# In Situ Insights into Ni Phyllosilicate Evolution: Cationic Ni Species as Key to Enhanced Stability in Methane-Rich Dry Reforming

## TL;DR

This study explores how nickel phyllosilicates improve catalyst stability in methane reforming, revealing the role of cationic nickel species in reducing carbon formation.

## Contribution

The paper introduces a one-pot synthesis method for Ni phyllosilicate catalysts and identifies cationic Ni species as key to stability in dry reforming.

## Key findings

- In situ XAS-XRD confirmed the formation of thermally stable Ni3Si2O5(OH)4 phyllosilicate.
- Cationic Ni species (Ni+ and Ni2+) limit carbon formation via CO disproportionation.
- The one-pot synthesis improved Ni dispersion and crystallite size, enhancing catalytic stability.

## Abstract

Nickel (Ni) phyllosilicate-derived catalysts have recently
gained
attention for the CO2 reforming of methane. However, understanding
of the underlying reduction pathways and structural factors that determine
stable catalytic performance is still missing. Herein, we developed
a one-pot synthesis with ammonia solution to produce nickel catalysts
supported on silica, utilizing a modified KIT-6 protocol. Under the
proposed alkaline conditions (pH = 9), the silanol groups were deprotonated
(Si–O–) and the resulting negatively charged
oxide surface could interact with Ni2+. This approach facilitated
the in situ formation of Ni phyllosilicate within the silica framework,
which contained isolated surface hydroxyl groups. In situ XAS-XRD
revealed the presence of thermally stable crystalline Ni phyllosilicate,
Ni3Si2O5(OH)4, with time-resolved
XANES providing complementary insight into the redox transformation
of nickel species associated with dehydroxylation. Partially unreduced
nickel species retained a cationic state during the catalytic reaction
at 700 °C, with a higher amount of nickel phyllosilicate observed
after 50 h in contrast to the state after 1 h. On the whole, the one-pot
synthesis produced small Ni crystallites with improved dispersion,
both of which had a part in ensuring stable catalytic performance.
We also uncovered the crucial role of ionic species (Ni+ and Ni2+) limiting the carbon formation via CO disproportionation
(2CO ⇌ C(s) + CO2) on the KIT-6-templated
silica. This study provides valuable insights into the design of more
stable methane reforming catalysts.