HCOOH decomposition on Pd catalysts for potential use as a liquid H2 carrier

Abstract

Formic acid (HCOOH) has emerged as a promising liquid H2 energy carrier due to its reasonable gravimetric and volumetric H2 densities, low toxicity, low flammability, and ease of handling. HCOOH could enhance the use of H2 fuel due to its ability to stay in a liquid state at a wide range of temperatures and its ease of transportation. Pd-based catalysts have shown to be a selective, stable, and reactive catalyst for HCOOH dehydrogenation due to its high reactivity at near ambient temperatures. This research utilizes in-situ infrared spectroscopy and steady-state kinetic experiments to better understand why Pd-based catalysts are effective by determining what intermediates occur and the overall reaction pathway. A 1 wt% Pd/SiO2 catalyst was prepared using strong electrostatic adsorption. Particle size was adjusted using and oxidative treatment followed by a reductive treatment to try and achieve estimated particle sizes. Mass spectrometry was utilized to understand the effects of particle size on the reaction rates and the overall catalytic performance. Through kinetic analysis, the reaction pathways were narrowed down and supported by using infrared spectroscopy (IR). IR showed no evidence of monodentate formates (HCOOM*), bidentate formates (HCOOB*) or carboxylate (COOH*) intermediates resulting in an intermediate similar in structure to molecular HCOOH. Overall, it was observed that the Pd/SiO2 catalyst was highly selective towards H2 and CO2 products. Future work will include synthesizing varying particle sizes to address the hypothesis that reaction rate increases with decreasing particle size and characterizing the catalyst.