A study of the production of hydrogen by the decomposition of formic acid over Pd-based and Pt-based catalysts

As one of main products of acid hydrolysis procedure from biomass, formic acid is a promising hydrogen carrier that has recently been earning more and more attention. CO-free hydrogen production and mild reaction conditions have recently been the two main targets in the production of hydrogen by the catalytic decomposition of formic acid. This thesis reports investigations of the catalytic performance of modified Pd-based and Pt-based catalysts for this reaction. The doping by alkali metal ions of a C-supported Pd catalyst promotes both its activity and hydrogen selectivity, the effect being in the order: K≥Cs>Na>Li. The reaction rate is increased by 1-2 order of magnitude using the optimum modified catalyst, 10 wt.% K-Pd/C, and the content of CO in the product is limited TO 30 ppm. The apparent activation energy for the reaction increases from a value around 60 kJ mol-1 to 100 kJ mol-1 upon K-doping for both the Pd/C catalyst and a Pd powder catalyst, this showing that the reaction mechanism changes on doping. Based on the activity measurements under both steady state and unsteady state conditions as well as on catalyst characterization results (TEM/EDS, STEM/HAADF, XPS, XRD and TOF-SIMS) and DRIFTS measurements, a reaction mechanism is proposed to explain the results with the K-doped Pd/C catalysts. Pt-based catalysts supported on N-doped carbon nanofibers (CNFs) have also been studied in formic acid decomposition. The use of CNFs as catalyst supports gives the possibility of controlling the structure of the catalysts during preparation. Nitrogen doping of the CNFs changes the electronic properties and gives more structural defects in the CNFs. Sub-nano-sized Pt particles stabilized by the N-doped CNFs supports have been found to have improved activity in formic acid decomposition and to be inactive in ethylene hydrogenation.