Using Graphene Encapsulated Ni and Pd Catalysts with Solvent Effect to Achieve Highly Chemo-Selective Hydrogenation of 4-Nitrostyrene to Different Products

Abstract

Chemo-selective hydrogenation of challenging nitrostyrene to the corresponding product of vinylaniline, ethylbenzenamine, and ethylnitrobenzene separately in high yield is difficult since there exists competitive activation of the C=C double bond and the -NO2 group over most supported metal catalysts. Also, the currently reported catalysts still have some disadvantages of high cost, catalyst reusability and separation problem, catalyst stability and leaching during harsh reaction conditions, waste generation, which disagree with the requirements of low cost, highly active and selective, sustainable, environmentally friendlier, and industrially applicable. Herein we report thin graphene layer encapsulated Ni and Pd nanoparticles core-shell structures as highly active, chemo-selective, and reusable catalysts for hydrogenation of 4-nitrostyrene in both batch reactor and industrially applicable flow reactor. In the standard hydrogenation of 4-nitrostyrene, the optimized catalysts Ni/NiO@-700-200-1-H2O and Pd@NC-2 yield a selectivity to every single product of 4-vinylaniline 99%, 4-ethylbenzenamine 99%, 1-ethyl-4-nitrobenzene 99% through simple changing reaction conditions, the best achieved over Ni and other group metals and higher than the best result reported in the literature. In non-polar solvent toluene, in contrast to traditional catalysts, the Ni@C catalyst is inert for the C=C and is only active about the -NO2, while the N-doped Pd@NC-2 has opposite hydrogenation ability and can hydrogenate the C=C without touching -NO2 in non-polar solvent cyclohexane, which rarely reported in the previous literature. In addition, the catalysts show excellent stability and the 4-nitrostyrene's hydrogenation can be successfully applied in industrially applicable flow reactors for each of the three product syntheses separately with excellent yield. These discoveries may extend the design of non-noble catalysts with excellent chemoselectivity for use in fine chemicals' synthesis.