CaO-Ca_(3)Al_(2)O_(6)@Ni-SiO_(2)复合催化剂制备及制氢性能

Preparation and hydrogen production performance of CaO-Ca_(3)Al_(2)O6@Ni-SiO-2 composite catalyst

吸附强化CH4/H2O重整制氢技术通过原位移除反应产生的CO_(2)实现一步法制备高浓度H_(2),但该技术常用复合催化剂中的吸附组分CaO在吸脱附CO_(2)时的体积变化会造成复合催化剂结构的坍塌,同时活性组分Ni也被反应生成的CaCO_(3)包埋,造成催化和吸附性能的下降,严重影响制取H_(2)的浓度。本研究利用阳离子表面活性剂辅助刻蚀的机理采用自模板法制备了CaO-Ca_(3)Al_(2)O_(6)@Ni-SiO_(2)复合催化剂。在吸附强化CH_(4)/H_(2)O重整制氢实验中,该复合催化剂制氢浓度达到99.6%,且10次循环后制氢浓度为97.3%,其高活性高稳定性归因于复合催化剂中的吸附组分CaO-Ca_(3)Al_(2)O_(6)在反应-再生循环过程中体积反复膨胀收缩的过程均在SiO_(2)空腔内进行,不会造成复合催化剂结构的坍塌,同时复合催化剂制备过程中采用SiO_(2)包覆活性组分Ni防止了其在脱碳再生过程中团聚失活,但结构表征发现,复合催化剂的催化组分中仅有一部分是以Ni为核、SiO_(2)为壳的核壳结构,还存在部分Ni直接负载在壳层SiO_(2)上,这是导致10次循环反应中CH_(4)转化率从99.5%降至91.8%的原因。

Sorption-enhanced steam methane reforming achieves one-step production of high purity hydrogen by in-situ removal of CO_(2).However,the volume change of the adsorption component CaO in the composite catalyst during the adsorption and desorption of CO_(2) generally caused the structure collapse of the composite catalyst.At the same time,the active component Ni would also be embedded by the generated CaCO_(3),resulting in the decline of catalytic and adsorption performance and seriously affecting the purity of hydrogen production.How to prepare bifunctional composite catalyst with high stability is one of the key problems to be solved in the industrial application of this technology.In this work,CaO-Ca_(3)Al_(2)O_(6)@Ni-SiO_(2) composite catalyst was prepared by the self-template approach using the cationic surfactant-assisted etching mechanism.In the experiment of hydrogen production by adsorption enhanced CH_(4)/H_(2)O reforming,the hydrogen production concentration over the composite catalyst reached 99.6%,and it still remained 97.3%after 10 cycles,which was closely related to the special structure of the prepared CaO-Ca_(3)Al_(2)O_(6)@Ni-SiO_(2) composite catalyst.When the reaction was proceeded,the repeated expansion and contraction of CaO-Ca_(3)Al_(2)O_(6) volume in the composite catalyst was performed in the SiO_(2) cavity and would not cause the structure collapse of the composite catalyst.At the same time,the SiO_(2) coating on catalytic component Ni could prevent its agglomeration and deactivation during the decarburization and regeneration process.However,it was found that only part of the catalytic component Ni possessed a core-shell structure with Ni as the core and SiO_(2) as the shell,and there were some Ni directly loaded on the shell SiO_(2),leading to CH_(4) conversion dropping from 99.5%to 91.8%in 10 cycles.