Ni-Co双金属催化剂上沼气重整制氢机理

摘要

用传统湿式浸渍法制备了La2O3掺杂的商业γ-Al2O3负载的沼气重整催化剂Ni-Co/La2O3-γ-Al2O3,并用程序升温加氢(TPH)、程序升温氧化(TPO)、程序升温表面反应(TPSR)、程序升温脱附(TPD)及脉冲实验对催化剂进行了表征.结果表明,沼气重整过程中Ni-Co/La2O3-γ-Al2O3催化剂上的表面碳物种主要来源于CH4的裂解,CO2的贡献很小.CH4裂解能够产生三种活性不同的碳物种,即Cα、Cβ与Cγ.随着反应的进行,Cα物种减小而Cβ与Cγ物种增加,且Cγ物种能够转变为惰性的石墨碳.重整反应过程中CH4与CO2的活化能相互促进.催化剂表面的O物种与C反应生成CO或与CHx反应生成CHxO再分解为CO与吸附态的H物种,可能是Ni-Co/La2O3-γ-Al2O3催化剂上沼气重整的速率控制步骤.%Ni-Co bimetallic catalysts supported on commercial γ-Al2O3 modified with La2O3 were prepared by conventional incipient wetness impregnation for biogas reforming. The catalysts were characterized using temperature-programmed hydrogenation (TPH), temperature-programmed oxygenation (TPO),temperature-programmed surface reaction (TPSR), tempereature-programmed desorption (TPD), and a pulse experiment. During biogas reforming the surface carbon species on Ni-Co/La2O3-γ-Al2O3 originated mainly from the cracking of CH4 and the contribution of CO2 was insignificant. Cracking of CH4 results in three carbon species of Cα, Cβ, and Cγ, which have different reaction activities. During the reaction, the amount of Cα decreased but Cβ and Cγ increased. In addition, Cγ could be changed into inactive graphite carbon. The activation of CH4 and CO2 was mutually promoted in the reforming reaction. It was revealed that the controlling step for biogas reforming over the Ni-Co/La2O3-γ-Al2O3 catalyst could be the reaction of the surface species of O with C to form CO or with CHx to give CHxO followed by the formation of CO and adsorbed H.