Characterization of selective oxidation catalysts from polyoxometalate precursors using ammonia adsorption microcalorimetry and methanol oxidation studies

Phosphomolybdic acid (H3PMo12O40) along with niobium, pyridine and niobium/pyridine exchanged phosphomolybdic acid compounds were prepared. These compounds were converted to selective oxidation catalysts by pre-treating to 693 K in an inert atmosphere. As shown previously, the active catalyst consists of partially decomposed, partially reduced Keggin units and MoOx fragments with some MoOx fragments collected around the Nb. The amount of surface Mo species reduced to the 5+ oxidation state varied among the catalysts. Ammonia adsorption microcalorimetry and methanol oxidation studies were carried out to investigate the acid sites strength and the acid/base/redox properties of each catalyst. The addition of niobium, pyridine or both increased the ammonia heat of adsorption by 30-40 kJ/mol and the total ammonia uptake. The catalyst with both niobium and pyridine demonstrated the largest number of strong sites. For the parent H 3PMo12O40 catalyst, methanol oxidation favors the redox product (∼95% selectivity). However, catalyst deactivation occurs. The presence of niobium results in similar selectivity to redox products (∼93%) but also results in no catalyst deactivation. Incorporation of pyridine to the precursor compound, in contrast, changes the selectivity to initially favor the acid product (∼62%). Again, the catalyst deactivated and selectivity changed during deactivation to favor the redox product (∼55%). Finally, the inclusion of both niobium and pyridine results in strong selectivity to the acid product (∼95%) while also showing no catalyst deactivation and stable selectivity. Specific activity for the niobium and pyridine exchanged catalyst for the methanol oxidation reaction was twice any other catalyst. Selectivity to acid products was correlated with the amount of reduced surface Mo species. Thus, the presence of pyridine appears to enhance the acid property of the active site in the catalyst while niobium appears to stabilize the active site. © 2013 Elsevier B.V

Underwater sound in an urban estuarine river: Sound sources, soundscape contribution, and temporal variability

Human waterborne activities emit noise into the marine environment. This is of particular concern with regard to the potential impact on marine fauna such as cetaceans due to their acoustic specialisations. The Swan-Canning River system in Western Australia is home to a resident community of Indo-Pacific bottlenose dolphins (Tursiops aduncus), but is also a site regularly used for various human activities. As underwater noise levels increasingly become considered as an indicator of habitat quality, there is a need to characterise the soundscapes of such areas with regard to their cetacean fauna. This study aimed to provide a description of a site within the river system known as “The Narrows”. Acoustic data were collected over a six-week period with an autonomous underwater acoustic recorder. These data were analysed using a combination of weekly spectrograms, power spectral density percentile plots, 1/3 octave band levels, and generalised estimating equations to identify prominent soundscape contributors and investigate temporal patterns in their occurrence. The soundscape was found to be strongly influenced by wind, snapping shrimp, and vessel traffic, with the sounds of bridge traffic, waves, fish, machinery, dolphins, and precipitation also contributing to the acoustic environment. Furthermore, three of these sound sources (boats, waves, and fish) were found to vary at a range of temporal scales. These results take a vital step in characterising the acoustic habitat of this river system, highlighting the need to consider temporal patterns when assessing the composition of underwater soundscapes