Application Of Carbon Nitrogen Material Supported Palladium Nanoparticles For Acetylene Dicarbonylation

In the context of the world’s petrochemical resource scarcity and China’s special energy structure,the development of new chemical synthesis routes through coal chemical industry is a feasible solution to alleviate the tension of traditional petroleum resources.Dimethyl butenedioate（dimethyl maleate,dimethyl fumarate）,an important intermediate chemical,can be prepared by using C₂H₂ and CO produced by coal chemistry to perform a dicarbonylation reaction at a lower temperature.Dimethyl maleate can be hydrogenated to synthesize chemicals such as 1,4-butanediol,which is further used to produce end products such as biodegradable plastics,spandex and lithium.Therefore,the use of acetylene bicarbonylation to synthesize dimethyl butenedioate is of great significance to China’s coal chemical downstream to open up new paths and alleviate energy tension,etc.The transition metal Pd is the main active metal in the acetylene bicarbonylation reaction and has good catalytic activity at lower temperatures.Homogeneous Pd catalysts have more problems such as recycling and addition of acid additives.Non-homogeneous catalysts are still less explored and mainly focus on the improvement of catalytic activity and stability of Pd.The use of carrier-limited structures,non-metallic and metallic element additions can not only prepare non-homogeneous catalysts,but also improve the catalytic activity,prevent the loss and agglomeration of active metal nanoparticles,and facilitate further interpretation of the catalytic reaction mechanism.Based on this,a series of monometallic and bimetallic catalysts are prepared in this paper using restricted domain structures,with the following main studies:（1）Using stable carbon nitride as a carrier,the hollow tubular structure with carbon defects is further calcined by regulating the hydrothermal temperature and time.The use of tubular carbon nitride as catalyst carrier enhances the catalyst reaction activity and stability by taking advantage of the mass transfer efficiency and domain-limiting effect of the tubular structure.The results show that the carbon nanotubes containing carbon defects can make the Pd nanoparticles uniformly dispersed on the carrier surface and within the pore structure,and the catalyst Pd/CNMT-500 has better catalytic activity and can reach 83.7%initial selectivity compared with the ordinary layer block carbon nitride.（2）Different nitrogen-containing compounds were used to cooperate with Pd as precursors,which were impregnated and calcined at high temperature to form a thin carbon-nitrogen shell layer on the surface of carbon nanotubes encapsulating the restricted domain structure of Pd nanoparticles.The catalytic activity of the catalysts calcined at 900°C was significantly higher,and the characterization indicated that more high-valent Pd would be formed at this temperature.The initial selectivity of the loaded catalyst with Pd-aniline complexes as precursors reached 83.7%.Using the formed carbon and nitrogen shell layer to prevent the dissolution loss of Pd nanoparticles,the selectivity was 63%of the initial selectivity after three uses.（3）The non-precious metal Fe was co-impregnated with Pd nitrogen to successfully synthesize the ordered PdFe alloy nanoparticles with carbon and nitrogen shell layer protection on the carrier.Using bimetallic stability and unique electronic properties,the in situ formation of carbon and nitrogen shells can prevent the agglomeration of ordered PdFe nanoparticles.The results show that the ordered structure of PdFe nanoparticles can promote the acetylene bicarbonylation reaction,and the initial selectivity of the reaction reaches 98.9%,and the activity of the reaction 3 times is 71.4%.