# Reversible Intrapore Redox Cycling of Platinum in Platinum-Ion-Exchanged HZSM-5 Catalysts

## TL;DR

This paper shows how platinum nanoparticles in a zeolite catalyst can be reversibly converted between dispersed and nanoparticle forms during redox cycles.

## Contribution

The study demonstrates reversible redox cycling of platinum in HZSM-5 catalysts, enabling stable catalytic performance and regeneration.

## Key findings

- Platinum nanoparticles in HZSM-5 are stably dispersed with an average size of 1.3 ± 0.4 nm.
- Oxidative fragmentation converts platinum back to its atomically dispersed state within the zeolite pores.
- Redox cycling maintains platinum within the pores under catalyst operation and regeneration conditions.

## Abstract

Isolated platinum(II)
ions anchored at acid sites in the pores
of zeolite HZSM-5, initially introduced by aqueous ion exchange, were
reduced to form platinum nanoparticles that are stably dispersed with
a narrow size distribution (1.3 ± 0.4 nm in average diameter).
The nanoparticles were confined in reservoirs within the porous zeolite
particles, as shown by electron beam tomography and the shape-selective
catalysis of alkene hydrogenation. When the nanoparticles were oxidatively
fragmented in dry air at elevated temperature, platinum returned to
its initial in-pore atomically dispersed state with a charge of +2,
as shown previously by X-ray absorption spectroscopy. The results
determine the conditions under which platinum is retained within the
pores of HZSM-5 particles during redox cycles that are characteristic
of the reductive conditions of catalyst operation and the oxidative
conditions of catalyst regeneration.