Tough core-shell catalysts

One approach for increasing the activity of precious metals in catalysis is to coat them onto less expensive earth-abundant transition metal cores such as nickel, but often these structures alloy and deactivate during reactions. Hunt et al. synthesized several types of transition metal carbide nanoparticles coated with atomically thin precious-metal shells. Titanium-doped tungsten carbide nanoparticles with platinum-ruthenium shells were highly active for methanol electrooxidation, stable over 10,000 cycles, and resistant to CO deactivation.

Abstract

We demonstrated the self-assembly of transition metal carbide nanoparticles coated with atomically thin noble metal monolayers by carburizing mixtures of noble metal salts and transition metal oxides encapsulated in removable silica templates. This approach allows for control of the final core-shell architecture, including particle size, monolayer coverage, and heterometallic composition. Carbon-supported Ti0.1W0.9C nanoparticles coated with Pt or bimetallic PtRu monolayers exhibited enhanced resistance to sintering and CO poisoning, achieving an order of magnitude increase in specific activity over commercial catalysts for methanol electrooxidation after 10,000 cycles. These core-shell materials provide a new direction to reduce the loading, enhance the activity, and increase the stability of noble metal catalysts.

Science 20 May 2016:
Vol. 352, Issue 6288, pp. 974-978
DOI: 10.1126/science.aad8471

http://science.sciencemag.org/content/352/6288/974

美国麻省理工学院和威斯康星大学麦迪逊分校的科学家利用高温自组装的方法合成了单层到多层一元贵金属或异种贵金属包覆的尺寸可控的过渡金属纳米颗粒催化剂（小于10纳米）。这种方法能够控制核壳的结构、颗粒尺寸、单层覆盖率和异种金属的成分。碳支撑的Ti0.1W0.9C纳米颗粒在覆盖了单层的Pt或PtRu之后表现出大幅提高的抗烧结能力和抗一氧化碳中毒能力，其催化活性在10000次循环后相比于传统的甲醇电氧化催化剂仍高出一个数量级。这种核壳结构的催化剂不仅表现出极好的催化活性和提高的稳定性，而且在各种环境的高温条件下仍然保持稳定。这种合成方法为大幅减少贵金属用量、增加催化剂的热催化或电催化活性提供了可控的新途径。（新材料在线）