Hydrogen production from formic acid dehydrogenation over Pd/C catalysts: Effect of metal and support properties on the catalytic performance

While formic acid dehydrogenation has become one of the most promising strategies for hydrogen storage, the crucial factors for realizing an efficient catalyst remain controversial. In this study, a range of Pd/C catalysts were systematically prepared by adopting either diverse metal deposition methods or different acid treatments, and the resulting catalysts were used for formic acid dehydrogenation under ambient conditions without additives. The volcano-type dependence of the activity on the Pd particle size, rate enhancement over Pd with smaller [111]/[200] ratios, and superior activity of Pd or Pd /Pd(OH)(2) mixture to Pd2+ clearly indicate that not only the particle size but also the surface structure or electronic states of active metal would be of prime importance to promote the reaction. Moreover, another volcano relation between the activity and the pH of a reaction solution determined by the functional groups of an acid-treated support obviously suggests that the catalytic activity is very sensitive to pH, and that a neutral reaction solution is preferred to maximize the catalytic performance. The unprecedented critical effect of a support on the catalytic performance may be rationalized in terms of two factors: (i) recombination of the formate ion with a proton and/or delay of formic acid deprotonation by excess protons in an acidic solution; (ii) competitive adsorption between the formate and hydroxyl ions in a basic solution. Therefore, tuning the nature of a support to achieve a balance between the two competitive factors is important to enhance the catalytic performance. (C) 2017 Elsevier B.V. All rights reserved.