Poisoning effect of some nitrogen compounds on nano-sized nickel catalysts in p-nitrophenol hydrogenation

The poisoning effect of some nitrogen compounds on the hydrogenation of p-nitrophenol to p-aminophenol over the nano-sized nickel catalysts prepared by the improved chemical reduction method was studied. Experimental results show that some nitrogen compounds are obvious poisons for p-nitrophenol hydrogenation on the nano-sized nickel. Traces of ammonia could cause the deactivation of the nano-sized nickel catalysts. The formation of complex compounds and the dissolution of nickel are two main reasons of poisoning. The as-synthesized nickel catalysts are also poisoned in the presence of some organic amines. The primary cause could be the strong adsorption of the organic amines on the hydrogenation sites. The poisoning effect of organic amines is correlated with their solution basicities. The poisoning of organic amines (such as dimethylamine) is reversible, while the poisoning of ammonia is irreversible. In addition, the deactivation degree of the nano-sized nickel was higher than that of Raney nickel in the presence of ammonia, may be due to the higher-density surface defect sites on the nano-sized nickel.