Optimization of the synthesis of Pd-Au nanoalloys confined in mesoporous carbonaceous materials.

Pd-Au nanoalloys confined in mesoporous carbonaceous materials were synthesized by a rapid one-pot microwave assisted approach. Green polymer resins based on phloroglucinol/glyoxylic acid or glyoxal were co-assembled in the presence of a template and metallic salts followed by microwave treatment between 40 and 80°C and subsequent thermal annealing, allowing simultaneous formation of mesoporous carbonaceous materials with in-situ confined Pd-Au nanoparticles. Several Pd-Au compositions were prepared (PdxAu100-x, where x=90; 80; 70 and 50) and their impact on the alloy structure and particle size/distribution evaluated. For Pd90Au10, homogeneously dispersed nanoalloy particles (∼8nm) are obtained in the carbonaceous framework. The increase in the Au content in the alloy gradually induces an increase in the particle size and agglomeration of the particles along with the formation of multiphased alloys, i.e., segregated Pd- and Au-rich nanoparticles. The particle agglomeration was avoided by decreasing the thermal annealing time. The homogeneity of the alloy structure was found to strongly depend by two parameters, the chelating/cross-linker agents and the microwave temperature, i.e., the chelating/cross-linker agents containing carboxylic groups and the higher temperatures inducing more heterogeneous structures. The hydrogen absorption in Pd90Au10 particles with different homogeneity degree was studied at room temperature up to 1bar. Generally, hydrogen absorbs in Pd-rich nanoalloys forming a hydride phase whereas Au-rich phases do not absorb hydrogen under the present conditions.