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Low temperature formic acid decomposition pathways on supported palladium nanoparticles
Schlussel, Sierra
Schlussel, Sierra
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2024
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2025-11-26
Abstract
Formic acid (HCOOH) has emerged as a promising liquid hydrogen (H2) carrier
due to its low toxicity, low flammability, and ease of handling. The utilization of HCOOH as a potential liquid H2 carrier requires a catalytic system that selectively dehydrogenates HCOOH at low temperatures without forming any dehydration products (CO) that can act as a poison for Pt electrodes in fuel cell applications. Pd-based catalysts are widely studied for this reaction due to its high reactivity at low temperatures. Yet, details of the reaction pathways and intermediates of HCOOH dehydrogenation on Pd-based catalysts have remained inconclusive. The catalytic stability and selectivity of Pd nanoparticles have remained controversial in current literature.
This work combines kinetic, isotopic, and spectroscopic methods to investigate the viability, reaction mechanism, and particle size effects of Pd/SiO2 catalysts for HCOOH decomposition pathways. In doing so, we show that supported Pd catalysts are highly active and selective towards the dehydrogenation products (H2/CO2) at low temperatures (≤383 K) without any detectable formation of dehydration products (H2O/CO). No apparent deactivation was observed up to 60 ks time-on-stream. In-situ infrared spectra measured at a range of HCOOH pressures (0.17-3.36 kPa; 353 K) detected molecularly bound HCOOH (HCOOH*) as the reaction intermediate. Such results contradict the formation of carboxylates (COOH*) and/or formates (HCOO*) that have been proposed as reactive intermediates in literature. Additional kinetic studies showed that the reaction followed a first-order reaction at low HCOOH pressures, which transitioned into zerothorder reaction at higher pressures. Isotopic studies with DCOOH and HCOOD show that both the cleaving of the O-H and C-H bonds are kinetically relevant steps. The change in Pd loading on the SiO2 support showed the importance of particle size on the rate of reaction. The smaller the particles, the more reactive they are, allowing for higher turnover rates. The results from this study can be utilized to provide design strategies for Pd-based catalysts for their use in HCOOH dehydrogenation reactions for its potential use as a liquid H2 carrier at industrial scale.
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