Study On Copper-Based Nanocatalyst For Synthesis Of Iminodiacetic Acid

Iminodiacetic acid is the main raw material of herbicide glyphosate and a widely used chemical intermediate.Iminodiacetic acid?IDA?was mainly produced by diethanolamine?DEA?method with Cu-ZrO₂ as catalyst.Although the Cu-ZrO₂catalyst has good catalytic activity and low cost in the synthesis of IDA,there are problems such as poor anti-coking property,large consumption,fast deactivation and short catalytic life.These disadvantages can be attributed to the ZrO₂ tending to aggregate into a block shape,resulting in a small specific surface area,a small active site,and the inability to disperse the copper component.Therefore,it is necessary to select carriers with large specific surface area and special structure to prevent the oxidation of copper components.Reduced graphene oxide?rGO?,with its excellent physicochemical properties and special pleated sheet structure,is widely used in the synthesis of composite materials;At the same time,the hollow ball material becomes an excellent carrier material because of its high specific surface area and special structure.In this paper,a series of Cu-ZrO₂/rGO composite catalysts with different preparation conditions?addition amount of hydrazine hydrate,reduction temperature,reduction time,molar ratio of copper to zirconium,GO content,precipitation temperature,precipitation pH value and hydrothermal temperature?were prepared by chemical reduction method.The crystal shape,specific surface area,pore volume,pore diameter,surface functional groups,morphology and structure were studied by XRD,N₂ physical adsorption desorption,FT-IR,SEM,etc.The catalytic performance of the catalyst was investigated by dehydrogenation of DEA.The results showed that the IDA yield of Cu-ZrO₂/rGO composite catalyst reached 97.6%,and the yield remained at 90%after 10 cycles,indicating that the introduction of rGO contributed to the improvement of catalytic activity and service life of the catalyst.At the same time,the preparation conditions have great influence on the structure and properties of the catalyst.The optimal preparation conditions are:copper hydrazine oxime molar ratio of 1:4,reduction temperature of 50°C,reduction time of 40 min,copper-zirconium molar ratio of 1:1,GO content was 4%of copper salt quality,the precipitation pH value was 10-12,precipitation temperature of 30°C,and hydrothermal temperature was 180°C.Secondly,two kinds of Cu-ZrO₂ hollow nanosphere catalysts with different particle sizes were prepared by one-step impregnation and two-step impregnation with hard template method.Meanwhile,The third Cu-ZrO₂ hollow nanosphere catalyst was prepared by hydrothermal method.The Cu-C catalyst was prepared by precipitation method.The structures of several catalysts were analyzed by various characterization methods.The results show that:By changing the block structure of Cu-ZrO₂ into a hollow ball structure,the catalyst not only reached the nanometer level,but also greatly increased the specific surface area.Compared with the specific surface area of the traditional Cu-ZrO₂ catalyst of 50-120 m²/g,the specific surface area of the Cu-ZrO₂ hollow nano-sphere catalyst prepared by one-step impregnation and distributed impregnation method were up to 459-672 m²/g and 370-373 m²/g,and the yield of IDA in DEA dehydrogenation synthesis was the highest of 90.8%and 96.9%,respectively.The IDA yield of Cu-ZrO₂ hollow nano-catalyst prepared by hydrothermal method was 92.3%.The results showed that the active components supported by hollow ball carrier had good catalytic activity.