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Water-Gas Shift Reaction Produces Formate at Extreme Pressures and Temperatures in Deep Earth Fluids
Nore Stolte1, Junting Yu1, Zixin Chen2
1Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
The Journal of Physical Chemistry Letters
|April 30, 2021
Summary
The water-gas shift reaction may not occur in Earth's upper mantle. Instead, formic acid forms directly from carbon monoxide and supercritical water, potentially acting as a deep Earth carbon carrier.
Area of Science:
- Geochemistry
- Chemical Kinetics
- Computational Chemistry
Background:
- The water-gas shift reaction is crucial for industrial hydrogen production and Fischer-Tropsch-type synthesis.
- Its behavior under extreme deep Earth conditions (high pressure-temperature) is largely unknown.
Purpose of the Study:
- To investigate the water-gas shift reaction under upper mantle conditions.
- To determine the stability of formic acid and reaction products at high pressures and temperatures.
Main Methods:
- Extensive ab initio molecular dynamics simulations.
- Free energy calculations.
Main Results:
- Direct formation of formic acid from CO and supercritical water at 10-13 GPa and 1400 K without a catalyst.
- Formic acid (HCOOH) is thermodynamically more stable than water-gas shift products above 3 GPa and 1000-1400 K.
Conclusions:
- The water-gas shift reaction is unlikely to occur in the Earth's upper mantle.
- Formic acid or formate may serve as significant carbon carriers in deep Earth's reducing environments, influencing geochemical processes.
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