K促进的Fe/椰壳炭催化剂对甲烷氮气常压合成氨性能的影响

Promoting Effect of Potassium on the Performance of Iron / cocoanut-char Catalyst in Direct Synthesis of Ammonia from Methane and Nitrogen at Atmospheric Pressure

采用等体积浸渍法制备了一系列催化剂用于甲烷氮气常压合成氨反应.对Si O2、γ-Al2O3、煤质柱状炭、椰壳活性炭为载体的Fe基催化剂的活性评价结果显示椰壳炭载体最优;通过对Zr、Ce、K等多种助剂的筛选,发现K促进的Fe基催化剂氨生成速率最高.利用XRD、SEM、BET等手段对载体和催化剂进行表征,结果表明椰壳炭具有规则孔道且孔容增大,催化剂还原后有新晶相KFe O2生成.最后在固定床微分反应器中,考察了常压合成氨催化剂的负载顺序及最优工况.结果表明,在常压700℃、VCH4/VN2=2/1、空速为2 800 m L/h时,催化剂3%K-5%Fe/椰壳炭的氨生成速率最高可达1.04×10-6mol·g-1·s-1,是现有文献值的83.5倍,将具有深远的工业应用前景.

A series of catalysts used for synthetic ammonia from methane and nitrogen at atmospheric pressure were prepared by the fractional wetness impregnation method. Based on the performance comparisons of iron catalysts a mong different supports,the coconut shell activated carbon displayed an excellent catalytic activity than Si O2,γ-Al2O3,and columnar carbon. Through the promoter selection experiments such as Zr,Ce and K,we found that the K promoted iron catalyst has the highest synthetic ammonia rate. XRD,SEM,and BET were carried out to characterize the supports and catalysts,and the results showed coconut shell activated carbon has the most uniform pore distribution with outstanding increase of average pore volume. A crystalline phase of KFe O2 was generated after the catalyst reduction. The optimal loading sequence and working conditions of synthetic ammonia catalysts were investigated in a fixed bed differential reactor. Experimental results prove that atmospheric pressure,700 ℃,VCH4/VN2= 2 /1,flow rate of 2 800 m L / h,3% K-5% Fe / cocoanut-char can achieve the most favorable synthetic ammonia rate of 1. 04 × 10- 6mol·g- 1·s- 1,which is 83. 5 times higher than current literature and would foresee an extensive prospects of industrial application in the future.