材料期刊网

用动态热重技术和色谱技术联用以及XRD和TEM等表征手段,研究了Ni/γ-Al2O3催化剂 上甲烷-二氧化碳重整体系的积碳和消碳及其与一氧化碳产率之间的关系. 结果表明,二氧 化碳与甲烷有不同的活性中心,二氧化碳的存在不改变甲烷活化积碳的本质,但可通过及时将 表面含碳物种转化为一氧化碳而降低积碳速率. 二氧化碳能消去活泼的须状碳,但不易消去 惰性的石墨碳. 等摩尔条件下二氧化碳消碳能力弱于甲烷活化积碳,二氧化碳适度过量可有 效抑制积碳,n(CO2)/n(CH4)≈1.3为进料比最佳值 ,此时积碳-消碳达到动态平衡,可获得最高的一氧化碳产率和较低的积碳速率,且该值不受 温度影响. Ni/γ-Al2O3催化剂有很强的再生能力,但反复积碳-消碳会使催化剂镍晶 粒度增大,分散度下降,从而导致不可逆失活.

The carbon deposition and carbon elimination during CH4 reforming with CO2 o ver Ni/γ-Al2O3 catalyst were investigated by means of TGA, XRD and TEM tec hniques. The yield of CO was also detected by an on-line chromatograph. The res ults showed that the activation of CH4 over Ni/γ-Al2O3 catalyst is diffe rent from that of CO2, and its inherent law can not be substantially changed i n the presence of CO2. However, the rate of decomposition of CH4 could be pr omoted by carbonaceous deposit from CH4 converted to CO by the dissociation of CO2. Correspondingly, the rate of carbon deposition dramatically decreased. W hen the feed stock of CH4 is equal to CO2, the rate of carbon elimination by CO2 is less than that of carbon deposition by CH4, but much more CO2 woul d inhibit carbon deposition, as well as the activation of CH4. Therefore, ther e is an optimum feed ratio of n(CO2)/n(CH4)=1.3, which seems to be unchanged with temperature. In this way, carbon depo sition and carbon elimination may be in balance and lead to maximum CO yield and low rate of carbon deposition. The Ni/γ-Al2O3 catalyst has very high capa city of carbon deposition, and is easily regenerated by carbon elimination, but the regeneration for many times leads to the growth of Ni particles, as a result , the catalytic activity decreases irreversibly.