Supported Potassium Oxide Catalyst For Dehydration Of 2-picolinamide To Form 2-cyanopyridine

The direct synthesis of dimethyl carbonate from CO₂ and methanol provides a pathway for the utilization of greenhouse gas CO₂.Dimethyl carbonate is a high-value industrial chemical.The only by-product is water for reaction of CO₂ and methanol.Therefore,this reaction has great application value.However,the yield of dimethyl carbonate is rather low due to the equilibrium limitation.2-cyanopyridine which acted as efficient dehydration agent by in situ hydrolysis can improve DMC yield remarkablely.Meanwhile,in terms of lowering production cost,it is also desirable for the regenaration of the 2-cyanopyridine by dehydrating 2-picolinamide.This paper mainly focused on the effect of catalyst preparation conditions and structure stability of molecular sieve on catalytic performance of dehydration of 2-picolinamide to2-cyanopyridine over K₂O/SiO₂ and K₂O/MCM-41.Catalytic dehydration of 2-picolinamide to 2-cyanopyridine over K₂O/SiO₂ was investigated.Precursor K₂CO₃ reacted with free Si-OH groups to generate medium basicity Si-O-K during the calcination process.The yield of 2-cyanopyridine showed linear relationship with the amounts of medium basicity of the K₂O/SiO₂ catalyst,and the yield of 2-cyanopyridine increased with the increase in the amounts of medium basicity,which indicated that Si-O-K was the active site for catalytic dehydration of2-picolinamide to 2-cyanopyridine.The amount of free Si-OH was adjusted by silylation and hydroxylation procedure.For hydroxylated silica,the medium basicity increased with the increase of free silanol which contributed to the higher catalyst activity.The yield of 2-cyanopyridine reached 26.3%with the catalyst loaded on hydroxylated silica.For silylated silica,the decreased free Si-OH led to the fewer medium basicity and hence lower catalyst activity.The dehydration of 2-picolinamide to 2-cyanopyridine was catalyzed by K₂O/MCM-41.The pore structure of K₂O/MCM-41 catalyst collapsed during calcination,hence the catalyst had ranther low activity.Restructured MCM-41 by secondary synthesis and MCM-41 modification with NO₃^-and Cl^-anions during synthesis were carried out to improve structure stability of MCM-41.XRD,TEM and N₂ adsorption results indicated both Recrys-MCM-41 and MCM-41-anion exhibited higher structure stability.The improved structure stability of recrys-MCM-41 was attributed to the increase of wall thickness.The structure stability of MCM-41-NaCl and MCM-41-NaNO₃ was improved owing to the formation of thicker pore wall and reduction of the amount of Si-OH.K₂O catalysts loaded on modified MCM-41 had favorable catalytic performance for the synthesis of 2-cyanopyridine.The highest2-cyanopyridine yield of 37.6%was achieved with K₂O/MCM-41-NaNO₃ catalyst.