# Selecting Reaction Pathways of CO2 Hydrogenation on Ni(111) by Kinetic Hindrance Associated with the Initial Surface Conditions in the Treatment of H2/CO2 Mixed Gas, Studied by Ambient-Pressure X‑ray Photoelectron Spectroscopy

## TL;DR

This study shows how the order of introducing CO2 and H2 gases on a nickel surface affects reaction pathways, potentially leading to more energy-efficient CO2 hydrogenation.

## Contribution

The novel finding is that initial surface conditions, determined by gas dosage order, control CO2 hydrogenation pathways on Ni(111).

## Key findings

- CO2 dissociation occurs when introduced before H2 at 300 K.
- Carboxyl (COOH) forms when H2 is introduced before CO2.
- COOH formation dominates above 370–420 K, leading to graphitization above 470 K.

## Abstract

Two types of surface reaction intermediates were observed
in the
presence of a H2/CO2 mixed gas on Ni(111), depending
on the dosage order of the gases. The observations were carried out
by in situ measurements with ambient-pressure X-ray
photoelectron spectroscopy. When the CO2 gas was introduced
at 300 K prior to the H2 gas, CO2 dissociation
occurred. With the opposite order of gas dosage at the same temperature,
carboxyl (COOH) formation was observed on the surface. The different
reaction pathways originate from initial surface conditions due to
the interaction between the first gas and Ni(111). In both cases,
the reaction is dominated by COOH formation above 370–420 K,
depending on the gas pressure, and is associated with graphitization
above 470 K. The different reaction pathways followed according to
the dosage order of the gases likely explain the various intermediates
observed in previous studies. These results pave a new way to develop
CO2 hydrogenation catalyst systems with lower energy consumption.