Catalytic Hydrogenation of Nitrophenols by Cubic and Hexagonal Phase Unsupported Ni Nanocrystals

The catalytic hydrogenation of nitrophenols to aminophenols by diverse catalysts has attracted much attention owing to its potential applications in wastewater purification, fine chemicals and pharmaceutical fields. Though great progress has been achieved, the catalytic hydrogenation of nitrophenols by different crystal phase structured Ni nanocrystals (NCs) has not been investigated until now. Here, the face centered cubic (fcc) Ni and hexagonal close packed (hcp) Ni NCs are controllably synthesized, and employed as the catalysts for hydrogenation of nitrophenols at ambient pressure by using NaBH₄ as the hydrogen carrier. The experimental results reveal that both fcc and hcp Ni NCs can catalyze hydrogenation of nitrophenols to related aminophenols. But the hcp Ni NCs exhibit much higher catalytic activity than fcc Ni NCs no matter which nitrophenols is used. Moreover, both hcp and fcc Ni NCs can be recycled at least ten times without obvious loss of activity, showing an exceptional durability that comparable or even superior to supported Ni catalysts. Deduced from the kinetics and XPS analyses, the higher catalytic activity of hcp Ni NCs is attributed to the more richness of active sites on their surfaces in relative to that of fcc Ni NCs. This work may shed some light on design and development of advanced hydrogenation catalysts based on crystal phase engineering.