Preparation of carbon supported Pt-Ni alloy nanoparticle catalyst with high metal loading using cation exchange resin and its application for hydrogen production

Abstract

Formic acid has been attracting interest as a promising hydrogen carrier because hydrogen can be produced over the catalysts under mild condition with low energy input. Though the catalytic activity for hydrogen production from formic acid is enhanced by increasing the metal loading, the trade-off between high metal loading and small metal particle size practically occurred with carbon catalyst prepared by impregnation method. To overcome this challenge, we herein utilized a noble catalyst preparation method which uses an ion-exchange resin as an initial carbon material. Five compositions of carbon supported Pt-Ni alloy catalysts were successfully prepared at high metal loading (25–50 wt%) with small metal particle sizes (2.3–3.8 nm observed by TEM). The metal particles were embedded in the carbon, which was contributed to small particle size of the loaded metal. The hydrogen production from formic acid was investigated over the prepared catalysts at 100–200 °C. It was elucidated that the turnover frequencies of Pt50Ni50/C and Pt75Ni25/C were higher than that of Pt/C at above 175 °C, suggesting that the decrease of Pt content without losing their catalytic activity could be achieved by Pt50Ni50/C and Pt75Ni25/C due to alloy formation. To further enhance the catalytic activity by increasing the active metal surface area, supercritical water treatment at 400 °C for 1 h was utilized. The metal surface area of catalysts was noticeably increased due to the gasification of the carbon support nearby metal particles. Formic acid conversion, likewise, drastically increased after the treatment.