Hydrogenation of p-Chloronitrobenzene on Mo-Doped NiB Cluster Catalysts

Abstract

The objective of this study was to investigate the effect of Mo content on the catalytic properties of Mo-NiB nanoclusters in the hydrogenation of p-chloronitrobenzene. A series of Mo-doped NiB nanoalloy catalysts with various Mo contents were prepared by chemical reduction method. An excess amount of NaBH 4 was used (B/Ni atomic ratio ) 3) to fully reduce Ni. Even adding a small amount of Mo on NiB had a significant effect on the activity and selectivity to p-chloroaniline. The catalyst with the atomic ratio of Mo/Ni ) 0.4 had the highest activity and selectivity to p-chloroaniline. The particle size of Mo-NiB decreased with an increase of Mo content, indicating that the molybdenum species suppressed the growth of the crystalline structure of NiB and helped the NiB nanocluster maintain its amorphous state. Mo-NiB formed a nanoalloy, and no discrete phase was found. High-resolution transmission electron microscopy (HRTEM) images confirmed that the shape of Mo-NiB was spherical and the particle size was in the range of 3-5 nm. The effect of molybdenum on the catalytic performance of the amorphous NiB catalysts was 2-fold. Molybdenum not only acted as a spacer but also donated partial electron to Ni. Since the -NO 2 was more electronegative than -Cl, -NO 2 was supposed to occupy the active site on the Ni catalytic surface at the start of the reaction. -NO 2 adsorbed on the catalyst surface is hydrogenated to form p-ceric ammonium nitrate (p-CAN), which was further desorbed. Therefore, the selectivity of p-CAN would increase as the Mo contents increased. It should be noticed the overdose of Mo would cover the active sites and decreased the activity. In addition, oxygen was even more electronegative, and alloying B could engage the oxygen to activate the polar -NO 2 group of p-CNB. The -NH 2 of p-CAN might adsorb on the surface, alloying B and coordinating with each other. Hence, it would improve the selectivity of p-CAN by depressing the dehalogenation reaction.

Reduction of Nitro Compounds Using 3d-Non-Noble Metal Catalysts

“…The same group also studied tungsten-modified Ni-Co-B-catalysts for the reduction of 4-chloronitrobenzene (vide infra) . In 2011, they investigated molybdenum-doped Ni-B cluster catalysts with different Mo/Ni ratios . The synthetic methodology was again comparable to the other systems, starting from a methanolic solution of nickel acetate and ammonium heptamolybdate.…”

Selective gas phase hydrogenation of nitroarenes over Mo2C-supported Au–Pd

“…Chemoselectivity in amine production is particularly relevant in the hydrogenation of p-chloronitrobenzene 70 where a range of intermediates and by-products, notably nitrobenzene and aniline, have been reported for reaction over Pd and Ni catalysts in both liquid and gas phases. 28,53,71,72 A simplified reaction pathway is presented in Fig. 7(A), where the target p-chloroaniline formed via -NO 2 reduction (step I) can undergo hydrodechlorination to aniline (step II) or alternatively nitrobenzene is first generated by hydrodechlorination (step III) with subsequent hydrogenation to aniline (step IV).…”

Facile Preparation of a Stable Fe3O4@LDH@NiB Magnetic Core‐Shell Nanocomposite for Hydrogenation

“…Particularly, the fabrication of highly active and stable catalysts plays a key role for their industrial applications. For example, Chen et al [8] investigated the effect of Mo content on the catalytic performance of NiB nanoclusters in the hydrogenation of p-chloronitrobenzene and found that the addition of Mo can markedly improve the activity and selectivity of NiB catalyst. [1][2][3][4][5] Although some of them have been applied, the high prices of noble metals have limited their further applications, making it desirable to search for more economical alternatives.…”