The selective oxidation of lower alkanes, such as ethane, remains a major research challenge in catalysis. In this study Fe and Cu containing zeolites are investigated as catalysts for the production of C-2 oxygenated products from ethane using H2O2 as an oxidant. We utilise a trickle bed reactor to effectively control the contact time between reactants and catalyst to minimise C-C scission and over oxidation to COx. Reaction conditions such as temperature, pressure and reactant concentration in combination with Fe and Cu content of the catalysts are investigated to optimise conversion and selectivity to C-2 oxygenated products. A marked effect is observed upon increasing pressure between 1 and 30 bar, as the oxygenate selectivity increases from 46% to 98%. Single pass conversion of ethane (22%) to acetic acid (73%, 16% yield) has been observed using a Fe/ZSM-5 catalyst under the optimum conditions. Catalysts are investigated for stability, and are observed to undergo no apparent deactivation under test conditions, despite low levels of Fe leaching. Through characterisation and assessment of leached Fe/ZSM-5 catalysts, we show that catalytic activity might be attributed to Fe species within the zeolite's channels and that surface FexOy are spectator species. Finally, relatively high selectivity to ethene (38%, I% yield) has been observed with Cu containing materials under these mild reaction conditions. (C) 2015 Elsevier Inc. All rights reserved.

Oxidation of octane in the presence of benzaldehyde over a AuPd catalysts leads to the formation of octyl benzoate.

Selective oxidation of methane using AuPdCu/TiO2 catalysts.

Journal Article Assessing and Controlling the Size, Morphology and Composition of Supported Bimetallic Catalyst Nanoparticles Get access Christopher J Kiely, Christopher J Kiely Department of Materials Science and Engineering, Lehigh University, PA 18015, U.S.A Search for other works by this author on: Oxford Academic Google Scholar Qian He, Qian He Department of Materials Science and Engineering, Lehigh University, PA 18015, U.S.A Search for other works by this author on: Oxford Academic Google Scholar Ramchandra Tiruvalam, Ramchandra Tiruvalam Department of Materials Science and Engineering, Lehigh University, PA 18015, U.S.A Search for other works by this author on: Oxford Academic Google Scholar Nikolaos Dimitratos, Nikolaos Dimitratos Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Wales, U.K Search for other works by this author on: Oxford Academic Google Scholar Michael M Forde, Michael M Forde Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Wales, U.K Search for other works by this author on: Oxford Academic Google Scholar Meenakshisundaram Sankar, Meenakshisundaram Sankar Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Wales, U.K Search for other works by this author on: Oxford Academic Google Scholar Graham J Hutchings Graham J Hutchings Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Wales, U.K Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 20, Issue S3, 1 August 2014, Pages 74–75, https://doi.org/10.1017/S1431927614002098 Published: 27 August 2014

Heat treating Fe/ZSM-5 under hydrogen leads to high dispersion of Fe species and higher alcohol selectivity in the oxidation of alkanes, as compared to oxygen treated catalysts.

As co-catalyst materials, metal nanoparticles (NPs) play crucial roles in heterogeneous photocatalysis. The photocatalytic performance strongly relies on the physical properties (i.e., composition, microstructure, and surface impurities) of the metal NPs. Here we report a convenient chemical vapour impregnation (CVI) approach for the deposition of monometallic-, alloyed, and core-shell structured metal co-catalysts onto the TiO2 photocatalyst. The as-synthesised metal NPs are highly dispersed on the support and show narrow size distributions, which suit photocatalysis applications. More importantly, the surfaces of the as-synthesised metal NPs are free of protecting ligands, enabling the photocatalysts to be ready to use without further treatment. The effect of the metal identity, the alloy chemical composition, and the microstructure on the photocatalytic performance has been investigated for hydrogen production and phenol decomposition. Whilst the photocatalytic H-2 production performance can be greatly enhanced by using the core-shell structured co-catalyst (Pd-shell-Au-core and Pt-shell-Au-core), the Pt-shell-Au-core modified TiO2 yields enhanced quantum efficiency but a reduced effective decomposition of phenol to CO2 compared to that of the monometallic counterparts. We consider the CVI approach provides a feasible and elegant process for the decoration of photocatalyst materials.

Fe- and Cu-containing zeolites have recently been shown to be efficient catalysts for the one-step selective transformation of methane into methanol in an aqueous medium at only 50 degrees C, using H2O2 as green oxidant. Previously, we have observed that Fe species alone are capable of catalyzing this highly selective transformation. However, further catalytic testing and spectroscopic investigations demonstrate that although these extra-framework Fe species are the active component of the catalyst, significant promotion is observed upon the incorporation of other trivalent cations, e.g., Al3+ or Ga3+, into the MFI-framework. While these additional framework species do not constitute active catalytic centers, promotion is observed upon their incorporation as they (1) facilitate the extraction of Fe from the zeolite framework and hence increase the formation of the active Fe species and (2) provide an associated negatively charged framework, which is capable of stabilizing and maintaining the dispersion of the cationic extra-framework Fe species responsible for catalytic activity. By understanding these phenomena and subsequently controlling the overall composition of the catalyst (Fe and Al), we have subsequently been able to prepare a catalyst of equal intrinsic activity (i.e., TOF) but five-times higher productivity (i.e., space-time-yield) compared with the best catalysts reported for this reaction to date.

Trimetallic Au–Pd–Pt nanoparticles have been supported on activated carbon by the sol-immobilisation method. They are found to be highly active and selective catalysts for the solvent-free aerobic oxidation of benzyl alcohol. The addition of Pt promotes the selectivity to the desired product benzaldehyde at the expense of toluene formation. Detailed aberration corrected STEM-XEDS analysis confirmed that the supported particles are indeed Au–Pd–Pt ternary alloys, but also identified composition fluctuations from particle-to-particle which vary systematically with nanoparticle size.

Supported nano-alloys have been prepared using the sol-immobilisation method for two bimetallic combinations, namely gold-platinum and palladium-platinum, using activated carbon and titania as supports. Some of the materials were prepared using a method where both metals are simultaneously reduced, thereby leading to homogeneous alloys being formed. In addition, sequential reduction of the metal combinations has also been investigated to facilitate the formation of core-shell structures. The materials have been characterized using X-ray photoelectron spectroscopy and aberration-corrected scanning transmission electron microscopy. The supported nanoparticles have been tested for a two selective oxidation reactions, namely the oxidation of toluene and benzyl alcohol using tertiary butyl hydroperoxide at 80 °C, in order to elucidate any potential structure-activity relationships.

Direkt und selektiv: Trägerfixierte Gold-Palladium-Nanopartikel sind aktiv in der Oxidation von Methan und zeigen mit Wasserstoffperoxid als Oxidationsmittel eine hohe Selektivität bei der Bildung von Methylhydroperoxid und Methanol (siehe Bild). Die optimale Selektivität für die Methanolbildung wird erreicht, wenn die Reaktion in Gegenwart von Wasserstoffperoxid, das in situ aus Wasserstoff und Sauerstoff entsteht, ausgeführt wird.

The development of a catalytic, one-step route for the oxidation of methane to methanol remains one of the greatest challenges within catalysis. Of particular importance is the need to develop an efficient route that proceeds under mild reaction conditions so as to avoid deeper oxidation and the economic limitations of the currently practiced syngas route. Recently, it was demonstrated that a copper- and iron-containing zeolite is an efficient catalyst for such a one-step process. The catalyst in question (Cu-Fe-ZSM-5) is capable of selectively transforming methane to methanol in an aqueous medium with hydrogen peroxide as the terminal oxidant. Nevertheless, despite its high activity and unparalleled methanol selectivity, the origin of its activity and the precise nature of its active species are not yet fully understood. Through a combination of catalytic and spectroscopic studies, we hereby demonstrate that extraframework Fe species are the active component of the catalyst for methane oxidation, although the speciation of these sites from synthesis to catalysis significantly alters the observed activity and selectivity. The analogies and differences between this system and other iron-containing zeolite-catalyzed processes, such as N2O-mediated benzene hydroxylation, are also considered.

Trimetallic Au-Pd-Pt nanoparticles have been supported on activated carbon by the sol-immobilisation method. They are found to be highly active and selective catalysts for the solvent-free aerobic oxidation of benzyl alcohol. The addition of Pt promotes the selectivity to the desired product benzaldehyde at the expense of toluene formation. Detailed aberration corrected STEM-XEDS analysis confirmed that the supported particles are indeed Au-Pd-Pt ternary alloys, but also identified composition fluctuations from particle-to-particle which vary systematically with nanoparticle size.

Iron and copper containing ZSM-5 catalysts are effective for the partial oxidation of ethane with hydrogen peroxide giving combined oxygenate selectivities and productivities of up to 95.2% and 65 mol kgcat(-1) h(-1), respectively. High conversion of ethane (ca. 56%) to acetic acid (ca. 70% selectivity) can be observed. Detailed studies of this catalytic system reveal a complex reaction network in which the oxidation of ethane gives a range of C2 oxygenates, with sequential C-C bond cleavage generating C1 products. We demonstrate that ethene is also formed and can be subsequently oxidized. Ethanol can be directly produced from ethane, and does not originate from the decomposition of its corresponding alkylperoxy species, ethyl hydroperoxide. In contrast to our previously proposed mechanism for methane oxidation over similar zeolite catalysts, the mechanism of ethane oxidation involves carbon-based radicals, which lead to the high conversions we observe.

The use of precious metals in heterogeneous catalysis relies on the preparation of small nanoparticles that are stable under reaction conditions. To date, most conventional routes used to prepare noble metal nanoparticles have drawbacks related to surface contamination, particle agglomeration, and reproducibility restraints. We have prepared titania-supported palladium (Pd) and platinum (Pt) catalysts using a simplified vapor deposition technique termed chemical vapor impregnation (CVI) that can be performed in any standard chemical laboratory. These materials, composed of nanoparticles typically below 3 nm in size, show remarkable activity under mild conditions for oxidation and hydrogenation reactions of industrial importance. We demonstrate the preparation of bimetallic Pd-Pt homogeneous alloy nanoparticles by this new CVI method, which show synergistic effects in toluene oxidation. The versatility of our CVI methodology to be able to tailor the composition and morphology of supported nanoparticles in an easily accessible and scalable manner is further demonstrated by the synthesis of Pdshell-Aucore nanoparticles using CVI deposition of Pd onto preformed Au nanoparticles supported on titania (prepared by sol immobilization) in addition to the presence of monometallic Au and Pd nanoparticles.

The oxidation of methane using hydrogen peroxide has been studied using supported gold palladium catalysts prepared using the incipient wetness technique. The effect of reaction conditions and catalyst parameters has been investigated. The supported gold palladium nanoparticles produce methyl hydroperoxide as the primary reaction product which is subsequently converted to methanol with high selectivity, ca. 40–70 %. The selectivity to methanol is influenced by the oxidation state the palladium component of the catalyst. In contrast to homogeneous gold and palladium catalysts the heterogeneous gold palladium nanoalloys are reusable and affords high oxygenate selectivity (ca. 90 %).