Selective Oxidation of Methane to Methanol Using Supported AuPd Catalysts Prepared by Stabilizer-Free Sol-Immobilization

Abstract

The selective oxidation of methane to methanol, using H2O2, under mild reaction conditions was studied using bimetallic 1 wt. % AuPd/TiO2 prepared by stabiliser-free sol-immobilisation.The as-prepared catalysts exhibited low, unselective oxidation activity and deleterious H2O2 decomposition, which was ascribed to the small mean particle size of the supported AuPd nanoparticles. Heat treatments were employed to facilitate particle size growth, yielding an improvement in the catalyst turn-over-frequency and decreasing the H2O2 decomposition rate. The effect of support phase was studied by preparing a range of AuPd catalysts supported on rutile TiO2. The low surface area rutile TiO2 yielded catalysts with effective oxygenate production, but poor H2O2 utilisation. The influence of the rutile-TiO2 support was investigated further by producing catalysts with a lower metal loading to maintain a consistent metal loading per m 2 to the 1 wt.% AuPd/ P25 TiO2 catalyst. When calcined at 800 °C the 0.13 wt.% AuPd catalyst demonstrated significantly improved turn-over frequency of 103 h -1 . In contrast, the turn-over frequency was found to be ca. 2 h -1 for the rutile-supported 1 wt. % AuPd catalyst calcined at 800 °C. The catalysts were probed by electron microscopy and XPS to understand the influence of particle size and oxidation state on the utilisation of H2O2 and oxygenate productivity. This work shows that the key to highly active catalysts involves the prevention of deleterious H2O2 decomposition and this can be achieved through carefully controlling the nanoparticle size, metal loading and metal oxidation state.

The Direct Synthesis of H2O2 Using TS‐1 Supported Catalysts

“…We have previously reported a correlation between mean nanoparticle size and catalytic selectivity towards H 2 O 2 for AuPd catalysts supported on TiO 2 with larger AuPd nanoparticles displaying a higher selectivity towards H 2 O 2. It is therefore possible to correlate this significant decrease in mean particle size with a loss of catalytic selectivity.…”

Low temperature selective oxidation of methane using gold-palladium colloids

“…Since the formation of the hydroperoxy intermediates was also found in methane oxidation, Au-Pd alloy particles have also been tested for the methane oxidation reaction. TiO2 supported bimetallic Au-Pd nanoparticles were shown to be active for methane oxidation at 50 °C using H2O2 as the oxidant [18,19]. The synergistic effect of gold and palladium was found to not only increase the catalytic activity but also to improve selectivity and the efficiency of the reaction.…”

High H2O2 Utilization Promotes Selective Oxidation of Methane to Methanol at Low Temperature

“…However, the gas-phase and high temperature processes generally have limited methanol yield due to the thermodynamically favored over-oxidation of methanol to CO x . During the last few years, increasing attention has been devoted to the low-temperature liquid-phase oxidation of methane to methanol using N 2 O, O 2 , and H 2 O 2 as oxidants (Agarwal et al, 2017;Williams et al, 2018;McVicker et al, 2020). Recently, Hutchings et al reported a low-temperature (50 • C) route in aqueous hydrogen peroxide (H 2 O 2 ) for oxidizing methane to methanol in high yield (92%).…”