https://ogma.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:40459 Wed 27 Jul 2022 11:43:27 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:37281 2O over Fe-ferrierite (Fe-FER) catalyst prepared by solid-state ion-exchange method at moderate temperatures was studied using spectroscopic and solid characterization techniques including H₂ temperature-programmed reduction (H₂-TPR), N₂O temperature-programmed desorption (N₂O-TPD), and in situ Fourier transform infrared (FTIR). The utilization of active oxygen species for the direct conversion of methane to value-added products at moderate temperatures was investigated. The active oxygen sites for the selective conversion of methane were identified by a TPR feature at 220 °C. This site is also characterized by an infrared band observed at 1872 and 1892 cm^-1 upon adsorption of NO. These bands are NO stretching vibrations of NO adsorbed on iron oxygen monomeric species, present in the zeolite cages and responsible for selective oxidation. We show that these oxidized species react with methane to form oxygenates but at higher temperatures form molecular oxygen. IR bands of surface methoxy groups were observed in significant concentration in the FTIR spectra and are suggested to be intermediate species of the selective oxidation of methane. Studies using continuous reactors demonstrated that cofeeding of methane and N₂O-promoted generation of desired products from methane conversion by N₂O over Fe-FER catalyst can be enhanced by optimizing the feed ratio of CH₄/N₂O. Furthermore, N₂, O₂ and NO were detected as the products of N₂O decomposition over Fe-FER catalysts.]]> Wed 19 Jul 2023 10:27:37 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:37280 4) to organic oxygenates utilizing heterogeneous and homogeneous processes conducted in the gaseous or liquid phase is reviewed. The most active catalytic systems are examined in terms of rates, longevity, and reaction mechanisms. Despite significant effort, the successful heterogeneous mimicking of selective CH₄ oxidation performed in an enzymatic system (methane monooxygenase) is still elusive. Under mild reaction conditions, the reaction is too slow, and under harsh conditions, total oxidation prevails. Thus, of particular interest herein is the assessment of oxidation at intermediate temperatures to 1) reduce total oxidation and 2) obtain sufficient concentration of activated oxygen and CH₄ species. Important operational parameters such as reaction conditions, catalyst preparation methods, and cofeeding of chemicals, which significantly affect the yield of desired products, are discussed. One particular system that is successful is the catalytic conversion of CH₄ to methanol under mild conditions using nitrous oxide (N₂O) with Fe-based catalysts or oxygen (O₂) with Cu-based catalysts. Special attention is paid to the controversy related to the identification of active sites, where the oxygen species suitable for CH₄ oxidation are purportedly formed.]]> Wed 16 Sep 2020 18:36:19 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:36551 Tue 30 Jun 2020 11:56:24 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:50988 Tue 14 Nov 2023 14:56:57 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:50501 Thu 27 Jul 2023 12:28:40 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:46380 Thu 17 Nov 2022 13:38:16 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:37767 2O as oxidant. Spectroscopic and solid characterization tools including H₂-TPR, in situ IR, N₂ gas adsorption, CO chemisorption, and TGA-MS were used in the investigation. Ammonia adsorption data suggested that among the studied zeolites, H-FER zeolite contained the highest concentration of framework Al atoms, which are essential for the formation of active extra-framework Fe species. The oxidation state and redox active species of Fe-ZSM-5, Fe-Beta, and Fe-FER catalysts were studied by H₂-TPR, which disclosed the presence of a unique reduction peak (originating from N₂O pretreatment) centered at approximately 235 °C over the samples. The hydrogen consumption peak was more prominent over Fe-FER than other catalysts, demonstrating that the Fe-FER catalyst contained more active sites for N₂O conversion in comparison to Fe-Beta and Fe-ZSM-5 catalysts. For IR spectra of NO adsorbed on the Fe zeolites, a band at 1874 cm^–1 with a shoulder at 1894 cm^–1 was observed over the three catalysts, suggesting the presence of extra-framework Fe clusters in ion exchange positions. We demonstrated these clusters are acting as active sites for the oxidation of methane with N₂O. Bands of methoxy groups were observed in FTIR profiles of CH4 and N₂O adsorbed on Fe-FER, Fe-ZSM-5, and Fe-Beta catalysts at 350 °C. Over Fe-FER, the concentration of silanol-bonded methoxy groups accounted for over 95% of all methoxy groups under all the reaction conditions studied. In comparison, for the Fe-ZSM-5 and Fe-Beta catalysts, the proportion was less than 80%. The catalytic activity studies showed that Fe-FER was the most active catalyst based on methane and N₂O conversion, and displayed the highest selectivity to C₁-oxygenates and dimethyl ether formation, while Fe-ZSM-5 obtained the highest selectivity to ethylene among the three catalysts. Fe-ZSM-5 was found to deactivate significantly due to coke formation.]]> Thu 15 Apr 2021 10:03:06 AEST ]]>