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.

Methane oxidation using N2O was carried out with Fe-MFI zeolite catalysts at 300 °C. Methane conversion over Fe-ZSM-5, Fe-silicalite-1 and Fe-TS-1 indicates that Brønsted acidity is required to support the Fe-based alpha-oxygen active site for the important initial hydrogen abstraction step. Increasing the calcination temperature of Fe-ZSM-5 from 550 to 950 °C showed that the catalyst retained the MFI structure. However, at 950 °C the Brønsted and Lewis acid sites were altered significantly due to the migration of aluminium, which led to a significant decrease in catalytic performance. Over Fe-ZSM-5 the desired partial oxidation product, methanol was observed to undergo a reaction path similar to the methanol to olefin (MTO) process, which predominately produced ethene and subsequently produced coke.Methanol control experiments over Fe-silicalite-1, Fe-ZSM-5, Fe-TS-1 and H-ZSM-5 indicated that with the presence of Brønsted acidity the catalyst were more effective at forming ethene and subsequent aromatic species from DME, which resulted in an increased level of catalyst fouling. The implication of these observations are that the desorption of methanol is crucial to afford high mass balances and selectivity, however, Brønsted acid sites appear to slow this rate. These sites appear to effectively retain methanol and DME under reaction conditions, leading to low mass balances being observed. Our results confirm that to afford efficient and continuous methane oxidation by N2O, the catalytic active site must be extra-framework Fe coordinated to Al.

The behavior of single Pt atoms and small Pt clusters was investigated for high‐temperature oxidations. The high stability of these molecular sites in CHA is a key to intrinsic structure–performance descriptions of elemental steps such as O2 dissociation, and subsequent oxidation catalysis. Subtle changes in the atomic structure of Pt are responsible for drastic changes in performance driven by specific gas/metal/support interactions. Whereas single Pt atoms and Pt clusters (> ca. 1 nm) are unable to activate, scramble, and desorb two O2 molecules at moderate T (200 °C), clusters <1 nm do so catalytically, but undergo oxidative fragmentation. Oxidation of alkanes at high T is attributed to stable single Pt atoms, and the C‐H cleavage is inferred to be rate‐determining and less sensitive to changes in metal nuclearity compared to its effect on O2 scrambling. In contrast, when combustion involves CO, catalysis is dominated by metal clusters, not single Pt atoms.

Catalytic methane oxidation using N O was investigated at 300 °C over Fe-ZSM-5. This reaction rapidly produces coke (retained organic species), and causes catalyst fouling. The introduction of water into the feed-stream resulted in a significant decrease in the coke selectivity and an increase in the selectivity to the desired product, methanol, from ca. 1 % up to 16 %. A detailed investigation was carried out to determine the fundamental effect of water on the reaction pathway and catalyst stability. The delplot technique was utilised to identify primary and secondary reaction products. This kinetic study suggests that observed gas phase products (CO, CO , CH OH, C H and C H ) form as primary products whilst coke is a secondary product. Dimethyl ether was not detected, however we consider that the formation of C products are likely to be due to an initial condensation of methanol within the pores of the zeolite and hence considered pseudo-primary products. According to a second order delplot analysis, coke is considered a secondary product and its formation correlates with CH OH formation. Control experiments in the absence of methane revealed that the rate of N O decomposition is similar to that of the full reaction mixture, indicating that the loss of active alpha-oxygen sites is the likely cause of the decrease in activity observed and water does not inhibit this process.

a b s t r a c tEthanol carbonylation is a potential route to valuable C3 products. Here, Rh supported on porous, Cs-exchanged heteropolyacid Cs 3 PW 12 O 40, is demonstrated as an effective catalyst for vapor-phase ethanol carbonylation, with higher selectivity and conversion to propionates than existing catalysts. Residual acidity or a Mo polyatom was strongly detrimental to yields. Propionate selectivity was maximized at 96% at 170°C and with added H 2 O. The catalyst displayed stable selectivity over 30 h on stream and up to 77% conversion. Ethyl iodide is a required co-catalyst but at levels as low as 2% relative to ethanol. XPS and in situ XANES indicate partial Rh reduction, consistent with the formation of low-valent reactive intermediates and slow deactivation through formation of Rh nanoparticles. With further optimization and understanding, these Rh/heteropolyacid catalysts may lead to stable and selective catalysts for the production of propionates through ethanol carbonylation.