Selective Catalytic Oxidation Of Chlorotoluene To Prepare Chlorobenzaldehyde

The chlorobenzaldehyde is an important intermediate for the synthesis of dyes,agricultural chemicals and pharmaceuticals.Chlorobenzaldehyde can be synthesized by chlorinated hydrolysis,electrochemical oxidation and direct oxidation.The chlorobenzaldehyde is almost exclusively produced by side-chain chlorination of chlorotoluene followed by acid hydrolysis.In industry,this process has insurmountable disadvantages of complex process,unmanageable chlorination degree,high production cost,severe environmental pollution.Recently,the direct oxidation of chlorotoluene to chlorobenzaldehyde with O2 as a promising alternative method due to its simple reaction procedure and pollution free feature.In this paper,(Co,Mn)(Co,Mn)2O4 spinel composite oxide was synthesized by solid-state synthesis and used as catalyst by liquid-phase catalytic oxidation of o-chlorotoluene.Furthermore,series metal supported heteroatom M-MCM-41 catalysts(M=Ti,Co,Mn)were prepared and used for the liquid phase catalytic oxidation of o-chlorotoluene.1.Preparation,characterization and catalytic performance of(Co,Mn)(Co,Mn)2O4A spinel cobalt-manganese composite oxide catalyst(Co,Mn)(Co,Mn)2O4 was synthesized by solid-state synthesis.The catalysts were characterized by XRD,FTIR,TEM,H2-TPR measurements.The XRD results showed that the cobalt-manganese composite oxide catalyst presents spinel structure,crystallinity was getting better with increasing calcination temperature of the catalyst.FTIR results showed that there were two characteristic absorption peaks in the range of 500-800cm-1 which can be assigned to the spinel structure.TEM results showed that the synthesized catalyst consists of cobalt and manganese composite oxide nano-particles nano-particles.H2-TPR of the composite oxide catalyst displayed three reduction peaks.The effects of reaction temperature,reaction time,the mass ratio of o-chlorotoluene and acetic acid,amount and calcination temperature of catalyst on the conversion of o-chlorotoluene and the selectivity of o-chlorobenzaldehyde were investigated in high pressure autoclave.The best reaction was obtained at molar ratio of Co/Mn=1:2,the mass ratio of catalyst/o-chlorotoluene(g/g)=0.3%,the molar ratio of o-chlorotoluene/acetic acid(g/g)=1.5,the calcination temperature=500?,the reaction time=4h and the reaction temperature=120?.The conversion of o-chlorotoluene and the selectivity of o-chlorobenzaldehyde was 20%and 48%,respectively at the reaction duration of 4h.2.Preparation,characterization and catalytic performance of heteroatom M-MCM-41 supported metal oxideThe mesoporous molecular sieves(M-MCM-41)doped with metal atoms M(M=Ti,Co,Mn)were synthesized by a hydrothermal crystallization method.Using the prepared M-MCM-41 molecular sieve as the support,the active component cobalt manganese was loaded on the support by the impregnation loading method to synthesize a heterogeneous M-MCM-41 supported metal oxide catalyst for the liquid phase catalytic oxidation of o-chlorotoluene.The catalysts were characterized by XRD,TEM,BET,SEM and EDS measutements.The XRD results showed that the synthesized M-MCM-41 presented the characteristic structure of MCM-41.Among them,the degree of ordering of Ti-MCM-41(nSi:nTi=20)was higher than that of Co-MCM-41(nSi:nCo=30)and Mn-MCM-41(nSi:nMn=30).The results showed that the doping amount of Ti in the Ti-MCM-41 became larger and the structure was destroyed.The wide-angle XRD results showed that the corresponding diffraction peaks of crystalline silicon oxide,titanium oxide,cobalt oxide and manganese oxide did not appear,indicating that the doped metal atoms may have entered the framework of the molecular sieve.The BET results showed that the synthesized zeolite presented a large specific surface area.After loading the components,the specific surface area decreased,but still higher,TEM results showed that the molecular sieve structure was clear and the pore size was uniform,the active component was dispersed evenly on the support.The effects of reaction temperature,reaction time,active ingredient loading,catalyst amount,oxygen flow and water addition on the conversion of o-chlorotoluene and the selectivity of o-chlorobenzaldehyde were investigated under normal pressure.The best reaction was obtained at reaction temperature=120?,reaction time=10h,active ingredient loading=6mmol/g,the mass ratio of catalyst/o-chlorotoluene(g/g)=10%,the flow rate of oxygen=50ml/min,the mass ratio of water/acetic acid(g/g)=30%.The conversion of o-chlorotoluene and the selectivity of o-chlorobenzaldehyde was 80%and 63%,respectively at the reaction of 10h.The synthesized(Co,Mn)(Co,Mn)2O4 catalyst and the M-MCM-41 supported metal oxide catalyst having the high activity and selectivity was proposed through systematic investigations in this work,which will give meaningful information of the development of o-chlorotoluene catalytic oxidation process in industry.