A complete sample of radio sources in the North Ecliptic Cap, selected at 38 MHz -- III. further imaging observations and the photometric properties of the sample

Further imaging observations of a sample of radio sources in the North Ecliptic Cap are presented and a number of new identifications are made. Using redshifts from spectroscopic data presented in a companion paper (Lacy et al.\ 1999b), the photometric properties of the galaxies in the sample are discussed. It is shown that: (1) out to at least z~0.6 radio galaxies are good standard candles irrespective of radio luminosity; (2) for 0.6~<z~<1 a large fraction of the sample have magnitudes and colours consistent with a non-evolving giant elliptical, and (3) at higher redshifts, where the R-band samples the rest-frame UV flux, most objects have less UV luminosity than expected if they form their stellar populations at a constant rate from a high redshift to $z\sim 1$ in unobscured star-forming regions (assuming an Einstein -- de Sitter cosmology). The consequences of these observations are briefly discussed.Comment: 10 pages, 6 figures, accepted by MNRA

Aqueous-phase methane oxidation over Fe-MFI zeolites: promotion through isomorphous framework substitution

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 ºC, using H2O2 as green oxidant. Previously, we have observed that Fe species alone are capable of catalysing this highly selective transformation. However, further catalytic testing and spectroscopic investigations demonstrates 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+, Ga3+, into the MFI-framework. Whilst these additional framework species do not constitute active catalytic centres, 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) to the best catalysts reported for this reaction to date