Hydrogen production from formic acid vapour over a Pd/C catalyst promoted by potassium salts: evidence for participation of buffer-like solution in the pores of the catalyst

Doping a 1 wt.% Pd/C catalyst with alkali metal carbonates has a very significant promotional effect on its activity in hydrogen production from the decomposition of formic acid vapour (2 vol.%, 1 bar), potassium and caesium carbonates giving the largest effects. The K carbonate species present on the fresh catalysts react with formic acid to form formate ions, these being dissolved in a formic acid/water solution condensed in the pores of the support. The steady-state activities of the samples containing formate ions were 1-2 orders of magnitude greater than those of the unpromoted Pd/C and CO content was lower than 30 ppm. The activation energies for the reaction increased with doping from 66 to 88-99 kJ mo1-1, relatively independent of the cation of the dopant. Similar but lesser effects were found with unsupported Pd nanocrystals doped with K carbonate. The rate-determining step for the promoted samples appears to be the decomposition of formate ions on the Pd surface. (C) 2014 Elsevier B.V. All rights reserved.