Ag/SiO 2 prepared by an in situ reduction method are found, for the first time, to be highly effective and recyclable catalysts for the selective hydrogenation of a range of chloronitrobenzes to their corresponding chloroanilines, which are of great potential as industrially viable and cheap novel catalysts for the production of chloroanilines.Chloroanilines (CAN), important intermediates for fine chemicals such as agrochemicals, pharmaceuticals and dyestuffs, are mainly produced by selective hydrogenation of the corresponding chloronitrobenzenes (CNB) over metal catalysts which include metallic Pt, Pd and Ru supported on active carbon, polymers and metal oxides, and Raney-Ni catalysts. [1][2][3][4][5][6][7][8][9][10][11][12] For most catalysts used right now that have high catalytic activity in the CNB hydrogenation reactions, a common drawback is the side reaction of catalytic hydrodechlorination of CNB over the metal catalysts. To solve the problem, several strategies have been developed, which include (1) alloying Pt with other metals 6 and the modification of Pt particles with sub-oxide species, 7 or with metal cations; 8 (2) using the synergic effect of bimetallic Pd-Ru catalysts 9 or (3) adding other reagents, such as NaOAc, pyridine, quinoline, to suppress the dechlorination reaction over Raney-Ni catalysts. 10 However, for Pd, Pt, Ni catalysts, the side reaction of hydrodechlorination still cannot be avoided completely. In the case of Rubased catalysts, although high selectivity can be obtained, in most cases, it is still hard to convert 100% of the substrates into the target products except when choosing suitable supports such as SnO 2 11 or Fe 2 O 3 . 12Supported silver catalysts have long been extensively studied as oxidizing catalysts and have been applied industrially to the epoxidation of ethylene. 13,14 However, the catalytic reduction properties of silver have not drawn much attention, especially its potential as a catalyst for the catalytic reduction of fine chemicals. So far, only Nagase et al. have reported the selective hydrogenation of unsaturated aldehydes to the corresponding alcohols over silver catalysts supported on metal oxides, 15 showing that the activity and selectivity were only moderate. Since metal nanoparticles have many extraordinary properties that bulky metals do not have, the unique catalytic properties of nano-metal catalysts have been extensively explored. In this paper, we report an Ag/SiO 2 catalyst, prepared by a novel synthetic method, exhibiting unprecedented catalytic activity and selectivity for the hydrogenation of CNBs to the corresponding CANs. To the best of our knowledge, this is the first report on the catalytic properties of a supported silver catalyst for the selective hydrogenation of chloronitrobenzenes.The Ag/SiO 2 catalysts were prepared by a new in-situ reduction method as shown in Scheme 1. The details of the preparation process can be found in the ESI.{ Fig. 1A shows a typical TEM image of a fresh Ag/SiO 2 catalyst, from which it can be seen that the...