W/O微乳液法制备贵金属Pt修饰Ni纳米催化剂及其甲烷催化裂解性能研究

Methane catalytic cracking to simultaneously produce pure hydrogen and carbon nano-materials has been an interesting research field in recent years. However, conducting methane cracking over traditional supported Ni catalysts will generate impurity gas like CO. Moreover, the interaction between Ni and support will make it difficult to get an agreement on the optimal Ni size for the reaction. In this project, the following will be studied: (1)By varying the surfactant, reducing agent, Ni precursor and water/surfactant mol ratio to alter water-core size, unsupported metallic nano-Ni catalysts with different particle size will be synthesized by W/O reverse mirco-emulsion method followed with a reasonable calcination condition; (2) In a fixed-bed reactor, the relationship between Ni particle size and catalytic performance including activity and productivity of hydrogen and carbon will be explored to build up an optimal Ni particle size model for methane cracking; (3) On the basis of Ni aggregation behavior analysis, the optimized Ni catalyst decorated with noble metal Pt will be synthesized to form bimetallic catalysts with Ni-Pt alloy and/or Ni@Pt core-shell structure. The influence of catalyst composition and structure towards its thermal stability will be investigated. As an achievement of this project, a new technology will be provided for designing a novel efficient methane cracking catalyst.

耦合了制造纯氢及纳米碳材料的甲烷催化裂解是当前的一个研究热点。使用传统负载型Ni催化剂，不但会生成CO杂质气体，而且由于载体与Ni之间的相互作用，很难得出统一的最适宜反应的Ni粒径。本项目将研究：（1）拟采用W/O型反相微乳液法，通过选择表面活性剂、还原剂、Ni前驱体的类型及水量/表面活性剂量的比例等控制微乳液体系中水核的尺寸，研究后续焙烧条件，设计合成不同尺寸的非负载型金属Ni纳米催化剂；（2）在固定床反应器上，以初始活性为指标，综合考察制氢和碳产量，探讨Ni粒径与催化性能的构效关系，构筑最优Ni粒径模型；（3）结合最优Ni粒径及Ni的聚集行为的解析，通过调变导入贵金属的操作参数，制备Ni-Pt合金或Ni@Pt核壳结构双金属催化剂，以实现贵金属对具有最优粒径的纳米Ni催化剂的修饰，揭示催化剂的组成、结构对其热稳定性的影响规律。本项目研究成果将为构建高效新型甲烷裂解制氢催化剂提供技术支持。

甲烷催化裂解是制氢的一条新路线。本项目利用反相微乳液法，通过调节微乳液的体系（包括水/表面活性剂的摩尔比、金属前驱体盐的浓度、Ni/Pt的摩尔比等），制备出了粒径、结构、组分可控的纳米金属Ni-Pt催化剂。同时，通过DFT模拟计算，构建了不同组分Ni-Pt催化剂的结构模型，推演出了在不同温度下催化剂结构的变化，进一步地耦合催化剂的反应性能，实现了催化剂的优化设计及反应条件的筛选。最后，利用固定床反应装置，评价了各类催化剂的甲烷裂解性能，详细考察了反应的条件，包括温度、气体组成、压力、时间等对催化剂活性、寿命，以及碳副产物形貌的影响规律。本项目研究发现，只有当催化剂中的Pt摩尔浓度在5-15mol％之间，Ni-Pt才能在反应温度条件下，形成均一的合金结构，从而提高催化剂的活性及稳定性。本项目研究同时发现，碳副产物的形貌对于反应的温度、催化剂的粒径十分敏感，在反应温度为700度，粒径为15nm的Ni-Pt催化剂上，可以连续地形成碳纳米管，并获得较高的碳产率。