the purpose of the present invention is providing a kind of nanocomposite materials composed of transition metals nanoclusters and magnetic iron oxides nanoparticles , and their preparation methods . the invented transition metals - magnetic iron oxides nanocomposite materials are essentially composed of transition metals or their alloys nanoparticles with particle sizes ranging from 0 . 7 to 5 nm and magnetic iron oxides nanoparticles having sizes ranging from 5 to 50 nm . the total contents of the related transition metals or alloys in the related nanocomposite materials range from 0 . 1 - 30 wt . %. the related magnetic iron oxides include γ - fe 2 o 3 , fe 3 o 4 , the composite derived from part reduction of γ - fe 2 o 3 , or the composite derived from part oxidation of fe 3 o 4 . the said composite derived from part reduction of γ - fe 2 o 3 was obtained by partly reducing the related transition metal - γ - fe 2 o 3 nanocomposite at 278 - 473 k in the presence of the reductants including hydrogen , glycolic acid , alcohol , aldehyde , etc . the said composite derived from part oxidation of fe 3 o 4 was obtained by partly oxidating the related transition metal - fe 3 o 4 nanocomposite at 313 - 523 k in the presence of oxygen . in the present invention , typical transition metals are selected from pt , ru , rh or ir , etc . typical transition metal alloys are selected from discretional two or more elements of pt , pd , rh , ru , ir and os . typical particle sizes of the related magnetic iron oxides nanoparticles range from 5 to 25 nm . the invented transition metals - magnetic iron oxides nanocomposite materials can be prepared by the following two methods : 1 ) preparing transition metal colloids : dissolving at least one kinds of soluble salts or acids containing the related transition metals into an alcohol solution or alcohol / water mixture to form a solution of transition metal compounds with concentration of 0 . 01 - 100 g / l , and adding an alcohol solution , or aqueous solution , or alcohol / water mixture of alkali metal hydroxides or alkaline - earth metal hydroxides into the said solution of the transition metal compounds , then heating the obtained mixture at 343 - 473 k to produce a colloidal solution of transition metal nanoclusters . the typical molar ratio of alkali metal hydroxides or alkaline - earth metal hydroxides to the salts or acids containing the said transition metals is in the range from 3 to 30 . typical alcohols are selected from alcohols containing one , or tow , or three hydroxyl groups and 1 - 8 carbon atoms , and unitary methoxyl or ethoxyl derivatives of the alcohols containing two or three hydroxyl groups and 1 - 8 carbon atoms . the typical volume content of water in the alcohol / water mixtures is 0 - 50 %; 2 ) preparing ferric hydroxide colloids : forming a precipitate of ferric hydroxide by adding an alkaline solution into a solution containing ferric ( fe 3 + ) salts to adjust the ph value to 4 - 12 , and peptizing the obtained precipitate in peptizing agents to produce a colloidal solution of ferric hydroxide with a concentration of 1 - 300 g / l . the said peptizing agents are selected from ferric chloride solution , ferric nitrate solution and hydrochloric acid ; 3 ) preparing nanocomposite materials composed of transition metals nanoclusters and magnetic iron oxides nanoparticles : mixing the transition metal colloidal solutions prepared in step 1 ) and the ferric hydroxide colloidal solutions prepared in step 2 ) at mass ratios of metal colloidal solution to ferric hydroxide colloidal solution of 1 : 3 - 1 : 13400 , and heat treating the mixture at 313 - 523 k for 1 - 200 h , then drying the obtained precipitates at 278 - 523 k to provide the related nanocomposite materials composed of transition metals nanoclusters and magnetic iron oxides nanoparticles . 1 ) preparing transition metal colloids : ( a ) dissolving at least one kinds of soluble salts or acids containing the related transition metals into an alcohol solution or alcohol / water mixture to form a solution of transition metal compounds with concentration of 0 . 01 - 100 g / l , and adding an alcohol solution , or aqueous solution , or alcohol / water mixture of alkali metal hydroxides or alkaline - earth metal hydroxides into the said solution of the transition metal compounds . the typical molar ratio of alkali metal hydroxides or alkaline - earth metal hydroxides to the salts or acids containing the said transition metals is in the range from 3 to 30 . typical alcohols are selected from alcohols containing one , or tow , or three hydroxyl groups and 1 - 8 carbon atoms , and unitary methoxyl or ethoxyl derivatives of the alcohols containing two or three hydroxyl groups and 1 - 8 carbon atoms . the typical volume content of water in the alcohol / water mixtures is 0 - 50 %; ( b ) heating the obtained mixture at 343 - 473 k , and adding an acidic aqueous solution to form a precipitate of transition metal nanoclusters , then dispersing the said precipitate into ethylene glycol solutions of alkali metal or alkaline - earth metal hydroxides , or into organic solvents , to produce a colloidal solution of transition metal nanoclusters . typical organic solvents are selected from alcohols containing tow or three hydroxyl groups and 1 - 8 carbon atoms , ketone , 1 , 4 - dioxane , dmso , thf and dmf ; 2 ) preparing ferric hydroxide colloids : forming a precipitate of ferric hydroxide by adding an alkaline solution into a solution containing ferric ( fe 3 + ) salts to adjust the ph value to 4 - 12 , and peptizing the obtained precipitate in peptizing agents to produce a colloidal solution of ferric hydroxide with a concentration of 1 - 300 μl . the said peptizing agents are selected from ferric chloride solution , ferric nitrate solution and hydrochloric acid ; 3 ) preparing nanocomposite materials composed of transition metals nanoclusters and magnetic iron oxides nanoparticles : mixing the transition metal colloidal solutions prepared in step 1 ) and the ferric hydroxide colloidal solutions prepared in step 2 ) at mass ratios of metal colloidal solution to ferric hydroxide colloidal solution of 1 : 3 - 1 : 13400 , and adding one or several kinds of organic reductants into the mixture , then heat treating the said mixture at 313 - 523 k for 1 - 200 h , followed by drying the obtained precipitate at 278 - 523 k to provide the related nanocomposite materials composed of transition metals nanoclusters and magnetic iron oxides nanoparticles . the related organic reductants are selected from formaldehyde , glycolic acid , sodium glycolate , isopropyl alcohol , glyoxal , oxalic acid and hydrogen . the typical molar ratio of organic reductants to ferric hydroxide is 0 . 1 - 10 . in the two preparation methods described above , soluble salts or acids containing the related transition metals in step 1 ) are selected from salts or acids containing pt , pd , ru , rh , os and ir . in step 2 ), the concentration of the related fe 3 + salts in the solutions is 0 . 01 - 4 mol / l ; the ferric salts are selected from ferric sulfate , ferric nitrate , ferric chloride , etc . typical alkalis include ammonia , potassium hydroxide , sodium hydroxide , lithium hydroxide , tetramethylammonium hydroxide , etc ; the typical temperature for precipitating ferric hydroxide is 278 - 370 k ; typical concentration of peptizing agents is in the range of 0 . 01 - 2 mol / l ; typical peptization temperature is 278 - 373 k . in step 3 ), the heat treating methods include solvothermal method , beating and refluxing method , and microwave irradiation method ; the drying processes can be conducted in the following manners : drying in vacuum can provide the nanocomposite materials composed of transition metal nanoclusters and fe 3 o 4 nanoparticles ; oxidation drying in oxygen - containing atmosphere can provide the nanocomposite materials composed of transition metal nanoclusters and γ - fe 2 o 3 nanoparticles ; part - oxidation drying in oxygen - containing atmosphere can provide the nanocomposite materials composed of transition metal nanoclusters and magnetic iron oxides nanoparticles , the said magnetic iron oxides are the composite produced by partly oxidating fe 3 o 4 in the transition metal - fe 3 o 4 nanocomposite . moreover , the related nanocomposite materials composed of transition metal nanoclusters and magnetic iron oxides nanoparticles can also be obtained by partly reducing the transition metal - γ - fe 2 o 3 nanocomposite materials at 278 - 473 k in the presence of the reductants selected from hydrogen , glycolic acid , alcohol and aldehyde , the said magnetic iron oxides are the composite produced by partly reducing γ - fe 2 o 3 in the transition metal - γ - fe 2 o 3 nanocomposite materials . the other purpose of the present invention is to provide the application of the invented transition metals - magnetic iron oxides nanocomposite materials . studies of the inventors of the present invention showed that the nanocomposite materials composed of the transition metal nanoclusters and magnetic iron oxides nanoparticles exhibited excellent catalytic properties , especially the high catalytic activity and superior selectivity in the selective hydrogenation of aromatic halonitro compounds . moreover , the magnetic property of the nanocomposite material provides a convenient route for separating the catalysts from the reaction system in an applied magnetic field . over the invented nanocomposite catalysts , the hydrogenation of many aromatic halonitro compounds , such as halonitrobenzenes , halodinitrobenzenes and halonitrobiphenyl , can be conducted with very high selectivity , i . e . the hydrodehalogenation of the corresponding aromatic haloamine products would not occur over these catalysts . generally , the hydrogenation conditions are as follows : temperature , 273 - 393 k ; pressure of hydrogen , 0 . 1 - 10 mpa . the typical solvents used in the hydrogenation can be selected from alcohols or other organic solvents such as thf , dmso and toluene . when the reaction is complete , the catalyst can be recovered from the reaction system by magnetic separation , centrifugation or filtration , and be reused . the typical structures of aromatic halonitro compounds mentioned above are shown as follows : in scheme ( i ), x = cl , br or i ; y = h x , r , coor , ro , cl , br , i , no 2 or nh 2 ( r is saturated alkyl of c 1 - c 4 ); in scheme ( ii ), x = cl , br or i ; x ′, y , y ′= h , r , coor , ro , cl , br or i ; z = h , no 2 or nh 2 ( r is saturated alkyl of c 1 - c 4 ). fig1 is a transmission electron microscope ( tem ) image of pt nanoclusters ( example 1 ). fig2 is a scanning transmission electron microscope ( stem ) image of the pt / γ - fe 2 o 3 nanocomposite according to the present invention ( example 1 ). fig3 is an energy dispersive x - ray ( edx ) pattern of the pt / γ - fe 2 o 3 nanocomposite according to the present invention ( example 1 ). fig4 is a raman spectrum of the pt / γ - fe 2 o 3 nanocomposite according to the present invention ( example 1 ). fig5 is a raman spectrum of the pt / fe 3 o 4 nanocomposite according to the present invention ( example 3 ). objects and advantages of this invention are further illustrated by the following examples , but the particular materials and amounts thereof recited in these examples , as well as other conditions and details , should not be construed to unduly limit this invention . preparation of pt / γ - fe 2 o 3 nanocomposite with 1 wt . % of pt loading 1 . 0 g of hexachloroplatinate hexahydrate ( h 2 ptcl 6 . 6h 2 o ) was dissolved into 50 ml of ethylene glycol ( eg ), followed by addition of 50 ml of eg solution containing naoh ( 0 . 5 mol / l ). after stirring at room temperature for 5 min , the mixture was refluxed at 453 k for 3 h , with a nitrogen flow passing through the reaction system . a homogeneous , dark - brown colloidal solution of “ unprotected ” pt nanoclusters ( pt : 3 . 75 g / l ) was obtained . the average diameter of the prepared pt nanoclusters was determined to be 2 . 0 nm by tem measurements . an aqueous solution of ammonia ( 10 %) was added dropwise into a solution of ferric chloride ( fecl 3 ) in 100 ml of water ( 4 %) to adjust the ph value to about 7 . 5 , after ageing for 5 min , the produced precipitate of ferric hydroxide was filtered , washed to remove cl − , and peptized in 30 ml of an aqueous solution of fecl 3 ( 4 %) by stirring and slightly heating under 323 k , resulting in a colloidal solution of ferric hydroxide , which was kept at room temperature for utilization . 2 . 6 ml of the pt colloidal solution was added dropwise into the prepared ferric hydroxide colloidal solution under stirring . the mixture was then heated in a teflonlined autoclave at 353 k for 72 h . a magnetic precipitate was produced , which was separated by filtration , washed to remove cl − , dried and oxidized at 353 k in air for 48 h to produce the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt . the average diameter of γ - fe 2 o 3 nanoparticles was determined to be 16 nm by tem . fig1 shows the tem image of the pt nanoclusters prepared in example 1 . fig2 shows the stem image of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt . fig3 shows the edx pattern of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt . the above characterization results illustrated that the pt nanoclusters were well dispersed in the matrix of the γ - fe 2 o 3 nanoparticles without obvious aggregation . fig4 shows the raman spectrum of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt , demonstrating that iron oxide in the nanocomposite is γ - fe 2 o 3 . preparation of pt / γ - fe 2 o 3 nanocomposite with 30 wt . % of pt loading 1 . 0 g of h 2 ptcl 6 . 6h 2 o was dissolved into 50 ml of eg , followed by addition of 125 ml of eg / h 2 o ( 4 : 1 , v : v ) solution containing ba ( oh ) 2 ( 0 . 1 mol / l ). after stirring at room temperature for 5 min , the mixture was refluxed at 433 k for 3 h under flowing nitrogen to produce a colloidal solution of “ unprotected ” pt nanoclusters ( pt : 3 . 75 g / l ). the average diameter of the obtained pt nanoclusters is 3 . 0 nm . an aqueous solution of ammonia ( 10 %) was added dropwise into a solution of fecl 3 in 100 ml of water ( 4 %) to adjust the ph value to about 8 . 0 , after ageing for 3 min , the produced precipitate of ferric hydroxide was then filtered , washed to remove cl − , and peptized in 30 ml of an aqueous solution of fecl 3 ( 4 %) by stirring and slightly heating under 323 k , resulting in a colloidal solution of ferric hydroxide , which was kept at room temperature for utilization . 78 . 0 ml of the pt colloidal solution was added dropwise into the prepared ferric hydroxide colloidal solution under stirring . the mixture was then heated in a teflonlined autoclave at 353 k for 72 h . a magnetic precipitate was produced , which was separated by filtration , washed to remove cl − , and dried at 353 k in air for 48 h to produce the pt / γ - fe 2 o 3 nanocomposite containing 30 wt . % of pt . particle size analyses showed that the average diameter of γ - fe 2 o 3 nanoparticles is 9 nm . preparation of pt / fe 3 o 4 nanocomposite with 3 wt . % of pt loading colloidal solutions of pt nanoclusters and ferric hydroxide nanoparticles were prepared as in example 1 . the pt / fe 3 o 4 nanocomposite was prepared as follows : 7 . 8 ml of the pt colloidal solution was added dropwise into 30 ml of the ferric hydroxide colloidal solution under stirring . the mixture was then heated in a teflonlined autoclave at 353 k for 72 h . a magnetic precipitate was produced , which was separated by a filtration , washed to remove cl − , and dried at 353 k in vacuum to produce the pt / fe 3 o 4 nanocomposite containing 3 wt . % of pt . particle size analyses showed that the average diameter of fe 3 o 4 nanoparticles is 16 nm . fig5 shows the raman spectrum of the pt / fe 3 o 4 nanocomposite containing 3 wt . % of pt , indicating that iron oxide in the nanocomposite is fe 3 o 4 . preparation of pt / fe 3 o 4 nanocomposite with 0 . 1 wt . % of pt loading 0 . 1 g of h 2 pt / cl 6 . 6h 2 o was dissolved into 50 ml of eg , followed by addition of 50 ml of eg solution containing naoh ( 0 . 05 mol / l ). after stirring at room temperature for 5 min , the mixture was refluxed at 433 k for 3 h to produce a colloidal solution of “ unprotected ” pt nanoclusters ( pt : 0 . 375 g / l ). particle size analyses showed that the average diameter of the obtained pt nanoclusters is 1 . 0 nm . an aqueous solution of ammonia ( 10 %) was added dropwise into a solution of fecl 3 in 200 ml of water ( 2 %) to adjust the ph value to about 12 , after ageing for 10 min , the produced precipitate of ferric hydroxide was then separated by filtration , washed to remove cl − , and peptized in 60 ml of an aqueous solution of fecl 3 ( 2 %) by stirring and heating under 363 k , resulting in a colloidal solution of ferric hydroxide , which was kept at room temperature for utilization . 2 . 6 ml of the pt colloidal solution was added dropwise into the ferric hydroxide colloidal solution under stirring . the mixture was then heated in a teflonlined autoclave at 413 k for 160 h . a magnetic precipitate was produced , which was separated by filtration , washed to remove cl − , and dried in vacuum for 48 h to produce the pt / fe 3 o 4 nanocomposite containing 0 . 1 wt . % of pt . particle size analyses showed that the average diameter of fe 3 o 4 is 45 nm . preparation of ru / γ - fe 2 o 3 nanocomposite with 1 wt . % of ru loading 1 . 0 g of rucl 3 . 3h 2 o was dissolved into 50 ml of ethylene glycol monomethyl ether , followed by addition of 50 ml of eg / h 2 o ( 1 : 1 , v : v ) solution containing koh ( 0 . 5 mol / l ). after stirring at room temperature for 5 min , the mixture was refluxed at 373 k for 3 h to produce a colloidal solution of “ unprotected ” ru nanoclusters ( ru : 3 . 75 g / l ). particle size analyses showed that the average diameter of the obtained ru nanoclusters is 1 . 3 nm . an aqueous solution of tetramethylammonium hydrate ( 10 %) was added dropwise into a solution of ferric nitrate in 150 ml of water ( 4 %) to adjust the ph value to about 4 , after ageing for 3 min , the produced precipitate of ferric hydroxide was then separated by filtration , washed , and peptized in 30 ml of a dilute aqueous solution of hcl ( 1 %) by stirring and slightly heating under 333 k , resulting in a colloidal solution of ferric hydroxide , which was kept at room temperature for utilization . 2 . 6 ml of the ru colloidal solution was added dropwise into the ferric hydroxide colloidal solution under stirring . the mixture was then heated in a teflonlined autoclave at 313 k for 72 h . a black precipitate was produced , which was separated by filtration , washed to remove cl − , dried and oxidized at 353 k in air for 48 h to produce the ru / γ - fe 2 o 3 nanocomposite containing 1 wt . % of ru . particle size analyses showed that the average diameter of γ - fe 2 o 3 nanoparticles is 6 nm . preparation of pt / γ - fe 2 o 3 nanocomposite with 5 wt . % of pt loading colloidal solutions of pt nanoclusters and ferric hydroxide nanoparticles were prepared as in example 1 . the pt / γ - fe 2 o 3 nanocomposite was prepared as follows : 13 ml of an aqueous solution of hcl ( 1 mol / l ) was added into 13 . 1 ml of the pt colloidal solution ( 3 . 75 g / l ) to form a precipitate of the pt nanoclusters , which was separated by centrifugation and then redispersed into 5 . 6 ml eg solution of naoh ( 0 . 5 mol / l ), followed by the addition of 0 . 3 g glycolic acid . the obtained colloidal solution of pt nanoclusters was added dropwise into 30 ml of the ferric hydroxide colloidal solution under vigorously stirring , the mixture was refluxed at 373 k for 72 h . the produced black precipitate was filtered , washed , dried and oxidized at 353 k in air for 48 h to produce the pt / γ - fe 2 o 3 nanocomposite containing 5 wt . % of pt . calcining the obtained sample at 773 k for 2 h to produce the calcined pt / γ - fe 2 o 3 nanocomposite containing 5 wt . % of pt . x - ray diffraction ( xrd ) patterns and other measurements demonstrated that iron oxide in the nanocomposite is γ - fe 2 o 3 . preparation of pt / magnetic iron oxides nanocomposite with 3 wt . % of pt loading colloidal solutions of pt nanoclusters and ferric hydroxide nanoparticles were prepared as in example 1 . the pt / magnetic iron oxides nanocomposite was prepared as follows : 7 . 8 ml of the pt colloidal solution ( 3 . 75 g / l ) was added into 30 ml of the ferric hydroxide colloidal solution under stirring . the mixture was then heated and refluxed under n 2 for 24 h . the obtained precipitate was filtered , washed , dried and oxidized at 333 k in air for 12 h to produce the nanocomposite composed of pt / γ - fe 2 o 3 and pt / fe 3 o 4 with 3 wt . % of pt loading . raman spectra proved that the nanocomposite consisted of γ - fe 2 o 3 and fe 3 o 4 . preparation of pt / fe 3 o 4 nanocomposite with 6 wt . % of pt loading colloidal solutions of pt nanoclusters and ferric hydroxide nanoparticles were prepared as in example 1 . the pt / fe 3 o 4 nanocomposite was prepared as follows : 15 ml of an aqueous solution of hcl ( 1 mol / l ) was added into 15 . 6 ml of the pt colloidal solution ( 3 . 75 g / l ) to produce a precipitate of the pt nanoclusters , which was separated by centrifugation and then redispersed into 9 ml thf solution of koh ( 0 . 1 mol / l ). the obtained colloidal solution of pt nanoclusters was added dropwise into 30 ml of the ferric hydroxide colloidal solution under vigorously stirring , followed by the addition of 10 ml thf solution containing 0 . 5 g of sodium glycolate . the mixture was heated by microwave irradiation under stirring for 2 h . the product was filtered , washed , and dried at 353 k in vacuum for 24 h to produce the pt / fe 3 o 4 nanocomposite containing 6 wt . % of pt . preparation of pt — ru / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / ru molar ratio of 1 : 1 0 . 5179 g of h 2 ptcl 6 . 6h 2 o and 0 . 2073 g of rucl 3 . 3h 2 o were dissolved into 25 ml of eg , followed by the addition of 25 ml eg solution containing naoh ( 1 . 0 mol / l ). after stirring at room temperature for 5 min , the mixture was refluxed at 453 k for 3 h to produce a colloidal solution of “ unprotected ” pt — ru alloy nanoclusters , wherein the total metal concentration of pt — ru is 5 . 92 g / l . an aqueous solution of ammonia ( 10 %) was added dropwise into a solution of fecl 3 in 2 . 5 ml of water ( 10 mol / l ) to adjust the ph value to about 7 . 5 , after ageing for 5 min the produced precipitate of ferric hydroxide was then filtered , washed to remove cl − , and peptized in 30 ml aqueous solution of fecl 3 ( 1 mol / l ) by stirring and slightly heating , resulting in a colloidal solution of ferric hydroxide , which was kept at room temperature for utilization . 1 . 65 ml of the pt — ru alloy colloidal solution was added into the ferric hydroxide colloidal solution under stirring . the mixture was then heated in a teflonlined autoclave at 393 k for 72 h . a black precipitate was produced , which was filtered , washed , dried and oxidized at 393 k in air for 48 h to produce the pt — ru / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / ru molar ratio of 1 : 1 . preparation of pt — ir / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / ir molar ratio of 1 : 1 0 . 5179 g of h 2 ptcl 6 . 6h 2 o and 0 . 2986 g of ircl 3 . 3h 2 o were dissolved into 50 ml glycerol , followed by the addition of 50 ml glycerol solution containing naoh ( 0 . 6 mol / l ). after stirring at room temperature for 5 min , the mixture was refluxed at 453 k for 3 h to produce a colloidal solution of “ unprotected ” pt — ir alloy nanoclusters , wherein the metal total concentration of pt — ir is 3 . 87 g / l . an aqueous solution of koh ( 2 %) was added dropwise into a solution of fecl 3 in 25 ml of water ( 1 mol / l ) to adjust the ph value to about 7 . 53 after ageing for 5 min , the produced precipitate of ferric hydroxide was then filtered , washed to remove cl − , and peptized in 30 ml aqueous solution of fecl 3 ( 4 %) by stirring at room temperature , resulting in a colloidal solution of ferric hydroxide . 2 . 52 ml of the pt — ir alloy colloidal solution was added dropwise into the ferric hydroxide colloidal solution under stirring . the mixture was then heated in a teflonlined autoclave at 353 k for 72 h . a black precipitate was produced , which was filtered , washed to remove cl − , dried and oxidized at 423 k in air for 48 h to produce the pt — ir / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / ir molar ratio of 1 : 1 . preparation of rh / γ - fe 2 o 3 nanocomposite with 1 wt . % of rh loading replacing h 2 ptcl 6 . 6h 2 o in example 1 with rhcl 3 . 3h 2 o of the same molar content , and using the same preparation method to produce the rh / γ - fe 2 o 3 nanocomposite containing 1 wt . % of rh . preparation of pt — pd / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / pd molar ratio of 4 : 1 replacing rucl 3 . 3h 7 o in example 9 with pdcl 2 . xh 2 o , keeping the pt / pd molar ratio to be 4 : 1 , and using the same preparation method to produce the pt — pd / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / pd molar ratio of 4 : 1 . heating the red - brown pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt prepared in example 1 at 333 k under hydrogen for 60 min to produce a black pt / magnetic iron oxide nanocomposite . raman analyses revealed that the obtained nanocomposite consisted of γ - fe 2 o 3 and fe 3 o 4 . selecting two or several kinds of soluble salts of pt , rh , ru , ir , os and pd , and adopting the similar methods as described in example 1 - 13 , can prepare nanocomposite materials composed of alloy nanoclusters of the selected transition metals and the magnetic iron oxides nanoparticles . the nanocomposite materials composed of transition metal nanoclusters and magnetic iron oxides nanoparticles according to the present invention exhibited high catalytic activity , excellent stability and superior selectivity in the hydrogenation of chlorine -, bromine -, and iodine - substituted aromatic nitro compounds ( such as halonitrobenzenes and halonitrobiphenyl containing several kinds of substituted groups ) to the corresponding aromatic haloamines . over the invented nanocomposite catalysts , the selectivities to the corresponding aromatic haloamines can reach a level higher than 99 . 9 % at 100 % conversion of the aromatic halonitro compounds . it should be pointed out that even when the aromatic halonitro compounds were completely exhausted in these catalytic reactions , the coexistence of the present nanocomposite catalysts and the aromatic haloamines products under 0 . 1 - 4 . 0 mpa of hydrogen pressure will not cause the decrease in the selectivity to the desirable products . in other words , over these nanocomposite catalysts , the hydrodehalogenation side reactions in the catalytic reactions of interest are complete inhibited . due to the fully suppression of the dehalogenation side reaction , the hydrogenation of the aromatic halonitro compounds can be conducted rapidly and completely under elevated hydrogen pressure , actualizing the aim of efficiently producing the corresponding aromatic haloamines with a high purity . meanwhile , the separation process of the reaction products is also facilitated . the magnetic or super - paramagnetic property of the nanocomposite catalysts provides a convenient route for separating the catalysts from the reaction systems in an applied magnetic field . in typical catalytic hydrogenation experiments , the invented magnetic transition metal - iron oxides nanocomposite materials were dispersed in suitable volume of organic solvents , activated under hydrogen ambience . then organic solutions of the aromatic halonitro compound were added into the reactor to start the reaction . the obtained products were analyzed by gas chromatography ( gc ). after the reaction was complete , the catalyst was separated from the reaction system in an applied magnetic field and washed before reusing in the next cycle of the reaction . the catalyst separation can also be conducted by the conventional methods such as filtration or centrifugation . the reaction temperature was in a range from 273 to 393 k , and the pressure of hydrogen ranged from 0 . 1 to 10 mpa . the reaction was carried out in a 50 - ml reactor with magnetic stirring at 333 k . prior to the reaction , air in the system was replaced by hydrogen . 0 . 2 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt prepared in example 1 was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of a methanol solution containing 13 . 0 mmol of o - cnb was added into the reactor to start the reaction . the products were analyzed by gc . 0 . 05 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt and 13 . 0 mmol of o - cnb were added into 25 ml of methanol in an autoclave , then the reaction was conducted at 333 k under 2 . 0 mpa of hydrogen pressure . the products were analyzed by gc . 0 . 05 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt and 13 . 0 mmol of o - cnb were added into 25 ml of methanol in an autoclave , then the reaction was conducted at 333 k under 4 . 0 mpa of hydrogen pressure . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 1 . 0 . 2 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of p - cnb was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 2 . after the reaction was complete , the catalyst was separated from the reaction system in an applied magnetic field , washed with methanol , and reused in the next cycle of reaction without obvious change in the catalytic properties . 0 . 10 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of 2 , 4 - dncb was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 3 . 0 . 04 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was added into 100 ml of methanol solution containing o - bnb ( 0 . 10 mol / l ), then the reaction was conducted at 303 k under 3 . 6 mpa of hydrogen pressure . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 4 . 0 . 15 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of thf , and activated at 303 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 10 ml of thf solution containing p - inb ( 0 . 15 mol / l ) was added into the reactor . the reaction was conducted at 303 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 5 . 0 . 2 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of 3 , 4 - dcnb was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 6 . 0 . 2 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of 2 - chloro - 6 - nitrotoluene was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 7 . 0 . 2 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of methyl 4 - chloro - 3 - nitrobenzoate was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 8 . 0 . 2 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 30 ml of methanol solution containing 1 . 27 mmol of 4 - chloro - 3 - nitro - methoxybenzene was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 9 . 0 . 2 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of thf , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 30 ml of thf solution containing 1 . 27 mmol of 4 - chloro - 3 - nitro - diphenyl was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 10 . 0 . 2 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of toluene , and activated at 383 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 30 ml of toluene solution containing 1 . 27 mmol of 4 - chloro - 3 - nitro - 4 ′- methyldiphenyl was added into the reactor . the reaction was conducted at 383 k under vigorous stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 11 . 0 . 2 g of the pt / γ - fe 2 o 3 nanocomposite containing 1 wt . % of pt was dispersed in 5 ml of thf , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 50 ml of thf solution containing 1 . 27 mmol of 4 - chloro - 3 - nitro - 4 ′- methyl - 3 ′- nitro - diphenyl was added into the reactor . the reaction was conducted at 333 k under vigorous stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 12 . 0 . 1 g of the pt / magnetic iron oxides nanocomposite containing 3 wt . % of pt prepared in example 7 was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of p - cnb was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 13 . 0 . 2 g of the pt / magnetic iron oxides nanocomposite prepared in example 13 was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of m - cnb was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 14 . 0 . 2 g of the pt — pd / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / pd molar ratio of 4 : 1 prepared in example 12 was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of p - cnb was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 15 . 0 . 2 g of the pt — ru / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / ru molar ratio of 1 : 1 prepared in example 9 was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of p - cnb was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 16 . 0 . 2 g of the pt — os / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / os molar ratio of 20 : 1 prepared by the same method described in example 9 was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of p - cnb was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 17 . 0 . 2 g of the pt — ir / γ - fe 2 o 3 nanocomposite with 1 wt . % of metal loading and a pt / ir molar ratio of 1 : 1 prepared in example 10 was dispersed in 5 ml of methanol , and activated at 333 k under 0 . 1 mpa of hydrogen pressure for 30 min , then 20 ml of methanol solution containing 1 . 27 mmol of p - cnb was added into the reactor . the reaction was conducted at 333 k under vigorously stirring . the products were analyzed by gc . the catalytic activity and selectivity over the catalyst are listed in table 18 . the experimental results of this section show that , the nanocomposite catalysts according to the present invention possess high catalytic activity and superior selectivity for the hydrogenation of aromatic halonitro compounds to the corresponding aromatic haloamines . the hydrodehalogenation side reaction is fully inhibited successfully over the invented nanocomposite catalysts , indicating that these catalysts can be used for efficiently producing aromatic haloamines with a high purity . in virtue of the catalytic function of the metal nanoclusters , the present invention succeeded in preparing a new kind of magnetic transition metals - iron oxides nanocomposite materials at relative low temperature . the main features of the preparation method according to the present invention are first to prepare the colloidal solutions of “ unprotected ” transition metal or alloy nanoclusters , which are then mixed with the colloidal solutions of ferric hydroxide nanoparticles to form complex sols , followed by the heat treatment in the presence of reductants , such as alcohol , aldehyde and glycolic acid . the obtained products are washed , dried or oxidized to produce the said nanocomposite materials composed of the transition metal nanoclusters and magnetic iron oxides nanoparticles . the invented nanocomposite materials composed of transition metal nanoclusters and magnetic iron oxides nanoparticles can catalyze the hydrogenation of aromatic halonitro compounds to aromatic haloamines with very high selectivity . the hydrodehalogenation side reaction in the hydrogenation of aromatic halonitro compounds to aromatic haloamines was fully suppressed for the first time over the present nanocomposite catalysts . moreover , due to the two or more functional components and the cooperative effect between the nanoparticles , the invented nanocomposite materials are of great value for application in the fields of catalyst , magnetic separation , wave - absorption materials , etc .