [2] Hence, according to this statement, the partial hydrogenation of ,-unsaturated aldehydes containing conjugated CC and CO bonds should selectively produce the saturated aldehyde (SAL), which is the thermodynamic product, instead of the unsaturated alcohol (UOL), which is in practice the desired product in the pharmaceutical and fragrance industries. Although this rule is respected for the hydrogenation of acrolein (propenal) on Pt(111), which yields almost exclusively the SAL (93 % of propanal versus only 2 % of propenol), it is violated for prenal (methylbutenal), for which the selectivity is reversed in favor of the UOL.[2], [3] Thus, understanding the selectivity requires a thorough knowledge of all the competitive steps involved in the reaction mechanism.