General Synthetic Route toward Highly Dispersed Ultrafine Pd–Au Alloy Nanoparticles Enabled by Imidazolium-Based Organic Polymers

Bimetallic Pd–Au nanoparticles (NPs) usually show superior catalytic performances over their single-component counterparts, the general and facile synthesis of subnanometer-scaled Pd–Au NPs still remains a great challenge, especially for electronegative ultrafine bimetallic NPs. Here, we develop an anion-exchange strategy for the synthesis of ultrafine Pd–Au alloy NPs. Simple treatment of main-chain imidazolium-based organic polymer (IOP) with HAuCl4 and Na2PdCl4, followed by reduction with NaBH4 generated Pd–Au alloy NPs (Pd–Au/IOP). These NPs possess an unprecedented tiny size of 1.50 ± 0.20 nm and are uniformly dispersed over IOP. The electronic structure of the surface Pd and Au atoms is optimized via electron exchange during alloying, a net charge flowing resulting from counteranions is injected into Au and Pd to form a strong ensemble effect, which is responsible for a remarkably higher catalytic activity of Pd–Au/IOP in the hydrolytic dehydrogenation of ammonia borane than those of monometallic cou...