Selective Liquid-phase Oxidation Of Benzyl Alcohol In Copper-iron Co-catalysis System

The liquid-phase oxidation of benzyl alcohol?BzOH?with H₂O₂ in H₂O is a simple,green process to produce high quality chlorinee-free benzaldehyde?Bz H?.Cu and Fe are two kinds of abundant non-precious metal elements in the earth's crust,the copper-iron bimetal can synergistically activate H₂O₂ to form·OH to oxidize organic compounds.However,there are few reports on oxidation of benzyl alcohol to benzaldehyde with H₂O₂ over copper-iron bimetallic catalysts.In this paper,the selective oxidation of benzyl alcohol was used as the target reaction.Different copper-iron catalysts were synthesized,and their catalytic activities were evaluated for selective oxidation of benzyl alcohol.The catalytic performance of copper/iron were compared to reveal the synergistic effects and possible mechanism between copper and iron.The main research contents are as follows:1.Instead of using expensive and complex organic ligands,simple copper-iron salts solutions were directly used as catalysts.CuCl₂/FeCl₃ salt solutions were choosen to test and compare the catalytic performance of copper/iron single component?conversion of Bz OH:8.4%?Cu Cl₂?,6.5%?FeCl₃?,35.5%?CuCl₂/FeCl₃??,the catalytic activity of CuCl₂/FeCl₃ salt solution system increased by 20.6%compared with the catalytic activity of CuCl₂ and FeCl₃alone,indicating that Cu²⁺ and Fe³⁺showed obvious synergistic effects.Adding liquid/solid acid such as HCl or H₂SO₄ or Hydrogen type zeolite A?HA?to CuCl₂/FeCl₃ salt solution system,the catalytic performance of the mixed system is significantly improved,indicating that HCl,H₂SO₄ and HA play a promoter role.Through the free radical quenching experiment,it was found that the oxidation of benzyl alcohol was a free radical oxidation reaction in the catalytic system of CuCl₂/FeCl₃ mixed salt solution.By correlating XRD,BET characterization and acid amount determination of HA with catalytic activity,it was found that the promoter effect of HA may be related to a large amount of hydroxyl groups in the aluminum species?acid amount:0.41 mmol/g?,which could adsorb the benzaldehyde to increase catalytic activity.2.The copper-iron supported catalyst CuO_x-Fe Oy/NH₄A was successfully synthesized by solid-phase ion exchange method,and characterized by XRD,EDX and BET.It was found that copper and iron were uniformly dispersed on the surface of CuO_x-FeO_y/NH₄A.The cyclic catalytic performance of CuO_x/NH₄A,FeO_y/NH₄A and CuO_x-Fe O_y/NH₄A were investigated.It was found that the catalytic activity of CuO_x/NH₄A?36.03%?is close to that of CuO_x-Fe O_y/NH₄A,and CuO_x-FeO_y/NH₄A can be recycled three times without significant loss of activity.However,CuO_x/NH₄A could not be recycled,indicating It indicates that the introduction of iron component in CuO_x-Fe O_y/NH₄A sample has little effect on the activity of supported copper catalyst,but it is beneficial to improve the stability of the catalyst.The reaction parameters of the catalyst prepared by solid-phase ion exchange method were investigated,it was found that the ion exchange temperature was 350°C,ammonia type zeolite A was used as the support,and the molar ratio of copper to iron was 1:1,CuO_x-FeO_y/NH₄A showed the highest catalytic activity?with a 36.85%conversion of benzyl alcohol?.Based on the experimental results and literature investigation,it is speculated that the Cu²⁺ Lewis acidic site is the active site for oxidation of benzyl alcohol with H₂O₂.3.Cu-modified Fe₂O₃ was successfully prepared by pyrolysis of copper/iron-containing PVP gel at high temperature.Cu-modified Fe₂O₃ was characterized by XRD,SEM and BET,and it was found that Cu-modified Fe₂O₃ sheets were obtained.The catalytic activities of Cu O and Fe₂O₃ and 0.05 mol% Cu-Fe₂O₃ under the same reaction conditions were investigated?Cu O:23.9%,Fe₂O₃:4.2%,0.05 mol% Cu-Fe₂O₃:57.9%?,and 0.05 mol%Cu-Fe₂O₃ catalyst exhibits a significant synergistic effect in enhancing catalytic activity?the catalytic activity of 0.05 mol% Cu-Fe₂O₃ is 29.8% higher than the sum of activity of CuO and Fe₂O₃?28.1%??.Through the investigation of the molar ratio of copper to iron and the reaction parameters,it was found that 0.05 mol% Cu-Fe₂O₃ exhibited higher catalytic activity and selectivity under the optimal reaction conditions?with a 54.0% conversion of benzyl alcohol and a 83.5%selectivity of benzaldehyde?.The cyclic catalytic performance of 0.05 mol% Cu-Fe₂O₃ catalyst was investigated.It was found that 0.05 mol%Cu-Fe₂O₃ catalyst can be reused four times without significant loss of activity.The decomposition ability of H₂O₂ with 0.05 mol%Cu-Fe₂O₃ and Fe₂O₃was studied by decomposition experiment of H₂O₂.It was found that the ability of decomposing H₂O₂ after Cu modifying was significantly enhanced(rate constant:0.741 h^-1 vs 0.183 h^-1),and the activation energy Ea of catalytic decomposition of H₂O₂ was reduced from 64.93 k J/mol to 55.45 k J/mol after Cu modifying,which explained improved catalytic activity of Fe₂O₃ after Cu modifying.