Gold-on-carbon catalysts are analogs of homogeneous gold catalysts that use a redox couple of Au(I) and Au(III) species.

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 ironcontaining 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 N 2 O-mediated benzene hydroxylation, are also considered.

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.

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Recent advances in the oxidation of alcohols to methyl esters using metal nanoparticles have paved the way for more environmentally benign processes, operating at lower reaction temperatures with high product selectivity. Here, we demonstrate the use of bimetallic 1 wt % Au–Pd/TiO2 catalysts that achieve high activity for the oxidation of methanol to methyl formate at low temperature. The application of a water extraction treatment to retain size-stabilized Au–Pd nanoparticles, in contrast to a more standard thermal treatment, provides the most active catalyst for this reaction. Using in situ DRIFTS, we demonstrate that in situ activation during methanol oxidation enhances the catalytic activity at low temperature and that this is a long-lived effect. Surface adsorbates, particularly formate species, build up on the catalyst surface during the reaction and are proven vital to enhancing the catalytic effect.

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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 °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.

The hydrogenation of lactic acid to form 1,2-propanediol has been investigated using Ru nanoparticles supported on carbon as a catalyst. Two series of catalysts were investigated which were prepared by wet impregnation and sol-immobilisation. Their activity was contrasted with that of a standard commercial Ru/C catalyst (all catalysts comprise 5 wt% Ru). The catalyst prepared using sol-immobilisation was found to be more active than the wet impregnation materials. In addition, the catalyst made by sol-immobilisation was initially more active than the standard commercial catalyst. However, when reacted for an extended time or with successive re-use cycles the sol-immobilised catalyst became less active, whereas the standard commercial catalyst became steadily more active. Furthermore, both catalysts exhibited an induction period during the first 1000s of reaction. Detailed scanning transmission electron microscopy, X-ray photoelectron spectroscopy and XAFS data, when correlated with the catalytic performance results, showed that the high activity can be ascribed to highly dispersed Ru nanoparticles. While the sol-immobilisation method achieved these optimal discrete Ru nanoparticles immediately, as can be expected from this preparation methodology, the materials were unstable upon re-use. In addition, Surface lactide species were detected on these particles using X-ray photoelectron spectroscopy which could contribute to their deactivation. The commercial Ru/C catalysts on the other hand, required treatment under reaction conditions to change from raft-like morphologies to the desired small nanoparticle morphology, during which time the catalytic performance progressively improved.