Efficient hydrogen production from formic acid using TiO2-supported AgPd@Pd nanocatalysts

Abstract

We report here the significant enhancement of catalytic activity of Ag–Pd bimetallic nanocatalysts with the formation of Ag–Pd catalysts having an average diameter of 4.2 ± 1.5 nm on TiO₂ nanoparticles using a two-step microwave (MW)–polyol method. Data obtained using XRD and STEM-EDS indicated that Ag-Pd bimetallic nanocatalysts consisted of Ag₈₂Pd₁₈ alloy core and about 0.5 nm thick Pd shell, denoted as AgPd@Pd. The hydrogen production rate of AgPd@Pd/TiO₂ from formic acid, 16.00 ± 0.89 L g⁻¹ h⁻¹, was 23 times higher than that of bare AgPd@Pd prepared under MW heating at 27 °C. It was even higher by 2–4 times than the best Ag@Pd and CoAuPd catalysts at 20–35 °C reported thus far. The apparent activation energy of the formic acid decomposition reaction using AgPd@Pd catalyst decreased from 22.8 to 7.2 kJ mol⁻¹ in the presence of TiO₂. Based on negative chemical shifts of the Pd peaks in the XPS data and the measured activation energies, the enhancement of catalytic activity in the presence of TiO₂ was explained by the lowered energy barrier in the reaction pathways because of the strong electron-donating effects of TiO₂ to Pd shells, which enhance the adsorption of formate to the catalyst and dehydrogenation from formate.