Semi-hydrogenation Of Alkynes Over Nickel-based Nanocatalyst

Catalytic semi-hydrogenation of alkynes?-C?C-?to corresponding alkenes?-CH=CH-?is an extremely important process in both the production of intermediates for fine chemicals and the purification of alkenes in the industry of polyolefins.Right now,although noble catalysts have achieved excellent activity for catalytic hydrogenation of alkynes,the high prices of noble metals,over-hydrogenation of alkenes,modification with complex organic ligands have hampered their practical applications.In this work,we have prepared a series of cheap,highly active,selective and stable nickel based nano catalysts to optimize the selective hydrogenation of alkynes.Firstly,an efficient catalytic system,involving in-situ generated ligand-free Ni NPs with an average size of 6.2 nm,methanol and sodium borohydride was developed,for the semi-hydrogenation of alkynes under ambient conditions.This catalytic system exhibited remarkably high activity with a turnover frequency of 2940 h^-1,satisfying cis-selectivity for semi-hydrogenation of diphenylacetylene?DPA?.Then,a series of NiZn/NC nano catalysts were developed by the direct pyrolysis of the mixture of nickel-zinc complexes for the semi-hydrogenation of DPA.It was found that the Ni₃ZnC_0.7/NC_5-5-10 nano catalyst showed excellent catalytic selectivity toward cis-diphenylethene.More importantly,the amounts of trans-isomer and alkanes,the over-hydrogenated product,did not obviously increase even if prolonging the reaction time up to 7 h.Finally,we report a straightforward concept to prepare inexpensive Ni₃N/NC catalysts by the direct pyrolysis the solid mixture of nickel salt and melamine,constituting the catalyst for semi-hydrogenation of a variety of alkynes to corresponding cis-alkenes with good activity and stability.XRD,TEM and XPS illustrate that there is a relationship between the structure and the catalytic performance of this catalyst.