Supported platinum–zinc oxide core–shell nanoparticle catalysts for methanol steam reforming†
Platinum–zinc oxide (Pt@ZnO) and palladium–zinc oxide (Pd@ZnO) core–shell nanoparticles were synthesized in solution using a method based on self-assembly and deposited onto a functionalized alumina (Si–Al2O3) support. TEM investigations of the samples confirm the formation of core–shell structures of approximately 6 nm of diameter following calcination to remove the ligands. In situ TEM and coulometric titration experiments suggest that Pt–Zn alloys are formed upon reduction and that these are highly tunable in size. While methanol steam reforming (MSR) measurements on conventional Pt/Al2O3 and Pd/Al2O3 catalysts show poor CO2 selectivities, a Pt (1 wt%)@ZnO (9 wt%)/Si–Al2O3 system showed comparable activity and selectivity for CO2 as a conventional Pt/ZnO catalyst, providing further indication that Pt@ZnO forms a Pt–Zn alloy upon reduction due to the intimate contact between the two materials. The Pd@ZnO/Si–Al2O3 exhibited lower CO2 selectivities than Pt@ZnO/Si–Al2O3.