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

Abstract

(D.A. Bulushev) 2 A B S T R A C T 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 steadystate 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 mol -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.

Recent strategies targeting efficient hydrogen production from chemical hydrogen storage materials over carbon-supported catalysts

“…In an attempt to enhance the catalytic performance, various additives in addition to the formate-based mixtures have been utilized thus far. For instance, Bulushev analyzed the effect of the addition of alkali metal carbonates (CsCO 3 , K 2 CO 3 , or Na 2 CO 3 ) and lithium formate in FA dehydrogenation in the gas phase 44 . According to the obtained conversion profiles, doping with potassium carbonate was the most effective among those investigated.…”

Single Isolated Pd2+ Cations Supported on N-Doped Carbon as Active Sites for Hydrogen Production from Formic Acid Decomposition

“…When comparing the activities of the Pd catalysts at low temperatures (<400 K), the conversions of formic acid ( Figure 3) and TOF values (Table 2) for the N-doped catalysts were 2-3 times higher than that for the N-free catalyst. It is also important that the TOF values for the N-doped samples were higher than those for the unsupported Pd powder 33 and commercial 1 wt.% Pd/C catalyst 17,18 with a mean particle size of 3.6 nm close to that for the Pd/N-C M (w)…”

“…52 Generally, the activity of homogeneous catalysts based on metal complexes is higher in formic acid dehydrogenation than that of heterogeneous catalysts containing metal nanoparticles. 2,33 Hence, the present research with N-functionalized carbon covers a gap between homogeneous and heterogeneous catalysis in this field discovering active isolated Pd 2+ cations stable at least up to 573 K in hydrogen. The obtained Pd sites attached to a couple of pyridinic nitrogen atoms on the edge of graphene sheet demonstrate also an excellent stability in the reaction conditions ( Figure 4).…”

Promotion Effect of Alkali Metal Hydroxides on Polymer-Stabilized Pd Nanoparticles for Selective Hydrogenation of C–C Triple Bonds in Alkynols

“…However, K-containing species either on the Pd NPs, in the form of islands, or at the interface between Pd and the support were not excluded. 9 This so-called "geometric effect" of alkali metal ions may help preserve catalytically active Pd NPs from sintering during catalyst reduction at high temperatures. However, due to the geometric effect, alkali metal ions, especially at high loadings, may decrease the catalytic activity by blocking active sites.…”