# Onion-like carbon unlocks high PdNiO nanocatalyst dispersion for outstanding thermal methane oxidation

## TL;DR

A new carbon-based catalyst enables efficient methane oxidation at lower temperatures, outperforming existing catalysts.

## Contribution

The use of onion-like carbon (OLC) as a support for PdNiO nanocatalysts improves thermal stability and catalytic performance.

## Key findings

- PdNiO/OLC achieves full methane oxidation at 400 °C, lower than Pd/OLC and commercial Pd/C.
- OLC provides enhanced graphitization, gas transport, and structural stability for the catalyst.
- Adding NiO improves surface area, metal dispersion, and reduces particle size in the catalyst.

## Abstract

Methane must undergo complete catalytic oxidation to reduce the emission of unburned methane from power plants and natural gas engines. However, the poor temperature stability of carbon-based supports frequently restricts their usage in methane oxidation. This limitation can be addressed by modifying the carbon structure to enable the development of thermally resilient catalysts. This study utilises onion-like carbon (OLC), a support material made from nanodiamonds by high-temperature calcination, to disperse palladium (Pd) nanoparticles (Pd/OLC). The choice of OLC as the support is based on its distinct physicochemical merits (i.e., enhanced graphitization, a more ordered but defect-rich architecture, better thermal transport and porosity, gas-accessible active sites, improved electrical conductivity and structural stability). The resultant OLC promoted exceptional catalytic activity in the Pd/OLC by offering increased graphitisation, superior gas transport, accessible active sites, and exceptional temperature stability. The effect of adding nickel oxide (NiO) to Pd/OLC in PdNiO/OLC was also investigated, and the results show increased catalytic effectiveness through improved surface area, refined metal dispersion, and reduced particle size. PdNiO/OLC achieves full methane oxidation (T100) at a lower temperature (400 °C) than Pd/OLC (450 °C) and commercial Pd/C (650 °C). These results demonstrate the potential of OLC as a strong carbon support for gas-phase catalytic processes at high temperatures, which extends beyond methane combustion.

Synthesized PdNiO nanocatalysts embedded with onion-like carbon (PdNiO/OLC) enable full methane oxidation at 400 °C, outperforming Pd/OLC and Pd/C due to its enhanced graphitization, high surface area, and optimized metal dispersion.