酒石酸插层NiMgAl-TA催化剂的制备及其甲烷裂解制氢的催化性能研究

Preparation of tartaric acid intercalated NiMgAl-TA catalyst and its catalytic performance in reaction of methane decomposition to hydrogen

甲烷裂解制氢(CDM)过程具有过程单位能耗低,且不产生碳氧化物排放的优点,为清洁高效制取氢气提供了一条可行技术路线。制备高效稳定镍基催化剂成为该反应研究的重点。采用离子交换法成功制备了酒石酸掺杂NiMgAl-TA类水滑石催化剂,酒石酸分子可均匀分散于水滑石层板间。借助于插层有机碳源的还原性,催化剂可在惰性气氛下焙烧时,发生自还原过程形成具有甲烷裂解催化活性的金属镍粒子。借助XRD、TPR、TEM等多种表征手段对预处理后催化剂性质进行分析,研究了焙烧温度对催化剂自还原过程的影响。结果表明,随着预处理温度的提高,催化剂上镍物种的还原度增加,还原后镍粒子尺寸增大。在甲烷裂解反应中,较低温度下(500℃、600℃)预处理的催化剂具有出色的初始氢气生成速率(241 mmol H2/(gNi·min)、87 mmol H2/(gNi·min)),但是反应中生成了较多的包覆碳,催化剂失活较快。对600℃预处理后的催化剂进行了甲烷裂解反应-再生实验,实验结果表明,催化剂可在多次反再循环中保持活性的稳定。

Production of hydrogen by catalytic decomposition of methane(CDM) has the advantages of low energy consumption and no carbon oxide emission, providing an alternative route for clean and efficient hydrogen production. The preparation of efficient and stable Ni-based catalysts has become the focus of research. In this paper, tartaric acid-doped NiMgAl-TA hydrotalcite catalysts were prepared by the ion-exchange method, in which tartaric acid molecules were evenly dispersed between the layers of hydrotalcite.By virtue of the reducibility of the intercalated organic carbon source, when the catalysts were calcined under an inert atmosphere,the active metal Ni particles were formed through a self-reduction process. The catalysts after pretreatment were characterized by XRD, TPR and TEM, and the influence of calcination temperature on the self-reduction process was investigated. The results showed that with the increase of pretreatment temperature, both the reduction degree of Ni species and the size of Ni particles increased. In CDM reaction, the catalysts pretreated at the lower temperatures of 500 ℃ and 600 ℃ gave the better hydrogen generation rates of241 mmol H2/(gNi·min) and 87 mmol H2/(gNi·min) respectively, but showed faster deactivation due to forming more encapsulated carbon. In multiple reaction-regeneration cycles, the catalyst pretreated at 600 ℃ could maintain the catalytic activity.