Preparation And Modification Of Nickel-based Catalyst For 2,2’-Bipyridine Reaction By Dehydrogenation Of Pyridine

2,2’-Bipyridine is a kind of important intermediates in modern chemical production,it has been widely applied in redox indicator,photosensitizer,supercritical CO₂ extraction,chemical copper plating,and other fields.Diquat synthesised by 2,2’-Bipyridine is the most widely promising herbicide in application market.The development of efficient 2,2’-Bipyridine production technology is the key to reduce the fast production cost of diqua,and the safest and greenest route to synthesize 2,2’-Bipyridine is direct dehydrogenation with pyridine,which is as raw material.Therefore,the development of a catalyst with high yield,low cost,low pollution and no operational risk to catalyze the direct coupling of pyridine into 2,2’-Bipyridine has important economic value and market prospect.In this paper,mesoporous alumina was selected as the carrier to investigate the effects of different active component precursors and catalytic auxiliaries on catalytic activity,catalytic stability,surface acidity and alkalinity of the catalyst,and some results were obtained.Specifically,the following three aspects are studied:（1）A short clavite mesoporous alumina carrier was prepared,and different NiO/Al₂O₃samples with same nickel content were successfully synthesized through dipping,drying,roasting by using three different kinds of nickel-based precursor materials（nitrate hexahydrate nickel,nickel acetate tetrahydrate,nickel carbonate（Ⅱ）hydrate）,respectively:NiO-N,NiO-AC and NiO-C.XRD,SEM,TEM,H₂-TPR,BET,XPS and other test methods were used to characterize the samples,and they were reduced to Ni/Al₂O₃by hydrogen in a fixed-bed reactor,which were Ni-N,Ni-AC and Ni-C,respectively.They were used in the synthesis of 2,2’-Bipyridine by dehydrogenation of pyridine to analyze the product yield and catalytic stability.The experimental results show that the catalysts synthesized by impregnating alumina with different nickel-based precursors had different catalytic effects,among which the Ni-C catalyst has the best product yield and catalytic stability,the highest activity was shown at 2 h（the yield of 2,2’-bipyridine was 5.6%）,the yield was 0.3%at 30 h.This is attributed to the high specific surface area and low temperature reduction of Ni-C on the carrier.The optimum reaction conditions were discussed on the basis of Ni-C catalyst,that is,reaction temperature is 200℃,pressure is 0.8 MPa.（2）In order to further improve the product yield and catalytic stability,on the basis of Ni-C,the typical rare earth metal Ce was selected to modify the catalyst,and the influence of rare earth metals on the catalytic performance was explored.Three NiO-Ce O₂/Al₂O₃ samples with different modification degrees were successfully prepared,namely,NiO-3Ce O₂/Al₂O₃、NiO-5Ce O₂/Al₂O₃ and NiO-10Ce O₂/Al₂O₃.XRD,SEM,TEM,H₂-TPR,BET,XPS and other test methods were used to characterize the samples,and they were reduced to Ni-Ce/Al₂O₃by hydrogen in a fixed-bed reactor,which were Ni-3Ce/Al₂O₃、Ni-5Ce/Al₂O₃ and Ni-10Ce/Al₂O₃,respectively.They were used in the synthesis of 2,2’-Bipyridine by dehydrogenation of pyridine to analyze the product yield and catalytic stability.The experimental results show that Ce improves the dispersion and pore structure performance of NiO on the carrier.In addition,an appropriate amount of Ce weakens the interaction between NiO and alumina,thus improving the low-temperature reduction ability of samples and significantly increasing the activity of catalysts.Finally,different Ce modification amounts have different effects on the catalytic effect of catalysts,among which the product yield and catalytic stability of Ni-5Ce/Al₂O₃catalyst is the best,the highest activity was shown at 2 h（the yield of 2,2’-bipyridine was 9.0%）,the yield was 1.7%at 30 h.（3）In order to modify Ni-5Ce/Al₂O₃ from the p H adjustment of the catalyst,two alkali metals Na and K were selected as auxiliary agents to successfully prepare four NiO-Ce O₂-Na₂O/Al₂O₃ and NiO-Ce O₂-K₂O/Al₂O₃ samples with different modification degrees,namely,NiO-Ce O₂-1Na₂O/Al₂O₃,NiO-Ce O₂-2Na₂O/Al₂O₃,NiO-Ce O₂-1K₂O/Al₂O₃ and NiO-Ce O₂-2K₂O/Al₂O₃.XRD,SEM,TEM,H₂-TPR,NH₃-TPD,BET,XPS and other test methods were used to characterize the samples,and they were reduced to Ni-Ce-Na₂O/Al₂O₃ and Ni-Ce-K₂O/Al₂O₃by hydrogen in a fixed-bed reactor,which were Ni-Ce-1Na₂O/Al₂O₃、Ni-Ce-2Na₂O/Al₂O₃、Ni-Ce-1K₂O/Al₂O₃ and Ni-Ce-2K₂O/Al₂O₃,respectively.They were used in the synthesis of 2,2’-Bipyridine by dehydrogenation of pyridine to analyze the product yield and catalytic stability.The experimental results show that the introduction of an appropriate amount of alkali metal modifier reduce the acidity of the sample,improve the dispersion of NiO,maintain a large specific surface area,and significantly increase the activity of the catalyst.However,the addition of too much alkali metal will cause the collapse of the pore structure of the carrier,resulting in a decrease in the catalytic activity.Different alkali metal auxilaries and different amount of auxilary modification have different effects on the catalytic effect of the catalyst.The Ni-Ce-1K₂O/Al₂O₃ catalyst shows the best effect in the two aspects of product yield and catalytic stability,the highest activity was shown at 2 h（the yield of 2,2’-bipyridine was 13.5%）,the yield was 2.4%at 30 h.