Volume 251, 2024

Identification of reaction intermediates in the decomposition of formic acid on Pd

Abstract

Uncovering the role of reaction intermediates is crucial to developing an understanding of heterogeneous catalysis because catalytic reactions often involve complex networks of elementary steps. Identifying the reaction intermediates is often difficult because their short lifetimes and low concentrations make it difficult to observe them with surface sensitive spectroscopic techniques. In this paper we report a different approach to identify intermediates for the formic acid decomposition reaction on Pd(111) and Pd(332) based on accurate measurements of isotopologue specific thermal reaction rates. At low surface temperatures (∼400 K) CO2 formation is the major reaction pathway. The CO2 kinetic data show this occurs via two temporally resolved reaction processes. Thus, there must be two parallel pathways which we attribute to the participation of two intermediate species in the reaction. Isotopic substitution reveals large and isotopologue specific kinetic isotope effects that allow us to identify the two key intermediates as bidentate formate and carboxyl. The decomposition of the bidentate formate is substantially slower than that of carboxyl. On Pd(332), at high surface temperatures (643 K to 693 K) we observe both CO and CO2 production. The observation of CO formation reinforces the conclusion of calculations that suggest the carboxyl intermediate plays a major role in the water–gas shift reaction, where carboxyl exhibits temperature dependent branching between CO2 and CO.

Graphical abstract: Identification of reaction intermediates in the decomposition of formic acid on Pd

Associated articles

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Article information

Article type
Paper
Submitted
17 12 2023
Accepted
07 2 2024
First published
13 3 2024
This article is Open Access
Creative Commons BY license

Faraday Discuss., 2024,251, 412-434

Identification of reaction intermediates in the decomposition of formic acid on Pd

J. Fingerhut, L. Lecroart, M. Schwarzer, S. Hörandl, D. Borodin, A. Kandratsenka, T. N. Kitsopoulos, D. J. Auerbach and A. M. Wodtke, Faraday Discuss., 2024, 251, 412 DOI: 10.1039/D3FD00174A

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