强化CO2吸附的NiMgAlCa复合催化剂制备及作用机制

CO2 enhanced sorption methane steam reforming for hydrogen production is a potential approach to economically provide hydrogen and to reduce CO2 emission. The key point for this process is to develop kind of proper composite catalyst with high catalytic and adsorptive capacity. When CO2 enhanced sorption methane steam reforming process is used to produce hydrogen under low steam/carbon ratio, the general nickel-based catalyst is easy to be deactivated due to carbon deposition, and the calcium-based absorbent is prone to be sintered during catalyst regeneration, leading to the poor recycle stability of the composite catalyst. In this project, considering the thermal decomposition reaction and tunable structure of NiMgAl layered double hydroxides, and the pore-generated property of polyethylene glycol, we employ different preparation methods to synthesize NiMgAlCa composite catalysts with high catalytic and adsorptive capacity, which could be realized by varying preparation parameters, such as the calcination temperature, the metal ions concentration, the type of anions, the molecule weight and dosage of polyethylene glycol. On-line analysis is used to monitor the variation of surface structure and chemical properties for the NiMgAlCa composite catalyst. Based on the above characterization and the activity evaluation results, we could achieve how the enhanced CO2 sorption is realized over NiMgAlCa composite catalyst in methane steam reforming process. These studies will provide a theoretical support for designing new composite catalyst in hydrogen production process.

CO2吸附强化CH4/H2O重整制氢是提供低成本高纯氢气和实现CO2减排的方法。研制兼具催化、吸附性能的复合催化剂是实现这一化学过程的关键。针对低水碳比条件下，CO2吸附强化CH4/H2O重整制氢常用镍基催化剂易积炭，钙基吸附剂易烧结等问题，申请项目拟利用NiMgAl层状复合金属氢氧化物热分解反应和其结构的可调变性及聚乙二醇的扩孔特性，通过控制焙烧温度、金属离子浓度、阴离子类型，改变聚乙二醇的分子量和添加量等方法制备兼具催化、吸附性能的NiMgAlCa复合催化剂。通过在线研究分析NiMgAlCa复合催化剂在反应过程中表面结构和化学性质的变化，结合复合催化剂反应活性变化规律，获得复合催化剂强化CO2吸附的作用机制，为制氢反应的新型复合催化剂设计提供理论依据。

CO2吸附强化CH4/H2O重整制氢是提供低成本高纯氢气和实现CO2减排的方法。研制兼具催化、吸附性能的复合催化剂是实现这一化学过程的关键。复合催化剂活性及稳定性与活性组分Ni分散度和吸附组分CaO的性质密切相关。本项目首先以提高吸附组分CaO的循环吸附稳定性为目标，利用溶胶凝胶法合成得到系列强循环吸附稳定性的CaO基吸附剂，且适量Al的添加可使吸附剂的CO2吸附容量显著提高，其中CaO/Al2O3质量比为9:1的吸附剂具有最高的CO2吸附容量。机理研究发现：制备得到的CaO/Ca3Al2O6系列合成吸附剂具有在高温下较稳定的小比表面、小孔体积结构，使其在循环吸附过程中结构保持稳定，循环吸附稳定性强；掺杂Al后经焙烧形成的惰性物质Ca3Al2O6均匀分散在CaO微粒间，减少了吸附剂颗粒在与CO2反应过程中体积的膨胀程度，为CO2向吸附剂颗粒内的扩散提供了一定的孔隙，使掺杂Al的合成吸附剂比不掺杂Al的合成吸附剂CO2吸附容量显著提高。在此基础上采用聚乙二醇、水蒸气和CO2分别对CaO/Ca3Al2O6进行预处理，考察了吸附剂孔结构与吸附性能的变化规律。借鉴类水滑石结构具有的特点，以掺杂Al的CaO为载体，采用共沉淀法制备了具有大比表面积和高金属分散度的Ni/CaO-Al2O3复合催化剂，考察了Ca/Al比、焙烧温度、助剂MgO添加量对复合催化剂吸附强化CH4/H2O重整制氢活性和稳定性的影响，并探究了其作用机制。当Ca/Al比为3，前驱体分解温度为700°C，MgO添加量为1%时，该复合催化剂的CO2吸附容量为5.05mol/g，且吸附强化CH4/H2O重整制氢过程中氢气浓度达到了98.7%。